Which emission sources are responsible for the volatile organic compounds in the atmosphere of Pearl River Delta?

Temporal evolution of speciated volatile organic compound (VOC) emissions from solvent use sources in the Pearl River Delta Region, China (2006-2019)

Volatile organic compounds (VOCs) emitted from solvent use sources constitute an important part of ozone (O3) and secondary organic aerosols (SOA) in the Pearl River Delta (PRD) region, China. While stringent control measures targeting VOCs have been implemented in recent years, an assessment of historical trends is imperative to evaluate their effectiveness. In this study, trends of VOC emissions, compositions, and reactivity from solvent use sources in the PRD region from 2006 to 2019 were estimated using a developed methodology, which considered the improvement of manufacturing equipment and removal efficiency. Results showed that total VOC emissions from solvent use sources displayed an overall increase from 277 kt in 2006 to 400 kt in 2019 despites some fluctuations, with metal products contributing more than 20 % each year. Aromatics and oxygenated VOCs (OVOCs) accounted for over 70 % of total VOC emissions, increasing by 21 kt and 52 kt respectively. OFP and SOAFP increased by 40 % and 23 % respectively from 2006 to 2019. Specific aromatic species, including m/p-xylene, toluene, 1,2,3,5-tetramethylbenzene, o-xylene and ethylbenzene were identified as key species in both VOC emission amount and reactivity. This study aims to facilitate the understanding of VOC emission evolution from solvent use sources in the region and provide insights into the impact of enacted measures, aiding in the future development of more targeted and efficient strategies in the PRD region.

Characteristics and source apportionment of ambient volatile organic compounds and ozone generation sensitivity in urban Jiaozuo, China

In recent years, many cities have taken measures to reduce volatile organic compounds (VOCs), an important precursor of ozone (O3), to alleviate O3 pollution in China. 116 VOC species were measured by online and offline methods in the urban area of Jiaozuo from May to October in 2021 to analyze the compositional characteristics. VOC sources were analyzed by a positive matrix factorization (PMF) model, and the sensitivity of ozone generation was determined by ozone isopleth plotting research (OZIPR) simulation. The results showed that the average volume concentration of total VOCs was 30.54 ppbv and showed a bimodal feature due to the rush-hour traffic in the morning and at nightfall. The most dominant VOC groups were oxygenated VOCs (OVOCs, 29.3%) and alkanes (26.7%), and the most abundant VOC species were acetone and acetylene. However, based on the maximum incremental reactivity (MIR) method, the major VOC groups in terms of ozone formation potential (OFP) contribution were OVOCs (68.09 µg/m3, 31.5%), aromatics (62.90 µg/m3, 29.1%) and alkene/alkynes (54.90 µg/m3, 25.4%). This indicates that the control of OVOCs, aromatics and alkene/alkynes should take priority. Five sources of VOCs were quantified by PMF, including fixed sources of fossil fuel combustion (27.8%), industrial processes (25.9%), vehicle exhaust (19.7%), natural and secondary formation (13.9%) and solvent usage (12.7%). The empirical kinetic modeling approach (EKMA) curve obtained by OZIPR on O3 exceedance days indicated that the O3 sensitivity varied in different months. The results provide theoretical support for O3 pollution prevention and control in Jiaozuo.

Unlocking the secrets: Volatile Organic Compounds (VOCs) and their devastating effects on lung cancer

Lung cancer (LCs) is still a serious health problem globally, with many incidences attributed to environmental triggers such as Volatile Organic Compounds (VOCs). VOCs are a broad class of compounds that can be released via various sources, including industrial operations, automobile emissions, and indoor air pollution. VOC exposure has been linked to an elevated risk of lung cancer via multiple routes. These chemicals can be chemically converted into hazardous intermediate molecules, resulting in DNA damage and genetic alterations. VOCs can also cause oxidative stress, inflammation, and a breakdown in the cellular protective antioxidant framework, all of which contribute to the growth of lung cancer. Moreover, VOCs have been reported to alter critical biological reactions such as cell growth, apoptosis, and angiogenesis, leading to tumor development and metastasis. Epidemiological investigations have found a link between certain VOCs and a higher probability of LCs. Benzene, formaldehyde, and polycyclic aromatic hydrocarbons (PAHs) are some of the most well-researched VOCs, with comprehensive data confirming their cancer-causing potential. Nevertheless, the possible health concerns linked with many more VOCs and their combined use remain unknown, necessitating further research. Identifying the toxicological consequences of VOCs in LCs is critical for establishing focused preventative tactics and therapeutic strategies. Better legislation and monitoring mechanisms can limit VOC contamination in occupational and environmental contexts, possibly reducing the prevalence of LCs. Developing VOC exposure indicators and analyzing their associations with genetic susceptibility characteristics may also aid in early identification and targeted therapies.

VOC source apportionment: How monitoring characteristics influence positive matrix factorization (PMF) solutions

Positive matrix factorization (PMF) can be used to develop more targeted air quality mitigation strategies by identifying major sources of a pollutant in an area. This technique is dependent, however, on the ability of PMF to resolve factors that accurately represent all sources of that pollutant in an area. We investigated how the accuracy of PMF solutions might be influenced by monitoring data characteristics, such as temporal resolution, monitoring location, and species composition, to better inform the use of PMF in VOC mitigation strategies. We applied PMF to five VOC monitoring programs collected within a four-year period in Colorado and found generally consistent factors, which we identified as oil extraction, processing, and evaporation; natural gas; vehicle exhaust; and liquid gasoline/short-lived oil and gas. The main determinant influencing whether or not a dataset resolved each of these sources was whether the dataset had a comprehensive list of VOC species covering key species of each source. Pollution spikes were not well-modeled in any of the solutions. Hyperlocal and volatile chemical product factors expected to be resolved in the industrialized, urban location were also missing, highlighting three limitations of PMF analysis. Wind direction dependence and diurnal trends aided in source identification, suggesting that high-time resolution data is important for developing actionable PMF results. Based on these findings, we recommend that air monitoring for PMF-informed VOC mitigation efforts include high temporal resolution and a comprehensive array of VOC species.

Source apportionment and ozone formation mechanism of VOCs considering photochemical loss in Guangzhou, China

Understanding the sources and impact of volatile organic compounds (VOCs) on ozone formation is challenging when the traditional method does not account for their photochemical loss. In this study, online monitoring of 56 VOCs was carried out in summer and autumn during high ozone pollution episodes. The photochemical age method was used to evaluate the atmospheric chemical loss of VOCs and to analyze the effects on characteristics, sources, and ozone formation of VOC components. The initial concentrations during daytime were 5.12 ppbv and 4.49 ppbv higher than the observed concentrations in the summer and autumn, respectively. The positive matrix factorization (PMF) model identified 5 major emission sources. However, the omission of the chemical loss of VOCs led to underestimating the contributions of sources associated with highly reactive VOC components, such as those produced by biogenic emissions and solvent usage. Conversely it resulted in overestimating the contributions from VOC components with lower chemical activity such as liquefied petroleum gas (LPG) usage, vehicle emissions, and gasoline evaporation. Furthermore, the estimation of ozone formation may be underestimated when the atmospheric photochemical loss is not taken into account. The ozone formation potential (OFP) method and propylene-equivalent concentration method both underestimated ozone formation by 53.24 ppbv and 47.25 ppbc, respectively, in the summer, and by 40.34 ppbv and 26.37 ppbc, respectively, in the autumn. The determination of the ozone formation regime based on VOC chemical loss was more acceptable. In the summer, the ozone formation regime changed from the VOC-limited regime to the VOC-NOx transition regime, while in the autumn, the ozone formation regime changed from the strong VOC-limited regime to the weak VOC-limited regime. To obtain more thorough and precise conclusions, further monitoring and analysis studies will be conducted in the near future on a wider variety of VOC species such as oxygenated VOCs (OVOCs).

Development of an enhanced method for atmospheric carbonyls and characterizing their roles in photochemistry in subtropical Hong Kong

Carbonyl compounds are ubiquitous and play vital roles in tropospheric photochemistry and oxidation capacity, particularly affecting radical cycling and ozone formation. An enhanced method based on ultra-high-performance liquid chromatography and electrospray ionization tandem mass spectrometry was developed to simultaneously quantify 47 carbonyl compounds with carbon (C) numbers from 1 to 13. Applying this new method to samples collected at ground and ship-borne field campaigns, we investigated the abundance, characteristic distribution, and photochemical activity of carbonyl species in the coastal atmosphere of Hong Kong. The total concentration of detected carbonyls ranged from 9.1 to 32.7 ppbv and exhibited distinct spatial variability. In addition to the usual abundant carbonyl species (formaldehyde, acetaldehyde, and acetone), aliphatic saturated aldehydes with C ≥ 5 (particularly hexaldehyde and nonanaldehyde), and di‑carbonyls, exhibit significant abundance and photochemical reactivity in the coastal site and on the sea. The measured carbonyls could contribute to an estimated peroxyl radical formation rate of 1.88-8.43 ppb/h via OH oxidation and photolysis, greatly enhancing oxidation capacity and radical cycling. The ozone formation potential (OFP) estimated from the maximum incremental reactivity (MIR) was dominated (69 %-82 %) by formaldehyde and acetaldehyde, with significant contribution (4 %-13 %) from di‑carbonyls. Furthermore, another dozens of long-chain carbonyls without MIR values, which were typically below detection or not included in the conventional analytical method, would increase the ozone formation rate by an additional 2 %-33 %. Additionally, the glyoxal, methylglyoxal, benzaldehyde and other α, β-unsaturated aldehydes also exhibited considerable contribution to secondary organic aerosol (SOA) formation potential. This study highlights the importance of various reactive carbonyls in the atmospheric chemistry of urban and coastal regions. The newly developed method can effectively characterize more carbonyl compounds and advance our understanding of their roles in photochemical air pollution.

Abundant oxygenated volatile organic compounds and their contribution to photochemical pollution in subtropical Hong Kong

Volatile organic compounds (VOCs), which are ubiquitous pollutants in the urban and regional atmosphere, promote the formation of ozone (O3) and secondary organic aerosols, thereby significantly affecting the air quality and human health. The ambient VOCs at a coastal suburban site in Hong Kong were continuously measured using proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) from November 2020 to December 2020. 83 VOC species, including 23 CxHy, 53 CxHyO1-3, and 7 nitrogen-containing species, were measured during the campaign, with a mean concentration of 36.75 ppb. Oxygenated VOCs (OVOCs) accounted for most (77.4%) of the measured species, including CxHyO1 (50.7%) and CxHyO2 (25.1%). The measured VOC species exhibited distinct temporal and diurnal variations. High concentrations of isoprene and OVOCs were measured in autumn with more active photochemistry, whereas large evening peaks of aromatics from local and regional primary emissions were prominent in winter. The OH reactivity and O3 formation potential (OFP) of key precursors were quantified. OVOCs contributed about half of the total OH reactivity and OFP, followed by alkenes and aromatics, and the contribution of aromatics increased significantly in winter. The potential source contribution function was used to investigate the potential source regions associated with high VOC concentrations. Through positive matrix factorization analysis, six major sources were identified based on fingerprint molecules. The contributions of biogenic sources and secondary formation to the observed species were notable in late autumn, whereas vehicle emissions and solid fuel combustion had higher contributions in winter. The findings highlight the important role of OVOCs in photochemical pollution and provide valuable insights for the development of effective pollution control strategies.

Sources-oriented contributions to ozone and secondary organic aerosol formation potential based on initial VOCs in an urban area of Eastern Asia

Over the past decades, the pollution of ozone (O3) and secondary organic aerosols (SOA) in the atmosphere has become a major concern worldwide due to their adverse effects on human health, air quality and climate. Volatile organic compounds (VOCs) are crucial precursors of O3 and SOA, but identifying the primary sources of VOCs that contribute to the formation of O3 and SOA has been challenging due to the rapid consumption of VOCs by oxidants in the air. To address this issue, a study was conducted in a Taipei urban area in Taiwan, where the hourly data of 54 VOC species were collected from March 2020 to February 2021 detected by Photochemical Assessment Monitoring Stations (PAMS). The initial mixing ratios of VOCs (VOCsini) were determined by combining the observed VOCs (VOCsobs) and the consumed VOCs resulting from photochemical reactions. Additionally, the ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) were estimated based on VOCsini. The OFP derived from VOCsini (OFPini) was found to exhibit a strong correlation with O3 mixing ratios (R2 = 0.82), whereas the OFP obtained from VOCsobs did not show such a correlation. Isoprene, toluene and m,p-xylene were the top three species contributing to OFPini, while toluene and m,p-xylene were the top two contributors to SOAFPini. Positive matrix factorization analysis revealed that biogenic, consumer/household products, and industrial solvents were the major contributors to OFPini in four seasons, and SOAFPini mostly came from consumer/household products and industrial solvents. This study highlights the importance of considering photochemical loss caused by different VOCs reactivity in the atmosphere when evaluating OFP and SOAFP. Moreover, it emphasizes the need to prioritize controlling the sources emitting the dominant VOC precursors of O3 and SOA to effectively alleviate the scenarios of elevated O3 and particulate matter.

Profile of atmospheric VOC over the Yellow Sea, China: A tale of distribution, constraints, and sources

In the winter of 2018-2019, 75 air samples were collected through four ship-borne measurements in the Yellow Sea (YS) to assess the levels, confinement processes, and source distribution of volatile organic compounds (VOCs). A total of 41 were eventually detected, which mainly were non-methane hydrocarbons (NMHCs), volatile halogenated hydrocarbons (VHCs), oxygenated volatile organic compounds (OVOCs), and volatile organic sulfur compounds (VSCs). Aromatics (31.93 %) and alkenes (11.04 %) in the atmosphere of the YS accounted for a larger proportion of NMHCs compared with the coastal areas. C3-C5 alkanes, propylene, and chloroform exhibited strong latitudinal gradients and opposite latitudinal distributions in the North and South YS, highlighting the strong contribution of regional outflow to YS's atmosphere. The level of Σ41VOCs increased significantly during the heavy pollution period with some chemical monomers detected, which was further enhanced by the emissions from industrial parks near the Liaodong Peninsula and the Shandong Peninsula. Five main VOC sources were identified by the Positive matrix factorization (PMF) model, which were industrial emissions (13.33 %), fuel use and volatilization (6.67 %), Freon R-22 emissions (33.33 %), oil and gas production (20.00 %), and solvent volatilization (26.67 %). These observations revealed the strong causal relationship between coastal air mass transport and the atmosphere in the marginal sea and emphasized that full attention should be paid to the unintentional and unorganized emission of chemical monomers in the industrial process.

Characteristics and source origin analysis of halogenated hydrocarbons in Hong Kong

Despite being regulated globally for almost three decades, halocarbon continues to play a vital role in climate change and ozone layer because of its long lifetime in the ambient air. In recent years, unexpected halocarbon emissions have been found in Asia, raising concerns about ozone recovery. As a number of studies focused on halocarbon variations and source profiles, there is an increasing need to identify halocarbon source origins. In this study, an eight-month regular air sampling was conducted at a coastal site in Hong Kong from November 2020 to June 2021, and seventeen halocarbon species were selected for extensive investigation after advanced sample analysis in our laboratory. The temporal variations of halocarbon mixing ratio enhancements were analyzed, and the spatial variations of source origins were investigated by wind sectors and backward trajectory statistics. Our results indicate lower enhancements beyond the background values for major regulated CFCs and CCl₄ than later controlled HCFCs and HFCs, suggesting the greater progress of Montreal Protocol implementation for the former species. The notable high enhancement values of non-regulated halocarbons from the north direction indicate their widespread usage in China. The source apportionment analysis estimates the contributions from six emission sectors on measured halocarbons, including solvent usage (43.57 ± 4.08 %), refrigerant residues (17.05 ± 5.71 %), cleaning agent/chemical production (13.18 ± 4.76 %), refrigerant replacements (13.06 ± 2.13 %), solvent residues (8.65 ± 3.28 %), and foaming agent (4.49 ± 1.08 %). Trajectories statistical analysis suggests that industrial solvent was mainly contributed by eastern China (i.e., Shandong and YRD), cleaning agent/chemical production was spread over southeast China (i.e., YRD and Fujian), and refrigeration replacements were dominant in Hong Kong surrounding regions. This work provides insight into the progress made in implementing the Montreal Protocol in Hong Kong and the surrounding region and the importance of continuous emission control.

Comparison of CO2, NOx, and VOCs emissions between CNG and E10 fueled light-duty vehicles

In China, natural gas (NG) is the main vehicle fuel after gasoline and diesel, and the number of NG vehicles ranks first in the world. At present, there are many studies on the conventional gaseous pollutants and particulate matter of NG vehicles, but very few studies on their VOCs. In this study, the chassis dynamometer is used to test CNG/E10 bi-fuel light-duty vehicles, analyze the advantages of CNG in CO₂, fuel thermal efficiency, and cost, and discuss its disadvantages in NO_x emission. Most importantly, the emission characteristics and ozone formation potential of VOCs in the exhaust of CNG vehicles were analyzed in the study. Compared with E10, CNG fuel can reduce CO₂ emission by about 20 %, improve thermal efficiency by about 13 %, and save fuel costs by about 50 %. However, it will increase NO_x and NO₂ emissions by about 10 % and 13 % respectively. As for VOCs, the emission factor of VOCs from CNG fuel is about 54 % of E10 fuel. The VOCs group with the highest proportion in the exhaust of CNG-fueled vehicles is alkanes, >80 %. while the alkanes and alkenes with the highest proportion in E10 fuel are 30 % and 23 % respectively. C2 VOCs emitted by CNG account for >70 %, while C2 VOCs emitted by E10 are <60 %, followed by C4 VOCs, about 10 % - 30 %. The OFPs of VOCs in CNG exhaust is about 13.7 % of E10. Alkenes contribute the most to ozone, and the OFPs of alkenes in CNG and E10 vehicle exhaust accounts for about 55.3 % and 78.8 % of TVOCs respectively. The results of this study are helpful to improve people's understanding of the environmental value of using NG vehicles.

Characteristics and sources of volatile organic compounds (VOCs) in Xinxiang, China, during the 2021 summer ozone pollution control

Real-time monitoring of volatile organic compounds (VOCs) was conducted in Xinxiang, China, during the implementation of Xinxiang's ozone pollution control period (CP) in June 2021. To evaluate the effectiveness of the control measures, three study periods were determined by combining meteorological conditions and the implementation time of the control measures: before, during, and after the CP of ozone pollution (BCP, CP, and ACP, respectively). The average concentrations of VOCs during the three periods were 41.20 ± 4.99 ppbv, 33.64 ± 5.65 ppbv, and 37.42 ± 2.59 ppbv, respectively, with the same top three components, namely oxygenated VOCs (OVOCs), alkanes, and halogenated hydrocarbons (XVOCs). However, the concentrations of these three components decreased substantially during the CP (by 19 %, 18 %, and 11 %, respectively). The ozone formation potential (OFP) during the BCP was 144.47 ppbv, which was 1.2 times and 1.3 times higher than those during the ACP and CP periods, respectively. During the CP, the proportion of alkenes that contributed to the OFP decreased significantly by 24 %. Five types of VOCs sources were determined by positive matrix factorization (PMF): (1) solvent use, (2) biogenic, (3) secondary formation, (4) industrial process, and (5) vehicle exhaust and fuel evaporation sources. The VOCs emissions from industrial processes decreased by 54 % during the CP, whereas those from vehicle exhaust and fuel evaporation sources decreased by 36 %, indicating the effectiveness of emission control measures and the importance of these two sources for VOCs control in Xinxiang. In terms of regional transport, the results of the spatial analysis revealed that Hebi and Anyang in the northeast and Zhengzhou and Pingdingshan in the southwest, affected significantly the VOCs of Xinxiang. These results highlight the importance of controlling VOCs emissions in Xinxiang. Furthermore, attention should be paid to controlling the regional transport of surrounding cities.

Spatial characteristics of VOCs and their ozone and secondary organic aerosol formation potentials in autumn and winter in the Guanzhong Plain, China

As critical precursors of tropospheric ozone (O₃) and secondary organic aerosol (SOA), volatile organic compounds (VOCs) largely influence air quality in urban environments. In this study, measurements of 102 VOCs at all five major cities in the Guanzhong Plain (GZP) were conducted during Sep.09-Oct. 13, 2017 (autumn) and Nov. 14, 2017-Jan. 19, 2018 (winter) to investigate the characteristics of VOCs and their roles in O₃ and SOA formation. The average concentrations of total VOCs (TVOCs) at Xi'an (XA), Weinan (WN), Xianyang (XY), Tongchuan (TC), and Baoji (BJ) sites were in the range of 55.2-110.2 ppbv in autumn and 42.4-74.3 ppbv in winter. TVOCs concentrations were reduced by 22.4%-43.5% from autumn to winter at XA, WN and BJ. Comparatively low concentrations of TVOCs were observed in XY and TC, ranging from 53.5 to 62.7 ppbv across the sampling period. Alkanes were the major components at all sites, accounting for 26.4%-48.9% of the TVOCs during the sampling campaign, followed by aromatics (4.2%-26.4%). The average concentration of acetylene increased by a factor of up to 4.8 from autumn to winter, indicating the fuel combustion in winter heating period significantly impacted on VOCs composition in the GZP. The OH radical loss rate and maximum incremental reactivity method were employed to determine photochemical reactivities and ozone formation potentials (OFPs) of VOCs, respectively. The VOCs in XA and WN exhibited the highest reactivities in O₃ formation, with the OFP of 168-273 ppbv and the OH loss rates of 19.3-40.8 s^-1. Alkenes and aromatics primarily related to on-road and industrial emissions contributed 57.8%-76.3% to the total OFP. The contribution of aromatics to the SOA formation at all sites reached 94.1%-98.6%. Considering the potential source-area of VOCs, regional transport of VOCs occurred within the GZP cities.

Characteristics and Sources of Volatile Organic Compounds in the Nanjing Industrial Area

In this study, 56 volatile organic compounds species (VOCs) and other pollutants (NO, NO2, SO2, O3, CO and PM2.5) were measured in the northern suburbs of Nanjing from September 2014 to August 2015. The total volatile organic compound (TVOC) concentrations were higher in the autumn (40.6 ± 23.8 ppbv) and winter (41.1 ± 21.7 ppbv) and alkanes were the most abundant species among the VOCs (18.4 ± 10.0 ppbv). According to the positive matrix factorization (PMF) model, the VOCs were found to be from seven sources in the northern suburbs of Nanjing, including liquefied petroleum gas (LPG) sources, gasoline vehicle emissions, iron and steel industry sources, industrial refining coke sources, solvent sources and petrochemical industry sources. One of the sources was influenced by seasonal variations: it was a diesel vehicle emission source in the spring, while it was a coal combustion source in the winter. According to the conditional probability function (CPF) method, it was found that the main contribution areas of each source were located in the easterly direction (mainly residential areas, industrial areas, major traffic routes, etc.). There were also seasonal differences in concentration, ozone formation potential (OFP), OH radical loss rate (LOH) and secondary organic aerosols potential (SOAP) for each source due to the high volatility of the summer and autumn temperatures, while combustion increases in the winter. Finally, the time series of O3 and OFP was compared to that PM2.5 and SOAP and then they were combined with the wind rose figure. It was found that O3 corresponded poorly to the OFP, while PM2.5 corresponded well to the SOAP. The reason for this was that the O3 generation was influenced by several factors (NOx concentration, solar radiation and non-local transport), among which the influence of non-local transport could not be ignored.

Decrease in ambient volatile organic compounds during the COVID-19 lockdown period in the Pearl River Delta region, south China

During the COVID-19 lockdown, ambient ozone levels are widely reported to show much smaller decreases or even dramatical increases under substantially reduced precursor NOx levels, yet changes in ambient precursor volatile organic compounds (VOCs) have been scarcely reported during the COVID-19 lockdown, which is an opportunity to examine the impacts of dramatically changing anthropogenic emissions on ambient VOC levels in megacities where ozone formation is largely VOC-limited. In this study, ambient VOCs were monitored online at an urban site in Guangzhou in the Pearl River Delta region before, during, and after the COVID-19 lockdown. The average total mixing ratios of VOCs became 19.1% lower during the lockdown than before, and those of alkanes, alkenes and aromatics decreased by 19.0%, 24.8% and 38.2%, respectively. The levels of light alkanes (C < 6) decreased by only 13.0%, while those of higher alkanes (C ≥ 6) decreased by 67.8% during the lockdown. Disappeared peak VOC levels in morning rush hours and the drop in toluene to benzene ratios during the lockdown suggested significant reductions in vehicle exhaust and industrial solvent emissions. Source apportioning by positive matrix factorization model revealed that reductions in industrial emissions, diesel exhaust (on-road diesel vehicles and off-road diesel engines) and gasoline-related emissions could account for 48.9%, 42.2% and 8.8%, respectively, of the decreased VOC levels during the lockdown. Moreover, the reduction in industrial emissions could explain 56.0% and 70.0% of the reductions in ambient levels of reactive alkenes and aromatics, respectively. An average increase in O₃-1 h by 17% and a decrease in the daily maximum 8-h average ozone by 11% under an average decrease in NOx by 57.0% and a decrease in VOCs by 19.1% during the lockdown demonstrated that controlling emissions of precursors VOCs and NOx to prevent ambient O₃ pollution in megacities such as Guangzhou remains a highly challenging task.

Pollution Characteristics and Health Risk Assessment of VOCs in Jinghong

In order to investigate the seasonal variation in chemical characteristics of VOCs in the urban and suburban areas of southwest China, we used SUMMA canister sampling in Jinghong city from October 2016 to June 2017. Forty-eight VOC species concentrations were analyzed using atmospheric preconcentration gas chromatography–mass spectrometry (GC–MS), Then, regional VOC pollution characteristics, ozone formation potentials (OFP), source identity, and health risk assessments were studied. The results showed that the average concentration of total mass was 144.34 μg·m−3 in the urban area and 47.81 μg·m−3 in the suburban area. Alkanes accounted for the highest proportion of VOC groups at 38.11%, followed by olefins (36.60%) and aromatic hydrocarbons (25.28%). Propane and isoprene were the species with the highest mass concentrations in urban and suburban sampling sites. The calculation of OFP showed that the contributions of olefins and aromatic hydrocarbons were higher than those of alkanes. Through the ratio of specific species, the VOCs were mainly affected by motor vehicle exhaust emissions, fuel volatilization, vegetation emissions, and biomass combustion. Combined with the analysis of the backward trajectory model, biomass burning activities in Myanmar influenced the concentration of VOCs in Jinghong. Health risk assessments have shown that the noncarcinogenic risk and hazard index of atmospheric VOCs in Jinghong were low (less than 1). However, the value of the benzene cancer risk to the human body was higher than the safety threshold of 1 × 10−6, showing that benzene has carcinogenic risk. This study provides effective support for local governments formulating air pollution control policies.

Sources of ambient non-methane hydrocarbon compounds and their impacts on O3 formation during autumn, Beijing

The field observation of 54 non-methane hydrocarbon compounds (NMHCs) was conducted from September 1 to October 20 in 2020 during autumn in Haidian District, Beijing. The mean concentration of total NMHCs was 29.81 ± 11.39 ppbv during this period, and alkanes were the major components. There were typical festival effects of NMHCs with lower concentration during the National Day. Alkenes and aromatics were the dominant groups in ozone formation potential (OFP) and OH radical loss rate (L_OH). The positive matrix factorization (PMF) running results revealed that vehicular exhaust became the biggest source in urban areas, followed by liquefied petroleum gas (LPG) usage, solvent usage, and fuel evaporation. The box model coupled with master chemical mechanism (MCM) was applied to study the impacts of different NMHCs sources on ozone (O₃) formation in an O₃ episode. The simulation results indicated that reducing NMHCs concentration could effectively suppress O₃ formation. Moreover, reducing traffic-related emissions of NMHCs was an effective way to control O₃ pollution at an urban site in Beijing.

Characterization of VOCs during Nonheating and Heating Periods in the Typical Suburban Area of Beijing, China: Sources and Health Assessment

In recent years, the “coal to electricity” project (CTEP) using clean energy instead of coal for heating has been implemented by Beijing government to cope with air pollution. However, VOC pollution after CTEP was rarely studied in suburbs of Beijing. To fill this exigency, 116 volatile organic compounds (VOCs) were observed during nonheating (P1) and heating (P2) periods in suburban Beijing. The results showed that the total of VOCs (TVOCs) was positively correlated with PM2.5, PM10, NO2, CO, and SO2 but negatively correlated with O3 and wind speed. The average TVOCs concentration was 19.43 ± 12.41 ppbv in P1 and 16.25 ± 8.01 ppbv in P2. Aromatics and oxygenated VOCs (OVOCs) were the main contributors to ozone formation potential (OFP). Seven sources of VOCs identified by the positive matrix factorization (PMF) model were industrial source, coal combustion, fuel evaporation, gasoline vehicle exhaust, diesel vehicle exhaust, background and biogenic sources, and solvent usage. The contribution of coal combustion to VOCs increased significantly during P2, whereas industrial sources, fuel evaporation, and solvent usage exhibited opposite trends. The potential source contribution function (PSCF) and concentration weighted trajectory (CWT) were used to analyze the source distributions. The results showed that VOC pollution was caused mainly by air mass from southern Hebei during P1 but by local emissions during P2. Therefore, although the contribution of coal combustion after heating increased, TVOCs concentration during P2 was lower than that during P1. Chronic noncarcinogenic risks of all selected VOC species were below the safe level, while the carcinogenic risks of most selected VOC species were above the acceptable risk level, especially for tetrachloromethane and 1,2-dichloroethane. The cancer risks posed by gasoline vehicle emissions, industrial enterprises, and coal combustion should be paid more attention.

Spatiotemporal distribution characteristics and potential sources of VOCs at an industrial harbor city in southern Taiwan: Three-year VOCs monitoring data analysis

Kaohsiung City is the largest harbor city in Taiwan. The Linhai Special Industrial Complex (LSIC), which is the largest heavy industrial zone in Taiwan, and other industrial zones and storage station of petrochemicals are adjacent to the Kaohsiung Port. Volatile organic compounds (VOCs), which are discharged from industrial processes in this large industrial area, are likely to cause the poor ambient air quality and atmospheric visibility in Kaohsiung City. This study uses the continuous monitoring data of 54 VOCs during 2018-2020 at eight air quality monitoring stations in the industrialized city to evaluate the spatiotemporal distributions and seasonal variations of VOC concentrations. Principal component analysis and ratios of benzene, toluene, ethylbenzene and xylenes (BTEX) are used to track the potential sources of VOCs for different stations. The highest average concentration of total volatile organic compounds (TVOC) was observed in winter (32.54 ppb), while the lowest TVOC concentration was observed in summer (25.84 ppb), which is related to the prevailing wind directions of monsoons. Kaohsiung is located in the weak monsoon wake area, and air pollutants are easily accumulated in the winter. The southwest wind prevailing in summer results in good diffusion and frequent rainfalls. However, the Qijin station close to the seashore has the highest average TVOC concentration among the eight stations. The seasonal prevailing winds caused the average TVOC concentrations in summer (41.3 ppb) to be higher than that in winter (31.62 ppb) at the Qijin station. It was attributed to the fact that the Qijin Peninsula is vulnerable to VOC emissions from ship sailing in the Taiwan Strait, the processing and export zone, and the shipbuilding yards nearby the Kaohsiung Harbor. Comparing the BTEX ratios of Kaohsiung City with the data of Hong Kong, we found that VOCs were mainly from industrial emissions in Kaohsiung City, which were significantly different from Hong Kong that VOCs were mainly emitted from traffic emissions. Overall, VOCs in Kaohsiung City have been decreased from 2018 to 2020; however, according to the analytical results of ozone formation potential, toluene and m,p-xylenes are the most potential photochemical precursors for ozone formation. The government should enforce and regulate aromatic hydrocarbons from industrial emission sources to reduce the potential formation of ozone.

Insights on In-Situ Photochemistry Associated with Ozone Reduction in Guangzhou during the COVID-19 Lockdown

Increases in ground-level ozone (O3) have been observed during the COVID-19 lockdown in many places around the world, primarily due to the uncoordinated emission reductions of O3 precursors. In Guangzhou, the capital of Guangdong province in South China, O3 distinctively decreased during the lockdown. Such a phenomenon was attributed to meteorological variations and weakening of local O3 formation, as indicated by chemical transport models. However, the emission-based modellings were not fully validated by observations, especially for volatile organic compounds (VOCs). In this study, we analyzed the changes of O3 and its precursors, including VOCs, from the pre-lockdown (Pre-LD) to lockdown period (LD) spanning 1 week in Guangzhou. An observation-based box model was applied to understand the evolution of in-situ photochemistry. Indeed, the ambient concentrations of O3 precursors decreased significantly in the LD. A reduction of 20.7% was identified for the total mixing ratios of VOCs, and the transportation-related species experienced the biggest declines. However, the reduction of O3 precursors would not lead to a decrease of in-situ O3 production if the meteorology did not change between the Pre-LD and LD periods. Sensitivity tests indicated that O3 formation was limited by VOCs in both periods. The lower temperature and photolysis frequencies in the LD reversed the increase of O3 that would be caused by the emission reductions otherwise. This study reiterates the fact that O3 abatement requires coordinated control strategies, even if the emissions of O3 precursors can be significantly reduced in the short term.

Ambient volatile organic compounds at a receptor site in the Pearl River Delta region: Variations, source apportionment and effects on ozone formation

We present the continuously measurements of volatile organic compounds (VOCs) at a receptor site (Wan Qing Sha, WQS) in the Pearl River Delta (PRD) region from September to November of 2017. The average mixing ratios of total VOCs (TVOCs) was 36.3 ± 27.9 ppbv with the dominant contribution from alkanes (55.5%), followed by aromatics (33.3%). The diurnal variation of TVOCs showed a strong photochemical consumption during daytime, resulting in the formation of ozone (O₃). Five VOC sources were resolved by the positive matrix factorization (PMF) model, including solvent usage (28.6%), liquid petroleum gas (LPG) usage (24.4%), vehicle exhaust (21.0%), industrial emissions (13.2%) and gasoline evaporation (12.9%). The regional transport air masses from the upwind cities of south China can result in the elevated concentrations of TVOCs. Low ratios of TVOCs/NO_x (1.53 ± 0.88) suggested that the O₃ formation regime at WQS site was VOC-limited, which also confirmed by a photochemical box model with the master chemical mechanism (PBM-MCM). Furthermore, the observation on high-O₃ episode days revealed that frequent O₃ outbreaks at WQS were mainly caused by the regional transport of anthropogenic VOCs especially for aromatics and the subsequent photochemical reactions. This study provides valuable information for policymakers to propose the effective control strategies on photochemical pollution in a regional perspective.

Variability and sources of non-methane hydrocarbons at a Mediterranean urban atmosphere: The role of biomass burning and traffic emissions

Levels and sources of non-Methane Hydrocarbons (NMHCs) were investigated at the urban background Thissio station, close to the historical center of Athens (Greece) from March 2016 to February 2017 (12 months), by means of an automated GC-FID. Alkanes dominated over aromatics and alkenes, with hourly mean levels ranging from detection limit up to 60 μg m^-3 for i-pentane and 90 μg m^-3 for toluene. Higher levels were recorded in the cold period relative to the warmer one. In addition, NMHCs seasonal diurnal cycles were characterized by a bimodal pattern, following the trend of tracers of anthropogenic sources. The Positive Matrix Factorization (PMF) was used for the allocation of NMHC to their sources. Five factors were identified and quantified, with traffic-related sources being the main one contributing up to 60% to total NMHCs, while biomass burning contributes up to 19%. A supplementary PMF assimilation was applied on a seasonal basis further including α-pinene, C6-C16 alkanes and aromatics. This PMF resulted to a seven-factor solution that allowed the examination of two additional sources, in addition to five already identified, highlighting the main contribution of anthropogenic sources (70%) to α-pinene.

Characteristics, sources and health risks assessment of VOCs in Zhengzhou, China during haze pollution season

Zhengzhou is one of the most haze-polluted cities in Central China with high organic carbon emission, which accounts for 15%-20% of particulate matter (PM_2.5) in winter and causes significantly adverse health effects. Volatile organic compounds (VOCs) are the precursors of secondary PM_2.5 and O₃ formation. An investigation of characteristics, sources and health risks assessment of VOCs was carried out at the urban area of Zhengzhou from 1^st to 31^st December, 2019. The mean concentrations of total detected VOCs were 48.8 ± 23.0 ppbv. Alkanes (22.0 ± 10.4 ppbv), halocarbons (8.1 ± 3.9 ppbv) and aromatics (6.5 ± 3.9 ppbv) were the predominant VOC species, followed by alkenes (5.1 ± 3.3 ppbv), oxygenated VOCs (3.6 ± 1.8 ppbv), alkyne (3.5 ± 1.9, ppbv) and sulfide (0.5 ± 0.9 ppbv). The Positive Matrix Factorization model was used to identify and apportion VOCs sources. Five major sources of VOCs were identified as vehicular exhaust, industrial processes, combustion, fuel evaporation, and solvent use. The carcinogenic and non-carcinogenic risk values of species were calculated. The carcinogenic and non-carcinogenic risks of almost all air toxics increased during haze days. The total non-carcinogenic risks exceeded the acceptable ranges. Most VOC species posed no non-carcinogenic risk during three haze events. The carcinogenic risks of chloroform, 1,2-dichloroethane, 1,2-dibromoethane, benzyl chloride, hexachloro-1,3-butadiene, benzene and naphthalene were above the acceptable level (1.0  ×  10^-6) but below the tolerable risk level (1.0  ×  10^-4). Industrial emission was the major contributor to non-carcinogenic, and solvent use was the major contributor to carcinogenic risks.

Heating events drive the seasonal patterns of volatile organic compounds in a typical semi-arid city

The emission characteristics, source apportionment and chemical behavior of volatile organic compounds (VOCs) are important for strategy-making on ozone (O₃) and fine particulate matter (PM_2.5) control. Based on the continuous observation during four seasons, the seasonal characteristics, chemical reactivity and source apportionment of 116 VOCs species were studied in a typical semi-arid city with no relevant research. The results showed that the annual average concentrations of total volatile organic compounds (TVOCs) in Hohhot was 44.67 ± 46.59 ppbv with the predominant of alkanes and oxygenated volatile organic compounds (OVOCs). The sharp increment of TVOCs were explained by the elevating OVOCs and alkanes in autumn, while alkanes and alkenes in winter. The levels of alkenes presented negative and positive correlations with solar radiation and PM₁₀, respectively. The mixing ratios accounted for 30% (alkanes) and 23% (alkenes and aromatics) of the TVOCs, respectively; while their ozone formation potential (OFP) ~15% and nearly 50% (even 75% in winter), respectively, indicating that the OFP of different VOCs species depends not only on their concentrations but more importantly on their chemical activity in atmosphere. According to the seasonal source apportionment, both the high levels of short-chain alkanes, alkenes and aromatics and the increasing coal sales volume suggested that the combustion sources were the predominant in heating seasons, while solvent uses was extracted as the most predominant during non-heating seasons. In non-heating seasons, the biogenic emission sources, ranking as the second contributor, were significantly higher than heating seasons. Isoprene was the most active biogenic VOCs species, bagging test results showed that deciduous trees were the predominant contributors for isoprene (~99%), while coniferous trees and shrub for monoterpenes (>95%). It will be helpful for understanding the characteristics of VOCs in Chinese national key development areas and informing policy to control semi-arid regional VOCs air pollution.

Biomass-burning emissions could significantly enhance the atmospheric oxidizing capacity in continental air pollution

Volatile organic compounds (VOCs) are important precursors of photochemical pollution. However, a substantial fraction of VOCs, namely, oxygenated VOCs (OVOCs), have not been sufficiently characterized to evaluate their sources in air pollution in China. In this study, a total of 119 VOCs, including 60 OVOCs in particular, were monitored to provide a more comprehensive picture based on different online measurement techniques, proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) and online gas chromatography/mass spectrometry (GC/MS), at a receptor site in southeastern China during a photochemically active period. Positive matrix factorization (PMF) and photochemical age-based parameterization were combined to identify and quantify different sources of major VOCs during daytime hours, with the advantage of including VOC decay processes. The results revealed the unexpected role of biomass burning (21%) in terms of ozone (O₃) formation potential (OFP) when including the contributions of OVOCs and large contributions (30-32%) of biomass burning to aldehydes, as more OVOCs were measured in this study. We argue that biomass burning could significantly enhance the continental atmospheric oxidizing capacity, in addition to the well-recognized contributions of primary pollutants, which should be seriously considered in photochemical models and air pollution control strategies.

A comparison investigation of atmospheric NMHCs at two sampling sites of Beijing city and a rural area during summertime

Atmospheric non-methane hydrocarbons (NMHCs) were measured synchronously at an urban site of Beijing city (BJ) and a rural site of Dongbaituo (DBT) in Hebei province from 1 July to 15 August 2016. The average concentration of the total NMHCs (TNMHCs) at DBT site were about a factor of 1.3 higher than that at BJ site. Ethane, ethylene, propane, acetylene, butane, isobutane, toluene and isopentane were the common species in the top ten NMHCs at the two sampling sites, and the contributions of the top ten NMHCs to TNMHCs at BJ and DBT sites were 65.6% and 75.1%, respectively. The diurnal variations of TNMHCs at BJ site exhibited one peak during the morning rush hours, whereas two peaks occurred at DBT site during the period from 3:00 to 8:00 (UTC/GMTC8). Based on the correlation coefficients of typical NMHCs pairs and the positive matrix factorization (PMF) results, the gasoline exhaust was found to be the dominant source (38.8%) for atmospheric NMHCs in Beijing, while coal combustion made the largest contribution (32.3%) at the rural site. Atmospheric ozone production over the BJ site was found to be NMHCs-sensitive, while it was in the transition regime at DBT site. Additionally, the largest contributions of atmospheric NMHCs groups to the ozone formation potential at BJ and DBT sites were alkenes and aromatics, with the proportions of 35.8% and 38.6%, respectively.

Volatile Organic Compounds Monitored Online at Three Photochemical Assessment Monitoring Stations in the Pearl River Delta (PRD) Region during Summer 2016: Sources and Emission Areas

Volatile organic compounds (VOCs) were monitored online at three photochemical assessment monitoring stations (MDS, WQS and HGS) in the Pearl River Delta region during the summer of 2016. Measured levels of VOCs at the MDS, WQS and HGS sites were 34.78, 8.54 and 8.47 ppbv, respectively, with aromatics and alkenes as major ozone precursors and aromatics as major precursors to secondary organic aerosol (SOA). The positive matrix factorization (PMF) model revealed that VOCs at the sites mainly came from vehicle exhaust, petrochemical industry, and solvent use. Vehicle exhaust and industrial processes losses contributed most to ozone formation potentials (OFP) of VOCs, while industrial processes losses contributed most to SOA formation potentials of VOCs. Potential source contribution function (PSCF) analysis revealed a north-south distribution for source regions of aromatics occurring at MDS with emission sources in Guangzhou mainly centered in the Guangzhou central districts, and source regions of aromatics at WQS showed an east-west distribution across Huizhou, Dongguan and east of Guangzhou, while that at HGS showed a south-north distribution across Guangzhou, Foshan, Zhaoqing and Yangjiang. This study demonstrates that multi-point high time resolution data can help resolve emission sources and locate emission areas of important ozone and SOA precursors.

The characteristics and sources of roadside VOCs in Hong Kong: Effect of the LPG catalytic converter replacement programme

In order to improve local air quality of Hong Kong, more than 99% taxies and public light buses were changed from diesel to liquefied petroleum gas (LPG) fuel type in the early 2000s. In addition to the catalytic converters wear and tear, it is necessary to control air pollutants emitted from LPG vehicles. Therefore, an LPG catalytic converter replacement programme (CCRP) was fulfilled from October 2013 to April 2014 by the Hong Kong government. Roadside volatile compounds (VOCs) were measured by on-line measurement techniques before and after the programme to evaluate the effectiveness of the LPG CCRP. The mixing ratios of total measured VOCs were found decreased from 69.3 ± 12.6 ppbv to 43.9 ± 6.5 ppbv after the LPG CCRP with the decreasing percentage of 36.7%. In addition, the total mixing ratio of LPG tracers, namely propane, i-butane, and n-butane, accounted for 49% of total measured VOCs before the LPG CCRP and the weighting percentage decreased to 34% after the programme. Moreover, the source apportionment of roadside VOCs also reflects the large decreasing trend of LPG vehicular emissions after the air pollution control measure. Due to the application of PTR-MS on measuring real-time VOCs and oxygenated volatile compounds (OVOCs) in this study, the emission ratios of individual OVOCs were investigated and being utilized to differentiate primary and secondary/biogenic sources of roadside OVOCs in Hong Kong. The findings demonstrate the effectiveness of the intervention programme, and are helpful to further implementation of air pollution control strategies in Hong Kong.

A comprehensive study on emission of volatile organic compounds for light duty gasoline passenger vehicles in China: Illustration of impact factors and renewal emissions of major compounds

BACKGROUND

Many volatile organic compounds (VOCs) are efficient precursors for both ozone and secondary organic aerosol (SOA) which are problematic to environmental controls in many global cities. Vehicle emission is one of the most important anthropogenic sources for VOCs. In between, light duty gasoline passenger vehicles (LDGPVs) contributed more than half of the on-road vehicles in China, demonstrating unique emission characteristics and also significant contributions in emission inventory.

OBJECTIVES

To illustrate the variation of VOCs emissions from LDGPVs under different conditions, evaluate the sensitivity of the potential influencing factors, such as emission standards, displacement, cumulative mileage, and driving mode, on the VOCs emissions profiles, and to update the emission inventory by taking into account of the most influential factor.

METHODS

In this study, seventy-four in-used LDGPVs were examined by the chassis dynamometer. A total of 25 VOCs in the emissions was quantified using an online time of flight mass spectrometer (TOF-MS). Fuel-based emission factors (EF) were calculated.

RESULTS

The results showed that the maximum ΣEF (260.4 ± 241.1 mg/L) was seen for LDGPVs at a high acceleration rate (0.9 m/s²). From the technical control emission standard aspect, the total emission factor of VOCs (expressed as ∑EF) was declined for China IV LDGPVs relative to China III vehicles, with the decreasing extent determined as 24.8%. Among LDGPVs with engine capacity of <1.5 L, 1.5-2.5 L and >2.5 L, it is for 1.5-2.5 L that the lowest ∑EF (101.2 ± 70.1 mg/L) was determined. Along with the increasing of cumulative mileage, the EF values of VOCs were uplift, and the ∑VOCs increased almost linearity, while the increasing trend became steady for ∑EF when the cumulative mileage more than 8 × 10⁴ km. As for different driving conditions, the sequence of EFs from high to low are presented as acceleration (239.3 ± 203.5 mg/L) >idle (226.1 ± 195.6 mg/L) >deceleration (218.5 ± 193.1 mg/L)>uniform (218.2 ± 182.5 mg/L)>slide (176.1 ± 165.2 mg/L). While the cruising speeds increased between 15 and 50 km/h, the linearity between ΣEF declined; however, an opposite trend was seen when the acceleration rates increased. In the chemical speciation, the reactive aromatics contributed the largest fraction of the VOCs (>40%). The ratio of benzene to toluene (B/T) was loaded in high interval (0.94-1.33) in this paper. Larger fluctuation of coefficient of variation (CV) was found among different cumulative mileage and displacement. By taking into account the deterioration effect related to cumulative mileage, emissions of butene, pentene, benzene and toluene were 42.9 Gg, 49.7 Gg, 109.6 Gg and 51.9 Gg in respect for LDGPVs that composed of China III and China IV.

CONCLUSIONS

Our results demonstrated the necessaries in upgrading the emission control technology. Cumulative mileages and displacements are the two most dominated factors that impacted on the EFs and chemical profiles of VOCs. The higher emission of benzene estimated demonstrated the possible elevation of VOCs in comparison with previous studies.

Long-term observations of oxygenated volatile organic compounds (OVOCs) in an urban atmosphere in southern China, 2014-2019

Oxygenated volatile organic compounds (OVOCs) are important precursors and intermediate products of atmospheric photochemical reactions, which can promote the formation of secondary pollutants such as ozone (O₃) and secondary organic aerosol (SOA). However, there have been few studies on the sources of and long-term variation in ambient OVOCs. This study combined sensitive, near real-time measurements of VOCs by proton transfer reaction-mass spectrometry (PTR-MS) with an improved photochemical age parameterization method to quantify daytime sources of OVOCs in an urban atmosphere in China from 2014 to 2019, permitting the observation of the impacts of emission control strategies that were implemented during this period. Temporal variation in six key OVOCs (methanol, acetaldehyde, acetone, methyl ethyl ketone (MEK), formic acid, and acetic acid) were observed. The sum of concentrations of OVOCs was averagely 13% higher during the dry season (November to April), when winds transported polluted air masses to Shenzhen from the continent, than during the wet season, and peak diurnal levels occurred during the daytime year-round due to photochemical production and higher daytime anthropogenic emissions. The average dry season concentration of OVOCs declined from a peak of 30.3 ppb in 2015 to 18.7 ppb in 2019. The results of source apportionment showed that primary anthropogenic sources contributed the most to methanol, MEK, and acetic acid (32-51%); the dominant sources of acetaldehyde and formic acid were both primary and secondary anthropogenic sources; and biomass burning contributed a small fraction (5-11%) to the six OVOCs. From 2014 to 2019, contributions from primary anthropogenic sources of OVOCs decreased significantly by 50-60% due to intensive pollution control measures in Shenzhen, whereas pollution control measures had no observable impact on secondary OVOCs, indicating their formation was not limited by availability of their primary VOC precursors.

Temporal and spatial discrepancies of VOCs in an industrial-dominant city in China during summertime

Ozone (O₃) pollution is currently problematic to cities across the globe. Many non-methane hydrocarbons (NMHCs) are efficient O₃ precursors. In this study, target volatile organic compounds (VOCs), including oxygenated VOCs (known as carbonyls), were monitored at eight sampling sites distributed in urban and suburban in the typical and industrial-dominant city of Shaoxing, Zhejiang province, China. At the suburban sites, C₈-C₁₂ alkanes, aromatics with lower reactivity (k_OH <13 × 10^-12 cm³ mol^-1 s^-1) and acetonitrile were more abundant than urban ones due to higher emissions from diesel-fueled trucks and biomass burning. In general, higher abundances of total quantified NMHCs (ΣNMHC) were found on high O₃ (HO) days. The increments of formaldehyde (C₁) and O₃ were higher in urban than suburban, while a reverse trend was seen for acetaldehyde (C₂). Substantial and local biogenic inputs of C₂ were found in suburban in the afternoon when both temperature and light intensity reached maximum of the day. In urban, higher increment was found for O₃ than the carbonyls, representing that the secondary formation of O₃ was more efficient. Distance decay gradient of most representative NMHCs were positively correlated to the distances from a westernmost industrial origin located at the upwind location. The net loss rates of the NMHCs ranged from -0.009 to -0.11 ppbv km^-1, while the higher rates were seen for the most reactive species like C₂-C₄ alkenes. The results and interpretation of this study are informative to establish efficient local control measures for O₃ and the related percussors for the microscale industrial cities in China.

Characteristics and sources of volatile organic compounds during high ozone episodes: A case study at a site in the eastern Guanzhong Plain, China

This study performed continuous measurements of 105 volatile organic compounds (VOCs) in Weinan in the eastern Guanzhong Plain from 1 July to September 19, 2019. Ozone (O₃) episode and non-episode days were identified according to China Ambient Air Quality Standard, and the concentrations of total quantified VOCs (TVOCs) were 33.43 ± 13.64 ppbv and 29.13 ± 14.31 ppbv, respectively. During different O₃ pollution episodes, alkanes comprised the highest proportion to TVOC concentrations, while alkenes contributed the most to ozone formation potential (OFP). In addition, O₃ episode days were mainly caused by enhanced emissions of precursors and meteorological conditions favorable to O₃ production. Based on Empirical Kinetic Modelling Approach (EKMA), the O₃ formation in Weinan was found in the transitional regime, in which the synergistic reduction of VOCs and nitrogen oxide (NOx) would be more effective for O₃ reduction. Eight sources were identified by positive matrix factorization (PMF) model, with natural gas (NG)/liquefied petroleum gas (LPG) usage as the most significant contributor to VOC concentration, followed by vehicle exhaust, biomass burning, solvent usage, fuel evaporation, rubber/plastic industrial emissions, biogenic source, and mixed industrial emissions. Furthermore, rubber/plastic industrial emissions, solvent usage, fuel evaporation, and vehicle exhaust were the most significant sources to O₃ formation. Based on conditional bivariate probability function (CBPF), vehicle exhaust, fuel evaporation, and solvent usage were mainly local emissions, while other sources were mainly affected by regional transport. This study provides useful reference for research on the atmospheric photochemical formation of O₃ and evidence for regional O₃ reduction strategies.

Variations in Levels and Sources of Atmospheric VOCs during the Continuous Haze and Non-Haze Episodes in the Urban Area of Beijing: A Case Study in Spring of 2019

To better evaluate the variations in concentration characteristics and source contributions of atmospheric volatile organic compounds (VOCs) during continuous haze days and non-haze days, hourly observations of atmospheric VOCs were conducted using a continuous on-line GC-FID (Airmo VOC GC-866) monitoring system during 1–15 March 2019, in urban areas of Beijing, China. The results showed that the total VOC concentrations during haze days and non-haze days were 59.13 ± 31.08 μg/m3 and 16.91 ± 7.19 μg/m3, respectively. However, the average O3 concentrations during the two haze days were lower than those of non-haze days due to the extremely low concentrations at night instead of the reported lower photochemical reaction in daytime. The ratio of OH radical concentration during haze and non-haze days indicating that the rate of photochemical reaction during haze days was higher than those of non-haze days from 13:00–19:00. The stable air conditions and the local diesel emission at night were the main reasons for the decreased O3 concentrations during haze days. Six major sources were identified by positive matrix factorization (PMF), namely, diesel exhaust, combustion, gasoline evaporation, solvent usage, gasoline exhaust, and the petrochemical industry, contributing 9.93%, 25.29%, 3.90%, 16.88%, 35.59% and 8.41%, respectively, during the whole observation period. The contributions of diesel exhaust and the petrochemical industry emissions decreased from 26.14% and 6.43% during non-haze days to 13.70% and 2.57%, respectively, during haze days. These reductions were mainly ascribed to the emergency measures that the government implemented during haze days. In contrast, the contributions of gasoline exhaust increased from 34.92% during non-haze days to 48.77% during haze days. The ratio of specific VOC species and PMF both showed that the contributions of gasoline exhaust emission increased during haze days. The backward trajectories, potential source contribution function (PSCF) and concentration weighted trajectory (CWT) showed that the air mass of VOCs during haze days was mainly affected by the short-distance transportation from the southwestern of Hebei province. However, the air mass of VOCs during non-haze days was mainly affected by the long-distance transportation from the northwest.

Improving VOCs control strategies based on source characteristics and chemical reactivity in a typical coastal city of South China through measurement and emission inventory

In China, the corresponding control directives for volatile organic compounds (VOCs) have been based on primary emissions, rarely considering reactive speciation. To seek more effective VOCs control strategies, we investigated 107 VOC species in a typical coastal city (Beihai) of South China, from August to November 2018. Meanwhile, a high-resolution anthropogenic VOCs monthly emission inventory (EI) was established for 2018. For source apportionments (SAs) reliability, comparisons of source structures derived from positive matrix factorization (PMF) and EI were made mainly in terms of reaction losses, uncertainties and specific ratios. Finally, for the source-end control, a comprehensive reactivity control index (RCI) was established by combing SAs with reactive speciation profiles. Ambient measurements showed that the average concentration of VOCs was 26.38 ppbv, dominated by alkanes (36.7%) and oxygenated volatile organic compounds (OVOCs) (29.4%). VOC reactivity was estimated using ozone formation potential (52.35 ppbv) and propylene-equivalent concentration (4.22 ppbv). EI results displayed that the entire VOC, OFP, and propylene-equivalent emissions were 40.98 Gg, 67.98 Gg, and 105.93 Gg, respectively. Comparisons of source structures indicated that VOC SAs agreed within ±100% between two perspectives. Both PMF and EI results showed that petrochemical industry (24.0% and 33.0%), food processing and associated combustion (19.1% and 29.2%) were the significant contributors of anthropogenic VOCs, followed by other industrial processes (22.2% and 13.3%), transportation (18.9% and 12.0%), and solvent utilization (9.1% and10.5%). Aimed at VOCs abatement according to RCI: for terminal control, fifteen ambient highly reactive species (predominantly alkenes and alkanes) were targeted; for source control, the predominant anthropogenic sources (food industry, solvent usage, petrochemical industry and transportation) and their emitted highly reactive species were determined. Particularly, with low levels of ambient VOC and primary emissions, in this VOC and NOx double-controlled regime, crude disorganized emission from food industry contributed a high RCI.

Characteristics of atmospheric volatile organic compounds in urban area of Beijing: Variations, photochemical reactivity and source apportionment

Atmospheric volatile organic compounds (VOCs) were observed by an on-line gas chromatography-flame ionization detector monitoring system from November 2016 to August 2017 in Beijing. The average concentrations were winter (40.27 ± 25.25 μg/m³) > autumn (34.25 ± 19.90 µg/m³) > summer (32.53 ± 17.39 µg/m³) > spring (24.72 ± 17.22 µg/m³). Although benzene (15.70%), propane (11.02%), ethane (9.32%) and n-butane (6.77%) were the most abundant species, ethylene (14.07%) and propene (11.20%) were the key reactive species to ozone formation potential (OFP), and benzene, toluene, ethylbenzene, m-xylene + p-xylene and o-xylene (54.13%) were the most reactive species to secondary organic aerosol formation potential (SOAFP). The diurnal and seasonal variations indicated that diesel vehicle emission during early morning, gasoline vehicle emission at the traffic rush hours and coal burning during the heating period might be important sources. Five major sources were further identified by positive matrix factorization (PMF). The vehicle exhaust (gasoline exhaust and diesel exhaust) was found to be contributed most to atmospheric VOCs, with 43.59%, 41.91%, 50.45% and 43.91%, respectively in spring, summer, autumn and winter; while solvent usage contributed least, with 11.10%, 7.13%, 14.00% and 19.87%, respectively. Biogenic emission sources (13.11%) were only identified in summer. However, both vehicle exhaust and solvent usage were identified to be the key sources considering contributions to the OFP and SOAFP. Besides, the contributions of combustion during heating period and gasoline evaporation source during warm seasons to OFP and SOAFP should not be overlooked.

Source-Specific Volatile Organic Compounds and Emergency Hospital Admissions for Cardiorespiratory Diseases

Knowledge gaps remain regarding the cardiorespiratory impacts of ambient volatile organic compounds (VOCs) for the general population. This study identified contributing sources to ambient VOCs and estimated the short-term effects of VOC apportioned sources on daily emergency hospital admissions for cardiorespiratory diseases in Hong Kong from 2011 to 2014. We estimated VOC source contributions using fourteen organic chemicals by positive matrix factorization. Then, we examined the associations between the short-term exposure to VOC apportioned sources and emergency hospital admissions for cause-specific cardiorespiratory diseases using generalized additive models with polynomial distributed lag models while controlling for meteorological and co-pollutant confounders. We identified six VOC sources: gasoline emissions, liquefied petroleum gas (LPG) usage, aged VOCs, architectural paints, household products, and biogenic emissions. We found that increased emergency hospital admissions for chronic obstructive pulmonary disease were positively linked to ambient VOCs from gasoline emissions (excess risk (ER%): 2.1%; 95% CI: 0.9% to 3.4%), architectural paints (ER%: 1.5%; 95% CI: 0.2% to 2.9%), and household products (ER%: 1.5%; 95% CI: 0.2% to 2.8%), but negatively associated with biogenic VOCs (ER%: -6.6%; 95% CI: -10.4% to -2.5%). Increased congestive heart failure admissions were positively related to VOCs from architectural paints and household products in cold seasons. This study suggested that source-specific VOCs might trigger the exacerbation of cardiorespiratory diseases.

An investigation into the role of VOCs in SOA and ozone production in Beijing, China

In recent years, PM2.5 and O₃ pollutions are prevalent in the atmosphere in Beijing. The study on pollution characteristics of VOC, which are important precursors of O₃ and secondary organic aerosols (SOA) contributing PM2.5, is of great significance for providing a reference to guide its reduction policy formulation. Herein, the seasonal variation of atmospheric VOCs and meteorological conditions at the sampling frequency of 1 time per hour were continuously measured from March 2016 to January 2017 in Beijing. Using the collected data combined with multiple models, the role of VOCs in SOA and O₃ production was investigated. Alkanes were the most abundant species, contributing 54.1-64.7% of the total VOC concentration for four seasons, followed by aromatics, alkenes and acetylene. The SOA potential (SOAP) was highest in winter at 2885.1 μg m^-3, followed by autumn, spring and summer. Aromatics were the main contributors to SOAP, accounting for ~98.2% of the total SOAP during the entire observation period. The empirical kinetic modeling approach results showed that O₃ production featured the VOC-limited regime in Beijing. Alkenes and aromatics were major contributors to O₃ formation potential (OFP), accounting for 33.1-45.6% and 27.2-45.2%, respectively, particularly ethylene and m,p-xylene. Positive matrix factorization results indicated that motor vehicle exhaust was still the largest local source of VOCs, but its proportion was considerably reduced. The potential source contribution function results revealed that regional transport sources of VOC pollution in Beijing mainly came from the northwest and southern areas. Thus, to control PM2.5 and O₃ pollution in Beijing, the restriction of alkenes and aromatics emission, accompanied by regional cooperation combined with local control, is essential.

Sources of oxygenated volatile organic compounds (OVOCs) in urban atmospheres in North and South China

Oxygenated volatile organic compounds (OVOCs) are critical precursors of atmospheric ozone (O₃) and secondary organic aerosols (SOA). Although China is experiencing increasing O₃ pollution from north to south, understanding the major sources of OVOCs in this region is still limited due to their active photochemical behaviors. In this study, five critical OVOCs at a northern urban site (Beijing) and a southern urban site (Shenzhen) were monitored in summer using proton transfer reaction-mass spectrometry (PTR-MS). The mean total concentration of VOCs measured in Beijing (39.4 ppb) was much higher than that measured in Shenzhen (16.7 ppb), with methanol and formaldehyde being the most abundant in concentration at both sites. The source apportionment of daytime OVOCs was conducted effectively using a photochemical age-based parameterization method. Biogenic and anthropogenic secondary sources were the main sources of formaldehyde, acetaldehyde, and acetone at both sites, with a total contribution of 46-82%; acetone also had a large regional-scale background contribution (36-38%); methanol and methyl ethyl ketone (MEK) were mainly derived from anthropogenic primary sources (35-55%) at both sites. In addition, the regional background levels of OVOCs measured in North China were shown to be much higher than those measured in South China. The calculation of the total O₃ formation potential (OFP) of OVOCs highlights the comparable contributions from anthropogenic and biogenic sources in both Beijing and Shenzhen, indicating the important role of biogenic OVOC sources even in polluted environments. Since biogenic sources are already important but uncontrollable, anthropogenic emissions in China need to be restricted even more critically in the future.

A case study on the characterization of non-methane hydrocarbons over the South China Sea: Implication of land-sea air exchange

We present the characteristics of non-methane hydrocarbons (NMHCs) over the northern South China Sea (SCS) during a cruise campaign from September to October 2013. The mixing ratios of the total NMHCs ranged from 1.45 to 7.13 ppbv with an average of 3.54 ± 1.81 ppbv. Among the measured NMHCs, alkanes and aromatics were the major groups, accounting for 45.8 ± 8.7% and 28.7 ± 12.3% of the total NMHCs, respectively. Correlations of NMHCs with typical source tracers suggest that light alkanes and benzene were largely contributed by vehicular exhaust via long-range transport, while the other aromatics might be related to industrial sources and marine ship emissions. The spatial variations of NMHCs were observed with higher mixing ratios of NMHCs in the samples collected in the offshore areas than those in the coastal areas. Air mass back-trajectory analysis and diagnostic ratios of NMHCs show that the elevations of the total NMHCs were caused by the regional pollution transport from the southeast coast of China and/or southern China. The ozone formation potentials (OFPs) of NMHCs were calculated and the results show that the aromatics associated with marine ship emissions were the important contributors to the total OFP. This study provides useful information on the interaction between continental outflow and marine atmosphere.

Hazardous volatile organic compounds in ambient air of China

Volatile organic compounds (VOCs) are ubiquitous in the atmosphere and the majority of them have been proved to be detrimental to human health. The hazardous VOCs were studied very insufficiently in China, despite the enormous emissions of VOCs. In this study, the concentrations and sources of 17 hazardous VOCs reported in literature were reviewed, based on which the health effects were assessed. In-depth survey indicated that benzene and toluene had the highest concentrations in eastern China (confined to the study regions reviewed, same for the other geographic generalization), which however showed significant declines. The southern China featured high levels of trichloroethylene. Dichloromethane and chloroform were observed to be concentrated in northern China. The distributions of 1,2-dichloropropane and tetrachloroethylene were homogeneous across the country. Basically consistent with the spatial patterns of ozone, the summertime formaldehyde exhibited higher levels in eastern and northern China, and increased continuously. While transportation served as the largest source of benzene and toluene, industrial emissions and secondary formation were the predominant contributors of halogenated hydrocarbons and aldehydes (formaldehyde and acetaldehyde), respectively. The chronic non-cancer effects of inhalation exposure to the hazardous VOCs were insignificant, however the probabilities of developing cancers by inhaling the hazardous VOCs in ambient air of China were quite high. Formaldehyde was identified as the primary carcinogenic VOC in the atmosphere of most regions. The striking results, especially the high inhalation cancer risks, alerted us that the emission controls of hazardous VOCs were urgent in China, which must be grounded upon full understanding of their occurrence, presence and health effects.

Spatiotemporal distribution of ground-level ozone in China at a city level

In recent years, ozone (O3) pollution in China has shown a worsening trend. Due to the vast territory of China, O3 pollution is a widespread and complex problem. It is vital to understand the current spatiotemporal distribution of O3 pollution in China. In this study, we collected hourly data on O3 concentrations in 338 cities from January 1, 2016, to February 28, 2019, to analyze O3 pollution in China from a spatiotemporal perspective. The spatial analysis showed that the O3 concentrations exceeded the limit in seven geographical regions of China to some extent, with more serious pollution in North, East, and Central China. The O3 concentrations in the eastern areas were usually higher than those in the western areas. The temporal analysis showed seasonal variations in O3 concentration, with the highest O3 concentration in the summer and the lowest in the winter. The weekend effect, which occurs in other countries (such as the USA), was found only in some cities in China. We also found that the highest O3 concentration usually occurred in the afternoon and the lowest was in the early morning. The comprehensive analysis in this paper could improve our understanding of the severity of O3 pollution in China.

Characteristics of Volatile Organic Compounds in Nanjing and Suzhou, Two Urban Sites in the Yangtze River Delta, China

A field measurement study of volatile organic compounds (VOCs) was performed in January 2015 in the urban areas of two of the most important cities of the Yangtze River Delta: Nanjing and Suzhou. The objectives of this study included comparing the characteristics of VOC concentrations, comparing the impacts of emissions on VOCs, using species ratios to assess air mass age, and evaluating ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAP) in air masses. The VOC concentrations in Nanjing (34.6 ± 5.8 ppbv) were higher than those of Suzhou (28.1 ± 5.6 ppbv). The most abundant VOC measured was ethane (6.6 ppbv in Nanjing and 3.6 ppbv in Suzhou). Relevant analysis shows that motor vehicle emissions in Suzhou were dominant, whereas industrial emissions in Nanjing also contributed to VOCs. During rush hour, the VOC concentrations in Nanjing were the highest (35.3 ppbv). The T/B ratio (0.92-1.79) for the two sites was observed to be relatively low in the other studied cities, indicating the source impact of traffic emissions in the two sites. Indicators X/B (0.26-0.39) and X/E (0.33-0.66) also confirmed an aging air mass was transported at the two sampling sites. According to principal component factor analysis results, vehicle emissions (44.8% in Nanjing and 30.6% in Suzhou) were the most important contribution to the two sites. Industrial sites were not only likely to experience industrial emissions but were affected by traffic emissions. Using the OFP method, both sites showed the largest percentage of alkenes (59.9% in Nanjing and 62.0% in Suzhou). When comparing SOAP, both sites showed an absolute majority of aromatics (97.6% in Nanjing and 98.3% in Suzhou). To control the formation of O₃ and SOA in the two sites, it is necessary to reduce the concentration of alkenes and aromatics, respectively. By CPF analysis, pollutants transported from the SE and NE have significant effects on the Nanjing site. In the Suzhou, roads and industrial parks in the SE and S of Suzhou have significant impacts on the site.

A Spatial-Temporal Resolved Validation of Source Apportionment by Measurements of Ambient VOCs in Central China

Understanding the sources of volatile organic compounds (VOCs) is essential in the implementation of abatement measures of ground-level ozone and secondary organic aerosols. In this study, we conducted offline VOC measurements at residential, industrial, and background sites in Wuhan City from July 2016 to June 2017. Ambient samples were simultaneously collected at each site and were analyzed using a gas chromatography–mass spectrometry/flame ionization detection system. The highest mixing ratio of total VOCs was measured at the industrial site, followed by the residential, and background sites. Alkanes constituted the largest percentage (>35%) in the mixing ratios of quantified VOCs at the industrial and residential sites, followed by oxy-organics and alkenes (15–25%).The values of aromatics and halohydrocarbons were less than 15%. By contrast, the highest values of oxy-organics accounted for more than 30%. The model of positive matrix factorization was applied to identify the VOC sources and quantify the relative contributions of various sources. Gasoline-related emission (the combination of gasoline exhaust and gas vapor) was the most important VOC-source in the industrial and residential areas, with a relative contribution of 32.1% and 40.4%, respectively. Industrial process was the second most important source with a relative contribution ranging from 30.0% to 40.7%. The relative contribution of solvent usage was 6.5–22.3%. Meanwhile, the relative contribution of biogenic emission was only within the range of 2.0–5.0%. These findings implied the importance of controlling gasoline-related and industrial VOC emissions in reducing the VOC emissions in Wuhan.

Source Apportionment of Volatile Organic Compounds (VOCs) by Positive Matrix Factorization (PMF) supported by Model Simulation and Source Markers - Using Petrochemical Emissions as a Showcase

This study demonstrates the use of positive matrix factorization (PMF) in a region with a major Petrochemical Complex, a prominent source of volatile organic compounds (VOCs), as a showcase of PMF applications. The PMF analysis fully exploited the quality and quantity of the observation data, sufficed by a cluster of 9 monitoring sites within a 20 km radius of the petro-complex. Each site provided continuous data of 54 speciated VOCs and meteorological variables. Wind characteristics were highly seasonal and played a decisive role in the source-receptor relationship, hence the dataset was divided into three sub-sets in accordance with the prevailing wind flows. A full year of real-time data were analyzed by PMF to resolve into various distinct source types including petrochemical, urban, evaporative, long-range air parcels, etc., with some sites receiving more petro-influence than others. To minimize subjectivity in the assignment of the PMF source factors, as commonly seen in some PMF works, this study attempted to solidify PMF results by supporting with two tools of spatially/temporally resolved air-quality model simulations and observation data. By exploiting the two supporting tools, the dynamic process of individual sources to a receptor were rationalized. Percent contributions from these sources to the receptor sites were calculated by summing over the occurrence of different source types. Interestingly, although the Petro-complex is the single largest local VOC source in the 20 km radius study domain, all monitoring sites in the region received far less influence from the Petro-complex than from other emission types within or outside the region, which together add up to more than 70% of the total VOC abundance.

Urban VOC profiles, possible sources, and its role in ozone formation for a summer campaign over Xi'an, China

To insight the urban volatile organic compound (VOC) profiles and its contribution to ozone, four-time per day (8:00-9:00, 15:00-16:00, 19:00-20:00, and 23:00-24:00) off-line VOC samples were collected from 16th July to 28th July 2018 for a summer investigation campaign over Xi'an, China. The diurnal variation was significant that the lowest TVOC concentrations were observed in the midnight period (28.4 ± 25.6 ppbv) while the highest was shown in the morning (49.6 ± 40.1 ppbv). The differences of total non-methane VOCs (TVOCs) between weekdays and weekend were also significant that the weekend showed significantly high VOC levels than weekdays (p < 0.05) but did not lead to significant ambient O₃ increase (p > 0.05). Isopentane, a general marker for vehicle exhaust, showed descending concentrations from morning to midnight and good correlation with vehicle numbers on road, indicating a potential source to the VOCs at this site. The results from PMF proved that vehicular exhaust was the largest source to the VOCs in this study (64.4%). VOC categories showed a reverse sequence in abundance of concentrations and OFP contributions that alkenes showed the highest OFPs although with the lowest abundance in TOVCs due to their high reactivity in photochemical reactions. High OFPs from ethylene and isopentane indicated that vehicular emissions could be the largest potential OFP source in this site. OFPs from isoprene (from 1.85 to 13.4 ppbv) indicated that biogenic VOCs should not be negligible in urban Xi'an city when controlling O₃ pollutants. Comparison of two OFP methods was conducted and MIR method was proved to be more reasonable and scientific in summer Xi'an. Therefore, vehicular emission, the largest contributor to ambient VOCs and also OFPs, as well as biological source should be priority controlled in guiding VOC emissions and reducing O₃ control policies.

Emission factors, ozone and secondary organic aerosol formation potential of volatile organic compounds emitted from industrial biomass boilers

To evaluate the potential benefits of biomass use for air pollution control, this paper identified and quantified the emissions of major reactive organic compounds anticipated from biomass-fired industrial boilers. Wood pellets (WP) and straw pellets (SP) were burned to determine the volatile organic compound emission profiles for each biomass-boiler combination. More than 100 types of volatile organic compounds (VOCs) were measured from the two biomass boilers. The measured VOC species included alkanes, alkenes and acetylenes, aromatics, halocarbons and carbonyls. A single coal-fired boiler (CB) was also studied to provide a basis for comparison. Biomass boiler 1 (BB1) emitted relatively high proportions of alkanes (28.9%-38.1% by mass) and alkenes and acetylenes (23.4%-40.8%), while biomass boiler 2 (BB2) emitted relatively high proportions of aromatics (27.9%-29.2%) and oxygenated VOCs (33.0%-44.8%). The total VOC (TVOC) emission factors from BB1 (128.59-146.16 mg/kg) were higher than those from BB2 (41.26-85.29 mg/kg). The total ozone formation potential (OFP) ranged from 6.26 to 81.75 mg/m³ with an average of 33.66 mg/m³ for the two biomass boilers. The total secondary organic aerosol potential (SOAP) ranged from 61.56 to 211.67 mg/m³ with an average of 142.27 mg/m³ for the two biomass boilers. The emission factors (EFs) of TVOCs from biomass boilers in this study were similar to those for industrial coal-fired boilers with the same thermal power. These data can supplement existing VOC emission factors for biomass combustion and thus enrich the VOC emission inventory.

Photochemical evolution of continental air masses and their influence on ozone formation over the South China Sea

To investigate photochemical ozone (O₃) pollution over the South China Sea (SCS), an intensive sampling campaign was conducted from August to November simultaneously at a continental site (Tung Chung, TC) and a marine site (Wan Shan Island, WSI). It was found that when continental air masses intruded the SCS, O₃ episodes often occurred subsequently. To discover the causes, a photochemical trajectory model (PTM) coupled with the near-explicit Master Chemical Mechanism (MCM) was adopted, and the photochemical processes of air masses during the transport from TC to WSI were investigated. The simulated O₃ and its precursors (i.e. NO_x and VOCs) showed a reasonably good agreement with the observations at both TC and WSI, indicating that the PTM was capable of simulating O₃ formation for air masses traveling from TC to WSI. The modeling results revealed that during the transport of air masses from TC to WSI, both VOC and NO_x decreased in the morning while O₃ increased significantly, mainly due to rapid chemical reactions with elevated radicals over the SCS. The elevated radicals over the SCS were attributable to the fact that higher NO_x at TC consumed more radicals, whereas the concentration of radicals increased from TC to WSI because of NO_x dilution and destruction. Subsequently, the photochemical cycling of radicals accelerated, leading to high O₃ mixing ratios over the SCS. Furthermore, based on the source profiles of the emission inventory used, the contributions of six sources, i.e. gasoline vehicle exhaust, diesel vehicle exhaust, gasoline evaporation and LPG usage, solvent usage, biomass and coal burning, and biogenic emissions, to maritime O₃ formation were evaluated. The results suggested that gasoline vehicles exhaust and solvent usage largely contributed the O₃ formation over the SCS (about 5.2 and 3.8 ppbv, respectively). This is the first time that the contribution of continental VOC sources to the maritime O₃ formation was quantified.

Elevated levels of glyoxal and methylglyoxal at a remote mountain site in southern China: Prompt in-situ formation combined with strong regional transport

The dicarbonyls glyoxal (Gly) and methylglyoxal (Mgly) are key tracers for the oxidation of volatile organic compounds (VOCs) in the atmosphere, but their atmospheric chemistry in remote forest environments is not well understood. A study was carried out during Jul. 31-Nov. 5 of 2016 at the summit of Mt. Tianjing (1690 m.a.s.l.), a remote mountaintop site in southern China, to measure the levels of Gly and Mgly and explore their sources and fate. During the study period, the average mixing ratios of Gly and Mgly were 509 ± 31 pptv and 340 ± 32 pptv, respectively, with the Gly/Mgly ratios averaging 1.8 ± 0.2. Both the dicarbonyl concentrations and the Gly/Mgly ratios were significantly higher than those observed in other background sites. Production yield calculations and meteorological data analysis indicate that high levels of Gly and Mgly observed at the study site were largely a combined result of rapid in-situ formation and regional transport by prevailing winds. On average, in-situ formation from precursors is estimated to account for 67% of the observed Mgly and about 9% of the observed Gly. There were significant changes in Gly and Mgly mixing ratios among different time periods when air masses from different source regions dominated, indicating contribution of regional transport to the observed dicarbonyl mixing ratios at the study site. Biogenic emissions in eastern China and anthropogenic emissions in the Pearl River Delta region were the two main sources responsible for the dicarbonyls observed at the site during most of the sampling period, but large-scale biomass burning in central China was also important in the late autumn, as supported by a backward trajectory analysis of fire spot data and the identification of biomass burning tracers. This study provides insights into the background atmospheric chemistry and the impact of biogenic and anthropogenic sources on the dicarbonyls speciation.

Exploration of sources of OVOCs in various atmospheres in southern China

Oxygenated volatile organic compounds (OVOCs) are critical atmospheric ozone and secondary organic aerosol (SOA) precursors and radical sources, while understanding of OVOC sources in the atmosphere, especially with large anthropogenic emissions, still has large uncertainties. A high-sensitivity proton transfer reaction mass spectrometer (PTR-MS) was deployed in vastly different atmospheres in southern China, including an urban site (SZ-U), a regional site (NA-R), and a background site (NL-B). Four critical OVOCs, i.e., methanol, acetone, methyl ethyl ketone (MEK) and acetaldehyde, five groups of aromatic hydrocarbons, isoprene and acetonitrile were measured with a high time resolution. The featured relative abundance and diurnal variations of the OVOCs indicated that methanol, acetone and MEK had prominent contributions from urban industrial activities, while acetaldehyde was closely related to the photochemical formation at all three sites. The photochemical age-based parameterization method was improved locally and then applied to quantify different sources of daytime OVOCs: anthropogenic secondary and biogenic sources (together 60-73%) were always the dominant source for acetaldehyde in various atmospheres; in addition to a significant background for methanol, acetone and MEK, anthropogenic primary emissions (mostly industrial) were their dominant source at SZ-U (38-73%), while biogenic sources played the key role for them at NL-B (30-43%); biomass burning contributed a small fraction of 5-17% for the four OVOCs at the three sites.

Sources of methacrolein and methyl vinyl ketone and their contributions to methylglyoxal and formaldehyde at a receptor site in Pearl River Delta

Methacrolein (MACR) and methyl vinyl ketone (MVK) are two major intermediate products from the photochemical oxidation of isoprene, the most important biogenic volatile organic compound. In addition, MACR and MVK have primary emissions. Investigating the sources and evolution of MACR and MVK could provide helpful information for the oxidative capacity of the atmosphere. In this study, hourly measurements of isoprene, MACR, and MVK were conducted at a receptor site in the Pearl River Delta region (PRD), i.e., the Heshan site (HS), from 22 October to 20 November, 2014. The average mixing ratios of isoprene, MACR and MVK were 151 ± 17, 91 ± 6 and 79 ± 6 pptv, respectively. The daily variations and the ratios of MVK/MACR during daytime and nighttime suggested that other sources besides isoprene photooxidation influenced the MACR and MVK abundances at the HS. Positive matrix factorization was utilized to resolve the sources of MACR and MVK. Five sources were identified and quantified, including biogenic emissions, biomass burning, secondary formation, diesel, and gasoline vehicular emissions. Among them, secondary formation made the greatest contribution to observed MACR and MVK with average contributions of ~45% and ~70%, respectively. Through the yields of secondary products from the oxidation of MACR and MVK by the OH radical and the concentrations of MACR and MVK, it was found that methylglyoxal and formaldehyde were the main oxidation products of MACR and MVK at the HS site. Overall, this study evaluated the roles of primary emissions on ambient levels of MACR and MVK and advanced the understanding of photochemical oxidation of MACR and MVK in the PRD.