Geochemical studies of low molecular weight organic acids in the atmosphere: sources, formation pathways, and gas/particle partitioning

Low molecular weight monocarboxylic acids (LMW monoacids, C₁-C₁₀) are the most abundant gaseous organic compound class in the atmosphere. Formic or acetic acid is the dominant volatile organic compound (VOC) in Earth's atmosphere. They can largely contribute to rainwater acidity, especially in the tropical forest, and react with alkaline metals, ammonia, and amines, contributing to new particle formation and secondary organic aerosol production. Gaseous and particulate LMW monoacids were abundantly reported in China. They can be directly emitted from fossil fuel combustion and biomass burring; however, the secondary formation is more important than primary emissions via the photochemical oxidation of anthropogenic and biogenic VOCs. In this paper, we review the distributions of LMW monoacids from urban, mountain, and marine sites as well as from rainwater and alpine snow samples and discuss their sources and formation mechanisms in the atmosphere. We also discuss their importance as cloud condensation nuclei (CCN) and provide future perspectives of LMW monoacids study in the warming world.

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.

Identification of NO2 and SO2 Pollution Hotspots and Sources in Jiangsu Province of China

Nitrogen dioxide (NO2) and sulfur dioxide (SO2) are important atmospheric trace gases for determining air quality, human health, climate change, and ecological conditions both regionally and globally. In this study, the Ozone Monitoring Instrument (OMI), total column nitrogen dioxide (NO2), and sulfur dioxide (SO2) were used from 2005 to 2020 to identify pollution hotspots and potential source areas responsible for air pollution in Jiangsu Province. The study investigated the spatiotemporal distribution and variability of NO2 and SO2, the SO2/NO2 ratio, and their trends, and potential source contribution function (PSCF) analysis was performed to identify potential source areas. The spatial distributions showed higher values (>0.60 DU) of annual mean NO2 and SO2 for most cities of Jiangsu Province except for Yancheng City (<0.50 DU). The seasonal analyses showed the highest NO2 and SO2 in winter, followed by spring, autumn, and summer. Coal-fire-based room heating and stable meteorological conditions during the cold season may cause higher NO2 and SO2 in winter. Notably, the occurrence frequency of NO2 and SO2 of >1.2 was highest in winter, which varied between 9.14~32.46% for NO2 and 7.84~21.67% for SO2, indicating a high level of pollution across Jiangsu Province. The high SO2/NO2 ratio (>0.60) indicated that industry is the dominant source, with significant annual and seasonal variations. Trends in NO2 and SO2 were calculated for 2005–2020, 2006–2010 (when China introduced strict air pollution control policies during the 11th Five Year Plan (FYP)), 2011–2015 (during the 12th FYP), and 2013–2017 (the Action Plan of Air Pollution Prevention and Control (APPC-AC)). Annually, decreasing trends in NO2 were more prominent during the 12th FYP period (2011–2015: −0.024~−0.052 DU/year) than in the APPC-AC period (2013–2017: −0.007~−0.043 DU/year) and 2005–2020 (−0.002 to −0.012 DU/year). However, no prevention and control policies for NO2 were included during the 11th FYP period (2006–2010), resulting in an increasing trend in NO2 (0.015 to 0.031) observed throughout the study area. Furthermore, the implementation of China’s strict air pollution control policies caused a larger decrease in SO2 (per year) during the 12th FYP period (−0.002~−0.075 DU/year) than in the 11th FYP period (−0.014~−0.071 DU/year), the APPC-AC period (−0.007~−0.043 DU/year), and 2005–2020 (−0.015~−0.032 DU/year). PSCF analysis indicated that the air quality of Jiangsu Province is mainly influenced by local pollution sources.

Concurrent Influence of Different Natural Sources on the Particulate Matter in the Central Mediterranean Region during a Wildfire Season

Wildfire occurrence and severity in the Mediterranean region during the summer season is increasing, being favoured by climate change-induced conditions (i.e., drought, heatwaves). Moreover, additional natural sources frequently impact this region, particularly Saharan dust intrusions. This study focuses on the combined effect of wildfires and Saharan dust on the air quality of the central Mediterranean Basin (CMB) during 2017, an exceptional year for forested burned areas in southern Italy. The annual behaviors of PM2.5, PM10, CO, benzene, and benzo(a)pirene measurements that were recorded at a rural regional-background station located in southern Italy, highlighted a concentration increase during summer. Both Saharan dust and wildfire events were identified while using Navy Aerosol Analysis and Prediction System (NAAPS) model maps, together with high-resolution Weather Research and Forecast—Hybrid Single-Particle Lagrangian Integrated Trajectory (WRF-HYSPLIT) back-trajectories. Additionally, Visible Infrared Imaging Radiometer Suite (VIIRS) satellite detections were considered to establish the enrichment of air masses by wildfire emissions. Finally, the occurrence of these natural sources, and their influence on particulate matter, were examined. In this case study, both PM2.5 and PM10 exceedances occurred predominantly in conjunction with wildfire events, while Saharan dust events mainly increased PM10 concentration when overlapping with wildfire effects.

Real-time monitoring of air pollutants in seven cities of North India during crop residue burning and their relationship with meteorology and transboundary movement of air

Air pollutants emissions due to the burning of crop residues could adversely affect human health, environment, and climate. Hence, a multicity campaign was conducted during crop residue burning period in Indo Gangetic Plains (IGP) to study the impact on ambient air quality. Seventeen air pollutants along with five meteorological parameters, were measured using state of the art continuous air quality monitors. The average concentration of PM₁₀, PM_2.5, and PM₁ during the whole campaign were 196.7±30.6, 148.2±20, and 51.2±8.9 μgm^-3 and daily average concentration were found several times higher than national ambient air quality standards for 24h. Amritsar had the highest average concentration of PM_2.5 (178.4±83.8 μgm^-3) followed by Rohtak and Sonipat (158.4±79.8, 156.5±105.3μgm^-3), whereas Chandigarh recorded the lowest concentration (112.3±6.9μgm^-3). The concentration of gaseous pollutants NO, NO₂, NO_x, and SO₂ were also observed highest at Amritsar location, i.e., 6.6±2.6ppb, 6.2±0.7ppb, 12.7±3.0ppb, and 7.5±3.3ppb respectively. The highest average O₃ and CO were 22.5±19.3ppb and 1.5±1.2ppm during the campaign. The level of gaseous pollutants and Volatile organic compounds (VOCs) found to be elevated during the campaign, which can play an important role in the formation of secondary air pollutants. The correlation of meteorology and air pollutants was also studied, and O₃ shows a significant relation with temperature and UV (R=0.87 and 0.74) whereas VOCs shows a significant correlation with temperature (R=-0.21 to -0.47). Air quality data was also analyzed to identify sources of emissions using principal component analysis, and it identifies biomass burning and vehicular activities as major sources of air pollution.

Characteristics of atmospheric bacterial and fungal communities in PM2.5 following biomass burning disturbance in a rural area of North China Plain

Biomass burning (BB) in North China Plain has been urgent issue in recent years due to the severe environmental impaction. Bacteria and fungi are ubiquitous in particulate matter. Their taxonomic composition, concentration, ecophysiological functions have potentially important implications in atmospheric biochemical cycle and human health. However, current knowledge about airborne microbes during biomass burning period is scant. Here we investigated bacterial and fungal community composition, abundance and potential function in Yucheng, the center of the North China Plain during summer harvest season in 2014. Monthly field observation suggested serious pollution with high concentration of PM_2.5 and water-soluble ions during biomass burning period. Elevated total bacterial and fungal concentration determined by real-time quantitative PCR was observed for samples during burning events. The predominant bacterial taxa were gram-negative, e.g. Acinetobacter, Cyanobacterium, Janthinobacterium, Massilia, Pseudomonas, accounted for 70.9% of total bacteria. The filamentous fungi Alternaria, Aspergillus, Cladosporium and Penicillium were predominant fungal genera. Metastats analysis showed significant disparity in terms of carbohydrate, amino acids metabolism, human and plant disease predicted by PICRUSt analysis between BB and non-BB events. Microbial community structure were mainly influenced by organic carbon and water-soluble ions (magnesium and potassium) suggested by redundancy analysis (RDA) and co-occurrence analysis. Our data yielded insights into microbial community dynamics following biomass burning disturbance. This study may provide potentially important reference for environmental, agricultural and health management.

Temporal-spatial analysis of crop residue burning in China and its impact on aerosol pollution

China has performed crop residue burning (CRB) for a long time and has suffered from resultant environmental pollution. High temporal resolution has not been fully discussed in attempts to address the temporal and spatial impact of CRB in China on air quality. Our study used the MOD14A1 product of the MODerate resolution Imaging Spectrometer (MODIS) to extract the daily CRB for China during the period from 2014 to 2016, and the daily aerosol optical depth (AOD) provided by MODIS Collection 6 was obtained to simultaneously reflect the air pollution. First, the study area was classified into five subregions. A temporal analysis was conducted on the daily variation in the number of CRB events and the regional mean value of AOD, the spatial contribution ratio of CRB on aerosol pollution was then calculated, and finally, a temporal and spatial Pearson correlation was calculated to find the spatially varying relationship between CRB and aerosol. The results suggest the following: (1) CRB possesses seasonal characteristics that are associated with the harvest time or sowing time of major crops in the region. (2) The impact of CRB on aerosol was delayed by 1-6 days. (3) High contribution ratios (70%-90%) occurred in northeast China on a large scale; even when the impact of the CRB on aerosol pollution in the Huang-Huai-Hai river basin occurred on a large scale, the value was merely approximately 30%. Relatively low contributions of CRB have been found in other places, whereas the contribution of CRB was severe in some places with high-density populations. (4) Temporal-spatial correlation provided an accurate index to reflect the correlation of CRB and aerosol in a specific location, which suggests that, in places with large scale and dense CRB, CRB tends to have a high positive correlation with aerosol pollution for each day.

Long-term (2005-2015) trend analysis of PM2.5 precursor gas NO2 and SO2 concentrations in Taiwan

Ground air monitoring stations have been installed in Taiwan since 1993 to ensure whether the criteria air pollutants meet the ambient air quality standards. In the present study, the data from the monitoring stations were used to evaluate long-term (2005-2015) trend of NO₂ and SO₂ in three metropolitan cities (northern Taipei, central Taichung, and southern Kaohsiung), two eastern coastal cities (Hualien and Taitung), and one agricultural city in west-central plain (Douliu); those cities essentially covered the entire region of Taiwan. The results indicate that SO₂ and NO₂ concentrations of all studied six cities meet the annual average standards of 30 and 50 ppb, respectively. After deseasonalizing the original data and using 7-month moving average, the trend analysis reveals a decreasing trend ranging from 0.15 to 0.57 ppb/year (R² from 0.33 to 0.85) for NO₂ and 0.06 to 0.45 ppb/year (R² from 0.32 to 0.92) for SO₂; the corresponding reductions over the 10-year span are 4 to 42% for NO₂ and 22 to 52% for SO₂. The reduction trend, despite the growth in GDP, vehicle numbers and energy consumption, industrial output, etc., is similar to those of developed countries. Clearly, there are seasonal/monthly variation patterns for these two precursor gases with minimum levels in summer (July) and maximum in winter (December). The concentration reductions, however, were lagging behind the respective emission reductions. There are significant correlations among six cites for NO₂ (r = 0.58-0.93) and, to some extent, SO₂ (0.32-0.66). The correlation between SO₂ and NO₂ (r = 0.46-0.74) indicates same or similar emission sources. Furthermore, the correlation between observed pollutant concentrations and their emission is excellent for SO₂ in two cities (0.79-0.96). The SO₂/NO₂ ratios vary with city and time and the value is site specific. For example, in 2005, the SO₂/NO₂ ratio was 0.38 in Kaohsiung and 0.18 in both Taipei and Taichung, the latter reflecting significant contribution from mobile sources. However, they all converged to 0.18-0.28 in 2015 in the six cities evaluated. All in all, the policies/measures made by the central and local government are effective in reducing ambient SO₂ and NO₂ levels.

Abundance and origin of fine particulate chloride in continental China

Particulate chloride can be converted to nitryl chloride (ClNO₂) through heterogeneous reactions with dinitrogen pentoxide (N₂O₅), and photolysis of ClNO₂ affects atmospheric oxidative capacity. However, the characteristics and sources of chloride, especially those with an anthropogenic origin, are poorly characterized, which makes it difficult to evaluate the effects of ClNO₂ on radical chemistry and air quality in polluted regions. Aerosol composition data from the literature were compiled to derive the spatial distributions of particulate chloride across China, and hourly aerosol composition data collected at a highly polluted inland urban site in eastern China and at a coastal site in southern China were analysed to gain further insights into non-oceanic sources of chloride. The results show that particulate chloride is concentrated mainly in fine particles and that high chloride loadings are observed in the inland urban areas of northern and western China with higher Cl^-/Na⁺ mass ratios (2.46 to 5.00) than sea water (1.81), indicative of significant contributions from anthropogenic sources. At the inland urban site, the fine chloride displays distinct seasonality, with higher levels in winter and summer. Correlation analysis and positive matrix factorization (PMF) results indicate that coal combustion and residential biomass burning are the main sources (84.8%) of fine chloride in winter, and open biomass burning is the major sources (52.7%) in summer. The transport of plumes from inland polluted areas leads to elevated fine chloride in coastal areas. A simulation with WRF-Chem model confirmed a minor contribution of sea-salt aerosol to fine chloride at the inland site during summer with winds from the East Sea. The widespread sources of chloride, together with abundant NOx and ozone, suggest significant ClNO₂ production and subsequent enhanced photochemical processes over China.

Lagged Influence of Fine Particulate Matter and Geographic Disparities on Clinic Visits for Children's Asthma in Taiwan

Recent studies have revealed the influence of fine particulate matter (PM_2.5) on increased medication use, hospital admission, and emergency room visits for asthma attack in children, but the lagged influence of PM_2.5 on children’s asthma and geographic disparities of children’s asthma have rarely been discussed simultaneously. This study investigated the documented diagnosis of children’s asthma in clinic visits for children aged less than 15 years old that were associated with PM_2.5 in two counties located in west-central Taiwan during 2005–2010. The result shows that PM_2.5 had a significant lagged effect on children’s asthma for up to 6 days. A significantly higher relative risk for children’s asthma was more likely to happen at 2-day lag compared to the present day when PM_2.5 increased from 36.17 μg/m³ to 81.26 μg/m³. Considering all lagged effects, the highest relative risk for children’s asthma was 1.08 (95% CI = 1.05, 1.11) as PM_2.5 increased as high as 64.66 μg/m³. In addition, geographic disparities of children’s asthma were significant, and 47.83% of areas were identified to have children vulnerable to asthma. To sum up, our findings can serve as a valuable reference for the implementation of an early warning to governmental agencies about a susceptible population of children.

Typical atmospheric haze during crop harvest season in northeastern China: A case in the Changchun region

This study presents the mass concentrations of PM_2.5, O₃, SO₂ and NO_x at one urban, one suburban and two rural locations in the Changchun region from September 25 to October 27 2013. Major chemical components of PM_2.5 at the four sites were daily sampled and analyzed. Most of daily concentrations of SO₂ (7-82μg/m³), O₃ (27-171μg/m³) and NO_x (14-213μg/m³) were below the limits of the National Ambient Air Quality Standard (NAAQS) in China. However, PM_2.5 concentrations (143-168μg/m³) were 2-fold higher than NAAQS_. Higher PM_2.5 concentrations (~150μg/m³) were measured during the pre-harvest and harvest at the urban site, while PM_2.5 concentrations significantly increased from 250 to 400μgm^-3 at suburban and rural sites with widespread biomass burning. At all sites, PM_2.5 components were dominated by organic carbon (OC) and followed by soluble component sulfate (SO₄^2-), ammonium (NH₄⁺) and nitrate (NO₃^-). Compared with rural sites, urban site had a higher mineral contribution and lower potassium (K⁺ and K) contribution to PM_2.5. Severe atmospheric haze events that occurred from October 21 to 23 were attributed to strong source emissions (e.g., biomass burning) and unfavorable air diffusion conditions. Furthermore, coal burning originating from winter heating supply beginning on October 18 increased the atmospheric pollutant emissions. For entire crop harvest period, the Positive Matrix Factorization (PMF) analysis indicated five important emission contributors in the Changchun region, as follows: secondary aerosol (39%), biomass burning (20%), supply heating (18%), soil/road dust (14%) and traffic (9%).

A review of biomass burning: Emissions and impacts on air quality, health and climate in China

Biomass burning (BB) is a significant air pollution source, with global, regional and local impacts on air quality, public health and climate. Worldwide an extensive range of studies has been conducted on almost all the aspects of BB, including its specific types, on quantification of emissions and on assessing its various impacts. China is one of the countries where the significance of BB has been recognized, and a lot of research efforts devoted to investigate it, however, so far no systematic reviews were conducted to synthesize the information which has been emerging. Therefore the aim of this work was to comprehensively review most of the studies published on this topic in China, including literature concerning field measurements, laboratory studies and the impacts of BB indoors and outdoors in China. In addition, this review provides insights into the role of wildfire and anthropogenic BB on air quality and health globally. Further, we attempted to provide a basis for formulation of policies and regulations by policy makers in China.

Ozone pollution in China: A review of concentrations, meteorological influences, chemical precursors, and effects

High concentrations of ozone in urban and industrial regions worldwide have long been a major air quality issue. With the rapid increase in fossil fuel consumption in China over the past three decades, the emission of chemical precursors to ozone-nitrogen oxides and volatile organic compounds-has increased sharply, surpassing that of North America and Europe and raising concerns about worsening ozone pollution in China. Historically, research and control have prioritized acid rain, particulate matter, and more recently fine particulate matter (PM_2.5). In contrast, less is known about ozone pollution, partly due to a lack of monitoring of atmospheric ozone and its precursors until recently. This review summarizes the main findings from published papers on the characteristics and sources and processes of ozone and ozone precursors in the boundary layer of urban and rural areas of China, including concentration levels, seasonal variation, meteorology conducive to photochemistry and pollution transport, key production and loss processes, ozone dependence on nitrogen oxides and volatile organic compounds, and the effects of ozone on crops and human health. Ozone concentrations exceeding the ambient air quality standard by 100-200% have been observed in China's major urban centers such as Jing-Jin-Ji, the Yangtze River delta, and the Pearl River delta, and limited studies suggest harmful effect of ozone on human health and agricultural corps; key chemical precursors and meteorological conditions conductive to ozone pollution have been investigated, and inter-city/region transport of ozone is significant. Several recommendations are given for future research and policy development on ground-level ozone.

Heavy metal in sediments of Ziya River in northern China: distribution, potential risks, and source apportionment

The concentration partitioning between the sediment particle and the interstitial water phase plays an important role in controlling the toxicity of heavy metals in aquatic systems. The aim of this study was to assess the sediment quality in a polluted area of the Ziya River, Northern China. The contamination potential and bioavailability of six metals were determined from the concentrations of total metals and the bioavailable fractions. The results showed that the concentrations of Cr, Cu, Ni, Zn, and Pb exceeded the probable effect concentration at several sites. The high geoaccumulation indices showed that the sediments were seriously contaminated by Cd. The ratio of acid-volatile sulfide (AVS) to simultaneously extracted metal (SEM) was higher than 1, which indicated that the availability of metals in sediments was low. The risk assessment of interstitial waters confirmed that there was little chance of release of metals associated with acid-volatile sulfide into the water column. Values of the interstitial water criteria toxicity unit indicated that none of the concentrations of the studied metals exceeded the corresponding water quality thresholds of the US Environmental Protection Agency. Positive matrix factorization showed that the major sources of metals were related to anthropogenic activities. Further, if assessments are based on total heavy metal concentrations, the toxicity of heavy metals in sediment may be overestimated.

Concentrations, correlations and chemical species of PM2.5/PM10 based on published data in China: Potential implications for the revised particulate standard

Particulate matter (PM) has been of great concern in China due to the increasing haze pollution in recent years. In 2012, the Chinese national ambient air quality standard (NAAQS) was amended with a "more strict" regulation on the PM concentrations, i.e., 35 and 70 µg/m(3) for annual PM2.5 and PM10 averages, respectively (Grade-Ⅱ, GB3095-2012). To evaluate the potential of China to attain such new NAAQS and provide a more generalized chemical profile of PM in China, a comprehensive statistical analysis was carried out based on the published data of parallel PM2.5 and PM10 mass concentrations and chemical compositions of PM2.5 and PM10. The results show that most of the measured concentrations far exceed the new NAAQS. PM2.5 and PM10 show a strong positive correlation (R(2) = 0.87, p < 0.01) with PM2.5 accounting for about 65% of PM10, suggesting that the abatement of PM2.5 is crucial for reducing PM pollution and hence improving air quality in China. Organic carbon (OC), sulfate and crustal species are the three major components of PM. The NO3(-)/SO4(2-) ratios are 0.43 ± 0.26 in PM2.5 and 0.56 ± 0.29 in PM10, and the OC/EC ratios are 3.63 ± 1.73 in PM2.5 and 4.17 ± 2.09 in PM10, signifying that the stationary emissions from coal combustion remain the main PM source. An evaluation of PM2.5 situation in current China was carried out and the results show that it would take about 27 years to meet the limit value of 35 µg/m(3) in the revised standard, implying a rigorous challenge in PM2.5 control in China in the future.

Variations of surface O3 in August at a rural site near Shanghai: influences from the West Pacific subtropical high and anthropogenic emissions

Large day-to-day variability in O(3) and CO was observed at Chongming, a remote rural site east of Shanghai, in August 2010. High ozone periods (HOPs) that typically lasted for 3-5 days with daily maximum ozone exceeding 102 ppb were intermittent with low ozone periods (LOPs) with daily maximum ozone less than 20 ppb. The correlation analysis of ozone with meteorological factors suggests that the large variations of surface ozone are driven by meteorological conditions correlated with the changes in the location and intensity of the west Pacific subtropical high (WPSH) associated with the East Asian summer monsoon (EASM). When the center of WPSH with weaker intensity is to the southeast of Chongming site, the mixing ratios and variability of surface ozone are higher. When the center of WPSH with stronger intensity is to the northeast of Chongming site, the mixing ratios and variability of surface ozone are lower. Sensitivity simulations using the GEOS-Chem chemical transport model indicate that meteorological condition associated with WPSH is the primary factor controlling surface ozone at Chongming in August, while local anthropogenic emissions make significant contributions to surface ozone concentrations only during HOP.

Characteristics and sources of non-methane hydrocarbons and halocarbons in wintertime urban atmosphere of Shanghai, China

The characteristics and sources of major hydrocarbons and halocarbons in the wintertime ambient air of urban center of Shanghai, a mega city of China, were investigated. Propane, toluene, ethyl acetate, and benzene were the most abundant hydrocarbons. The majority of species showed significant variability in mixing ratios with occasional episodic increases. The more common use of liquefied petroleum gas fuel for taxis and light motorcycles was believed to lead to high levels of ambient propane over the urban center of Shanghai. Correlating with toluene, dichloromethane, and 1,2-dichloroethane (1,2-DCE), abundant chloromethane (up to a daily mean of 1.61 ± 0.99 ppbv and a maximum of 5.34 ppbv) was mainly associated with industrial emissions, although biomass burnings exist widely in east China. The Chinese New Year (CNY) holiday period with no industrial activity over China provides a platform for the study of industrial emissions over the urban atmosphere of Shanghai. The normal weekly cycles were characterized by higher and more variable mixing ratios during weekdays which dropped during weekends. Enhanced mixing ratios were observed in the fortnight before the CNY holidays due to increased industrial emissions as a result of overtime production to make up for the holiday losses. During the CNY holidays, lower level and less variable mixing ratios were observed. A benzene/toluene (B/T) ratio of 0.6 ± 0.4 (mean ± std.) for the morning rush hour samples was identified to be the characteristic ratio of vehicular emissions. However, a B/T ratio of 0.4 ± 0.2 from vehicles and other sources was derived for the ambient air.

On the relationship between ozone and its precursors in the Pearl River Delta: application of an observation-based model (OBM)

BACKGROUND, AIM, AND SCOPE

Photochemical smog, characterized by high concentrations of O(3) and fine particles, is of great concern in the urban areas, in particular megacities and city clusters like the Pearl River Delta.

MATERIALS, METHODS, AND RESULTS

Ambient ozone (O(3)) and its precursors were simultaneously measured at two sites in the Pearl River Delta, namely, Wan Qing Sha (WQS) in Guangzhou and Tung Chung (TC) in Hong Kong, from 23 October to 01 December 2007 in order to explore their potential relationship. Eight high O(3) episode days were identified at WQS and two at TC during the sampling campaign, indicating a more serious O(3) pollution in Guangzhou than in Hong Kong. An observation-based model was employed to determine the ozone-precursor relationship. At both sites, O(3) production was found to be volatile organic compound (VOC)-limited, which is consistent with previous observations. Anthropogenic hydrocarbons played a key role in O(3) production, while reducing nitric oxide emissions aided the buildup of O(3) concentrations. Among VOC species, the summed relative incremental reactivity (RIR) of the top 12 compounds accounted for 89% and 85% of the total RIR at WQS and TC, respectively, indicating that local photochemical O(3) formation can be mainly attributed to a small number of VOC species.

DISCUSSION AND CONCLUSIONS

A large increment in both simulated HO(2) and O(3) concentrations was achieved with additional input of hourly carbonyl data. This suggested that apart from hydrocarbons, carbonyls might significantly contribute to the O(3) production in the Pearl River Delta.

Exposure to PM2.5 and PAHs from the Tong Liang, China epidemiological study

Chemically speciated PM2.5 and particle-bound polycyclic aromatic hydrocarbon (PAH) measurements were made at three sites near urban Tong Liang, Chongqing, a Chinese inland city where coal combustion is used for electricity generation and residential purposes outside of the central city. Ambient sampling was based on 72-hr averages between 3/2/2002 and 2/26/2003. Elevated PM2.5 and PAH concentrations were observed at all three sites, with the highest concentrations found in winter and the lowest in summer. This reflects a coupling effect of source variability and meteorological conditions. The PM2.5 mass estimated from sulfate, nitrate, ammonium, organics, elemental carbon, crustal material, and salt corresponded with the annual average gravimetric mass within +/-10%. Carbonaceous aerosol was the dominant species, while positive correlations between organic carbon and trace elements (e.g., As, Se, Br, Pb, and Zn) were consistent with coal-burning and motor vehicle contributions. Ambient particle-bound PAHs of molecular weight 168-266 were enriched by 1.5 to 3.5 times during the coal-fired power plant operational period. However, further investigation is needed to determine the relative contribution from residential and utility coal combustion and vehicular activities.