Observation and analysis of atmospheric volatile organic compounds in a typical petrochemical area in Yangtze River Delta, China

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.

Photochemical loss with consequential underestimation in active VOCs and corresponding secondary pollutions in a petrochemical refinery, China

The photochemical loss of volatile organic compounds (VOCs) significantly alters the capturing source profiles in high-reactivity VOC species and results in an underestimation of secondary pollutants such as ozone (O3) and secondary organic aerosol (SOA). Utilising speciated VOC data from large petrochemical refineries, the research assesses the photochemical loss of various VOC species. Air samples from multiple sites revealed over 99 VOCs, with initial concentrations estimated via a photochemical age-based parameterisation method. The comparative analysis of initial and measured VOC values provided insights into the VOCs' photochemical degradation during transport. Findings highlight that the average photochemical loss of total VOCs (TVOCs) across different refinery process areas varied between 4.9 and 506.8 ppb, averaging 187.5 ± 128.7 ppb. Alkenes dominated the consumed VOCs at 83.1 %, followed by aromatic hydrocarbons (9.3 %), alkanes (6.1 %), and oxygenated VOCs (OVOCs) at 1.6 %. The average consumption-based ozone formation potential (OFP) and SOA formation potential (SOAP) were calculated at 1767.3 ± 1251.1 ppb and 2959.6 ± 2386.3 ppb, respectively. Alkenes, primarily isoprene, 1,3-butadiene, and acetylene, were the most significant contributors to OFP, ranging from 19.9 % to 95.5 %. Aromatic hydrocarbons, predominantly monocyclic aromatics like toluene, xylene, styrene, and n-dodecane, were the primary contributors to SOAP, accounting for 5.0 % to 81.3 %. This research underscores the significance of considering photochemical losses in VOCs for accurate secondary pollution assessment, particularly in high-reactivity VOC species. It also provides new detection methods and accurate data for the characterization, source analysis and chemical conversion of volatile organic compounds in the petroleum refining industry.

Historical emission and reduction of VOCs from the petroleum refining industry and their potential for secondary pollution formation in Guangdong, China

China became the world leader in crude oil processing capacity in 2021. However, petroleum refining generates significant volatile organic compound (VOC) emissions, and the composite source profile, source-specific emission factors, and emission inventories of VOCs in the petroleum refining industry remain poorly understood. In this study, we focused on Guangdong, China's major province for crude oil processing, and systematically evaluated the historical emissions and reduction of VOCs in the petroleum refining industry from 2001 to 2020. We accomplished this by establishing local source-specific emission factors and composite source profiles. Finally, we quantitatively assessed the potential impact of these emissions on ozone and secondary organic aerosol formation. Our results revealed that VOC emissions from the petroleum refining industry in Guangdong followed an increasing-then-decreasing trend from 2001 to 2020, peaking at 37.3 Gg in 2016 and declining to 18.7 Gg in 2020. Storage tanks and wastewater collection and treatment remained the two largest sources, accounting for 41.9 %-53.4 % and 20.6 %-27.5 % of total emissions, respectively. Initially, Guangzhou and Maoming made the most significant contributions, with Huizhou becoming a notable contributor after 2008. Emission reduction efforts for VOCs in Guangdong's petroleum refining industry began showing results in 2017, with an average annual VOC emission reduction of 21.5 Gg from 2017 to 2020 compared to the unabated scenario. Storage tanks, wastewater collection and treatment, and loading operations were the primary sources of emission reduction, with significant contributions from Maoming, Huizhou, and Guangzhou. Alkanes made the largest contribution to VOC emissions, while alkenes/alkynes and aromatics comprised the most significant portions of ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAP). We also estimated VOC emissions and reduction from petroleum refining for China from 2001 to 2020, and measures such as "one enterprise, one policy" and deep control strategies could reduce emissions by at least 103.9 Gg.

A Three-Year Analysis of Toxic Benzene Levels and Associated Impact in Ploieşti City, Romania

This study examines the levels of benzene and the potential health impact during three years of continuous monitoring (2019-2021), including the COVID-lockdown period from 2020 in a city that is an important Romanian center for petroleum refining and associated product manufacturing. The dataset contains benzene, toluene, NOx, PM10 concentrations, and meteorological factors monitored by six automatic stations from the national network of which four are in the city and two outside. Special attention was given to the benzene dynamics to establish patterns related to the health impact and leukemia. An assessment of the exposure was performed using EPA's ExpoFIRST v. 2.0 for computing the inhalation Average Daily Dose (ADD) and Lifetime Average Daily Dose (LADD). The health impact was estimated based on several indicators such as lifetime cancer risk (LCR), Hazard Quotient (HQ), Disability-Adjusted Life Years (DALY), and Environmental burden of disease (EBD). Overall, the annual average of all stations was almost similar between years i.e., 3.46 in 2019, 3.41 in 2020, and 3.63 µg/m3 in 2021, respectively. The average of all stations during the lockdown period was 2.67 µg/m3, which was lower than the multiannual average of the 2019-2021 period, i.e., 3.5 µg/m3. Significant correlations were present between benzene and other pollutants such as NOx (r = 0.57), PM10 fraction (r = 0.70), and toluene (r = 0.69), and benzene and temperature (r = -0.46), humidity (r = 0.28), and wind speed (r = -0.34). Regarding the ADD, in all scenarios, the most affected age categories are small children, despite a lower outdoor exposure time. From birth to <70 years, the ADD varied depending on the exposure scenario resulting in 3.27 × 10-4, 5.6 × 10-4, and 4.04 × 104 mg/kg-day, and 3.95 × 10-4, 10.6 × 10-4, and 6.76 × 10-4 mg/kg-day for the LADD, respectively. The Integrated Lifetime Cancer Risk (ILTCR) values were 14.1 × 10-5 in winter, 9.04 × 10-5 in spring, 8.74 × 10-5 in summer, and 10.6 × 10-4 in autumn. The ILTCR annual averages were 1.08 × 10-4 (2019), 1.07 × 10-4 (2020), 1.04 × 10-4 (2021), and 1.06 × 10-4 for the entire period. The resulting ILTCR values point out very risky conditions, with the annual averages reaching the definite cancer risk category. The corresponding burden based on the DALY's loss due to leukemia in Ploieşti was estimated at 0.291 (2 μg/m3 benzene), 0.509 (3.5 μg/m3 benzene), 0.582 (4 μg/m3 benzene), and 0.873 DALYs per 100,000 inhabitants (6 μg/m3 benzene), respectively. The current study provides useful insights for a better understanding of the exposure levels to benzene and associated health impact in Ploieşti despite the limitations determined by the data hiatus and incomplete or missing information regarding the health impact.

Atmospheric gaseous aromatic hydrocarbons in eastern China based on mobile measurements: Spatial distribution, secondary formation potential and source apportionment

Monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs) are both well known as hazardous air pollutants and also important anthropogenic precursors of tropospheric ozone (O₃) and secondary organic aerosols (SOA). In recent years, there have been intensive studies covering MAHs emission from various sources and their behavior under stimulated photochemical conditions. Yet in-situ measurements of PAHs presence and variations in ambient air are sparse. Herein we conducted large geometrical scale mobile measurements for 16 aromatic hydrocarbons (AHs, including 7 MAHs and 9 PAHs) in eastern China between October 27 and November 8, 2019. This unique dataset has allowed for some insights in terms of AHs concentration variations, accompanying chemical composition, source contributions and spatial distributions in eastern China. In general, AHs showed a clear concentration variability between the south and the north of the Yangtze River Delta (YRD). The concentrations of PAHs were approximately 9% of AHs, but contributed 23% of SOA formation potential. Source apportionment via positive matrix factorization (PMF) model revealed that industrial processes as the largest source (44%) of observed AHs, followed by solvent usage (21%), vehicle exhaust (19%), coal combustion (11%) and coking processes (6%). In the perspective of PAHs sources, coal combustion emissions were identified as the dominating factor of a share of 41%-52% in eastern China. Our findings complemented the simultaneously monitoring information of PAHs and MAHs in eastern China, revealed the importance of PAHs to SOA formation and highlighted the necessity of formulating strategies to reduce emissions from anthropogenic sources and reduce risks to human health.

Chemical drivers of ozone change in extreme temperatures in eastern China

Surface ozone pollution has become the biggest issue in China's air pollution since particulate matters have been improved in the atmosphere. Compared with normal winter/summer, extremely cold/hot weather sustained several days and nights by unfavorable meteorology is more impactful in this regard. However, ozone changes in extreme temperatures and their driving processes remain rarely understood. Here, we combine comprehensive observational data analysis and 0-D box models to quantify the contributions of different chemical processes and precursors to ozone change in these unique environments. Analyses of radical cycling indicate that temperature accelerates OH-HO₂-RO₂, optimizing ozone production efficiency in higher temperatures. The HO₂ + NO → OH + NO₂ reaction was the most influenced by temperature change, followed by OH + VOCs → HO₂/RO₂. Although most reactions in ozone formation increased with temperature, the increase in ozone production rates was greater than the rate of ozone loss, leading to a fast net ozone accumulation in heat waves. Our results also show that the ozone sensitivity regime is VOC-limited in extreme temperatures, highlighting the significance of volatile organic compound (VOC) control (particularly the control of alkenes and aromatics). In the context of global warming and climate change, this study helps us deeply understand ozone formation in extreme environments and design abatement policies for ozone pollution in such conditions.

VOC characteristics and their source apportionment in a coastal industrial area in the Yangtze River Delta, China

Volatile organic compounds (VOCs) are important precursors of secondary organic compounds and ozone, which raise major environmental concerns. To investigate the VOC emission characteristics, measurements of VOCs based on proton transfer reaction-mass spectrometry during 2017 were conducted in a coastal industrial area in Ningbo, Zhejiang Province, China. Based on seasonal variation in species concentration, the positive matrix factorization (PMF) receptor model was applied to apportion the sources of VOCs in each season. The PMF results revealed that unknown acetonitrile source, paint solvent, electronics industry, biomass burning, secondary formation and biogenic emission were mainly attributed to VOC pollution. Biomass burning and secondary formation were the major sources of VOCs and contributed more than 70% of VOC emissions in spring and autumn. Industry-related sources contributed 8.65%-31.2% of the VOCs throughout the year. The unknown acetonitrile source occurred in winter and spring, and contributed 7.6%-43.73% of the VOC emissions in the two seasons. Conditional probability function (CPF) analysis illustrated that the industry sources came from local emission, while biomass burning and biogenic emission mainly came from the northwest direction. The potential source contribution function (PSCF) model showed that secondary formation-related source was mainly from Jiangsu Province, northeastern China and the surrounding ocean. The potential source areas of unknown acetonitrile source were northern Zhejiang Province, southern Jiangsu Province and the northeastern coastal marine environments.

Diagnosis of photochemical O3 production of urban plumes in summer via developing the real-field IRs of VOCs: A case study in Beijing of China

This study mainly developed an estimate method for photochemical ozone (O₃) production from urban plumes in hot season, through simulating O₃ evolution from precursors locally emitted and determining the real-field O₃ increment reactivity (IR) of volatile organic compounds (VOCs) based on the box chemical model. Our simulation on June-2019 indicated that Beijing local emissions produced O₃ at the rate of 0.7-9.2 ppb/h and led to an O₃ increase of 48.9 ppb during 05:00-18:00, accounting for 68.3% of the observed O₃ increase. The maximum level and production rate of simulated O₃ showed a linear response to VOCs, therefore we can use VOCs levels in urban plumes to quantify O₃ formation in summer. The IR (g O₃ formed per g VOCs) was calculated on the actual precursor and meteorology condition of this megacity, 0.12-4.90 g/g for individual VOCs and 1.49 g/g for comprehensive TVOCs. The weighted average of individual IRs agreed well with that of TVOCs, but these IRs were 34.5% of MIR values that were widely used in references. It's noteworthy that these IRs had greater sensitivity to precursor levels, and broadly remained stable under the fixed VOCs:NOx. Considering the synchronous reductions of precursors in Beijing, we applied these IRs to quantify chemical O₃ evolution from Beijing local emissions in summer of recent years, declining from 63.5 ppb in 2016 to 44.0 ppb in 2020 for June. The contributions of the diagnosed chemical O₃ to Beijing O₃ better matched with the atmospheric transport paths on daily basis, higher than 100% when the transport paths starting from the clean neighbor cities, but lower to 45%-66% when the transport paths originating from the highly-polluted neighbor cities. This consistence indicated the reliability of our IR calculation method for quickly estimating chemical O₃ production of urban plumes in summer.

Pioneering observation of atmospheric volatile organic compounds in Hangzhou in eastern China and implications for upcoming 2022 Asian Games

Understanding the emission sources of volatile organic compounds (VOCs) is critical for air pollution mitigation. Continuous measurements of atmospheric VOCs were conducted from January to February in Hangzhou in 2021. The average measured concentration of total VOCs (TVOCs) was 38.2 ± 20.9 ppb, > 42% lower than that reported by previous studies at the urban center in Hangzhou. The VOC concentrations and proportions were similar between weekdays and weekends. During the long holidays of the Spring Festival in China, the concentrations of TVOCs were ∼50% lower than those during the regular days, but their profiles showed no significant difference (p > 0.05). Further, we deduced that aromatics and alkenes were the most crucial chemicals promoting the formation of O₃ and secondary organic aerosol (SOA) in Hangzhou. According to interspecies correlations, combustion processes and solvent use were inferred as major VOC emission sources. This study provides implications for air quality improvements before and during the upcoming Asian Games that will be hosted in Hangzhou in 2022.

A review of the factors affecting the emission of the ozone chemical precursors VOCs and NOx from the soil

The soil environment is one of the main places for the generation, emission, and absorption of various atmospheric pollutants, including nitrogen oxides (NO_x) and volatile organic compounds (VOCs), which are the main chemical precursors for the formation of ground-level ozone. Ground-level ozone pollution has become a concerning environmental problem because of the harm it poses to human health and the surrounding ecological environment. However, current studies on chemical precursors of ozone mainly focus on emissions from industrial sources, forest vegetation, and urban vehicle exhaust; by contrast, few studies have examined the role of the soil environment on NO_x and VOCs emissions. In addition, the soil environment is complex and heterogeneous. Agricultural activities (fertilization) and atmospheric deposition provide nutrients for the soil environment, with a significant effect on NO_x and VOCs emissions. There is thus a need to study the environmental factors related to the release of NO_x and VOCs in the soil to enhance our understanding of emission fluxes and the types of NO_x and VOCs in the soil environment and aid efforts to control ground-level ozone pollution through appropriate measures such as management of agricultural activities. This paper reviews the generation of NO_x and VOCs in the soil environment and the effects of various environmental factors on this process. Some suggestions are provided for future research on the regulation of NO_x and VOCs emissions in the soil environment and the ability of the soil environment to contribute to ground-level ozone pollution.

Characteristics and sources of ambient Volatile Organic Compounds (VOCs) at a regional background site, YRD region, China: Significant influence of solvent evaporation during hot months

Continuous measurement of 98 volatile organic compounds (VOCs) was conducted during 2017-2019 at a regional background site (Shanxi) located at northeast of Zhejiang Province, YRD region, China. The average concentration of total VOCs (TVOCs) was 25.4 ± 18.4 ppbv, and an increasing trend (+12.2 %) was observed. Alkanes were the most abundant VOC group among all seasons, accounting for 43.5 % of TVOCs. Oxygenated VOCs (OVOCs), aromatics, halides and alkenes contributed 15.9 %, 15.7 %, 11.7 % and 10.3 % of TVOCs concentration, respectively. Biogenic VOCs (BVOCs) and OVOCs showed distinguished diurnal cycle from primary anthropogenic VOCs. Photochemical reactivity analysis based on ozone formation potential (OFP) and OH loss rate (L^OH) indicated that aromatics and alkenes were the most significant contributor, respectively. Toluene, xylene (m/p- and o-), ethene and propene were the largest contributor of annual OFP, with the mean OFP being 33.8 ± 44.3 μg·m^-3, 31.9 ± 32.1 μg·m^-3, 9.29 ± 11.4 μg·m^-3, 22.1 ± 21.3 μg·m^-3 and 12.8 ± 19.5 μg·m^-3, respectively. Seven sources were identified with positive matrix factorization (PMF): petrochemical industry (13.8 %), biogenic emission (1.0 %), solvent usage-toluene (16.9 %), vehicular exhaust (43.8 %), Integrated circuits industry (3.8 %), solvent usage-C8 aromatics (10.9 %), and gasoline evaporation (9.8 %). Vehicular exhaust was the most significant source (43.8 %) during the whole measurement period. Solvent usage, petrochemical industry, and gasoline evaporation showed high temperature dependency. The integrated contribution of solvent usage and industrial processes were higher than vehicular exhaust during hot months. These sources also have higher chemical reactivities and can contribute more on O₃ formation. Our results are helpful on determining the control strategies aiming at alleviating O₃ pollution.

Characterization, reactivity, source apportionment, and potential source areas of ambient volatile organic compounds in a typical tropical city

Based on one-year observation, the concentration, sources, and potential source areas of volatile organic compounds (VOCs) were comprehensively analyzed to investigate the pollution characteristics of ambient VOCs in Haikou, China. The results showed that the annual average concentration of total VOCs (TVOCs) was 11.4 ppbV, and the composition was dominated by alkanes (8.2 ppbV, 71.4%) and alkenes (1.3 ppbV, 20.5%). The diurnal variation in the concentration of dominant VOC species showed a distinct bimodal distribution with peaks in the morning and evening. The greatest contribution to ozone formation potential (OFP) was made by alkenes (51.6%), followed by alkanes (27.2%). The concentrations of VOCs and nitrogen dioxide (NO₂) in spring and summer were low, and it was difficult to generate high ozone (O₃) concentrations through photochemical reactions. The significant increase in O₃ concentrations in autumn and winter was mainly related to the transmission of pollutants from the northeast. Traffic sources (40.1%), industrial sources (19.4%), combustion sources (18.6%), solvent usage sources (15.5%) and plant sources (6.4%) were identified as major sources of VOCs through the positive matrix factorization (PMF) model. The southeastern coastal areas of China were identified as major potential source areas of VOCs through the potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models. Overall, the concentration of ambient VOCs in Haikou was strongly influenced by traffic sources and long-distance transport, and the control of VOCs emitted from vehicles should be strengthened to reduce the active species of ambient VOCs in Haikou, thereby reducing the generation of O₃.

Chemical Characteristics and Source-Specific Health Risks of the Volatile Organic Compounds in Urban Nanjing, China

This work comprehensively investigated the constituents, sources, and associated health risks of ambient volatile organic compounds (VOCs) sampled during the autumn of 2020 in urban Nanjing, a megacity in the densely populated Yangtze River Delta region in China. The total VOC (TVOC, sum of 108 species) concentration was determined to be 29.04 ± 14.89 ppb, and it was consisted of alkanes (36.9%), oxygenated VOCs (19.9%), halogens (19.1%), aromatics (9.9%), alkenes (8.9%), alkynes (4.9%), and others (0.4%). The mean TVOC/NO_x (ppbC/ppbv) ratio was only 3.32, indicating the ozone control is overall VOC-limited. In terms of the ozone formation potential (OFP), however, the largest contributor became aromatics (41.9%), followed by alkenes (27.6%), and alkanes (16.9%); aromatics were also the dominant species in secondary organic aerosol (SOA) formation, indicative of the critical importance of aromatics reduction to the coordinated control of ozone and fine particulate matter (PM_2.5). Mass ratios of ethylbenzene/xylene (E/X), isopentane/n--pentane (I/N), and toluene/benzene (T/B) ratios all pointed to the significant influence of traffic on VOCs. Positive matrix factorization (PMF) revealed five sources showing that traffic was the largest contributor (29.2%), particularly in the morning. A biogenic source, however, became the most important source in the afternoon (31.3%). The calculated noncarcinogenic risk (NCR) and lifetime carcinogenic risk (LCR) of the VOCs were low, but four species, acrolein, benzene, 1,2-dichloroethane, and 1,2-dibromoethane, were found to possess risks exceeding the thresholds. Furthermore, we conducted a multilinear regression to apportion the health risks to the PMF-resolved sources. Results show that the biogenic source instead of traffic became the most prominent contributor to the TVOC NCR and its contribution in the afternoon even outpaced the sum of all other sources. In summary, our analysis reveals the priority of controls of aromatics and traffic/industrial emissions to the efficient coreduction of O₃ and PM_2.5; our analysis also underscores that biogenic emissions should be paid special attention if considering the direct health risks of VOCs.

Accurate identification of key VOCs sources contributing to O3 formation along the Liaodong Bay based on emission inventories and ambient observations

In order to achieve the precise control of the volatile organic compounds (VOCs) species with high ozone (O₃) formation contribution from key sources in Panjin and Yingkou, two coastal industrial cities with severe O₃ pollution along the Liaodong Bay, northeast China, the ambient concentrations of 99 VOCs species were measured online at urban-petrochemical (XLT), suburban-industrial (PP), and rural (XRD) sites in July 2019, contemporary monthly anthropogenic VOCs emission inventories were developed. The source contribution of ambient VOCs resolved by positive matrix factorization (PMF) model was comparable with emission inventories, and the location of VOCs sources were speculated by potential source contribution function (PSCF). 17.5 Gg anthropogenic VOCs was emitted in Panjin and Yingkou in July 2019 with potential to form 54.7 Gg-O₃ estimated by emission inventories. The average VOC mixing ratios of 47.1, 26.7, and 16.5 ppbv was observed at XLT, PP, and XRD sites, respectively. Petroleum industry (22 %), organic chemical industry (21 %), and mobile vehicle emission (19 %) were identified to be the main sources contributing to O₃ formation at XLT site by PMF, while it is organic chemical industry (33 %) and solvent utilization (28 %) contributed the most at PP site. Taking the subdivided source contributions of emission inventories and source locations speculated by PSCF into full consideration, organic raw chemicals manufacturing, structural steel coating, petroleum refining process, petroleum products storage and transport, off-shore vessels, and passenger cars were identified as the key anthropogenic sources. High O₃-formation contribution sources, organic chemical industry and solvent utilization were located in the industrial parks at the junction of the two cities and the southeast of Panjin, and petroleum industry distributed in the whole Panjin and offshore areas. These results identify the key VOCs species and sources and speculate the potential geographical location of sources for precisely controlling ground-level O₃ along the Liaodong Bay.

Investigation of VOC characteristics, source analysis, and chemical conversions in a typical petrochemical area through 1-year monitoring and emission inventory

To effectively investigate the characteristics, source analysis, and chemical conversions of volatile organic compounds (VOCs) pollution in a typical petrochemical area, 81 VOC species from nine sampling sites were collected from 1st January to 31th December 2019 in Jinshan District. Results showed the concentration of VOCs was 51.63 ± 36.05 ppbv, and VOCs were dominated by alkane (40.10%) and alkenes (39.91%). The temporal variations of VOCs showed that the highest average VOC concentration appeared in July, and the lowest concentration of VOCs was in February. The concentration of VOCs was mainly connected with industrial processes and was transported to other areas through the downwind direction. Six PMF-derived sources including petrochemical industry, solvent utilization, vehicle exhaust, fuel evaporation, combustion, and other industry processes, contributing 37.08%, 16.74%, 16.69%, 14.99%, 9.53%, and 4.97%, respectively. Meanwhile, an anthropogenic VOC emission inventory was established by emission factors and the activity statistics for 2019, results indicated that the total emission of VOCs was estimated as 6.22 kt, petrochemical industry was the most important contributor of human-produced VOCs. The L_OH concentration was 396.12 ppbv via OH radical loss rate method, and the OFP was 210.44 ppbv based on the MIR factor. Alkenes and aromatics were the important components of O₃ formation. This study provides effective information for corresponding governments to establish VOCs contamination control directives.

Characteristics, influence factors, and health risk assessment of volatile organic compounds through one year of high-resolution measurement at a refinery

From January 2020 to December 2020, high-resolution data of volatile organic compound (VOC) concentrations were monitored by online instruments at a petroleum refinery. The measurement results showed that the external contaminants, meteorological conditions and photochemical reactions had a great influence on the VOC data measured in the petroleum refineries. Some significant differences were observed in the emission composition of different refineries, while propene (34.2%), propane (10.2%), n-butane (5.6%), i-pentane (5.0%) were the dominant species emitted from the refinery in this study. The correlations between compounds with similar atmospheric lifetimes were strong (R² > 0.9), which indicated that the diagnostic ratios of these compounds could be used as indicators to identify the refinery emission source. Chronic health effects of non-carcinogenic risk results showed that acrolein had the highest non-carcinogenic risk and other compound-specific health risks may be of less concern in the refining area. Halogenates and aromatics accounted for 97.4% of the total carcinogenic risk values, while 1,2-dibromoethane, chloromethane, benzene, trichloromethane, 1,2-dichloroethane contributed approximately 80% of the total carcinogenic risk assessment values. This research has recorded valuable data about the VOC emission characteristics from the perspective of the high-resolution monitoring of the petroleum refinery. The results of this work will provide a reference to accurately quantify and identify the emission of petroleum refineries and further throw some light on effective VOC abatement strategies.

Characteristics and Impact of VOCs on Ozone Formation Potential in a Petrochemical Industrial Area, Thailand

In this study, the ambient concentrations of volatile organic compounds (VOCs) were intensively measured from January 2012 to December 2016 using an evacuated canister and were analyzed using a gas chromatography/mass spectrophotometer (GC/MS) based on the US EPA TO-15 in the community and industrial areas of the largest petroleum refinery and petrochemical industrial complex in Map Ta Phut Thailand. The ternary diagram was used to identify the source of VOCs. Reactivity of VOCs on their ozone formation potential (OFP) were quantified by the maximum incremental reactivity coefficient method (MIR) and propylene-equivalent concentration methods. Results from the study revealed that aromatic hydrocarbon was the dominant group of VOCs greatly contributing to the total concentration of measured VOCs. Among the measured VOCs species, toluene had the highest concentration and contributed as the major precursor to ozone formation. The ternary analysis of benzene:toluene:ethybenzene ratios indicated that VOCs mainly originated from mobile sources and industrial processes. Within the industrial area, measured VOC concentration was dominated by halogenated hydrocarbons, and alkene was the highest contributor to ozone formation. The propylene-equivalent concentration method was also used to evaluate the reactivity of VOCs and their role in ozone formation, and secondly to support findings from the MIR method.

Tracer-based characterization of source variations of ambient isoprene mixing ratios in a hillocky megacity, India, influenced by the local meteorology

The ambient biogenic volatile organic compounds (BVOCs), mainly isoprene, are potentially involved in the formation of secondary pollutants, hence, they are significant in terms of air quality and climate. Although the largest sources of BVOCs are tropical regions, the measurements of isoprene in the Indian subcontinent are limited. We conducted the measurements of isoprene, benzene, and toluene at an urban site in a hillocky megacity of India using a high-sensitivity proton transfer reaction quadrupole mass spectrometer (PTR-QMS). The mixing ratios of isoprene were compared with those of aromatic compounds like benzene and toluene, which represent typical anthropogenic VOCs. Isoprene and isoprene/benzene (>5 ppbv ppbv^-1) showed higher levels in the pre-monsoon months, most likely due to large emissions by urban vegetation during physiological activities in plants which was enhanced by the high ambient temperatures and solar radiation. While Benzene and toluene showed higher mixing ratios during winter, which were due to shallower boundary layer depths and transport of air masses from polluted Indo-Gangetic Plain during this season. The mixing ratios of VOCs show significant diurnal variation as a result of their different origins and the role of different meteorological parameters. The robust emission ratios of isoprene/benzene obtained from nighttime data were used to separate the non-anthropogenic and anthropogenic isoprene emissions. ∼30% enhancement observed in non-anthropogenic emissions to isoprene from winter to pre-monsoon season when temperatures and solar radiation were stronger, although traffic in the city. Isoprene/benzene ratio at lower temperatures (<25 °C) and solar radiation (<100 W m^-2) was predominantly controlled by anthropogenic sources. Overall, toluene and isoprene are the most frequent species in terms of having the highest ozone-forming potential (OFP) values but biogenic isoprene became more important to ozone formation during the afternoon hours in the pre-monsoon months with high air temperatures (>25 °C).

Measurement and minutely-resolved source apportionment of ambient VOCs in a corridor city during 2019 China International Import Expo episode

In this study, real-time measurement of Volatile Organic Compounds (VOCs) was conducted at an urban site in Changzhou, a typical corridor city in the Yangtze River Delta (YRD) region in China, by Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) during 2019 China International Import Expo (CIIE) episode. An improved method based on Air Quality Index (AQI) value is applied to identify polluted and clean periods. Diurnal pattern of VOC levels revealed elevated photochemical reactivity during polluted periods. Five VOC sources were identified by Positive Matrix Factorization (PMF) model, including secondary formation (22.71 ± 12.33%), biogenic (21.50% ± 11.76%), solvent usage (20.50 ± 10.07%), vehicle exhaust (18.32 ± 8.32%), and industrial process and fuel usage (16.96 ± 13.21%). The mean contribution of vehicular exhaust was 10.84% higher during the nighttime than the daytime under polluted days. The biogenic source contributed more during clean periods, while the secondary formation presented the opposite. Spatial analysis displayed that the VOC concentration was higher in the S and SSE. In terms of the regional transport, short-distance air masses from the northeast and the south within the YRD region led to high VOC levels and biogenic VOC derived from the ocean might affect the entire region. Stringent emission control policies enforced over the YRD for 2019 CIIE provided an excellent opportunity to determine the source-receptor response. As joint control area, the VOC level of Changzhou exhibited a substantial reduction and the VOC amounts emitted by solvent usage showed the biggest decrease (-58%). The findings of this study highlight the superiority of high time-resolved data in identifying the dynamic variation pattern (with the change of time and wind) of VOC levels and emission intensities.

Chemical Characterization, Source, and SOA Production of Intermediate Volatile Organic Compounds during Haze Episodes in North China

The growth of secondary organic aerosols (SOA) is a vital cause of the outbreaks of winter haze in North China. Intermediate volatile organic compounds (IVOCs) are important precursors of SOA. Therefore, the chemical characteristics, source, and SOA production of IVOCs during haze episodes have attracted much attention. Hourly time resolution IVOC samples during two haze episodes collected in Hebei Province in North China were analyzed in this study. Results showed that: (1) the concentration of IVOCs measured was within the range of 11.3~85.1 μg·cm−3 during haze episodes, with normal alkanes (n-alkanes), polycyclic aromatic hydrocarbons (PAHs), branched alkanes (b-alkanes), and the residue unresolved complex mixture (R-UCM) accounting for 8.6 ± 2.3%, 6.8 ± 2.2%, 24.1 ± 3.8%, and 60.5 ± 6.5% of IVOCs, respectively. NC12-nC15 in n-alkanes, naphthalene and its alkyl substitutes in PAHs, b-alkanes in B12–B16 bins, and R-UCM in B12–B16 bins are the main components, accounting for 87.0 ± 0.2%, 87.6 ± 2.9%, 85.9 ± 5.4%, 74.0 ± 8.3%, respectively. (2) Based on the component characteristics of IVOCs and the ratios of n-alkanes/b-alkanes in emission sources and the hourly variation of IVOCs during haze episodes, coal combustion (CC), biomass burning (BB), gasoline vehicles (GV), and diesel vehicles (DV)were identified as important emission sources of IVOCs in Hebei Province. (3) During haze episodes, temporal variation of the estimated SOA production based on different methods (such as IVOCs concentration, OC/ECmin tracer, and the PMF model) were similar; however, the absolute values were different. This difference may be due to the transformation of IVOCs to SOA affected by various factors such as SOA production from different IVOC components, meteorological conditions, atmospheric oxidation, etc.

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.

VOC Characteristics and Their Source Apportionment in the Yangtze River Delta Region during the G20 Summit

To evaluate the effectiveness of measures to reduce the levels of volatile organic compounds (VOCs), which are important precursors of ground-level ozone formation, the real-time monitoring data of VOCs at the urban Zhaohui supersite (ZH), the Dianshan Lake regional supersite (DSL) and the urban Yixing station (YX) in the Yangtze River Delta region were analyzed from 23 August to 15 September 2016 during the G20 Hangzhou Summit. The average mole ratios of VOCs at the three sites were 6.56, 21.33 and 19.62 ppb, respectively, which were lower than those (13.65, 27.72 and 21.38 ppb) after deregulation. The characteristics of the VOCs varied during the different control periods. Synoptic conditions and airmass transport played an important role in the transport and accumulation of VOCs and other pollutants, which affected the control effects. Using the positive matrix factorization (PMF) method in source apportionment, five factors were identified, namely, vehicle exhaust (19.66–31.47%), plants (5.59–17.07%), industrial emissions (13.14–33.82%), fuel vaporization (12.83–26.34%) and solvent usage (17.84–28.95%) for the ZH and YX sites. Factor 4 was identified as fuel vaporization + incomplete combustion (21.69–25.35%) at the DSL site. The Non-parametric Wind Regression (NWR) method showed that regional transport was the main factor influencing the VOC distribution.

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.

Kriging-Based Land-Use Regression Models That Use Machine Learning Algorithms to Estimate the Monthly BTEX Concentration

This paper uses machine learning to refine a Land-use Regression (LUR) model and to estimate the spatial–temporal variation in BTEX concentrations in Kaohsiung, Taiwan. Using the Taiwanese Environmental Protection Agency (EPA) data of BTEX (benzene, toluene, ethylbenzene, and xylenes) concentrations from 2015 to 2018, which includes local emission sources as a result of Asian cultural characteristics, a new LUR model is developed. The 2019 data was then used as external data to verify the reliability of the model. We used hybrid Kriging-land-use regression (Hybrid Kriging-LUR) models, geographically weighted regression (GWR), and two machine learning algorithms—random forest (RF) and extreme gradient boosting (XGBoost)—for model development. Initially, the proposed Hybrid Kriging-LUR models explained each variation in BTEX from 37% to 52%. Using machine learning algorithms (XGBoost) increased the explanatory power of the models for each BTEX, between 61% and 79%. This study compared each combination of the Hybrid Kriging-LUR model and (i) GWR, (ii) RF, and (iii) XGBoost algorithm to estimate the spatiotemporal variation in BTEX concentration. It is shown that a combination of Hybrid Kriging-LUR and the XGBoost algorithm gives better performance than other integrated methods.

Observation and analysis of VOCs in nine prefecture-level cities of Sichuan Province, China

The observation and analysis of volatile organic compounds (VOCs) were conducted during January 2018 in nine prefecture-level cities of Sichuan, China, covering the period of heavily polluted weather. Air samples collected in nine prefecture-level cities were analyzed using a preconcentration method coupled with GC-MS/FID. The characteristics and ozone generation potential (OFP) of VOCs were analyzed. The relationship between air quality index (AQI) and VOCs and gross domestic product (GDP) and VOCs were also discussed, respectively. The results show that the characteristics of VOCs in cities are highly related to their industrial structure and GDP. Generally, areas with high AQI values are accompanied by high VOC concentrations. Alkanes and halocarbons were the most abundant VOCs in the atmospheric environment in the nine prefecture-level cities, accounting for 24.5~61.6% and 15.6~23.6% of total VOC concentration, respectively. The MIR method was used to analyze the OFP, and olefins contributed the most to ozone formation. Among the nine cities located in Sichuan, Dazhou was found to be the city with the highest OFP value (1191.49 μg/m³).

Intraday and interday variations of 69 volatile organic compounds (BVOCs and AVOCs) and their source profiles at a semi-urban site

To study the intraday and interday patterns and possible sources of volatile organic compounds (VOCs), 6-h active sampling was performed in April, May, June, July, and August 2017 and in January 2018 in a semi-urban site in Bolu, Turkey. Totally 69 VOCs having biogenic (BVOCs, i.e., isoprene, monoterpenes and oxygenated VOCs) and anthropogenic origins (AVOCs) were examined. Fifty-four of sixty-nine analyzed VOCs could be detected. Decanal followed by benzaldehyde, benzene, phenol, and toluene were detected as the leading anthropogenic VOCs whereas alpha-pinene and hexanal were the dominant biogenic VOCs. There was a decrease in concentrations of most of the VOCs in January and April when light intensity and temperature were relatively low. Atmospheric levels of total biogenic VOCs exceeded that of anthropogenic VOCs in all months except for January and April. Dependence of biogenic VOC emissions on the light intensity, temperature and the increase in leaves were considered to be effective in their higher levels in summer and daytime periods. The daytime anthropogenic VOCs concentrations were higher than the nighttime anthropogenic VOCs probably due to intense vehicle traffic during working hours and/or increased volatilization from their sources at elevated temperatures. The VOCs that significantly and negatively correlated with ozone were evaluated as effective BVOCs in the ozone formation while the maximum incremental reactivity (MIR) method gave the contribution of AVOCs. Positive Matrix Factorization (PMF) was applied for the source apportionment. G score graphs and G score pollution roses were also used to identify possible sources of investigated VOCs. Solvent evaporation, gasoline-powered vehicle emissions, fossil fuel (residential heating), biogenic (hornbeam, grass, oak, beech) emissions, diesel/domestic activities and forested city atmosphere were identified as the possible VOC sources in the study area.

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.

Emission profiles, ozone formation potential and health-risk assessment of volatile organic compounds in rubber footwear industries in China

The emission characteristics of VOCs in the rubber footwear industry (RFI) and its effect on human health are poorly understood to date. Herein, up to 68 VOCs, sorted into seven classes including alkanes, alkenes, acetylene, aromatics, halocarbons, carbon disulfide, and oxygenated VOCs, were monitored. VOCs emitted from three main processing stages of RFI, including shaping, painting and vulcanizing, were 383, 1507 and 1026 mg/m³, respectively. The top 10 VOCs contributing to the concentration and ozone formation potential were identified. Generally, alkanes were the major component emitted from three stages, contributing 48.58%-63.07% of the total VOCs. Alkenes contributed most to the OFP, accounting for 37.2%-69.1%. Based on the risk assessment, a definite cancer risk for workers in shaping workshop should be noticed. Several VOCs with a life carcinogenic risk higher than 10^-4, especially benzene, bromodichloromethane, ethylbenzene and 1,1,2-trichloroethane, should be focused on. Therefore, more attention should be taken for the extended-ranges of VOCs in subordinate RFI, except for the publicly concerned aromatics in rubber industry. A VOCs emission inventory from the production process of Chinese RFI in 2000-2016 was compiled. It is estimated that Chinese RFIs have emitted a total of 319 × 10⁴ t VOCs in those past 17 years.

An Integrated Method for Factor Number Selection of PMF Model: Case Study on Source Apportionment of Ambient Volatile Organic Compounds in Wuhan

The positive matrix factorization (PMF) model is widely used for source apportionment of volatile organic compounds (VOCs). The question about how to select the proper number of factors, however, is rarely studied. In this study, an integrated method to determine the most appropriate number of sources was developed and its application was demonstrated by case study in Wuhan. The concentrations of 103 ambient volatile organic compounds (VOCs) were measured intensively using online gas chromatography/mass spectrometry (GC/MS) during spring 2014 in an urban residential area of Wuhan, China. During the measurement period, the average temperature was approximately 25 °C with very little domestic heating and cooling. The concentrations of the most abundant VOCs (ethane, ethylene, propane, acetylene, n-butane, benzene, and toluene) in Wuhan were comparable to other studies in urban areas in China and other countries. The newly developed integrated method to determine the most appropriate number of sources is in combination of a fixed minimum threshold value for the correlation coefficient, the average weighted correlation coefficient of each species, and the normalized minimum error. Seven sources were identified by using the integrated method, and they were vehicular emissions (45.4%), industrial emissions (22.5%), combustion of coal (14.7%), liquefied petroleum gas (LPG) (9.7%), industrial solvents (4.4%), and pesticides (3.3%) and refrigerants. The orientations of emission sources have been characterized taking into account the frequency of wind directions and contributions of sources in each wind direction for the measurement period. It has been concluded that the vehicle exhaust contribution is greater than 40% distributed in all directions, whereas industrial emissions are mainly attributed to the west southwest and south southwest.