The role of atmospheric volatile organic compounds (VOCs) in ozone formation around China's largest plywood manufacturer

The volatile organic compounds (VOCs) are a dominant contributor to the formation of ozone (O3) in Linyi, the plywood capital of China. However, the temporal variations and source origins of VOCs in Linyi remain unclear. This study gathered ambient air samples (n = 214) from the urban center of Linyi during the period April to October of 2021-2023. The total volatile organic compounds (TVOCs) concentrations ranged from 28 ppbv to 32 ppbv with oxygenated volatile organic compounds (OVOCs) taking the large portion (50.76 %) of TVOCs, followed by alkanes (28.11 %), aromatics (13.71 %), alkenes (6.66 %), and alkynes (0.76 %). The OVOCs (44.10 %) were the dominant contributors to ozone formation potential (OFP). Formaldehyde, an OVOC and particular pollutant from plywood industries contributed the most to OFP (∼21.60 %). The average concentration of TVOCs in 2022 was the lowest (28.61 ± 10.76 ppbv), with VOCs species, such as isobutane and propane having the lowest concentrations in 2022 (p < 0.05), reflecting a decrease in transportation activity due to the impacts of pandemic lockdowns. Concentrations of OVOCs were annually increasing because of the annual growth of plywood yield. The TVOCs and OVOCs levels were significantly correlated to O3 levels (p < 0.01). The concentrations of TVOCs and OVOCs as well as O3 were highest in June and September (p < 0.05), when the temperature and the degree of photochemical reactions were high. The source apportionment analysis found that plywood industries were the main source (32.90 %) of TVOCs, followed by liquefied petroleum gas (LPG, 21.32 %). Trajectory statistical models (TSM) analysis suggested that Linyi is greatly affected by regional transport from the southwest (31.63 %). This study provides new insights into the mitigation and management of VOCs and O3 pollution in plywood industry cities.

Insights into the source characterization, risk assessment and ozone formation sensitivity of ambient VOCs at an urban site in the Fenwei Plain, China

The ground-level O3 concentration has shown a deteriorating trend in the Fenwei Plain of China, which poses a greater challenge for formulating control strategies of O3 precursor (VOCs). To accurately control VOCs sources and effectively reduce O3 concentration from a seasonal perspective, online monitoring of 114 VOCs was conducted at Yuncheng Middle School Station from January 1, 2021 to December 31, 2021. The VOCs concentration showed a seasonal variation with the highest in winter and the lowest in summer. During the four seasons, alkanes (34.5-41.7 %) and OVOCs (36.6-46.9 %) were the most abundant species. The emission ratios of specific VOCs species indicated that vehicular exhaust, industrial source, and combustion were the major VOCs sources. The Positive Matrix Factorization (PMF) model identified that industrial source and secondary conversion were the main contributors in summer, while combustion and LPG/NG contributed more significantly in winter. The 2021-based VOCs emission inventory showed that the total VOCs emissions in the central urban area of Yuncheng was 8128.8 t, in which industrial process was the largest contributor. Alkanes, aromatics, and OVOCs accounted for 31.0 %, 25.8 %, and 25.7 % of the annual VOCs emission, respectively. In addition, the calculated relative incremental reactivity (RIR) values of O3 precursors demonstrated that alkenes and aromatics were the most sensitive groups to O3 formation during the four seasons. The ambient VOCs posed the non-carcinogenic risk across all seasons, which can be attributed to acrolein and three main sources (industrial source, secondary conversion, and combustion). However, ambient VOCs exposed to definite carcinogenic risks due to the appearance of 1,2-dichloroethane, 1,2-dichloropropane, and benzene, and the main risks arose from industrial source, vehicular exhaust, and solvent usage. These findings emphasize the necessity of undertaking scientific and systematic measures for priority species and control sources of VOCs emission.

Volatile Organic Compounds on Rhodes Island, Greece: Implications for Outdoor and Indoor Human Exposure

Volatile organic compounds (VOC) are considered a class of pollutants with a significant presence in indoor and outdoor air and serious health effects. The aim of this study was to measure and evaluate the levels of outdoor and indoor VOCs at selected sites on Rhodes Island, Greece, during the cold and warm periods of 2023. Spatial and seasonal variations were evaluated; moreover, cancer and non-cancer inhalation risks were assessed. For this purpose, simultaneous indoor-outdoor air sampling was carried out on the island of Rhodes. VOCs were determined by Thermal Desorption-Gas Chromatography/Mass Spectroscopy (TD-GC/MS). Fifty-six VOCs with frequencies ≥ 50% were further considered. VOC concentrations (∑56VOCs) at all sites were found to be higher in the warm period. In the warm and cold sampling periods, the highest concentrations were found at the port of Rhodes City, while total VOC concentrations were dominated by alkanes. The Positive Matrix Factorization (PMF) model was applied to identify the VOC emission sources. Non-cancer and cancer risks for adults were within the safe levels.

Sources of atmospheric oxygenated volatile organic compounds in different air masses in Shenzhen, China

As precursors of photochemical secondary pollutants, oxygenated volatile organic compounds (OVOCs) play an important role in atmospheric photochemistry. In this study, 23 OVOCs were monitored using a commercial proton transfer reaction time-of-flight mass spectrometer at an urban site in Shenzhen, China. During the campaign, the mean total concentration of OVOCs was 23.3 ± 15.5 ppb (mean ± standard deviation), with a total ozone formation potential (TOFP) of 87.3 ± 58.7 ppb. Aldehydes contributed the most to the concentration and TOFP of OVOCs, followed by ketones, alcohols, and carboxylic acids. Formaldehyde, acetone, and acetaldehyde were the three most abundant atmospheric carbonyls. An optimized photochemical age-based parameterization method was locally applied for the source apportionment of OVOCs. OVOCs in Shenzhen primarily originated from biogenic sources during the summer. Secondary anthropogenic sources were also important contributors of most carbonyl compounds. The campaign was divided into four periods. Two periods were dominated by the east wind from the relatively clean coastal areas, with the mean concentration of anthropogenic OVOCs largely decreasing during the Chinese National Day holidays. The other two periods were dominated by northwest wind and northeast wind, respectively, with larger OVOC contributions from anthropogenic sources, suggesting that pollution transport from the inland was a main contributor to OVOCs. This study highlights the important contributions of both local and regional OVOC sources in urban atmospheres.

Characterization of photochemical losses of volatile organic compounds and their implications for ozone formation potential and source apportionment during summer in suburban Jinan, China

Volatile organic compounds (VOCs) undergo substantial photochemical losses during their transport from emission sources to receptor sites, resulting in serious implications for their source apportionment and ozone (O3) formation. Based on the continuous measurements of VOCs in suburban Jinan in August 2022, the effects of photochemical losses on VOC source contributions and O3 formation were evaluated in this study. The observed and initial concentrations of total VOCs (TVOC) were 12.0 ± 5.1 and 16.0 ± 7.4 ppbv, respectively. Throughout the observation period, alkenes had the most prominent photochemical losses (58.2%), followed by aromatic hydrocarbons (23.1%), accounting for 80.6% and 6.9% of the total losses, respectively. During high O3 episodes, the photochemical loss of VOCs was 6.9 times higher than that during the cleaning period. Alkene losses (exceeding 67.3%), specifically losses of isoprene, propylene, ethylene, and n-butene, dominated the total losses of VOCs during the O3 increase period. Eight sources of VOCs were identified by positive matrix factorization (PMF) based on the observed and initial concentration data (OC-PMF and IC-PMF, respectively). Concentrations of all emission sources in the OC-PMF were underestimated by 2.4%-57.1%. Moreover, the contribution of each emission source was over- or underestimated compared with that in case of the IC-PMF. The contributions of biogenic and motor vehicle exhaust emissions were underestimated by 5.3 and 2.8 percentage points, respectively, which was associated with substantial oxidation of the emitted high-reactive species. The contributions of coal/biomass burning and natural gas were overestimated by 2.4 and 3.9 percentage points, respectively, which were related to the emission of low-reactive species (acetylene, ethane, and propane). Based on our results, the photochemical losses of VOCs grossly affect their source apportionment and O3 formation. Thus, photochemical losses of VOCs must be thoroughly accounted to establish a precise scientific foundation for air-pollution control strategies.

A compensation mechanism for air pollutants generated by tourism-related land-based transportation: An exergy-based case study from Macao

This paper discusses the compensation standard for exhaust pollution and devises a compensation mechanism for Macao's tourism-related transport sector based on an integration of chemical exergy and universal exergy, using data on gasoline consumption by automobile sector retrieved from the transportation industry. The results reveal that: (1) the exergy values of air pollutant emissions increased from 1.53 × 10¹² kJ in 2010 to 2.03 × 10¹² kJ in 2019 (an increase of 1.33 times), and the exergy of CO, NO_x, and SO₂ emissions accounted for 77.5%, 20.4% and 2.1% of total exhaust emissions in Macao respectively. (2) In 2019, the monetary value of emission exergy, and the environmental costs of air pollution, were 1.7 times greater than in 2010. (3) If Light Rail Transit is compensated for, then the mean interval's values of the upper and lower limits of the compensation standard are 0.55 USD and 0.05 USD, respectively. When gasoline tax is used as a means of compensation it is necessary to raise its rate by about 8% based on the tax rate. A three-stage bargaining game model is used to provide evidence that this compensation standard is practical and acceptable.

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.

Ozone episodes during and after the 2018 Chinese National Day holidays in Guangzhou: Implications for the control of precursor VOCs

The impact of reducing industrial emissions of volatile organic compounds (VOCs) on ozone (O₃) pollution is of wide concern particularly in highly industrialized megacities. In this study, O₃, nitrogen oxides (NOx) and VOCs were measured at an urban site in the Pearl River Delta region during the 2018 Chinese National Day Holidays and two after-holiday periods (one with ozone pollution and another without). O₃ pollution occurred throughout the 7-day holidays even industrial emissions of VOCs were passively reduced due to temporary factory shutdowns, and the toluene to benzene ratios dropped from ∼10 during non-holidays to ∼5 during the holidays. Box model (AtChem2-MCM) simulations with the input of observation data revealed that O₃ formation was all VOC-limited, and alkenes had the highest relative incremental reactivity (RIR) during the holiday and non-holiday O₃ episodes while aromatics had the highest RIR during the non-pollution period. Box model also demonstrated that even aromatics decreased proportionally to levels with near-zero contributions of industrial aromatic solvents, O₃ concentrations would only decrease by less than 20% during the holiday and non-holiday O₃ episodes and ozone pollution in the periods could not be eliminated. The results imply that controlling emissions of industrial aromatic solvents might be not enough to eliminate O₃ pollution in the region, and more attention should be paid to anthropogenic reactive alkenes. Isoprene and formaldehyde were among the top 3 species by RIRs in all the three pollution and non-pollution periods, suggesting substantial contribution to O₃ formation from biogenic VOCs.

The world-wide waste web

Countries globally trade with tons of waste materials every year, some of which are highly hazardous. This trade admits a network representation of the world-wide waste web, with countries as vertices and flows as directed weighted edges. Here we investigate the main properties of this network by tracking 108 categories of wastes interchanged in the period 2001–2019. Although, most of the hazardous waste was traded between developed nations, a disproportionate asymmetry existed in the flow from developed to developing countries. Using a dynamical model, we simulate how waste stress propagates through the network and affects the countries. We identify 28 countries with low Environmental Performance Index that are at high risk of waste congestion. Therefore, they are at threat of improper handling and disposal of hazardous waste. We find evidence of pollution by heavy metals, by volatile organic compounds and/or by persistent organic pollutants, which are used as chemical fingerprints, due to the improper handling of waste in several of these countries.

The 2001–2019 web of international waste trade is investigated, allowing the identification of countries at threat of improper handling and disposal of waste. Chemical tracers are used to identify the environmental impact of waste in these countries.

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.

Source apportionment of VOCs in a typical medium-sized city in North China Plain and implications on control policy

Characteristics of atmospheric VOCs (volatile organic compounds) have been extensively studied in megacities in China, however, they are scarcely investigated in medium/small-sized cities in North China Plain (NCP). A comprehensive research on possible sources of VOCs was conducted in a medium-sized city of NCP, from May to September 2019. A total of 143 canister samples of 8 sites in Xuchang city were collected, and 57 VOC species were detected. The average VOC concentrations were 42.6 ± 31.6 μg/m³, with 53.7 ± 31.0 μg/m³ and 32.1 ± 27. 8 μg/m³, in the morning and afternoon, respectively. Alkenes and aromatics contributed 80% of the total ozone formation potential (OFP). Aromatics accounted for more than 95% of secondary organic aerosol potential (SOAP). VOCs were dominated by the local emission with significant transport from the southeast direction. PMF analysis extracted 6 sources, which were combustion (33.1%), LPG usage (19.3%), vehicular exhaust & fuel evaporation (15.8%), solvent usage (15.2%), industrial (9.11%) and biogenic (7.51%), respectively and they contributed 33.4%, 17.6%, 12.9%, 18.6%, 9.28% and 8.22% to the OFP, respectively. Combustion and LPG usage were the dominant VOC sources; and combustion, solvent usage and LPG usage were the main sources of OFP in Xuchang city, which were different to megacities in China with a high contribution from vehicular exhaust, solvent usage and industry, suggesting specific control strategies on VOCs need to be implemented in medium-sized city such as Xuchang city.

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.

Ambient Non-Methane Hydrocarbons (NMHCs) Measurements in Baoding, China: Sources and Roles in Ozone Formation

Ambient non-methane hydrocarbons (NMHCs) are important precursors of ozone (O3) and secondary organic aerosol (SOA). Online and offline measurements of NMHCs were conducted during September 2015 in Baoding, Hebei province of China, in order to investigate their sources and roles in ozone formation. Average levels of total NMHCs online measured at the urban site were 44.5 ± 26.7 ppb. Aromatics was the largest contributor to NMHCs levels and OH reactivity, with fraction of 27.1% and 35.9%, respectively. Based on offline measurements at eight sites, we found that toluene, ethylbenzene, and m,p-xylene displayed the highest level at the site close to automobile manufacturing factories, followed by downwind receptor sites and other sites. Positive matrix factorization (PMF) model was then used to analyze NMHCs sources. Four factors were identified, including traffic-related emission, automobile manufacturing coating, biogenic emission, and NG/LPG usage and background. Average relative contribution of automobile manufacturing coating to NMHCs levels during the entire online measurement period was 33.4%, and this value increased to 42% during two O3 pollution days. Sensitivity of O3 formation to NMHCs and NOX during an O3 pollution episode were analyzed using a box model based on observations. Relative incremental reactivity (RIR) results suggested that O3 formation was in NOx-titration regime (i.e., highly NMHCs-limited regime). Further scenario analyses on relationship of O3 formation with reduction of NOx and anthropogenic NMHCs (AHC) indicated that AHC and NOx should be reduced by a ratio greater than two and three to achieve 5% and 10% O3 control objectives, respectively. The largest RIR value for anthropogenic NMHC species was from xylenes, which were also an important contributor to SOA formation and dominantly from sources related to automobile manufacturing coating and traffic emission. This means reducing NMHCs emission from automobile manufacturing coating and traffic emission should be given priority for synergetic control of O3 and PM2.5.

Health risk-oriented source apportionment of PM2.5-associated trace metals

In health-oriented air pollution control, it is vital to rank the contributions of different emission sources to the health risks posed by hazardous components in airborne fine particulate matters (PM_2.5), such as trace metals. Towards this end, we investigated the PM_2.5-associated metals in two densely populated regions of China, the Yangtze River Delta (YRD) and Pearl River Delta (PRD) regions, across land-use gradients. Using the positive matrix factorization (PMF) model, we performed an integrated source apportionment to quantify the contributions of the major source categories underlying metal-induced health risks with information on the bioaccessibility (using simulated lung fluid) and speciation (using synchrotron-based techniques) of metals. The results showed that the particulate trace metal profiles reflected the land-use gradient within each region, with the highest concentrations of anthropogenically enriched metals at the industrial sites in the study regions. The resulting carcinogenic risk that these elements posed was higher in the YRD than in the PRD. Chromium was the dominant contributor to the total excessive cancer risks posed by metals while manganese accounted for a large proportion of non-carcinogenic risks. An elevated contribution from industrial emissions was found in the YRD, while traffic emissions and non-traffic combustion (the burning of coal/waste/biomass) were the common dominant sources of cancer and non-cancer risks posed by metals in both regions. Moreover, the risk-oriented source apportionment of metals did not mirror the mass concentration-based one, suggesting the insufficiency of the latter to inform emission mitigation in favor of public health. While providing region-specific insights into the quantitative contribution of major source categories to the health risks of PM_2.5-associated trace metals, our study highlighted the need to consider the health protection goal-based source apportionment and emission mitigation in supplement to the current mass concentration-based framework.

Distribution, Sources, and Health Risk Assessment of Volatile Organic Compounds in Hefei City

Volatile organic compounds (VOCs) are involved in the formation of ozone formation, which plays a significant role in regional air contamination and poses a great threat to human health. The VOCs were collected from the urban area of Hefei city via an off-line sampling method (SUMMA canister) and determined by gas chromatography-mass spectrometer. The average concentrations of VOCs were 17.65 ± 28.36 ppbv, which were mainly contributed by aromatics (10.02 ± 13.37 ppbv), haloalkane (5.37 ± 8.90 ppbv), ally halide (1.25 ± 3.36 ppbv), and aryl halid (1.02 ± 2.73 ppbv). According to the principal component analysis, three major sources were identified, including solvent use, vehicle exhaust, and industrial release, accounting for 70.6% of the total variance of the data. Health risk assessment was utilized to evaluate the potential adverse health effects of the individual VOC. The total hazard ratio in the selected area was higher than 1, where could pose health threat to exposed population. The cancer risk for benzene, carbon tetrachloride, trichloromethane, and 1, 2-dichloroethane were 4.8 × 10^-5, 4.5 × 10^-5, 3.3 × 10^-5, and 2.5 × 10^-5, respectively, indicating definite health risks.

Characteristics and source implications of aromatic hydrocarbons at urban and background areas in Beijing, China

The characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) concentrations, their temporal and spatial variations, and their source origins from September-December 2017 at an urban and a background site in Beijing, China were investigated. The averaged (±σ) total mixing ratios of benzene, toluene, ethylbenzene, m, p-xylenes, and o-xylene were 0.40 ± 0.39 ppbv, 0.31 ± 0.34 ppbv, 0.08 ± 0.07 ppbv, 0.08 ± 0.08 ppbv, and 0.05 ± 0.05 ppbv at the SDZ site, which were 63%, 79%, 83%, 85%, and 89% lower than those at the Chinese Academy of Meteorological Sciences site (CMA). It is worth noting that the average mixing ratios of BTEX at SDZ and CMA were 0.86 ± 1.03 ppbv and 3.38 ± 2.80 ppbv during the heating period (HP), which were 2.3% and 21.9% lower than those before the HP, a decrease that was mainly related to the frequent occurrence of strong northerly and northwesterly winds and low relative humidity (RH) during the HP. Obvious differences were also observed between the BTEX composition proportions at the SDZ and CMA sites. On average, benzene comprised 44% of the total BTEX at SDZ, whereas toluene was the largest contributor to the total BTEX at CMA, accounting for 37%. In addition, the contributions of C8 aromatics (the sum of ethylbenzene, m, p-xylenes, and o-xylene) at CMA (36%) were also higher than those at SDZ (21%), reflecting the different emission sources of the two sites. In addition, the BTEX species showed similar and pronounced diurnal profiles at SDZ and CMA, all characterized by much higher values at night than during the day. Diagnostic ratios and source implications suggested that SDZ was affected mainly by biomass/biofuel/coal burning, with substantially elevated benzene levels during the winter HP, whereas CMA was affected both by traffic-related emissions and biomass/biofuel/coal burning emissions. These findings suggest the necessity of regionally-tailored control strategies both to reduce BTEX levels and to mitigate their environmental impact. Further analysis of the backward trajectories revealed that the BTEX compounds varied greatly in terms of air mass origins, but generally exhibited high values for slow air masses passing over areas south of Beijing, with dominant contributions from benzene, toluene, and m, p-xylenes.

Characterization of organic aerosols and their precursors in southern China during a severe haze episode in January 2017

The rapid industrialization and economic development in the Pearl River Delta (PRD) region of southern China have led to a substantial increase in anthropogenic emissions and hence frequent haze pollution over the past two decades. In early January 2017, a severe regional haze pollution episode was captured in the PRD region, with a peak PM_2.5 concentration of around 400μgm^-3, the highest value ever reported at this site. During the haze episode, elevated concentrations of oxygenated volatile organic compounds (OVOCs, 33±16 ppbv) and organic matter (41±15μg m^-3) were observed, indicating the enhanced roles of secondary organic aerosols (SOAs) in the formation of haze pollution. Water-soluble organic carbon (WSOC, 12.8±5.5μg C m^-3) dominated the organic aerosols, with a WSOC/OC ratio of 0.63±0.12 and high correlation (R=0.85) with estimated secondary organic carbon (SOC), suggesting the predominance of a secondary origin of the measured organic aerosols during the haze episode. Four carboxylic acids (oxalic, acetic, formic, and pyruvic acids) were characterized in the aerosols (1.30±0.38μgm^-3) and accounted for 3.6±1.2% of WSOC in carbon mass, with oxalic acid as the most abundant species. The simultaneous measurements of volatile organic compounds (VOCs), OVOCs, and organic acids in aerosols at this site provided an opportunity to investigate the relationship between the precursors and the products, as well as the potential formation pathways. Water-soluble aldehydes and ketones, predominantly produced via the oxidation of anthropogenic VOCs (mainly propane, toluene, n-butane, and m, p-xylene), were the main contributors of the organic acids. The formation of OVOCs is largely attributed to gas-phase photochemical oxidation, whereas the WSOC and dicarboxylic acids were produced from both photochemistry and nocturnal heterogeneous reactions. These findings provided further insights into the oxidation and evolution of organic compounds during the haze pollution episode.

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.

Investigation of emission characteristics of NMVOCs over urban site of western India

This is the first study to characterize the variation and emission of C₂-C₅ non-methane volatile organic compounds (NMVOCs) in a semi-urban site of western India based on measurements during February-December 2015. Anthropogenic NMVOCs show clear seasonal dependence with highest in winter and lowest in monsoon season. Biogenic NMVOCs likes isoprene show highest mixing ratios in the pre-monsoon season. The diurnal variation of NMVOC species can be described by elevated values from night till morning and lower values in the afternoon hours. The elevated levels of NMVOCs during night and early morning hours were caused mainly by weaker winds, temperature inversion and reduced chemical loss. The correlations between NMVOCs, CO and NOx indicate the dominant role of various local emission sources. Use and leakage of liquefied petroleum gas (LPG) contributed to the elevated levels of propane and butanes. Mixing ratios of ethylene, propylene, CO, NOx, etc. show predominant emissions from combustion of fuels in automobiles and industries. The Positive Matrix Factorization (PMF) source apportionments were performed for the seven major emission sectors (i.e. Vehicular exhaust, Mixed industrial emissions, Biomass/Fired brick kilns/Bio-fuel, Petrochem, LPG, Gas evaporation, Biogenic). Emissions from vehicle exhaust and industry-related sources contributed to about 19% and 40% of the NMVOCs, respectively. And the rest (41%) was attributed to the emissions from biogenic sources, LPG, gasoline evaporation and biomass burning. Diurnal and seasonal variations of NMVOCs were controlled by local emissions, meteorology, OH concentrations, long-range transport and planetary boundary layer height. This study provides a good reference for framing environmental policies to improve the air quality in western region of India.

Characteristics of one-year observation of VOCs, NOx, and O3 at an urban site in Wuhan, China

A continuous online observation of ozone and its precursors (NOx, VOCs) was carried out in central urban Wuhan from September 2016 to August 2017. The concentration levels of ozone, NOx, VOCs and their variations in urban Wuhan were analyzed, as well as effects of VOCs on ozone photochemical generation and the main controlling factors for ozone production. During the observation period, the average concentrations of ozone and NOx in Wuhan was 22.63 and 30.14 ppbv, respectively, and the average concentration of VOCs was 32.61 ppbv (42.3% alkanes, 13.0% alkenes, 10.0% aromatics, 7.3% acetylene, 9.9% OVOCs, and 10.5% halohydrocarbons). Ozone concentration was higher in spring and summer as compared with autumn and winter, wheras VOCs and NOx concentratios were lower in spring and summer but higher in autumn and winter. Aromatics and alkenes, two of VOCs species, showed the highest contributions to ozone formation potential in Wuhan (35.7% alkenes, 35.4 aromatics, 17.5% alkanes, 8.6% OVOCs, 1.6% halogenated hydrocarbons, and 1.4% acetylene). Among all VOCs species, those with the highest contribution were ethylene, m-xylene, toluene, propylene and o-xylene. The contribution of these five compounds to the total ozone formation potential concentration was 43.90%. Ozone-controlling factors in Wuhan changed within one day; during the early morning hours (6:00-9:00), VOCs/NOx was low, and ozone generation followed a VOCs-limited regime. However, during the peak time of ozone concentration (12:00-16:00), the ratio of VOCs/NOx was relatively high, suggesting that ozone generation followed a NOx-limited regime.

Novel Butane-Oxidizing Bacteria and Diversity of bmoX Genes in Puguang Gas Field

To investigate the diversity of butane-oxidizing bacteria in soils contaminated by long-term light hydrocarbon microseepage and the influence of butane on the soil microbial community, a quantitative study and identification of butane-oxidizing bacteria (BOB) in soils at the Puguang gas field were performed by DNA-based stable isotope probing (DNA-SIP). For the first time, two phylotypes corresponding to the genera Giesbergeria and Ramlibacter were identified as being directly involved in butane oxidation, in addition to the well-known light hydrocarbon degrader Pseudomonas. Furthermore, bmoX genes were strongly labeled by ¹³C-butane, and their abundances in gas field soils increased by 43.14-, 17.39-, 21.74-, and 30.14-fold when incubated with butane for 6, 9, 12, and 14 days, respectively, indicating that these bmoX-harboring bacteria could use butane as the sole carbon and energy source and they play an important role in butane degradation. We also found that the addition of butane rapidly shaped the bacterial community and reduced the diversity of bmoX genes in the gas field soils. These findings improve our understanding of BOB in the gas field environment and reveal the potential for their applications in petroleum exploration and bioremediation.

Aromatic hydrocarbons in a controlled ecological life support system during a 4-person-180-day integrated experiment

Indoor air quality is vital to the health and comfort of people who live inside a controlled ecological life support system (CELSS) built for long-term space explorations. Here we measured aromatic hydrocarbons to assess their sources and health risks during a 4-person-180-day integrated experiment inside a CELSS with four cabins for growing crops, vegetables and fruits and other two cabins for working, accommodations and resources management. During the experiment, the average concentrations of benzene, ethylbenzene, m,p-xylenes and o-xylene were found to decrease exponentially from 7.91±3.72, 37.2±35.2, 100.8±111.7 and 46.8±44.1μg/m³ to 0.39±0.34, 1.4±0.5, 2.8±0.7 and 2.1±0.9μg/m³, with half-lives of 25.3, 44.8, 44.7 and 69.3days, respectively. Toluene to benzene ratios indicated emission from construction materials or furniture to be a dominant source for toluene, and concentrations of toluene fluctuated during the experiment largely due to the changing sorption by growing plants. The cancer and no-cancer risks based on exposure pattern of the crews were insignificant in the end of the experiment. This study also suggested that using low-emitting materials/furniture, growing plants and purifying air actively would all help to lower hazardous air pollutants inside CELSS. Broadly, the results would benefit not only the development of safe and comfort life support systems for space exploration but also the understanding of interactions between human and the total environment in closed systems.

Air Pollution Control Policies in China: A Retrospective and Prospects

With China’s significant role on pollution emissions and related health damage, deep and up-to-date understanding of China’s air pollution policies is of worldwide relevance. Based on scientific evidence for the evolution of air pollution and the institutional background of environmental governance in China, we examine the development of air pollution control policies from the 1980s and onwards. We show that: (1) The early policies, until 2005, were ineffective at reducing emissions; (2) During 2006–2012, new instruments which interact with political incentives were introduced in the 11th Five-Year Plan, and the national goal of reducing total sulfur dioxide (SO₂) emissions by 10% was achieved. However, regional compound air pollution problems dominated by fine particulate matter (PM_2.5) and ground level ozone (O₃) emerged and worsened; (3) After the winter-long PM_2.5 episode in eastern China in 2013, air pollution control policies have been experiencing significant changes on multiple fronts. In this work we analyze the different policy changes, the drivers of changes and key factors influencing the effectiveness of policies in these three stages. Lessons derived from the policy evolution have implications for future studies, as well as further reforming the management scheme towards air quality and health risk oriented directions.

Ambient air benzene at background sites in China's most developed coastal regions: exposure levels, source implications and health risks

Benzene is a known human carcinogen causing leukemia, yet ambient air quality objectives for benzene are not available in China. The ambient benzene levels at four background sites in China's most developed coastal regions were measured from March 2012 to February 2013. The sites are: SYNECP, in the Northeast China Plain (NECP); YCNCP, in the North China Plain (NCP); THYRD, in the Yangtze River Delta (YRD) and DHPRD, in the Pearl River Delta (PRD). It was found that the mean annual benzene levels (578-1297 ppt) at the background sites were alarmingly higher, especially when compared to those of 60-480 pptv monitored in 28 cities in the United States. Wintertime benzene levels were significantly elevated at both sites (SYNECP and YCNCP) in northern China due to heating with coal/biofuels. Even at these background sites, the lifetime cancer risks of benzene (1.7-3.7E-05) all exceeded 1E-06 set by USEPA as acceptable for adults. At both sites in northern China, good correlations between benzene and CO or chloromethane, together with much lower toluene/benzene (T/B) ratios, suggested that benzene was largely related to coal combustion and biomass/biofuel burning. At the DHPRD site in the PRD, benzene revealed a highly significant correlation with methyl tert-butyl ether (MTBE), indicating that its source was predominantly from vehicle emissions. At the THYRD site in the YRD, higher T/B ratios and correlations between benzene and tetrachloroethylene, or MTBE, implied that benzene levels were probably affected by both traffic-related and industrial emissions.

Sources of C₂-C₄ alkenes, the most important ozone nonmethane hydrocarbon precursors in the Pearl River Delta region

Surface ozone is becoming an increasing concern in China's megacities such as the urban centers located in the highly industrialized and densely populated Pearl River Delta (PRD) region, where previous studies suggested that ozone production is sensitive to VOC emissions with alkenes being important precursors. However, little was known about sources of alkenes. Here we present our monitoring of ambient volatile organic compounds at four representative urban, suburban and rural sites in the PRD region during November-December 2009, which experienced frequent ozone episodes. C2-C4 alkenes, whose total mixing ratios were 11-20% of non-methane hydrocarbons (NMHCs) quantified, accounted for 38-64% of ozone formation potentials (OFPs) and 30-50% of the total hydroxyl radical (OH) reactivity by NMHCs. Ethylene was the most abundant alkene, accounting for 8-15% in total mixing ratios of NMHCs and contributed 25-46% of OFPs. Correlations between C2-C4 alkenes and typical source tracers suggested that ethylene might be largely related to vehicle exhausts and industry activities, while propene and butenes were much more LPG-related. Positive Matrix Factorization (PMF) confirmed that vehicle exhaust and liquefied petroleum gas (LPG) were two major sources that altogether accounted for 52-62%, 58-77%, 73-83%, 68-79% and 73-84% for ethylene, propene, 1-butene, trans-2-butene and cis-2-butene, respectively. Vehicle exhausts alone contributed 32-49% ethylene and 35-41% propene. Industry activities contributed 13-23% ethylene and 7-20% propene. LPG instead contributed the most to butenes (38-65%) and substantially to propene (23-36%). Extensive tests confirmed high fractions of propene and butenes in LPG then used in Guangzhou and in LPG combustion plumes; therefore, limiting alkene contents in LPG would benefit regional ozone control.

Bio-organic materials in the atmosphere and snow: measurement and characterization

Bio-organic chemicals are ubiquitous in the Earth's atmosphere and at air-snow interfaces, as well as in aerosols and in clouds. It has been known for centuries that airborne biological matter plays various roles in the transmission of disease in humans and in ecosystems. The implication of chemical compounds of biological origins in cloud condensation and in ice nucleation processes has also been studied during the last few decades, and implications have been suggested in the reduction of visibility, in the influence on oxidative potential of the atmosphere and transformation of compounds in the atmosphere, in the formation of haze, change of snow-ice albedo, in agricultural processes, and bio-hazards and bio-terrorism. In this review we critically examine existing observation data on bio-organic compounds in the atmosphere and in snow. We also review both conventional and cutting-edge analytical techniques and methods for measurement and characterisation of bio-organic compounds and specifically for microbial communities, in the atmosphere and snow. We also explore the link between biological compounds and nucleation processes. Due to increased interest in decreasing emissions of carbon-containing compounds, we also briefly review (in an Appendix) methods and techniques that are currently deployed for bio-organic remediation.

Source attributions of hazardous aromatic hydrocarbons in urban, suburban and rural areas in the Pearl River Delta (PRD) region

Aromatic hydrocarbons (AHs) are both hazardous air pollutants and important precursors to ozone and secondary organic aerosols. Here we investigated 14 C6-C9 AHs at one urban, one suburban and two rural sites in the Pearl River Delta region during November-December 2009. The ratios of individual aromatics to acetylene were compared among these contrasting sites to indicate their difference in source contributions from solvent use and vehicle emissions. Ratios of toluene to benzene (T/B) in urban (1.8) and suburban (1.6) were near that of vehicle emissions. Higher T/B of 2.5 at the rural site downwind the industry zones reflected substantial contribution of solvent use while T/B of 0.8 at the upwind rural site reflected the impact of biomass burning. Source apportionment by positive matrix factorization (PMF) revealed that solvent use, vehicle exhaust and biomass burning altogether accounted for 89-94% of observed AHs. Vehicle exhaust was the major source for benzene with a share of 43-70% and biomass burning in particular contributed 30% to benzene in the upwind rural site; toluene, C8-aromatics and C9-aromatics, however, were mainly from solvent use, with contribution percentages of 47-59%, 52-59% and 41-64%, respectively.

Sources of ambient volatile organic compounds and their contributions to photochemical ozone formation at a site in the Pearl River Delta, southern China

The Positive Matrix Factorization (PMF) receptor model and the Observation Based Model (OBM) were combined to analyze volatile organic compound (VOC) data collected at a suburban site (WQS) in the PRD region. The purposes are to estimate the VOC source apportionment and investigate the contributions of these sources and species of these sources to the O(3) formation in PRD. Ten VOC sources were identified. We further applied the PMF-extracted concentrations of these 10 sources into the OBM and found "solvent usage 1", "diesel vehicular emissions" and "biomass/biofuel burning" contributed most to the O(3) formation at WQS. Among these three sources, higher Relative Incremental Reactivity (RIR)-weighted values of ethene, toluene and m/p-xylene indicated that they were mainly responsible for local O(3) formation in the region. Sensitivity analysis revealed that the sources of "diesel vehicular emissions", "biomass/biofuel burning" and "solvent usage 1" had low uncertainties whereas "gasoline evaporation" showed the highest uncertainty.

Nonmethane hydrocarbon measurements at a suburban site in Changsha City, China

The concentration, composition, and variability of nonmethane hydrocarbons (NMHCs) and carbon monoxide (CO) were characterized in a suburban region of south-central China. Weekly samples were collected in 2007 in the Changsha suburban area and analyzed with a three-stage preconcentration method coupled with GC-MS. A time series of NMHC measurements showed seasonal variation, with a higher level occurring in winter and a lower level in summer. Toluene was the most abundant species with an average concentration of 2.51+/-1.87 ppbv, followed by benzene (2.04+/-1.30 pptv). According to the level of identified NMHCs, vehicular exhaust appears to be the main source of NMHCs in Changsha. Among alkanes, the highest level is propane with a concentration of 1.31+/-0.71 ppbv, it indicated an extensive use and leakage of liquefied petroleum gas (LPG) in Changsha. The concentrations of NMHCs were influenced by the wind direction; a high level of NMHCs was carried by winds from southern China. Significant biogenic isoprene emissions were observed, with good correlation between isoprene level and temperature. Finally, when the typical individual NMHC species and CO in the morning and afternoon were compared, the shorter lifetime of NMHC species relative to CO could explain the poorer correlation observed in the afternoon.

Speciated VOC emission inventory and spatial patterns of ozone formation potential in the Pearl River Delta, China

The Pearl River Delta region (PRD) of China has long suffered from severe ground-level ozone pollution. Knowledge of the sources of volatile organic compounds (VOCs) is essential for ozone chemistry. In this work, a speciated VOC emission inventory was established on the basis of updated emissions and local VOC source profiles. The top 10 species, in terms of ozone formation potentials (OFPs), consisted of isoprene, mp-xylene, toluene, ethylene, propene, o-xylene, 1,2,4-trimethylbenzene, 2-methyl-2-butene, 1-butene, and alpha-pinene. These species contributed only 35.9% to VOCs emissions but accounted for 64.1% of the OFP in the region. The spatial patterns of the VOC source inventory agreed well with city-based source apportionment results, especially for vehicle emissions and industry plus VOC product-related emissions. Mapping of the OFPs and measured ozone concentrations indicated that the formation of higher ozone in the south and southeast of the PRD region differed from that in the Conghua area, a remote area in the north of the PRD. We recommend that the priorities for the control of VOC sources include motorcycles, gasoline vehicles, and solvent use because of their larger OFP contributions.

Using a source-receptor approach to characterise VOC behaviour in a French urban area influenced by industrial emissions. Part I: study area description, data set acquisition and qualitative data analysis of the data set

The global objective of this two part study was (1) to conduct VOC measurements in order to further understand VOC behaviour in an urban area influenced by industrial emissions and (2) to evaluate the role of these specific sources relative to urban sources. In this first paper a thorough descriptive and qualitative analysis is performed. A second article will be devoted to the quantitative analysis using Chemical Mass Balance (CMB) modelling. In the Dunkerque (France) area most industrial sources are situated in the north and the west of the receptor site whereas urban and traffic sources are located in the south and the east. A data set constituted of nearly 330,000 VOC data has been developed from the hourly measurements of 53 VOCs for 1 year from September 2002 to August 2003. It also contains meteorological parameters such as temperature, wind direction and wind speed. Using different graphical methods, the influence of the different sources on the ambient VOC concentrations has been highlighted at different time scales. In this work, the analysis of daily time series for the 53 VOCs shows the influence of traffic exhaust emissions because of the increases at traffic rush hours. Besides, the seasonal evolution of the VOC/acetylene ratio points out the influence of evaporative sources on ambient VOC concentration. Concerning other point sources, the variations of measured VOC concentrations for different wind directions and scatter plots of VOC hourly concentrations highlight the influence of some industrial sources.