Ozone Formation Potential Research Articles

Characteristics and Influence of Atmospheric VOCs in Ozone Formation Potential in Suburb of Shanghai During Summer

To help promote ozone pollution control and understand the influence of atmospheric volatile organic compounds （VOCs） on O3 during the summer ozone pollution season, the analyses of variation characteristics and ozone formation potentials of VOCs during O3 pollution episodes were carried out based on the online monitoring data of VOCs and O3, as well as the meteorological parameters in the suburban site of Shanghai. The impact of key meteorological factors and regional transport on O3 and VOCs was investigated. The results showed that the mean value of atmospheric φ（VOCs） during summer in the suburban area of Shanghai was （20.91 ± 9.82）×10-9, and the largest proportion of each component was with alkanes and OVOCs, both of which were 30.2%. The mean value of φ（VOCs） on O3 polluted days was （23.84 ± 9.69）×10-9, which was 28.1% higher than that on clean days. The OFP of VOCs on polluted days was 126.92 μg·m-3, which was 31.9% higher than that on clean days. The contribution of olefins to OFP accounted for a significant increase, and species such as propylene and acetone were the most significant compared to on clean days, indicating that these components and species need to be the focus of mitigation. The variation characteristics of the ratio of ethane to acetylene （E/E） and the ratio of m/p-xylene to ethylbenzene（X/E） indicated that there was a significant regional transport influence of the summer air masses in the suburban area of Shanghai, and it occurred mainly in the afternoon and at night. The results of the pollution rose diagram and the backward trajectory of air masses indicated that air masses from the south and southwest directions had the greatest influence on the transport of VOCs in suburban Shanghai. In particular, it is necessary to focus on controlling olefin and OVOCs from southern air masses and aromatic hydrocarbons from southwestern air masses.

Sensitivity Analysis of Atmospheric Ozone and Source Apportionment of Volatile Organic Compounds in Yinchuan City

Based on the observation data of O3 concentration in Yinchuan in 2022, the monthly variation characteristics of O3 concentrations were analyzed. Further, based on the observation data of meteorological elements, conventional pollutants, and volatile organic compounds （VOCs） concentrations at an urban site in Yinchuan from May to July, the difference in meteorological elements and precursor concentrations between the polluted days and the non-polluted days were compared. Then, the O3 sensitivity and the VOCs sources were discussed using the Framework for 0-D Atmospheric Modeling （F0AM） and positive matrix factorization （PMF） model, respectively. The results showed that： ① The O3 pollution occurred from May to July in 2022, and the concentrations of O3-8h-90per were 156 μg·m-3, 170 μg·m-3, and 174 μg·m-3, respectively, with exceeding standard rates of 9.7%, 26.7%, and 29.0%, respectively. ② Compared with those on the non-polluted days, the hourly mean values of temperature, total solar radiation, and concentrations of various precursors on the O3-polluted days increased, including the volume concentrations of propane, isobutane, ethane, n-butane, and dichloromethane, which increased significantly by 33.1%, 29.1%, 25.0%, 22.7%, and 21.3%, respectively. The results showed that the combined increase in pollutant emissions and adverse meteorological conditions contributed to the formation of O3. ③ From May to July 2022, the top five VOCs species in terms of ozone formation potential （OFP） value on whole, non-polluted, and polluted days were the same. They were acetaldehyde, m/p-xylene, ethylene, isoprene, and toluene, mainly from solvent use sources, natural sources, and chemical industry emissions. ④ The local O3 production was mostly controlled by VOCs, and the relative incremental reactivity （RIR） results revealed that O3 production showed strong positive sensitivity to alkene and aromatic hydrocarbon but showed negative sensitivity to NOx on both polluted and non-polluted days. The relative contributions of active species such as acetone, ethylene, and isobutane to O3 production were high, and the implementation of an emission reduction scheme with the ratio of VOCs to NOx emission reduction much greater than 1 could effectively reduce the local O3 concentration. ⑤ The main sources of atmospheric VOCs in Yinchuan were motor vehicle emission sources （32.3%）, process sources （20.7%）, combustion sources （19.2%）, solvent use sources （12.7%）, gasoline volatile sources （9.1%）, and natural sources （6%）, and the contribution rate of motor vehicle emission sources on polluted days increased by 4.6% compared with that on non-polluted days, indicating that the motor vehicle emission source was an important object of summer VOCs control in Yinchuan.

Failure of the three-way catalyst (TWC) introduces “super emitters”

Vehicle exhaust is one of the major organic sources in urban areas. Old taxis equipped with failed three-way catalysts (TWCs) have been regarded as “super emitters”. Compressed natural gas (CNG) is a regular substitution fuel for gasoline in taxis. The relative effect of fuel substitution and TWC failure has not been thoroughly investigated. In this work, vehicle exhausts from gasoline and CNG taxis with optimally functioning and malfunctioning TWCs are sampled by Tenax TA tubes and then analyzed by a comprehensive two-dimensional gas chromatography-mass spectrometer (GC×GC–MS). A total of 216 organics are quantified, including 80 volatile organic compounds (VOCs) and 132 intermediate volatility organic compounds (IVOCs). Failure of TWC introduces super emitters with 30 – 70 times emission factors (EFs), 60 – 112 times ozone formation potentials (OFPs), and 34 – 92 times secondary organic aerosols (SOAs) more than normal vehicles. Specifically, for the taxi with failed TWC, the total organic EF of CNG is 16 times that of gasoline, indicating that the failure of TWC exceeds the emission reduction achieved by CNG-gasoline substitution. A significant but unbalanced reduction of ozone and SOA is observed after TWC, whereas a notable “enrichment” in IVOCs was observed. Naphthalene is a typical IVOC component strongly associated with CNG-gasoline substitution and TWC failure, which is lacking in current VOC measurement. We especially emphasize that there is an urgent need to scrap vehicles with failed TWCs in order to significantly reduce air pollution.

Characteristics and Source Apportionment of Volatile Organic Compounds in a Coastal Industrial Area: A Case Study in the Yangtze River Delta of China.

In recent years, the coastal area in East China has experienced elevated volatile organic compounds (VOCs) levels during specific periods. VOCs have become one of the major atmospheric pollutants in these areas. In this study, 64 compounds including alkanes, alkenes, halohydrocarbons, aromatics, and oxygenated VOCs (OVOCs) were obtained by the TO-15 method through a 12-month campaign in industrial, urban and suburban areas in the Yangtze River Delta of China. The overall trends of total VOC (TVOC) concentrations at eight sampling sites were as follows: winter > autumn > spring > summer. The proportion of VOC categories was various at industrial sites, while OVOCs and halohydrocarbons had high proportions at urban sites and suburban sites, respectively. Coating, vehicle emission, petrochemical source, industrial source, and gasoline volatilization were identified as the major VOC emission sources by the positive matrix factorization model. Petrochemical and coating sources were the prime VOC sources at industrial sites. Aromatics contributed the most ozone formation potential at industrial sites, while OVOCs provided the main contributions at both urban and suburban sites during four seasons. According to the health risk assessment, a high probability of non-carcinogenic risk existed at three industrial sites. Special attention should be given to certain VOCs, such as acrolein and 1,2-dibromoethane in industrial areas.

Characterization of emissions from rubber modified asphalt and their impact on environmental burden: Insights into composition variability and hazard assessment

Rubber modified asphalt (RMA) is a promising avenue for recycling waste tires but faces concerns over hazardous fumes emission during production and construction. This study employs a specialized apparatus to analyze RMA's emission behavior, focusing on crumb rubber size variations under thermal conditions. Ozone Formation Potential (OFP) and Secondary Organic Aerosol Formation Potential (SOAFP) were quantified to evaluate the environmental burden. Results indicate distinct periods of emission behavior for different pollutants, with H2S emissions primarily occurring within the initial 150 min while volatile organic compounds (VOCs) dominate within the first 270 min. The size of rubber particles and thermal exposure duration influence the VOCs microscopic emission characteristics and environmental burdens. Polycyclic aromatic hydrocarbons (PAHs) emerge as the primary contributors to OFP and SOAFP, accounting for nearly 65 % and 25 %−60 %, respectively. High molecular weight aliphatic hydrocarbons (ALHs) also significantly contribute to SOAFP, with PAHs dominating throughout, while ALHs peak during the middle stage. H2S emissions likely stem from rubber, while early VOC emissions originate from rubber, transitioning to petroleum asphalt during the middle and late stages. Asphalt fractions influence emission behavior and property evolution. These findings inform emission suppression strategies and highlight the need for tailored approaches to mitigate emissions effectively.

Comparison of NMHC measurements between 2010 and 2020 in Wuxi City, Yangtze River Delta region: Levels, compositions, sources, and impacts

Field observation analyses of volatile organic compounds (VOCs) have gained significant attention due to their potential explaining atmospheric temporal trends. This study measured non-methane hydrocarbons (NMHCs) in Wuxi City, located in the Yangtze River Delta (YRD) of China, in 2010 and 2020. The aim was to gain a better understanding of the ten-year change of VOCs in terms of their mixing ratios, sources, role in ozone, secondary organic aerosol (SOA) formation, and health risks. The average NMHC level 2020 was 20.67 ppbv, which indicated a 20% drop from 2010. A notable shift was observed in the chemical composition of NMHCs. The contribution of alkanes increased from 45% to 62% in 2020, while that of the aromatics decreased from 25% in 2010 to 21% in 2020. Ratio analysis and receptor modelling for 2010 and 2020 were used to identify the source changes of VOC species. The source apportionment model showed that the contribution of vehicle exhaust decreased from 34.5% to 20.9% from 2010 to 2020, and that of the solvent increased from 15.1% to 25.3%. The chemical reactivity results suggested that aromatics played significant roles in photochemical reactions in Wuxi City. The ozone formation potential (OFP) and SOA potential of VOCs also showed decreasing trends from 2010 to 2020. The total OFP of alkenes decreased by 34.0%, from 30.6 to 20.2 ppbvO3/ppbv. The total non-carcinogenic risk value for the key VOC species was 0.034 in 2010 and 0.024 in 2020. Although the carcinogenic risks for benzene have decreased significantly, the value is still above the acceptable carcinogenic risk level. The results of this study demonstrate the effectiveness of air pollution control measures in Wuxi City and highlight the positive impacts on reducing secondary pollution and health risks in this region over one decade.

How do different marine engine fuels and wet scrubbing affect gaseous air pollutants and ozone formation potential from ship emissions?

Sulphur Emission Control Areas (SECAs), mandated by the International Maritime Organization (IMO), regulate fuel sulphur content (FSC) to mitigate the environmental and health impact of shipping emissions in coastal areas. Currently, FSC is limited to 0.1% (w/w) within and 0.5% (w/w) outside SECAs, with exceptions for ships employing wet sulphur scrubbers. These scrubbers enable vessels using non-compliant fuels such as high-sulphur heavy fuel oils (HFOs) to enter SECAs. However, while sulphur reduction via scrubbers is effective, their efficiency in capturing other potentially harmful gases remains uncertain. Moreover, emerging compliant fuels like highly aromatic fuels or low-sulphur blends lack characterisation and may pose risks.Over three years, we assessed emissions from an experimental marine engine at 25% and 75% load, representative of manoeuvring and cruising, respectively. First, characterizing emissions from five different compliant and non-compliant fuels (marine gas oil MGO, hydro-treated vegetable oil HVO, high-, low- and ultra-low sulphur HFOs), we calculated emission factors (EF). Then, the wet scrubber gas-phase capture efficiency was measured using compliant and non-compliant HFOs.NOx EF varied among fuels (5200–19700 mg/kWh), with limited scrubber reduction. CO (EF 750–13700 mg/kWh) and hydrocarbons (HC; EF 122–1851 mg/kWh) showed also insufficient abatement. Carcinogenic benzene was notably higher at 25% load and about an order of magnitude higher with HFOs compared to MGO and HVO, with no observed scrubber reduction. In contrast, carbonyls such as carcinogenic formaldehyde and acetaldehyde, acting as ozone precursors, were effectively scrubbed due to their polarity and water solubility. The ozone formation potential (OFP) of all fuels was examined.Significant EF differences between fuels and engine loads were observed, with the wet scrubber providing limited or no reduction of gaseous emissions. We suggest enhanced regulations and emission abatements in the marine sector to mitigate gaseous pollutants harmful to human health and the environment.

Analysis of Ozone and VOCs Pollution Characteristics, Sources, and Abatement Control Strategies in Hebi

In order to control the increasing ozone （O3） pollution in Hebi, Henan Province, clarifying the pollution characteristics of ozone and its precursors is vital. Therefore, we conducted a comprehensive analysis of O3 pollution utilizing the OFP-PMF-EKMA method combined with online hourly resolution monitoring data of conventional pollutants and volatile organic compounds （VOCs） in the summer of 2022 （June-September）. Ozone formation potential （OFP） was used to identify the key VOCs species, and the PMF model was used to identify the VOCs emission sources, whereas EKMA curves and scenario analysis were used to identify the main ozone control area in Hebi and to determine the reduction ratio of VOCs and NOx in a scientifically refined way. In 2022, Hebi had persistent O3 pollution, with the highest concentration in June. Conditions of high temperature, low humidity, and low atmospheric pressure contributed to the O3 accumulation. Aromatic and oxygenated volatile organic compounds （OVOCs） contributed significantly to the OFP and VOCs fraction, which were the dominant active substance and concentration dominant species. The results of the VOCs source analysis indicated that vehicle exhaust sources （25.3%） were the main source of atmospheric VOCs, followed by process sources （17.7%） and biomass combustion sources （17.6%）. Thus, emission sources associated with the combustion of fossil fuels and industrial production emissions were the most urgent sources of atmospheric VOCs to be controlled in Hebi. The O3 generation in Hebi occurred in the VOCs-sensitive zones, and the emission reduction results showed that a synergistic emission reduction of VOCs and nitrogen oxide （NOx） could effectively control O3 pollution with a 75% reduction in VOCs and a 10% reduction in NOx.

Characterization of VOCs emissions and associated health risks inherent to the packaging and printing industries in Shandong Province, China

Comprehensive volatile organic compounds (VOCs) emission control is imperative to decreasing occupational health risks and environmental impact of the packaging and printing industries. In this work, we investigated the VOCs emission characteristics and concentrations of individual contaminants generated by the packaging and printing industries, with regard to various categories, processes, and geographic regions. VOCs emissions, ozone formation potential (OFP), and associated health risks were assessed at 10 representative packaging and printing firms across several cities in Shandong Province, China. Plastic packaging enterprises had the greatest levels of unorganized VOCs emissions, consisting predominantly of oxygenated volatile organic compounds (OVOCs), followed by alkanes and halocarbons. From metal and paper packaging enterprises, OVOCs, alkanes, and aromatics were significant components of unorganized VOCs emissions. Aromatics, halocarbons, and OVOCs contributed significantly to OFP in workshops. The potential carcinogenic risk associated with VOCs in the packaging and printing industries was not significant. However, according to the findings in this study, the workshop environment may provide a comparatively elevated non-carcinogenic risk attributable to ethyl acetate, isopropanol, acrolein, 1,1,2-Trichloroethane, 1,2-Dichloropropane, and naphthalene exposure. In particular, the endocrine-disrupting and genetic toxic effects caused by benzene, toluene, styrene, and naphthalene should not be overlooked. Thus, it is essential to provide precedence to the working environment conditions of workshop laborers, while also undertaking scientific and systematic measures to mitigate the detrimental impacts of VOCs on the environment and human welfare.

Temperature-dependent emissions dominate aerosol and ozone formation in Los Angeles.

Despite declines in transportation emissions, urban North America and Europe still face unhealthy air pollution levels. This has challenged conventional understanding of the sources of their volatile organic compound (VOC) precursors. Using airborne flux measurements to map emissions of a wide range of VOCs, we demonstrate that biogenic terpenoid emissions contribute ~60% of emitted VOC OH reactivity, ozone, and secondary organic aerosol formation potential in summertime Los Angeles and that this contribution strongly increases with temperature. This implies that control of nitrogen oxides is key to reducing ozone formation in Los Angeles. We also show some anthropogenic VOC emissions increase with temperature, which is an effect not represented in current inventories. Air pollution mitigation efforts must consider that climate warming will strongly change emission amounts and composition.

Seasonal and height dynamics of volatile organic compounds in rubber plantation: Impacts on ozone and secondary organic aerosol formation

Rubber trees emit a range of volatile organic compounds (VOCs), including isoprene, monoterpenes, and sesquiterpenes, as part of their natural metabolism. These VOCs can significantly influence air quality through photochemical reactions that produce ozone and secondary organic aerosols (SOAs). This study examines the impact of VOCs detected in a rubber tree plantation in Northeastern Thailand on air quality, highlighting their role in atmospheric reactions that lead to the formation of ozone and SOAs. VOCs were collected at varying heights and seasons using Tenax-TA tubes paired with an atmospheric sampler pump and identified by gas chromatography–mass spectrometry. In total, 100 VOCs were identified, including alkanes, alkenes, terpenes, aromatics, and oxygenated VOCs. Principal Coordinate Analysis (PCoA) revealed distinct seasonal VOC profiles, with hydrocarbons, peaking in summer and terpenes in the rainy season. The Linear Mixed-Effects (LME) model indicates that VOC concentrations are more influenced by seasonal changes than by sampling heights. Secondary organic aerosol potential (SOAP) and ozone formation potential (OFP) of selected VOC species were also determined. The total SOAP ranged from 67.24 μg/m3 in summer to 17.87 μg/m3 in winter, while the total OFP ranged from 377.87 μg/m3 in summer to 139.39 μg/m3 in winter. Additionally, positive matrix factorization (PMF) analysis identified four main VOC sources: gasoline combustion (18.3 %), microbial activity (38.6 %), monoterpene emissions during latex production (15.0 %), and industrial sources (28.1 %). These findings provide essential information for managing air pollution in rubber tree plantations. By adopting focused air quality management strategies, plantation operators can mitigate the adverse effects of VOCs, promoting a healthier and more sustainable future.

Atmospheric chemistry of the coastal area is influenced by the convergence between the inland and marine air: Insight into carbonyl compounds

Marine biological activity has long been recognized to impact the atmospheric chemistry of coastal areas. In this work, we monitored the seasonal variation of carbonyl compounds in the coastal city of Qingdao, located in the north of China's coastline and the south of Jiaodong Peninsula, with the vast hinterland in the west. The mean total concentration of the 15 carbonyls varied significantly between seasons, with the highest observed in autumn (10.2 ± 6.2 ppbv), followed by spring (9.0 ± 3.0 ppbv), winter (6.4 ± 4.0 ppbv) and summer (3.4 ± 1.4 ppbv). Using bivariate analysis, the agricultural emissions from inland areas were responsible for the high levels of carbonyls in the autumn. In summer, clean and humid sea winds helped reduce the concentration of carbonyls, but they also brought air masses from vegetation, and marine organisms, which contributed to high levels of carbonyls in the spring of coastal areas. The observation-based chemistry box model found that the formation of formaldehyde and acetaldehyde was primarily controlled by the RO + O2 reaction, and alkenes oxidation was the main contributing factor. Based on the OH radical loss rate (LOH) and ozone formation potential (OFP) calculation, we found that autumn and spring seasons have significantly higher values of LOH and OFP than winter and summer due to the presence of high concentrations of carbonyl compounds. Therefore, it is believed that these carbonyl compounds primarily originate from agricultural activities, and marine air influences the atmospheric chemistry of the coastal areas.

A comprehensive study on the spatial and temporal variation of BTEX and asbestos in the northwest of Iran: Human risk assessment

Substances like asbestos and other air pollutants, such as BTEX (benzene, toluene, ethylbenzene, and xylene), are hazardous compounds due to their adverse effects on human health. This study aims to investigate the levels, seasonal variations, spatial distribution, potential sources, and associated health risks associated with BTEX compounds and asbestos fibers in the ambient air of Tabriz. Air samples were taken at 16 different locations during the 2020–2021 period. Glass containers with charcoal were used for sample collection, and the BTEX content was determined using the GC-FID method. Phase-contrast microscopy (PCM) analysis was conducted with a low-volume peripheral pump for asbestos fiber sampling. The results showed that the average concentration of ∑BTEX was 37.94 and 27.98 μg/m3 in autumn and spring, respectively. The same parameter was 2.26 and 1.68 f/L for asbestos in the autumn and winter, respectively. The contribution of BTEX to ozone formation potential (OFP) in the research area showed that xylene and toluene were the major contributors to ozone production in different seasons. The risk of exposure to benzene compounds was 24 × 10−4 in children and 55.9 × 10−4 in adults, while the risk of exposure to ethylbenzene was 3.78 × 10−4 in children and 3.25 × 10−4 in adults. The estimated lifetime cancer risk was found to be the highest for benzene, followed by ethylbenzene. The estimated cancer risk for benzene and ethylbenzene exceeded the threshold values set by EPA, which signals a significant carcinogenic risk due to exposure to these substances in the ambient air of Tabriz. According to the EPA guidelines, the low carcinogenicity risk levels are between 10−4 and 10−6. According to the findings for the exposure to asbestos fibers, the maximum values of excess cancer risk (ECR) and estimated lifetime cancer risk (ELCR) were observed in the 16–30 age range across all locations, suggesting increased exposure to asbestos fibers compared to other age groups.

Characteristics, sources, and health risks of volatile organic compounds in different functional regions of Shenyang

The concentration of 56 volatile organic compounds (VOCs) in the ambient air of Shenyang was continuously monitored at four sites in 2021. The characteristics, sources, secondary pollution potential and health risks of VOCs in different functional regions of Shenyang were discussed. The results indicate that the concentration of VOCs in industrial regions was significantly higher than that in non-industrial regions, with a mean of 41.09 ± 69.82 parts per billion volumes (ppbv) compared to 19.99 ± 17.86 ppbv (commercial & residential region in urban fringe), 27.51 ± 28.81 ppbv (educational & scenic region) and 29.71 ± 23.97 ppbv (commercial & residential region in urban center). The positive matrix factorization (PMF) model was utilized to assign the sources of VOCs in Shenyang, and six factors were recognized: gasoline vehicles (34.8 %), diesel vehicles (28.3 %), combustion (11.4 %), biogenic emissions (9.7 %), industrial processes (8.2 %), and fuel evaporation (7.7 %). The results of the reactivity evaluation indicated that the ozone (O3) formation potential (OFP) was primarily influenced by industrial processes (29.2 %), diesel vehicles (25.7 %), biogenic emissions (17.0 %). These three factors were also the top three contributors to secondary organic aerosol formation potential (SOAP), accounting for 44.2 %, 9.4 % and 30.3 %, respectively. At the all four sites, the non-carcinogenic and carcinogenic risks of VOCs ranged from 1.6 × 10−2 to 3.8 × 10−2 and from 2.3 × 10−6 to 3.3 × 10−6, respectively. And the main risks can be attributed to emissions from industrial processes and gasoline vehicles. These findings suggested to strengthen the control of vehicle emissions throughout all regions in Shenyang and industrial processes emissions in industrial regions.

A Year-Long Measurement and Source Contributions of Volatile Organic Compounds in Nanning, South China

Severe ozone (O3) pollution has been recorded in China in recent years. The key precursor, volatile organic compounds (VOCs), is still not well understood in Nanning, which is a less developed city compared to other megacities in China. In this study, a year-long measurement of VOCs was conducted from 1 October 2020 to 30 September 2021, to characterize the ambient variations and apportion the source contributions of VOCs. The daily-averaged concentration of VOCs was measured to be 26.4 ppb, ranging from 3.2 ppb to 136.2 ppb across the whole year. Alkanes and oxygenated VOCs (OVOCs) were major species, contributing 46.9% and 25.2% of total VOC concentrations, respectively. Propane, ethane, and ethanol were the most abundant in Nanning, which differed from the other significant species, such as toluene (3.7 ppb) in Guangzhou, ethylene (3.8 ppb) in Nanjing, and isopentane (5.5 ppb), in Chengdu. The positive matrix factorization (PMF) model resolved six source factors, including vehicular emission (contributing 33% of total VOCs), NG and LPG combustion (19%), fuel burning (17%), solvent use (16%), industry emission (10%), and biogenic emission (5%). This indicated that Nanning was less affected by industrial emission compared with other megacities of China, with industry contributing 12–50%. Ethylene, m/p-xylene, butane, propylene, and isoprene were key species determined by ozone formation potential (OFP) analysis, which should be priority-controlled. The variations in estimated OFP and observed O3 concentrations were significantly different, suggesting that VOC reactivity-based strategies as well as meteorological and NOx effects should be considered collectively in controlling O3 pollution. This study presents a year-long dataset of VOC measurements in Nanning, which gives valuable implications for VOC control in terms of key sources and reactive species and is also beneficial to the formulation of effective ozone control strategies in other less developed regions of China.

Updating vehicle VOCs emissions characteristics under clean air actions in a tropical city of China

In the context of clean air actions in China, vehicle emission limits have been continuously tightened, which has facilitated the reduction of volatile organic compounds (VOCs) emissions. However, the characteristics of VOC emissions from vehicles with strict emission limits are poorly understood. This study investigated the VOC emission characteristics from vehicles under the latest standards based on tunnel measurements, and identified future control strategies for vehicle emissions. The results showed that the highest percentage of VOCs from vehicle consisted of alkanes (80.9 %), followed by aromatics (15.8 %) and alkenes (3.1 %). Alkanes had the most significant ozone formation potential due to their high concentrations, in contrast to the aromatics that have been dominant in previous studies. The measured fleet-average VOC emission factor was 71.3 mg·km−1, including tailpipe emissions of 39.6 mg·km−1 and evaporative emissions of 31.7 mg·km−1. The VOC emission factors of the subgroups were obtained. The emission of evaporated VOCs accounted for 44.5 % of the total vehicle VOC emissions, which have increased substantially from previous studies. In addition, the emission characteristics of vehicles that are under the latest emission threshold values have changed significantly, and the mixing ratio of toluene/benzene (T/B) has been updated to 3:1. This study updates the VOCs emission factors of vehicles under clean air actions and highlights the future mitigation policies should focus on reducing evaporative VOC emissions.

Ethanol, acetaldehyde, and methanol in the gas phase and rainwater in different biomes and urban regions of Brazil

In the context of the increasing global use of ethanol biofuel, this work investigates the concentrations of ethanol, methanol, and acetaldehyde, in both the gaseous phase and rainwater, across six diverse urban regions and biomes in Brazil, a country where ethanol accounts for nearly half the light-duty vehicular fuel consumption. Atmospheric ethanol median concentrations in São Paulo (SP) (12.3 ± 12.1 ppbv) and Ribeirão Preto (RP) (12.1 ± 10.9 ppbv) were remarkably close, despite the SP vehicular fleet being ∼13 times larger. Likewise, the rainwater VWM ethanol concentration in SP (4.64 ± 0.38 μmol L−1) was only 26 % higher than in RP (3.42 ± 0.13 μmol L−1). This work demonstrated the importance of evaporative emissions, together with biomass burning, as sources of the compounds studied. The importance of biogenic emissions of methanol during forest flooding was identified in campaigns in the Amazon and Atlantic forests. Marine air masses arriving at a coastal site led to the lowest concentrations of ethanol measured in this work. Besides vehicular and biomass burning emissions, secondary formation of acetaldehyde by photochemical reactions may be relevant in urban and non-urban regions. The combined deposition flux of ethanol and methanol was 6.2 kg ha−1 year−1, avoiding oxidation to the corresponding and more toxic aldehydes. Considering the species determined here, the ozone formation potential (OFP) in RP was around two-fold higher than in SP, further evidencing the importance of emissions from regional distilleries and biomass burning, in addition to vehicles. At the forest and coastal sites, the OFP was approximately 5 times lower than at the urban sites. Our work evidenced that transition from gasoline to ethanol or ethanol blends brings the associated risk of increasing the concentrations of highly toxic aldehydes and ozone, potentially impacting the atmosphere and threatening air quality and human health in urban areas.

Characteristic, source apportionment and effect of photochemical loss of ambient VOCs in an emerging megacity of Central China

During the transportation from emission sources to sampling site, volatile organic compounds (VOCs) undergo photochemical losses which have significant effects for tropospheric ozone (O3) formation and VOCs source apportionment. In this study, based on hourly speciated VOC data from May 23, to July 8, 2019 with high O3 concentrations, the concentration level, chemical composition, and diurnal variation of observed VOCs were studied, and the initial concentration of VOCs was obtained by combining the local emission inventory in Zhengzhou, Central China. The impact of photochemical loss on source apportionment was evaluated using the Positive Matrix Factorization/Multilinear Engine 2-Species Ratio (PMF/ME2-SR) model based on observed and initial VOCs concentration (OC-PMF and IC-PMF). Results suggest that during the observed period, the average concentration of total VOCs (TVOCs) was 23.74 ± 9.20 ppbv, and alkanes (3.92 ± 2.40 ppbv) were the predominant component. The photochemical losses of TVOCs were approximately 10.15 ± 7.13 ppbv, with an average loss rate of 29.9%. The ozone formation potential (OFP) based on the initial VOCs concentration was 2.2 times higher than that observed VOCs concentration. Alkenes contributed the most to OFP and were also the largest contributors to photochemical losses. TVOC concentrations increased by 5.0% during O3 pollution compared to non-O3 pollution. Seven sources of VOCs were determined, including biomass burning, liquefied petroleum gas (LPG), vehicle emission, industrial emission, solvent usage, gasoline evaporation, and biogenic emission. Compared to the results of IC-PMF, the contributions of these sources in OC-PMF were underestimated by 15.4%, 14.4%, 13.0%, 11.7%, 31.5%, 7.6%, and 4.7%, respectively. This study still exhibits certain limitations in calculation method, and further exploration can be conducted in the future.

Elucidating the unexpected importance of intermediate-volatility organic compounds (IVOCs) from refueling procedure

Evaporative emissions release organic compounds comparable to gasoline exhaust in China. However, the measurement of intermediate volatility organic compounds (IVOCs) is lacking in studies focusing on gasoline evaporation. This study sampled organics from a real-world refueling procedure and analyzed the organic compounds using comprehensive two-dimensional gas chromatography coupled with a mass spectrometer (GC×GC-MS). The non-target analysis detected and quantified 279 organics containing 93 volatile organic compounds (VOCs, 64.9 ± 7.4 % in mass concentration), 182 IVOCs (34.9 ± 7.4 %), and 4 semivolatile organic compounds (SVOCs, 0.2 %). The refueling emission profile was distinct from that of gasoline exhaust. The b-alkanes in the B12 volatility bin are the most abundant IVOC species (1.9 ± 1.4 μg m−3) in refueling. A non-negligible contribution of 17.5 % to the ozone formation potential (OFP) from IVOCs was found. Although IVOCs are less in concentration, secondary organic aerosol potential (SOAP) from IVOCs (58.1 %) even exceeds SOAP from VOCs (41.6 %), mainly from b-alkane in the IVOC range. At the molecular level, the proportion of cyclic compounds in SOAP (12.1 %) indeed goes above its mass concentration (3.1 %), mainly contributed by cyclohexanes and cycloheptanes. As a result, the concentrations and SOAP of cyclic compounds (>50 %) could be overestimated in previous studies. Our study found an unexpected contribution of IVOCs from refueling procedures to both ozone and SOA formation, providing new insights into secondary pollution control policy.

Characteristics and ozone formation potentials of volatile organic compounds in a heavy industrial urban agglomeration of Northeast China

Characteristics and ozone formation potentials of volatile organic compounds in a heavy industrial urban agglomeration of Northeast China