OH Radical Loss Rate Research Articles

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.

VOC source apportionment, reactivity, secondary transformations, and their prioritization using fuzzy-AHP method in a coal-mining city in India.

This study assessed the air quality status in different functional zones of Dhanbad-a coal-mining and industrial hub, based on the measurement of aromatic and halogenated volatile organic compounds (VOCs) using gas chromatography. The study encompasses source apportionment of VOCs and their chemical reactivity in terms of OH radical loss rate (LOH), ozone-forming potential (OFP), and their secondary organic aerosol forming potential (SOAp). Furthermore, prioritization of VOCs based on a fuzzy-analytical hierarchical process (F-AHP) has also been done. The results found xylene species to have the highest concentration in all three seasons across traffic-intersection and industrial zones and toluene at the institutional zone. The study identified four sources using positive matrix factorization (PMF) model, viz., mixed traffic exhaust (35%), coal combustion sources (30%), industrial (26%), and solvent usage (9%). LOH and SOAp were ~ 16 times more at the industrial and traffic-intersection zone than the institutional zone. The aromatic species contributed 97% to the OFP, and many species exhibited less contribution to the mixing ratio of VOCs but displayed a high contribution to LOH, OFP, and SOAp, suggesting the need to prefer reactivity-based strategies in addition to concentration-based strategies in the future for their regulation. The F-AHP-based priority component analysis identified 16 species out of 29 in the priority watch list (nine in tier-1, four in tier-2, and three in tier-3). The paucity of data and lack of ambient air quality standards on VOCs (except benzene) make it difficult to determine which aspect should be dealt with first and which species require more attention. Therefore, the F-AHP method used in this study could help identify the influencing parameters to be considered while devising efficient VOC management policies.

Spatiotemporal variations, sources, and atmospheric transformation potential of volatile organic compounds in an industrial zone based on high-resolution measurements in three plants

Industrial emissions are significant sources of volatile organic compounds (VOCs). This study conducted a field campaign at high temporal and spatial resolution to monitor VOCs within three plants in an industrial park in southern China. VOC concentrations showed significant spatial variability in this industrial zone, with median concentrations of 75.22, 40.53, and 29.41 μg/m3 for the total VOCs in the three plants, respectively, with oxygenated VOCs (OVOCs) or aromatics being the major VOCs. Spatial variability within each plant was also significant but VOC-dependent. Seasonal variations in the VOC levels were governed by their industrial emissions, meteorological conditions, and photochemical losses, and they were different for the four groups of VOCs. The temporal and spatial variations in the VOC compositions suggest similar sources of each class of VOCs during different periods of the year in each plant. The diurnal patterns of VOCs (unimodal or bimodal) clearly differed from those at most industrial/urban locations previously, reflecting a dependence on industrial activities. The secondary transformation potential of VOCs also varied temporally and spatially, and aromatics generally made the predominant contributions in this industrial park. The loss rate of OH radicals and ozone formation potential were highly correlated, but the linear relationship substantially changed in summer and autumn due to the intensive emissions of an OVOC species. The lifetime cancer and non-cancer risks via occupational inhalation of the VOCs in the plants were acceptable but merit attention. Taking the secondary transformation potential and health risks into consideration, styrene, xylene, toluene, trichloroethylene, and benzene were proposed to be the priority VOCs regulated in the plants.

Analysis of Influencing Factors of Ozone Pollution Difference Between Chengdu and Chongqing in August 2022

In August 2022, Chengdu and Chongqing showed significant differences in ozone (O3) pollution. Chengdu had O3 pollution days for 20 days, whereas Chongqing had no O3 pollution days. In this study, we analyzed the influencing factors of this difference from the emission level of precursors and meteorological conditions. The results showed that:① the total mixing ratio of 52 VOCs (volatile organic compounds) (including 26 alkanes, 16 aromatics, and 10 alkenes) in Chengdu (18.8×10-9) was 2.8 times that of Chongqing (6.6×10-9), and the total O3 formation potential (OFP) (51.2×10-9) was 2.0 times that of Chongqing (25.0×10-9). The·OH radical loss rate (L·OH) (3.9 s-1) was 1.7 times that of Chongqing (2.3 s-1). The top three OFP in Chengdu were ethylene, m/p-xylene, and isoprene, and those in Chongqing were isoprene, ethylene, and propylene. The contribution rate of alkenes to O3 in Chongqing was 60.7%, whereas the OFP of alkenes and aromatics in Chengdu were 1.6 times and 2.9 times that in Chongqing. In conclusion, the total mixing ratio of VOCs, atmospheric photochemical activity, and O3 formation potential of Chengdu were higher than those of Chongqing. ② Isoprene was ranked first place in L·OH in both Chengdu and Chongqing, indicating that the contribution of biogenic sources to O3 pollution in August was significant. However, the biogenic source emission activity was in response to temperature. From August 14 to 24, the high temperature in Chongqing (38.3℃) decreased biogenic source emission activity, whereas the temperature in Chengdu (34.9℃) increased the biogenic sources emission activity. ③ The horizontal and vertical atmospheric diffusion conditions of Chongqing were better than those of Chengdu, and Chengdu was affected by regional pollution transmission.

Characteristics, Secondary Transformation Potential and Health Risks of Atmospheric Volatile Organic Compounds in an Industrial Area in Zibo, East China

As an important anthropogenic source of volatile organic compounds (VOCs), industrial emissions have a significant impact on air quality and human health. In this study, the characteristics, chemical reactivities, and health risks of VOCs around an industrial park in Zibo were analyzed at two sampling sites. The results showed that the concentrations of total VOCs at Dongzhang Community (DZ) and Special School (SS) sites were 113.12 ppb and 139.40 ppb, respectively, with oxygenated VOCs (OVOCs) as the most abundant species, accounting for 42–45%, followed by alkanes (19.3–19.6%). Diurnal variation of OVOCs exhibited noticeable peaks at 3:00, which may be related to the nighttime sneaky emissions of some enterprises. OVOCs were the species with the highest photochemical activity, with an average contribution of 56.5% to OH radical loss rate and 57% to ozone generation. In addition, OVOCs contributed 40% to secondary organic aerosol formation potential at both sites, second only to aromatics (55%). Acrolein and 1,2-dichloropropane presented the highest non-cancer and cancer risks to human health. The results highlight the importance of OVOCs in some industrial areas.

Exploring formation mechanism and source attribution of ozone during the 2019 Wuhan Military World Games: Implications for ozone control strategies

A series of emission reduction measures were conducted in Wuhan, Central China, to ensure good air quality during the 7th Military World Games (MWG) in October 2019. To better understand the implications for ozone (O3) pollution control strategies, we applied integrated analysis approaches based on the de-weathered statistical model, parameterization methods, chemical box model, and positive matrix factorization model. During the MWG, concentrations of O3, NOx, and volatile organic compound (VOCs), OFP (O3 formation potential), LOH (OH radical loss rate) were 83 µg/m3, 43 µg/m3, 26 ppbv, 188 µg/m3, and 3.9 s−1, respectively, which were 26%, 18%, 3%, 15%, and 13% lower than pre-MWG values and 6%, 39%, 30%, 33%, and 50% lower than post-MWG values, respectively. After removing meteorological influence, O3 and its precursors during the MWG decreased largely compared with post-MWG values, and only O3, NO2, and oxygenated VOCs (OVOCs) declined compared with pre-MWG values, which revealed the emission reduction measures during the MWG played an important role for O3 decline. For six VOCs sources, the mass contributions of biomass burning and solvents usage during the MWG decreased largely compared with pre-MWG values. O3 production was sensitive to VOCs and the key species were aromatics, OVOCs, and alkenes, which originated mainly from solvents usage, biomass burning, industrial-related combustion, and vehicle exhaust. Decreasing O3 concentration during the strict control was mainly caused by OVOCs reduction due to biomass burning control. Generally, the O3 abatement strategies of Wuhan should be focused on the mitigation of high-reactivity VOCs.

Characteristics and Reactivity of VOCs in a Typical Industrial City in Summer

To investigate the ambient pollution caused by volatile organic compounds (VOCs) in a typical industrial city in summer, the characteristics and chemical reactivity from VOCs and the causes of ozone (O3) pollution were analyzed using online VOCs measurements during polluted and non-polluted periods in Zibo city in July 2020. The results showed that the average hourly concentration of total volatile organic compounds (TVOC) during the polluted period[(50.6±28.3)] μg·m-3 was 32.5% higher than that during the non-polluted period[(38.2±24.9) μg·m-3]. The contribution of all VOCs categories were as follows:alkanes>aromatics>alkenes>alkynes, and the diurnal averages of TVOC and O3 concentrations were opposite during the polluted and non-polluted period. Ozone formation potential (OFP),·OH radical loss rate (L·OH), and secondary organic aerosol formation potential (SOAp) during the polluted period were higher than those during the non-polluted period. Alkenes contributed most to OFP and L·OH, whereas aromatics contributed most to SOAp. The tendency of the diurnal average of OFP and SOAp was overall consistent with that of TVOC. The priority species of OFP, L·OH, and SOAp were alkenes and aromatics. The VOCs/NOx method was applied to identify the O3-VOC-NOx sensitivity during the polluted and non-polluted periods, and the results showed that the photochemical regimes were VOCs-limited and transition regions. In addition, the smog production model (SPM) was employed to identify the O3 formation regime, and the results showed that those during the polluted period were identified as VOCs-limited and transition regions from 08:00 to 16:00, whereas the non-polluted period was mainly considered to be VOCs-limited. To mitigate the O3 pollution in summertime, the synergistic control of VOCs (especially alkenes and aromatics) and NOx emissions should be enforced.

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.

Spatiotemporal variation, source and secondary transformation potential of volatile organic compounds (VOCs) during the winter days in Shanghai, China

The spatiotemporal concentration variations, sources, and secondary transformation potential of volatile organic compounds (VOCs) were analyzed at three sampling sites, including the rural (DSL), urban (PD) and industrial (JS) sites, in December 2019, in Shanghai, China. The VOC concentrations in the DSL, PD and JS sites were 13.32 ± 3.33 ppb, 24.72 ± 4.31 ppb and 30.66 ± 5.83 ppb, respectively. The observed “weekend effects” showed the importance of traffic levels and human activities at weekend. By the PMF model, vehicle emission was identified as the largest source of VOCs, accounting for 34.29% in the DSL site, 35.38% in the PD site and 30.07% in the JS site, respectively. During the observation period, in addition to the local sources, regional transport from the provinces nearby was an essential source for VOCs. Although alkanes were the most abundant VOC species in Shanghai, alkenes were the species with the highest chemical activity according to the measurements of OH radical loss rate (LOH) and ozone formation potential (OFP), which played the dominant roles in ozone formation. Haze pollution was largely driven by secondary aerosol formation. The SOA yields from VOCs were 11.29 ± 7.21 μg/m3 and 18.91 ± 8.36 μg/m3 in the clean and haze days, respectively, with aromatics, especially toluene, being the most abundant precursor. The SOA yields in the JS site were much higher than those at the other two sites during the measurement. The VOCs in the DSL site held the highest sensitivity to PM2.5, followed by the JS and PD sites, and aromatics were more sensitive to PM2.5 than other VOC species. Thus, the critical way to reduce PM2.5 formation in Shanghai, especially in the industrial sites, is controlling the concentration of aromatics. This study highlights the vehicle-related source and the secondary transformation from VOCs, which can provide references for local governments regarding controlling strategies of VOCs.

Characteristics, source analysis and chemical reactivity of ambient VOCs in a heavily polluted city of central China

From 2020.8.21 to 2020.9.30, continuously atmospheric volatile organic compounds (VOCs) were measured in the Central Plain to analyze the pollution characteristic, source distribution, chemical reactivity, and contribution to the formation of O3. The concentration of total VOCs (TVOC) was 29.47 ± 13.78 ppbv, and the main VOCs component was alkanes (46%). Ethane, propane, and n-butane were the first three species of VOCs. Six emission sources were identified through positive matrix decomposition (PMF) model, including biogenic source (4%), vehicle emission (28%), fuel evaporation (7%), industrial source (27%), solvent usage (23%) and combustion (11%). Backward trajectory analysis showed that VOCs were mainly derived from short-distance air masses (51%) traveling southeast of Zhengzhou, with the average mixing ratio of VOCs was 31.87 ppbv. Through the potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models, Zhengzhou and its surrounding areas are the main potential sources areas of VOCs. Finally, results of the OH radical loss rate (LOH) and ozone formation potential (OFP) showed that alkenes and aromatics were the species with highest chemical activity, of which both LOH was 34%, and aromatics contributes the most to the formation of O3, accounting for 49%. In addition, solvent usage, industrial source, and vehicular emission were important sources to OFP.

Spatial characteristics of VOCs and their ozone and secondary organic aerosol formation potentials in autumn and winter in the Guanzhong Plain, China

As critical precursors of tropospheric ozone (O3) and secondary organic aerosol (SOA), volatile organic compounds (VOCs) largely influence air quality in urban environments. In this study, measurements of 102 VOCs at all five major cities in the Guanzhong Plain (GZP) were conducted during Sep.09-Oct. 13, 2017 (autumn) and Nov. 14, 2017–Jan. 19, 2018 (winter) to investigate the characteristics of VOCs and their roles in O3 and SOA formation. The average concentrations of total VOCs (TVOCs) at Xi'an (XA), Weinan (WN), Xianyang (XY), Tongchuan (TC), and Baoji (BJ) sites were in the range of 55.2–110.2 ppbv in autumn and 42.4–74.3 ppbv in winter. TVOCs concentrations were reduced by 22.4%–43.5% from autumn to winter at XA, WN and BJ. Comparatively low concentrations of TVOCs were observed in XY and TC, ranging from 53.5 to 62.7 ppbv across the sampling period. Alkanes were the major components at all sites, accounting for 26.4%–48.9% of the TVOCs during the sampling campaign, followed by aromatics (4.2%–26.4%). The average concentration of acetylene increased by a factor of up to 4.8 from autumn to winter, indicating the fuel combustion in winter heating period significantly impacted on VOCs composition in the GZP. The OH radical loss rate and maximum incremental reactivity method were employed to determine photochemical reactivities and ozone formation potentials (OFPs) of VOCs, respectively. The VOCs in XA and WN exhibited the highest reactivities in O3 formation, with the OFP of 168–273 ppbv and the OH loss rates of 19.3–40.8 s−1. Alkenes and aromatics primarily related to on-road and industrial emissions contributed 57.8%–76.3% to the total OFP. The contribution of aromatics to the SOA formation at all sites reached 94.1%–98.6%. Considering the potential source-area of VOCs, regional transport of VOCs occurred within the GZP cities.

Comparison of VOCs Pollution Characteristics Between an Urban Site and a Background Site in Summer in Zibo

To study the differences in volatile organic compound (VOCs) pollution characteristics between an urban site and a background site in summer, ambient VOCs were monitored using an online gas chromatograph (GC) at an urban site and a background site (Mt. Lu) in Zibo in July 2020. The VOCs pollution characteristics and chemical reactivity were analyzed, and the sources of VOCs were identified using the positive matrix factorization model(PMF). The results showed that ρ(TVOC) and ρ(NOx) were higher at the urban site, but ρ(O3) was higher at the background site. Diurnal average characteristics of ρ(TVOC) and ρ(NOx) were high at night and low during the day at the urban site, and there were no obvious variation characteristics at the background site. The diurnal average characteristics of ρ(O3) were consistent at the urban and background sites, showing low level at night and high level during the day; however, the peak in the background site was later than that at the urban site. The average ρ(TVOC) at the urban site and background site were (44.9±27.5) μg·m-3 and (17.3±9.1) μg·m-3, respectively, and the mass fraction of each component was ordered as alkanes>aromatics>alkenes>alkynes in both sites. The average ozone formation potentials(OFP)were (115.5±63.1) μg·m-3 and (38.0±20.2) μg·m-3, and the contribution of each component was ordered as alkenes>aromatics>alkanes>alkynes. The respective average values of·OH radical loss rate(L·OH) were (3.9±2.3) s-1 and (1.0±0.6) s-1, with the highest contribution of alkenes and the lowest contribution of alkynes in both sites. The average values of secondary organic aerosol formation potential(SOAp) were (0.5±0.3) μg·m-3 and (0.2±0.06) μg·m-3, respectively, with aromatic being the most abundant group. According to the source appointment by the PMF model, the main source of VOCs in the urban site was traffic sources (52.4%), followed by petroleum evaporation (19.2%), solvent evaporation (17.3%), and oil and biological sources (11.1%). The source of VOCs in the background site mainly came from traffic sources (40.2%), followed by solvent evaporation (31.3%), combustion sources (19.3%), and biological sources (9.2%). Zibo City should strengthen the management and control of motor vehicle emissions, petroleum evaporation, and the use of industrial solvents.

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

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

Low-molecular-weight carbonyl volatile organic compounds on the North China Plain

To understand the photochemical pollution characteristics of low-molecular-weight carbonyl compounds on the North China Plain (NCP), 2,4-dinitrophenylhydrazine (DNPH) was used to sample low-molecular-weight carbonyl compounds in the atmosphere in Beijing, Tianjin, Shijiazhuang, Xianghe and Xinglong from June 2019 to January 2020, and the samples were then analyzed by a high-performance liquid chromatography (HPLC) to obtain the concentration, daytime variations, seasonal variations, OH radical loss rate, ozone formation potential and sources of five low-molecular-weight carbonyl compounds in the NCP region. The total concentrations at the five sites were 7.70 ± 1.94 ppbv (Beijing), 10.20 ± 1.83 ppbv (Tianjin), 15.31 ± 2.35 ppbv (Shijiazhuang), 10.53 ± 1.82 ppbv (Xianghe) and 5.42 ± 1.15 ppbv (Xinglong), respectively. The contribution of primary source from anthropogenic emission was higher in Tianjin, Shijiazhuang and Xianghe than that in Beijing. The primary and secondary generation contributions were similar in Xinglong. The concentration in Beijing was highest in autumn and lowest in winter. For Tianjin, Shijiazhuang, Xianghe and Xinglong, the highest concentrations occurred in summer. At the five sites, formaldehyde and acetaldehyde contributed the most to L·OH and OFP, while acetone contributed the least. Both L·OH and OFP in Shijiazhuang were the highest, and those in Xinglong were the lowest. The North China Plain was mainly influenced by short-range airflow from the sea and coastal areas during the summer, with the airflow mainly coming from the south in autumn, while the long-range air mass transport was more influential during the winter. In addition, most pollutants were found to be generated locally. By utilizing a source-tracer-ratio method in the source analysis, with the change of season, the anthropogenic source contribution of each site was found to gradually increase while that of other sources gradually decreased.

Sources of ambient non-methane hydrocarbon compounds and their impacts on O3 formation during autumn, Beijing

The field observation of 54 non-methane hydrocarbon compounds (NMHCs) was conducted from September 1 to October 20 in 2020 during autumn in Haidian District, Beijing. The mean concentration of total NMHCs was 29.81 ± 11.39 ppbv during this period, and alkanes were the major components. There were typical festival effects of NMHCs with lower concentration during the National Day. Alkenes and aromatics were the dominant groups in ozone formation potential (OFP) and OH radical loss rate (LOH). The positive matrix factorization (PMF) running results revealed that vehicular exhaust became the biggest source in urban areas, followed by liquefied petroleum gas (LPG) usage, solvent usage, and fuel evaporation. The box model coupled with master chemical mechanism (MCM) was applied to study the impacts of different NMHCs sources on ozone (O3) formation in an O3 episode. The simulation results indicated that reducing NMHCs concentration could effectively suppress O3 formation. Moreover, reducing traffic-related emissions of NMHCs was an effective way to control O3 pollution at an urban site in Beijing.

Source Apportionment of VOCs and O3 Production Sensitivity at Coastal and Inland Sites of Southeast China

Urbanization and industrialization levels have a significant impact on the pollution of O3 and its precursors. However, current studies of VOC sources and O3 formation sensitivity in the regions with different urbanization and industrialization levels remained limited. Therefore, offline and online VOC observations were conducted at coastal sites (CS) and inland sites (IS) of southeast China to analyze spatial-temporal characteristics, source apportionment of VOCs based on the positive matrix factorization (PMF) model, and their effects on O3 formation using the observation-based model (OBM). The results showed that the average concentrations of TVOCs at CS and IS were 49.1 ± 14.4 and 28.4 ± 9.6 ppb, respectively, with higher levels in autumn compared to those in spring and summer. Alkene species contributed the largest to the OH radical loss rate (LOH) and ozone formation potential (OFP). The contributions of vehicle exhaust and combustion sources, industrial sources, solvent usage, biogenic sources, and fuel evaporation at CS and IS were 42.2% and 34.5%, 22.4% and 18.2%, 12.7% and 4.5%, 11.7% and 19.4%, and 11.0% and 23.4%, respectively. Meanwhile, vehicle exhaust and combustion sources (31.8%), fuel evaporation (21.3%) were the major contributors to O3 formation in Ningde. The results of sensitivity analysis indicated that O3 formation at CS was mainly VOC control in spring and autumn, and controlled by both VOCs and NOx in summer, but the VOCs is the key factor for the O3 formation at IS, and the emission control of alkenes and aromatics was conductive to decrease O3 levels. The scenario analysis suggested that the 20% reduction of VOC concentrations and 3% reduction of NOx concentrations could realize the 5% reduction of O3 concentrations. This study might enhance the understanding of O3 and its precursors in southeast China with different urbanization levels, as well as the emission reduction strategies.

Spatial-temporal Characteristics and Source Apportionment of Ambient VOCs in Southeast Mountain Area of China

Seasonal variations and sources of ambient volatile organic compounds (VOCs) were conducted at the county and rural sites in a mountain area of southeastern China. The results showed that the pattern of VOC concentrations was dominated by oxygenated VOCs (37.6%) and alkanes (25.8%), followed by halocarbons (16.8%), alkenes (11.9%), aromatics (6.87%), and alkynes (1.04%). Based on the OH radical loss rate (LOH) and ozone formation potential (OFP) analysis, alkenes had the highest chemical activity, especially the contribution of isoprene in rural areas. Aromatics contributed the most to secondary organic aerosols (SOA) formation in both county and rural areas. Source apportionment of VOCs were quantified by the positive matrix factorization (PMF) model, including industrial emissions and combustion burning (30.1% and 43.3% in the county and rural areas, respectively) and vehicle exhausts (30.3% and 10.8%), followed by solvent usage (17.1% and 5.2%), liquid petroleum gas (LPG) usage and fuel evaporation (14.2% and 10.0%), and biogenic source (8.3% and 30.6%). The backward air trajectories showed that air mass in spring was mainly originated from the intercity transmission, while the air clusters in autumn came from the northern areas through long-range transport. The study was helpful to understand the pollution characteristics in the mountainous area and provides a scientific basis for local O3 and PM2.5 pollution control.

Measurement report: High contributions of halocarbon and aromatic compounds to atmospheric volatile organic compounds in an industrial area

Abstract. Volatile organic compounds (VOCs) are key components of tropospheric chemistry. We investigated ambient VOCs in an industrial area in Nanjing, China, between July 2018 and May 2020. The sum of the suite of measured total VOC (TVOC) concentrations was 59.8 ± 28.6 ppbv (part per billion by volume) during the investigation period. About twice the TVOC concentrations were observed in the autumn (83 ± 20 ppbv) and winter (77.5 ± 16.8 ppbv) seasons compared to those in spring (39.6 ± 13.1 ppbv) and summer (38.8 ± 10.2 ppbv). In previous studies in Nanjing, oxygenated VOCs (OVOCs) and halocarbons were not measured, and the current TVOC concentration without halocarbons and OVOCs was similar to the previous investigation in the same study area. However, it was twofold higher than the one reported in the nonindustrial suburban area of Nanjing. Due to the industrial influence, the halocarbons VOC group (14.3 ± 7.3 ppbv, 24 %) was the second-largest contributor to the TVOCs after alkanes (21 ± 7 ppbv, 35 %), which is in contrast with the previous studies in Nanjing and also in almost all other regions in China. Relatively high proportions of halocarbons and aromatics were observed in autumn (25.7 % and 19.3 %, respectively) and winter (25.8 % and 17.6 %, respectively) compared to those in summer (20.4 % and 11.8 %, respectively) and spring (20.3 % and 13.6 %, respectively). According to the potential source contribution function (PSCF), short-distance transport from the surrounding industrial areas and cities was the main reason for the high VOC concentrations in the study area. According to positive matrix factorization (PMF) model results, vehicle-related emissions (33 %–48 %) contributed to the major portion of the ambient VOC concentrations. Aromatics, followed by alkenes, were the top contributors to the loss rate of OH radicals (LOH; 37 % and 32 %, respectively). According to the empirical kinetic modelling approach (EKMA) and relative incremental reactivity (RIR) analysis, the study area was in the VOC-sensitive regime for ozone (O3) formation during all measurement seasons. Therefore, alkenes and aromatics emissions from automobiles need to be decreased to reduce secondary air pollution formation in the study area.

Tower-based measurements of NMHCs and OVOCs in the Pearl River Delta: Vertical distribution, source analysis and chemical reactivity

Measurements of vertical distribution of volatile organic compounds (VOCs) have attracted wide attentions, which could help to understand atmospheric oxidation mechanism and provide implications for VOC control. This study measured the non-methane hydrocarbons (NMHCs) and oxygenated VOCs (OVOCs) simultaneously for the first time at three different heights, namely ground, 118 m and 488 m, in the Canton Tower located in the urban core of the Pearl River Delta (PRD). The results show that NMHCs decreased while some OVOC species such as formaldehyde and acetaldehyde increased with increasing height. It was mainly attributed to the dilution and chemical loss of NMHCs but secondary production of OVOCs during vertical transport. Ratio analysis and receptor modeling indicate that vehicle exhausts (47%) and fuel evaporation (39%) were major sources of the total NMHCs. Interestingly, industry contributed much more at 118 m, probably affected by organic gas discharge from the high chimney of industrial factories. The chemical reactivities in terms of OH radical loss rate (LOH), ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) were lowest at 118 m, smaller than those influenced by high fresh NMHC emissions at ground and strong formation of secondary species (e.g. OVOCs) at 488 m. OH exposure estimated by isoprene and m,p-xylene/ethylbenzene was different depending on their time scale of vertical turbulent mixing and chemical loss. OVOC species measured at different heights were positively correlated with Ox (R = 0.48–0.87), indicating that OVOCs were largely contributed by secondary formation in photochemical process. The tower measurements of NMHCs and OVOCs provided a unique opportunity to investigate the VOC distribution and chemical behaviors, which could give important information for understanding O3 and PM2.5 pollution mechanism in the PRD region with fast developing urban setting and substantially changing air quality.

VOCs characteristics and their ozone and SOA formation potentials in autumn and winter at Weinan, China.

Frequent ozone and fine particulate matter (PM2.5) pollution have been occurring in the Guanzhong Plain in China. To effectively control the tropospheric ozone and PM2.5 pollution, this study performed measurements of 102 VOCs species from Sep.19-25 (autumn) and Nov.27-Dec. 8, 2017 (winter) at Weinan in the central Guanzhong Plain. The total volatile organic compounds (TVOCs) concentrations were 95.8 ± 30.6 ppbv in autumn and 74.4 ± 37.1 ppbv in winter. Alkanes were the most abundant group in both of autumn and winter, accounting for 33.5% and 39.6% of TVOCs concentrations, respectively. The levels of aromatics and oxygenated VOCs were higher in autumn than in winter, mainly due to changes in industrial activities and combustion strength. Photochemical reactivities and ozone formation potentials (OFPs) of VOCs were calculated by applying the OH radical loss rate (LOH) and maximum incremental reactivity (MIR) method, respectively. Results showed that Alkenes and aromatics were the key VOCs in term ozone formation in Weinan, which together contributed 59.6% ̶ 65.3% to the total LOH and OFP. Secondary organic aerosol formation potentials (SOAFP) of the measured VOCs were investigated by employing the fractional aerosol coefficient (FAC) method. Aromatics contributed 94.9% and 96.2% to the total SOAFP in autumn and winter, respectively. The regional transport effects on VOCs and ozone formation were investigated by using trajectory analysis and potential source contribution function (PSCF). Results showed that regional anthropogenic sources from industrial cities (Tongchuan, Xi'an city) and biogenic sources from Qinling Mountain influenced VOCs levels and OFP at Weinan. Future studies need to emphasize on meteorological factors and sources that impact on VOCs concentrations in Weinan.