Total Ozone Formation Potential Research Articles

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.

Sources and Distribution of Light NMHCs in the Marine Boundary Layer of the Northern Indian Ocean During Winter: Implications to Aerosol Formation

AbstractNon‐methane hydrocarbons (NMHCs) are ubiquitous trace gases and profoundly affect the Earth's atmosphere and climate change. Mixing ratios of light NMHCs were measured over the northern Indian Ocean during winter‐2018 as part of the Integrated Campaign for Aerosols, gases, and Radiation Budget (ICARB‐2018). Higher levels of NMHCs over the coastal regions were due to the efficient transport of anthropogenic and biogenic air masses and higher air‐sea exchanges due to the higher biological productivity. Although oceanic emissions dominated the open ocean, the transport of aged continental air also influenced the levels of some NMHCs. The higher and lower propane/ethane ratios of 2.41 ± 0.34 and 1.13 ± 0.78 ppbv ppbv−1 over coastal and open oceans indicated the prevalence of fresh and aged air masses, respectively. Ethene and propene show a strong correlation, but the ethene/propene ratios over open ocean (2.2 ± 0.25 ppbv ppbv−1) were slightly lower than the coastal region (2.5 ± 0.34 ppbv ppbv−1). Principal component analysis reveals the major associated sources identified in this study are from oceanic and nearby anthropogenic sources, explaining nearly 51% and 21% of variance. Light alkenes accounted for ∼70% of the total ozone and secondary organic aerosol formation potential. A higher alkene/alkane ratio, strong correlation of alkene with organic aerosol mass, and new particle formation events highlight the role of alkenes in secondary aerosol formation over the equatorial Indian Ocean. Overall, the levels of NMHCs were much higher than those measured nearly two decades ago during the Indian Ocean Experiment (INDOEX)‐1999.

A high-resolution (0.1° × 0.1°) emission inventory for the catering industry based on VOCs and PM2.5 emission characteristics of Chinese multi-cuisines

Catering enterprises gather in densely populated areas, whose pollutant emission has an important impact on human health and environmental quality. This study investigated detailed information of 5456 catering enterprises in a typical city, and analyzed PM2.5 and VOCs components of 15 catering cuisines and different scales. Based on the measured emission factors, the basic information of nationwide catering enterprises and the population density, this study established the national catering pollutant emission inventory with the spatial resolution of 0.1° × 0.1°. As the results showed, alkanes, alkenes and oxygenated volatile organic compounds (OVOCs) were the main components in VOCs of most catering cuisines, accounting for 36.6%–96.7%, while organic carbon (OC) was the dominant component in PM2.5, accounting for 55.4%–68.6%. The same cuisine of different scales also presented certain differences in emission characteristics. The total emissions of the ozone formation potential (OFP) and secondary organic aerosols formation potential (SOAFP) were 1737.8 kt and 76.4 kt, respectively, with alkanes and OVOCs being the main contributors, contributing 27.5% and 22.3%, respectively. Acetaldehyde, ethylene, propylene and the other top ten VOC species contribute 81.0% of the total OFP emissions, while toluene contributed much more to total SOAFP emissions than other VOC species, contributing 35.9%. The air pollutant emissions showed the highest correlation with the population, and the regions with prominent emissions were mainly concentrated in the Beijing-Tianjin-Hebei (BTH) region and coastal cities. This study is a systematic understanding of air pollutant emission characteristics of the catering industry in China, which has important supporting value for pollutant emission reduction planning in the catering industry.

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.

Quantification of Ozone Pollution Transport Based on Four-dimensional Flux Method in Foshan, China

Quantifying the contribution of transport processes to air pollution events has been a prominent challenge and an important need in regional air pollution prevention and control. The WRF-Chem model was used to simulate a typical regional ozone (O3) pollution event in Foshan, and the four-dimensional flux method was applied to quantify the transport fluxes of ozone and its precursors from the surrounding areas to Foshan and to clarify the contributions of the direct transport of ozone and transport of precursors. The average ozone flux from the surrounding areas to Foshan was 120.3 t·h-1, the volatile organic compound (VOCs) flux was 30.2 t·h-1, and the corresponding ozone formation potential (OFP) was 114.8 t·h-1. By counting the transport fluxes of each ozone pollution event, it was found that the city with the largest ozone flux into Foshan during the pollution period was Guangzhou (contributed 44%); the city with the largest input VOCs flux was Zhaoqing (contributed 48%). The analysis of ozone generation potential due to transported VOCs emissions found that oxygenated volatile organic compounds (OVOCs) contributed the most to OFP, accounting for 47% of the "maximum input events." OVOCs and aromatic hydrocarbons such as formaldehyde, xylenes, aldehydes, acetone, and phenols were the top five species contributing to the OFP, contributing more than 50% of the total OFP, mainly from industrial solvent sources.

Composition Characteristics of Volatile Organic Compounds and Associated Contributions to Secondary Pollution in Shenyang Industrial Area in Summer

Based on the observation data of volatile organic compounds (VOCs) in the industrial area of Shenyang during the summer of 2019 and 2020, the composition characteristics and sources of VOCs were preliminarily studied. The ozone formation potential (OFP) and aerosol formation potential (AFP) of VOCs were also estimated using the max incremental reactivity (MIR) and aerosol formation coefficient (FAC) methods, respectively. The results showed that the average concentration of VOCs was 41.66 μg·m-3, and the proportions of alkanes, olefins, aromatics, and acetylene were 48.50%, 14.08%, 15.37%, and 22.05%, respectively. The top ten species of VOCs were primarily C2-C5 alkanes, also including acetylene, ethylene, and some aromatics, accounting for 69.25% of the total VOCs. VOCs showed obvious diurnal variation characteristics with a high concentration in the morning and evening (at 06:00 and 22:00) and a low concentration in the afternoon (11:00-16:00). According to the value of toluene/benzene (T/B) and isopentane/n-pentane, the atmosphere of the industrial area was mainly affected by vehicle exhaust emissions, solvent use, combustion sources, and LPG/NG. The total AFP of VOCs was up to 41.43×10-2 μg·m-3, and aromatics were the largest contributor. The total OFP of VOCs reached 117.59 μg·m-3, in which the alkenes contributed the most.

Characteristics of atmospheric non-methane hydrocarbon compounds (NMHCs) and their sources in urban typical secondary transformation in Beijing, China

Non-methane hydrocarbon compounds (NMHCs) paly the leading role in the formation of ozone (O3) and secondary organic aerosols (SOA), which can affect severely global climate change, air quality, and human health. NMHCs pollution became a meaningful and crucial research topic in Beijing. From the Eleventh Five-Year Plan to the present, volatile organic compounds (VOCs) have received widespread and great attention in environmental governance, especially the NMHCs. Due to successive stages to control air pollution, the concentration of NMHCs has dropped gradually nearly three years in Beijing. In this study, 54 NMHCs was measured from March 1 to March 30 in 2021. The mean concentration of NMHCs was 33.54 ± 16.69 ppbv during the whole observation period. The mean concentration of NMHCs was 40.69 ± 17.09 ppbv during the haze days, which was greater than non-haze days (26.68 ± 12.75 ppbv). Alkenes, alkanes, aromatics, and acetylene accounted for 34.22%, 33.02%, 32.60%, and 016% in total ozone formation potential (OFP), respectively. Aromatics accounted for 96.61% in total secondary organic aerosol potential (SOAP). All the sources of NMHCs (except for fuel evaporation) made non-negligible contribution to O3 formation. Solvent usage and gasoline exhaust contributed 52.19%, which were the largest contributor to SOAP. Therefore, Beijing should focus on the NMHCs pollution caused by the local emission (especially solvent usage and gasoline exhaust) to control and solve secondary pollution further in this study.

Emission of volatile organic compounds from landfill working surfaces: Formation potential of ozone and secondary organic aerosols

The working surface of landfills is an important source of volatile organic compounds (VOCs), which have received increasing attention because of their role in potentially forming ozone and secondary organic aerosols (SOAs). In this study, 99 monitoring datasets on VOC emissions from a landfill working surface were obtained in 9 months and used to evaluate their ozone formation potential (OFP) and SOA formation potential (SOAFP) from a statistical perspective and compared using various methods. December was found to have the highest total OFP and SOAFP caused by VOC emissions from the landfill working surface. Both the propylene equivalent concentration (PEC) and maximum incremental reactivity (MIR) methods indicated that oxygenated compounds, especially ethanol, contributed the most to the OFP, accounting for 16.1 %–95.4 % and 44.9 %–98.6 % of the total OFP during the entire observation period, respectively. The fraction aerosol coefficient (FAC) method highlighted the effect of aromatic hydrocarbons which contributed to over 97 % of the total SOAFP. In contrast, the SOA potential (SOAP) method indicated that both aromatic hydrocarbons and oxygenated compounds play important roles, contributing 26.6 %–93.9 % and 21.6 %–73.4 % of the total SOAFP, respectively. Based on their mechanisms and comprehensiveness, PEC and SOAP methods are considered more appropriate for evaluating the OFP and SOAFP of VOCs released from landfill working surfaces. The annual total OFP and SOAFP of VOCs from landfill working surfaces of China in 2020 were thus estimated as 1.5 × 104 t and 135 t, respectively, with high variations among different regions along with the population, waste management system, and the amount of landfilled waste. This study provides a comprehensive understanding of the potential impacts and evaluation methods of local waste landfills in the atmospheric environment from a statistical perspective.

Photochemical Mechanism and Control Strategy Optimization for Summertime Ozone Pollution in an Industrial City in the North China Plain

To investigate the characteristics and formation mechanism of ozone (O3) pollution in an industrial city, an extensive one-month field campaign focusing on O3 and its precursors (e.g., volatile organic compounds[VOC] and nitrogen oxides[NOx]) was conducted in Zibo City, a highly industrializd city in the North China Plain, in June 2021. The 0-D box model incorporating the latest explicit chemical mechanism (MCMv3.3.1) was applied using an observation dataset (e.g., VOC, NOx, HONO, and PAN) as model contraints to explore the optimal reduction strategy for O3 and its precursors. The results showed that ① during high-O3 episodes, stagnant weather conditions with high temperature and solar radiation as well as low relative humidity were observed, and oxygenated VOCs and alkenes from anthropogenic VOCs contributed the most to the total ozone formation potential and OH reactivity (k·OH). ② The in-situ O3 variation was primarily affected by local photochemical production and export process horizontal to downwind areas or vertical to the upper layer. The reduction in local emissions was essential to alleviate O3 pollution in this region. ③ During high-O3 episodes, high concentrations of ·OH (10×106 cm-3) and HO2· (14×108 cm-3) radical drove and generated a high O3 production rate (daytime peak value reached 36×10-9 h-1). The reaction pathways of HO2·+NO and ·OH+NO2 contributed the most to the in-situ gross Ox photochemical production (63%) and photochemical destruction (50%), respectively. ④ Compared to those during low-O3 episodes, the photochemical regimes during high-O3 episodes were more inclined to be considered as the NOx-limited regime. Detailed mechanism modeling based on multiple scenarios further suggested that the synergic emission reduction strategy of NOx and VOC, while focusing on NOx emission alleviation, would be practical options for controlling local O3 pollutions. This method could also provide policy-related guidance for the precise O3 pollution prevention and control in other industrialized Chinese cities.

Chemical Characteristics and Source Apportionment for VOCs During the Ozone Pollution Episodes and Non-ozone Pollution Periods in Qingdao

The ambient concentration of ozone is high in Qingdao, and ozone pollution episodes occur frequently in summer. The refined source apportionment of ambient volatile organic compounds (VOCs) and their ozone formation potential (OFP) during ozone pollution episodes and non-ozone pollution periods can play an important role in effectively reducing air ozone pollution in coastal cities and continuously improving ambient air quality. Therefore, this study applied the online VOCs monitoring data with hourly resolution in summer (from June to August) in 2020 in Qingdao to analyze the chemical characteristics of ambient VOCs during the ozone pollution episodes and non-ozone pollution periods and conducted the refined source apportionment of ambient VOCs and their OFP using a positive matrix factorization (PMF) model. The results showed that the average mass concentration of ambient VOCs in Qingdao in summer was 93.8 μg·m-3, and compared with that during the non-ozone pollution period, the mass concentration of ambient VOCs during the ozone pollution episodes increased by 49.3%, and the mass concentration of aromatic hydrocarbons increased by 59.7%. The total OFP of ambient VOCs in summer was 246.3 μg·m-3. Compared with that in the non-ozone pollution period, the total OFP of ambient VOCs in the ozone pollution episodes increased by 43.1%; that of alkanes increased the most, reaching 58.8%. M-ethyltoluene and 2,3-dimethylpentane were the species with the largest increase in OFP and its proportion during the ozone pollution episodes. The main contributors of ambient VOCs in Qingdao in summer were diesel vehicles (11.2%), solvent use (4.7%), liquefied petroleum gas and natural gas (LPG/NG) (27.5%), gasoline vehicles (8.9%), gasoline volatilization (26.6%), emissions of combustion- and petrochemical-related enterprises (16.4%), and plant emissions (4.8%). Compared with that in the non-ozone pollution period, the contribution concentration of LPG/NG in the ozone pollution episodes increased by 16.4 μg·m-3, which was the source category with the largest increase. The contribution concentration of plant emissions increased by 88.6% in the ozone pollution episodes, which was the source category with the highest increase rate. In addition, emissions from combustion- and petrochemical-related enterprises were the largest contributor to the OFP of ambient VOCs in summer in Qingdao, with its OFP and contribution proportion being 38.0 μg·m-3and 24.5%, respectively, followed by that of LPG/NG and gasoline volatilization. Compared with the non-ozone pollution period, the total contributions of LPG/NG, gasoline volatilization, and solvent use to the increase in OFP for ambient VOCs in the ozone pollution episodes were 74.1%, which were the main contribution source categories.

Characteristics of summertime ambient volatile organic compounds in Beijing: Composition, source apportionment, and chemical reactivity

Comprehensive observations of ambient volatile organic compounds (VOCs) were conducted in Beijing (the capital of China) in the summer of 2018 with high temporal resolution, and the compositions, sources, ozone formation potential (OFP), and secondary organic aerosol formation potential (SOAP) were examined. A high mixing ratio of total VOCs (TVOCs) (26.6 ± 9.5 ppbv) was observed in this study, which was similar to that obtained in 2014 and 2016 in Beijing. The dominant components were alkanes (51.1% of TVOCs), alkenes (24.1%), and aromatics (19.5%). According to backward trajectories and potential source contribution function analysis, medium-distance transport from the south of the sampling region contributed more than 50% of the trajectories, and the potential source regions were mainly located in Shandong and Hebei Provinces. The seven sources identified by the positive matrix factorization receptor model included natural/liquified petroleum gas (NG/LPG) usage and gasoline evaporation (21.68%), solvent usage (20.14%), combustion sources (16.07%), industrial emissions (15.24%), diesel exhaust (14.89%), gasoline exhaust (6.05%), and biological emissions (5.92%). Alkenes (50.05%) and aromatics (36.20%) contributed the most to the total OFP, whereas aromatics contributed more than 90.00% to the total SOAP. The source with the greatest contribution to OFP and SOAP was solvent usage, the contribution of which exceeded 50%. The results of this study are favorable for the development of control strategies for VOCs and for reducing the formation of photochemical smog and secondary particulate matter.

Flare exhaust: An underestimated pollution source in municipal solid waste landfills

Flares are commonly used in municipal solid waste landfills, and the pollution from flare exhaust is usually underestimated. This study aimed to reveal the odorants, hazardous pollutants, and greenhouse gas emission characteristics of the flare exhaust. Odorants, hazardous pollutants, and greenhouse gases emitted from air-assisted flares and a diffusion flare were analyzed, the priority monitoring pollutants were identified, and the combustion and odorant removal efficiencies of the flares were estimated. The concentrations of most odorants and the sum of odor activity values decreased significantly after combustion, but the odor concentration could still exceed 2,000. The odorants in the flare exhaust were dominated by oxygenated volatile organic compounds (OVOCs), while the major odor contributors were OVOCs and sulfur compounds. Hazardous pollutants, including carcinogens, acute toxic pollutants, endocrine disrupting chemicals, and ozone precursors with the total ozone formation potential up to 75 ppmv, as well as greenhouse gases (methane and nitrous oxide with maximum concentrations of 4,000 and 1.9 ppmv, respectively) were emitted from the flares. Additionally, secondary pollutants, such as acetaldehyde and benzene, were formed during combustion. The combustion performance of the flares varied with landfill gas composition and flare design. The combustion and pollutant removal efficiencies could be lower than 90%, especially for the diffusion flare. Acetaldehyde, benzene, toluene, p-cymene, limonene, hydrogen sulfide, and methane could be priority monitoring pollutants for flare emissions in landfills. Flares are useful for odor and greenhouse gas control in landfills, but they are also potential sources of odor, hazardous pollutants, and greenhouse gases.

Variations, sources, and effects on ozone formation of VOCs during ozone episodes in 13 cities in China

In recent years, ozone (O3) pollution has worsened in China and contributes frequently to air pollution problems. To support the implementation of coordinated control for ozone and fine particulate matter, it is essential to study the chemical compositions and sources of volatile organic compounds (VOCs), which are the crucial precursor of both ozone and fine particulate matter. In this study, 117 volatile organic compounds were monitored in 13 cities in Beijing-Tianjin-Hebei Urban Agglomeration and Fenwei plain. Concentrations of total volatile organic compounds ranged from 42 to 279 μg/m3 during the monitoring episode. In all 13 cities, alkanes, halogenated hydrocarbons, aromatics and oxygenated volatile organic compounds (OVOCs) were the dominant volatile organic compounds. Contributions of alkanes, halogenated hydrocarbons, aromatics and oxygenated volatile organic compounds to total ozone formation potential (OFP) were 21.7%–32.6%, 21.0%–27.9%, 24.3%–50.8% and 28.6%–52.3%, respectively. Furthermore, the results of source apportionment by positive matrix factorization (PMF) model indicated that solvent usage, gasoline evaporation, vehicle emissions, petrochemical industry and combustion were essential volatile organic compounds sources in 13 cities. Moreover, the sensitivity of ozone production was studied using an Empirical Kinetic Modeling Approach (EKMA) model, and it was found that ozone formation was volatile organic compounds limited in all 13 cities.

Emission Characteristics, OFPs, and Mitigation Perspectives of VOCs from Refining Industry in China's Petrochemical Bases

China's petroleum refining industry has set off another climax and has entered a new rapid development by building seven petrochemical bases. Sector-based volatile organic compound (VOC) emissions from the refining industry in seven petrochemical-developed provinces in China were estimated for 1990–2019 and projected for 2020–2030 under the business-as-usual (BAU), new policy control (NPC), and the highest control (HC) scenarios. Furthermore, speciated VOCs and their ozone formation potentials (OFP) were estimated in 2019. Total VOC emissions from existing refineries were 541.14 Gg in 2019, of which 43.9%, 31.3%, 18.3%, and 6.6% were from fugitive, end-of-pipe, tank storage, and wastewater treatment sources, respectively. Alkanes were the most dominant compound in refineries, accounting for 55.2% of total emissions, followed by alkenes (18.9%) and aromatics (12.5%). Alkenes were the highest contributor to OFP, accounting for 59.5% of total OFP, followed by alkanes (22.3%) and aromatics (13.7%). n-Butane, ethylene, cis-2-Butene, n-Decane, and n-Pentane were the top five species with the highest emissions, accounting for approximately 50% of total emissions. Whilst, ethylene, cis-2-Butene, n-Pentane, n-Butane, and m/p-Xylene were the top five species with the highest contribution to OFPs, accounting for approximately 78% of total OFPs. In 2030, 741.03 and 165.28 Gg more VOC will be released than in 2019 under a non-control condition and the BAU scenario. It is estimated that 75.05 and 228.67 Gg of VOC from all refineries can be reduced under the NPC 2030 and the HC 2030 scenarios. To effectively reduce VOC emissions from refining industries, priority should be given to fugitive emissions by improving and upgrading the production processes and implementing enhanced leak detection and Repair system. More efficient control technologies should be invented for end-of-pipe sources. Vapor recovery systems and secondary seals have great potential for VOC emission reduction from storage tanks.

Improved emission factors and speciation to characterize VOC emissions in the printing industry in China

Printing industry is one of the most important sources of industrial volatile organic compound (VOC) emissions in China, and is thus a key industrial sector in terms of VOC control. However, process-based VOC emission and speciation from the printing industry have not been well identified, mainly owing to the poor emission factors (EFs) and diversity of source profiles. In this study, we systematically characterized process-based VOC emissions from the printing industry for the period of 2010–2019, through the establishment of improved emission factors and composite source profiles. VOC emissions from the printing industry were found to continuously increase from 2010 to 2018, reaching their maximum in 2018 at 939.8 Gg, but started to decrease afterwards. The substantial growth is driven by the large demand for ink and adhesive and the absence of effective control measures in the printing industry. The total VOC emissions and ozone formation potential (OFP) in China in 2019 were 916.1 Gg and 1834.5 Gg, respectively. Gravure printing and the compound process were the processes that contributed the most to both emissions and OFP. Rapidly developing provinces such as Guangdong, Jiangsu, and Zhejiang were the largest contributors to emissions. Oxygenated VOCs (OVOCs) accounted for most of the VOC emissions, followed by alkanes and aromatics, while aromatics were the dominant groups for total OFP, followed by alkenes/alkynes and OVOCs. Ethyl acetate, toluene, isopropanol, isopentane, and n-pentane were the top five VOC species in terms of emissions, while toluene, ethyl acetate, 1,3-butadiene, isopentane, and 1-butene were the top five species in terms of OFP. Scientific and precise control policy were proposed, involving four aspects: environmental access, emission standards, classification and management, and research on source substitution. We believe our study will provide an important reference for the systematic characterization and control policy of VOC emissions from other industries.

Spatial characterization of HCHO and reapportionment of its secondary sources considering photochemical loss in Taiyuan, China

Formaldehyde (HCHO) plays an important role in atmospheric ozone (O3) formation. To accurately identify the sources of HCHO, carbonyls and volatile organic compounds (VOCs) were measured at three urban sites (Taoyuan, TY-U; Jinyuan, JY-U; Xiaodian, XD-U) and a suburban site (Shanglan, SL-B) in Taiyuan during a high O3 period (from July 20 to August 3, 2020). The average mixing ratio of HCHO at XD-U (8.1 ± 2.8 ppbv) was comparable to those at TY-U (7.4 ± 2.1 ppbv) and JY-U (7.0 ± 2.3 ppbv) but higher (p < 0.01) than that at SL-B (4.9 ± 2.3 ppbv). HCHO contributed to 54.3–59.9 % of the total ozone formation potentials (OFPs) of non-methane hydrocarbons (NMHCs) at four sites. The diurnal variation of HCHO concentrations reached a peak value at 12:00–15:00, which may be attributed to the strong photochemical reaction. To obtain more accurate source results of HCHO under the condition of photochemical loss, the initial concentrations of NMHCs were estimated based on photochemical age parameterization and incorporated into the positive matrix factorization (PMF) model (termed IC-PMF). According to the IC-PMF results, secondary formation (SF) contributed the most to HCHO at XD-U (35.6 %) and SL-B (25.1 %), whereas solvent usage (SU) (40.9 %) and coking sources (CS) (36.0 %) were the major sources at TY-U and JY-U, respectively. Compared to the IC-PMF, the conventional PMF analysis based on the observed data underestimated the contributions of SU (100.5–154.2 %) and biogenic sources (BS) (28.5–324.7 %). Further reapportionment of secondary HCHO by multiple linear regression indicated that SU dominated the sources of HCHO at SL-B (28.3 %) and TY-U (41.7 %), while industrial emissions (IE) and CS contributed the most to XD-U (26.6 %) and JY-U (43.0 %) in Taiyuan from north to south, respectively.

Distribution characteristics, air-water exchange, ozone formation potential and health risk assessments of VOCs emitted from typical coking wastewater treatment process

Coking industry has been considered as important source of volatile organic compounds (VOCs) emissions. However, few studies have emphasized the occurrence and adverse effects of VOCs from coking wastewater treatment processes. In this research, pollution profiles of both air and water phase VOCs in a typical coking wastewater treatment plant were investigated in terms of distribution characteristics, air-water exchange, ozone formation potential (OFP) and associated human health risks. Thirty VOCs were detected in the air phase, in which benzene and naphthalene were found to be the major VOCs with total contribution of 87.81 %. Nineteen VOCs were detected in the water phase, in which benzene, naphthalene and toluene contribute most to total VOCs with total contribution of 75.1 %. The regulating tank (RT) was the major source of VOCs, and the emission rate of total VOCs from all unites was 2711.03 g/d with annual emission of 0.99 t. The emission factor was estimated to be 1.36 g VOCs/m3 wastewater. The air-water exchange was assessed using the Fugacity model, and water-to-air volatilization was predominant based on the net flux of air-water exchange. OFP evaluated by emission factor indicated that the total OFP in RT was the highest (1.52 g O3/m3 wastewater), and toluene contributed 41.8 % of the total OFP, followed by naphthalene accounting for 38.7 % The total carcinogenic risks were in the range of 8.60 × 10−6 to 2.18 × 10−3, in which the RT exceeded the significant risk threshold (>1 × 10−4). The non-carcinogenic risks of hazard quotient value in RT also exceeded the risk threshold (>1), and naphthalene was the major contributor accounting for 79.02 %. These results not only provided comprehensive knowledge on pollution profiles and environmental risks of VOCs during coking wastewater treatment processes, but also facilitated the implement of VOCs regulation and occupational health protection strategies in coking industries.

A retrospect of ozone formation mechanisms during the COVID-19 lockdown: The potential role of isoprene

Wuhan took strict measures to prevent the spread of COVID-19 from January 26 to April 7 in 2020. The lockdown reduced the concentrations of atmospheric pollutants, except ozone (O3). To investigate the increase in O3 during the lockdown, trace gas pollutants were collected. The initial concentrations of volatile organic compounds (VOCs) were calculated based on a photochemical ratio method, and the ozone formation potential (OFP) was obtained using the initial and measured VOC concentrations. The O3 formation regime was NOX-limited based on the VOCs/NOX diurnal ratios during the lockdown period. The reduced nitric oxide (NO) concentrations and lower wind speed (WS) could explain the night-time O3 accumulation. The initial total VOCs (TVOCs) during the lockdown were 47.6 ± 2.9 ppbv, and alkenes contributed 48.1%. The photochemical loss amounts of alkenes were an order of magnitude higher than those of alkenes in the same period in 2019 and increased from 16.6 to 28.0 ppbv in the daytime. The higher initial alkene concentrations sustained higher OFP during the lockdown, reaching between 252.4 and 504.4 ppbv. The initial isoprene contributed approximately 35.0–55.0% to the total OFP and had a positive correlation with the increasing O3 concentrations. Approximately 75.5% of the temperatures were concentrated in the range of 5 and 20 °C, which were higher than those in 2019. In addition to stronger solar radiation, the higher temperatures induced higher isoprene emission rates, partially accounting for the higher isoprene concentrations. Lower isoprene-emitting trees should be considered for future urban vegetation to control O3 episodes.

Species profile and reactivity of volatile organic compounds emission in solvent uses, industry activities and from vehicular tunnels

A survey was conducted of the volatile organic compounds (VOCs) released from sources of solvent use, industry activities and vehicle emissions in Guiyang, a capital city of China. Samples were collected by canisters and analyzed by GC-MS-FID. The species profiles of VOCs emitted from sources were obtained. Results showed that xylenes, ethylbenzene, acetone and dichloromethane were the characteristics species for painting, 2-propanol and ethyl acetate for printing, α-pinene for solid wood furniture manufacturing, and 2-butanone for biscuit baking. These characteristics species could be as tracers for the sources respectively. In most of samples from the solvent use, the benzene/toluene (B/T) ratio was less than 0.3, indicating that the ratio could be as the indicator for tracing the solvent use related sources. The results also suggested that the toluene/xylene (T/X) ratio be as the indicator to distinguish the VOCs sources of painting (<2) from the printing (>2). Aromatics contributed the most to ozone formation potential (OFP) of most painting and non-paper printing sources, and oxygen-containing VOCs (OVOCs) were major species contributing to OFP of the sources from food production and paper printing. The OFP of the VOCs emissions from vehicle in tunnels and from other manufactures were dominated by both aromatics and alkenes. The α-pinene could explain 56.94% and 32.54% of total OFP of the VOCs sources from filing cabinet and solid wood furniture manufacturing, which was rarely been involved in previous studies of VOCs source profiles, indicating that the species of concern for VOCs sources are still insufficient at present.

Volatile organic compounds in urban Lhasa: variations, sources, and potential risks

Lhasa is a typical high-altitude city with strong solar radiation and high background ozone levels. With the rapid development and urbanization, the emission of volatile organic compounds (VOCs) in Tibet has been increasing annually. However, VOCs activity and the impact on air quality and human health have scarcely been investigated. We conducted online measurement of VOCs in urban Lhasa during May 2019. The mean mixing ratio (with one standard deviation) of the total VOCs was 21.5 ± 18.6 ppb. Of the total VOCs, alkanes, alkenes, and aromatic hydrocarbons accounted for 57.7%, 20.9%, and 21.4%, respectively. On the basis of VOC atmospheric reactivity, the ozone formation potential (OFP) and hydroxyl radical loss rate (LOH) were 91.7 ppb and 3.1 s−1, respectively. Alkenes accounted for the largest proportion of the OFP and LOH, followed by aromatic hydrocarbons. The results of correlation analysis on the benzene series (BTEX), and the similarity of the diurnal changes in CO, NOy, BTEX, and TVOC mixing ratios indicated that Lhasa city strongly affected by motor vehicle emissions. Source apportionments using positive matrix factorization (PMF) model further confirmed that traffic related emissions, including gasoline automobiles, diesel vehicles, and public transportation vehicles fueled with liquid natural gas contributed the most in total VOCs concentration (44.5%–50.2%), LOH (41.6%–46.8%) and OFP (47.4%–52.3%). Biomass combustion, mainly from the traditional biomass fuel in the plateau, was the second contributor to ambient VOCs (41.3%), LOH (26.4%), and OFP (29.7%), and existed a less variation in diurnal changes with a feature of regional background. Plants contributed only about 1.5% to the VOCs concentration but a relatively high (approximately 14.6%) LOH. The noncarcinogenic risk of BTEX did not exceed the hazard quotient value, but the carcinogenic risk of benzene was 4.47 × 10–6, indicating a potential risk.