Source-resolved attribution of ground-level ozone formation potential from VOC emissions in Metropolitan Vancouver, BC

Long-term trends in British Columbia lower mainland air quality: Criteria air pollutants and VOC

The lower mainland of British Columbia is a geographic region that comprises the districts of Metro Vancouver and the Lower Fraser Valley. It is situated in a complex topographical and coastal location in southwestern British Columbia. Metro Vancouver is Canada's third largest population center. Accessing the Canadian National Air Pollution Surveillance Program (NAPS) database we calculated air pollutant statistics using the Canadian Ambient Air Quality Standards (CAAQS) averaging times, numerical forms, and numerical levels for the years 2001to 2020. Man Kendall and Sen statistical methods were used to test for the presence of trends and the slope of those trends in fine particulate matter (PM2.5), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and volatile organic compound (VOC) ambient air concentrations. We did not determine a significant trend in 98th percentile of the daily 24-hr average PM2.5 concentrations. We did determine significant negative trends in the annual average of the daily 24-hr average PM2.5 concentrations at 6 of the 9 locations. Episodic, multi-day duration elevated PM2.5 concentrations related to forest fires were a significant influence on PM2.5 ambient concentrations. Annual 4th highest daily maximum 8-hr average O3 concentrations showed no trend at 14 of 18 locations, declined at 3 locations, and increased at one location. We determined statistically significant declines in peak and average NO2 and SO2 concentrations, and in time-integrated annual VOC concentrations.Implications: This non-parametric, statistical analysis determines 20-year trends in British Columbia lower mainland ambient air quality for PM2.5, O3, NO2, SO2 and VOC, assesses air quality against Canadian Ambient Air Quality Standards, and highlights the importance of event-based wildfire-sourced PM2.5.

Passive air sampling of VOCs, O3, NO2, and SO2 in the large industrial city of Ulsan, South Korea: spatial-temporal variations, source identification, and ozone formation potential

Concerns about volatile organic compounds (VOCs) have increased due to their toxicity and secondary reaction with nitrogen oxides (NOX) to form ozone (O3). In this study, passive air sampling of VOCs, O3, NO2, and SO2 was conducted in summer, fall, winter, and spring from 2019 to 2020 at six industrial and ten urban sites in Ulsan, the largest industrial city in South Korea. Over the entire sampling period, the concentration of toluene (mean: 8.75 μg/m3) was the highest of the 50 target VOCs, followed by m,p-xylenes (4.52 μg/m3), ethylbenzene (4.48 μg/m3), 3-methylpentane (4.40 μg/m3), and n-octane (4.26 μg/m3). Total (Σ50) VOC levels did not statistically differ between seasons, indicating that large amounts of VOCs are emitted into the atmosphere throughout the year. On the other hand, O3, NO2, and SO2 exhibited strong seasonal variation depending on the meteorological conditions and emission sources. The spatial distribution of Σ50 VOCs, NO2, and SO2 indicated that industrial complexes were major sources in Ulsan, while O3 had the opposite spatial distribution. Using a positive matrix factorization model, five major sources were identified, with industrial effects dominant. Aromatic compounds, such as m,p,o-xylenes, toluene, and 1,2,4-trimethylbenzene, significantly contributed to O3 formation. The VOC/NO2 ratio and O3 concentrations suggested that reducing VOC emissions is more effective than reducing NO2 emissions in terms of preventing the secondary formation of O3. The findings of this study allow for a better understanding of the relationship between VOCs, O3, NO2, and SO2 in industrial cities.

VOC species controlling O3 formation in ambient air and their sources in Kaifeng, China

The concentration of ozone has been in a rising crescendo in the last decade while the fine particles (PM_2.5) is gradually decreasing but still at a high level in central China. Volatile organic compounds (VOCs) are the vital precursors of ozone and PM_2.5. A total of 101 VOC species were measured in four seasons at five sites from 2019 to 2021 in Kaifeng. VOC sources and geographic origin of sources were identified by the positive matrix factorization (PMF) model and the hybrid single-particle Lagrangian integrated trajectory transport model. The source-specific OH loss rates (L_OH) and ozone formation potential (OFP) were calculated to estimate the effects of each VOC source. The average mixing ratios of total VOCs (TVOC) were 43.15 parts per billion (ppb), of which the alkanes, alkenes, aromatics, halocarbons, and oxygenated VOCs respectively accounted for 49%, 12%, 11%, 14%, and 14%. Although the mixing ratios of alkenes were comparatively low, they played a dominant role in the L_OH and OFP, especially ethene (0.55 s^-1, 7%; 27.11 μg/m³, 10%) and 1,3-butadiene (0.74 s^-1, 10%; 12.52 μg/m³, 5%). The vehicle-related source which emitted considerable alkenes ranked as the foremost contributing factor (21%). Biomass burning was probably influenced by other cities in the western and southern Henan and other provinces, Shandong and Hebei.

Estimation of Anthropogenic VOCs Emission Based on Volatile Chemical Products: A Canadian Perspective

Volatile organic compounds (VOCs) in urban areas are of great interest due to their significant role in forming ground-level ozone and adverse public health effects. Emission inventories usually compile the outdoor VOCs emission sources (e.g., traffic and industrial emissions). However, considering emissions from volatile chemical products (e.g., solvents, printing ink, personal care products) is challenging because of scattered data and the lack of an effective method to estimate the VOCs emission rate from these chemical products. This paper aims to systematically analyse potential sources of VOCs emission in Canada's built environment, including volatile chemical products. Also, spatial variation of VOCs level in the ambient atmosphere is examined to understand the VOC relationship with ozone and secondary organic aerosol formation. The study shows that VOCs level may vary among everyday microenvironments (e.g., residential areas, offices, and retail stores) depending on the frequency of product consumption, building age, ventilation condition, and background ambient concentration in the atmosphere. However, it is very difficult to establish VOC speciation and apportionment to different volatile chemical products that contribute most significantly to exposure and target subpopulations with elevated levels. Thus, tracer compounds can be used to identify inventory sources at the consumer end. A critical overview highlights the limitations of existing VOC estimation methods and possible approaches to control VOC emissions. The findings provide crucial information to establish an emission inventory framework for volatile chemical products at a national scale and enable policymakers to limit VOCs emission from various volatile chemical products.

Gaseous ethylbenzene removal by photocatalytic TiO2 nanoparticles immobilized on glass fiber tissue under real conditions: evaluation of reactive oxygen species contribution to the photocatalytic process

Photocatalytic oxidation (PCO) using a TiO₂ catalyst is an effective technique to remove gaseous volatile organic compounds (VOCs). Herein, a lab-scale continuous reactor is used to investigate the photocatalytic performance toward ethylbenzene (EB) vapor removal over TiO₂ nanoparticles immobilized on glass fiber tissue. The role of the reactive species in the removal of EB and the degradation pathway were studied. Firstly, the effect of key operating parameters such as EB concentration (13, 26, 60 mg/m³), relative humidity levels (From 5 to 80%), gas carrier composition (dry air + EB, O₂ + EB and N₂ + EB) and ultraviolet (UV) radiation wavelength (UV-A _365 nm, UV-C _254 nm) were explored. Then, using superoxide dismutase and tert-butanol as trapping agents, the real contribution of superoxide radical anion (O₂^.-) and hydroxyl radicals (OH^.) to EB removal was quantified. The results show that (i) small water vapor content enhances the EB degradation; (ii) the reaction atmosphere plays an important role in the photocatalytic process; and (iii) oxygen atmosphere/UV-C radiation shows the highest EB degradation percentage. The use of radical scavengers confirms the major contribution of the hydroxyl radical to the photocatalytic mechanism with 75% versus 25% for superoxide radical anion.

Diagnosis of photochemical O3 production of urban plumes in summer via developing the real-field IRs of VOCs: A case study in Beijing of China

This study mainly developed an estimate method for photochemical ozone (O₃) production from urban plumes in hot season, through simulating O₃ evolution from precursors locally emitted and determining the real-field O₃ increment reactivity (IR) of volatile organic compounds (VOCs) based on the box chemical model. Our simulation on June-2019 indicated that Beijing local emissions produced O₃ at the rate of 0.7-9.2 ppb/h and led to an O₃ increase of 48.9 ppb during 05:00-18:00, accounting for 68.3% of the observed O₃ increase. The maximum level and production rate of simulated O₃ showed a linear response to VOCs, therefore we can use VOCs levels in urban plumes to quantify O₃ formation in summer. The IR (g O₃ formed per g VOCs) was calculated on the actual precursor and meteorology condition of this megacity, 0.12-4.90 g/g for individual VOCs and 1.49 g/g for comprehensive TVOCs. The weighted average of individual IRs agreed well with that of TVOCs, but these IRs were 34.5% of MIR values that were widely used in references. It's noteworthy that these IRs had greater sensitivity to precursor levels, and broadly remained stable under the fixed VOCs:NOx. Considering the synchronous reductions of precursors in Beijing, we applied these IRs to quantify chemical O₃ evolution from Beijing local emissions in summer of recent years, declining from 63.5 ppb in 2016 to 44.0 ppb in 2020 for June. The contributions of the diagnosed chemical O₃ to Beijing O₃ better matched with the atmospheric transport paths on daily basis, higher than 100% when the transport paths starting from the clean neighbor cities, but lower to 45%-66% when the transport paths originating from the highly-polluted neighbor cities. This consistence indicated the reliability of our IR calculation method for quickly estimating chemical O₃ production of urban plumes in summer.

Predicting ozone formation in petrochemical industrialized Lanzhou city by interpretable ensemble machine learning

Ground-level ozone (O₃) formation depends on meteorology, precursor emissions, and atmospheric chemistry. Understanding the key drivers behind the O₃ formation and developing an accurate and efficient method for timely assessing the O₃-VOCs-NOx relationships applicable in different O₃ pollution events are essential. Here, we developed a novel machine learning ensemble model coupled with a Shapley additive explanation algorithm to predict the O₃ formation regime and derive O₃ formation sensitivity curves. The algorithm was tested for O₃ events during the COVID-19 lockdown, a sandstorm event, and a heavy O₃ pollution episode (maximum hourly O₃ concentration >200 μg/m³) from 2019 to 2021. We show that increasing O₃ concentrations during the COVID-19 lockdown and the heavy O₃ pollution event were mainly caused by the photochemistry subject to local air quality and meteorological conditions. Influenced by the sandstorm weather, low O₃ levels were mainly attributable to weak sunlight and low precursor levels. O₃ formation sensitivity curves demonstrate that O₃ formation in the study area was in a VOCs-sensitive regime. The VOCs-specific O₃ sensitivity curves can also help make hybrid and timely strategies for O₃ abatement. The results demonstrate that machine learning driven by observational data has the potential to be a very useful tool in predicting and interpreting O₃ formation.

Characterization, reactivity, source apportionment, and potential source areas of ambient volatile organic compounds in a typical tropical city

Based on one-year observation, the concentration, sources, and potential source areas of volatile organic compounds (VOCs) were comprehensively analyzed to investigate the pollution characteristics of ambient VOCs in Haikou, China. The results showed that the annual average concentration of total VOCs (TVOCs) was 11.4 ppbV, and the composition was dominated by alkanes (8.2 ppbV, 71.4%) and alkenes (1.3 ppbV, 20.5%). The diurnal variation in the concentration of dominant VOC species showed a distinct bimodal distribution with peaks in the morning and evening. The greatest contribution to ozone formation potential (OFP) was made by alkenes (51.6%), followed by alkanes (27.2%). The concentrations of VOCs and nitrogen dioxide (NO₂) in spring and summer were low, and it was difficult to generate high ozone (O₃) concentrations through photochemical reactions. The significant increase in O₃ concentrations in autumn and winter was mainly related to the transmission of pollutants from the northeast. Traffic sources (40.1%), industrial sources (19.4%), combustion sources (18.6%), solvent usage sources (15.5%) and plant sources (6.4%) were identified as major sources of VOCs through the positive matrix factorization (PMF) model. The southeastern coastal areas of China were identified as major potential source areas of VOCs through the potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models. Overall, the concentration of ambient VOCs in Haikou was strongly influenced by traffic sources and long-distance transport, and the control of VOCs emitted from vehicles should be strengthened to reduce the active species of ambient VOCs in Haikou, thereby reducing the generation of O₃.

Accurate identification of key VOCs sources contributing to O3 formation along the Liaodong Bay based on emission inventories and ambient observations

In order to achieve the precise control of the volatile organic compounds (VOCs) species with high ozone (O₃) formation contribution from key sources in Panjin and Yingkou, two coastal industrial cities with severe O₃ pollution along the Liaodong Bay, northeast China, the ambient concentrations of 99 VOCs species were measured online at urban-petrochemical (XLT), suburban-industrial (PP), and rural (XRD) sites in July 2019, contemporary monthly anthropogenic VOCs emission inventories were developed. The source contribution of ambient VOCs resolved by positive matrix factorization (PMF) model was comparable with emission inventories, and the location of VOCs sources were speculated by potential source contribution function (PSCF). 17.5 Gg anthropogenic VOCs was emitted in Panjin and Yingkou in July 2019 with potential to form 54.7 Gg-O₃ estimated by emission inventories. The average VOC mixing ratios of 47.1, 26.7, and 16.5 ppbv was observed at XLT, PP, and XRD sites, respectively. Petroleum industry (22 %), organic chemical industry (21 %), and mobile vehicle emission (19 %) were identified to be the main sources contributing to O₃ formation at XLT site by PMF, while it is organic chemical industry (33 %) and solvent utilization (28 %) contributed the most at PP site. Taking the subdivided source contributions of emission inventories and source locations speculated by PSCF into full consideration, organic raw chemicals manufacturing, structural steel coating, petroleum refining process, petroleum products storage and transport, off-shore vessels, and passenger cars were identified as the key anthropogenic sources. High O₃-formation contribution sources, organic chemical industry and solvent utilization were located in the industrial parks at the junction of the two cities and the southeast of Panjin, and petroleum industry distributed in the whole Panjin and offshore areas. These results identify the key VOCs species and sources and speculate the potential geographical location of sources for precisely controlling ground-level O₃ along the Liaodong Bay.

Characteristics and sources of volatile organic compounds (VOCs) in Xinxiang, China, during the 2021 summer ozone pollution control

Real-time monitoring of volatile organic compounds (VOCs) was conducted in Xinxiang, China, during the implementation of Xinxiang's ozone pollution control period (CP) in June 2021. To evaluate the effectiveness of the control measures, three study periods were determined by combining meteorological conditions and the implementation time of the control measures: before, during, and after the CP of ozone pollution (BCP, CP, and ACP, respectively). The average concentrations of VOCs during the three periods were 41.20 ± 4.99 ppbv, 33.64 ± 5.65 ppbv, and 37.42 ± 2.59 ppbv, respectively, with the same top three components, namely oxygenated VOCs (OVOCs), alkanes, and halogenated hydrocarbons (XVOCs). However, the concentrations of these three components decreased substantially during the CP (by 19 %, 18 %, and 11 %, respectively). The ozone formation potential (OFP) during the BCP was 144.47 ppbv, which was 1.2 times and 1.3 times higher than those during the ACP and CP periods, respectively. During the CP, the proportion of alkenes that contributed to the OFP decreased significantly by 24 %. Five types of VOCs sources were determined by positive matrix factorization (PMF): (1) solvent use, (2) biogenic, (3) secondary formation, (4) industrial process, and (5) vehicle exhaust and fuel evaporation sources. The VOCs emissions from industrial processes decreased by 54 % during the CP, whereas those from vehicle exhaust and fuel evaporation sources decreased by 36 %, indicating the effectiveness of emission control measures and the importance of these two sources for VOCs control in Xinxiang. In terms of regional transport, the results of the spatial analysis revealed that Hebi and Anyang in the northeast and Zhengzhou and Pingdingshan in the southwest, affected significantly the VOCs of Xinxiang. These results highlight the importance of controlling VOCs emissions in Xinxiang. Furthermore, attention should be paid to controlling the regional transport of surrounding cities.

Traffic, transport, and vegetation drive VOC concentrations in a major urban area in Texas

The population of Texas has increased rapidly in the past decade. The San Antonio Field Study (SAFS) was designed to investigate ozone (O₃) production and precursors in this rapidly changing, sprawling metropolitan area. There are still many questions regarding the sources and chemistry of volatile organic compounds (VOCs) in urban areas like San Antonio which are affected by a complex mixture of industry, traffic, biogenic sources and transported pollutants. The goal of the SAFS campaign in May 2017 was to measure inorganic trace gases, VOCs, methane (CH₄), and ethane (C₂H₆). The SAFS field design included two sites to better assess air quality across the metro area: an urban site (Traveler's World; TW) and a downwind/suburban site (University of Texas at San Antonio; UTSA). The results indicated that acetone (2.52 ± 1.17 and 2.39 ± 1.27 ppbv), acetaldehyde (1.45 ± 1.02 and 0.93 ± 0.45 ppbv) and isoprene (0.64 ± 0.49 and 1.21 ± 0.85 ppbv; TW and UTSA, respectively) were the VOCs with the highest concentrations. Additionally, positive matrix factorization showed three dominant factors of VOC emissions: biogenic, aged urban mixed source, and acetone. Methyl vinyl ketone and methacrolein (MVK + MACR) exhibited contributions from both secondary photooxidation of isoprene and direct emissions from traffic. The C₂H₆:CH₄ demonstrated potential influence of oil and gas activities in San Antonio. Moreover, the high O₃ days during the campaign were in the NO_x-limited O₃ formation regime and were preceded by evening peaks in select VOCs, NO_x and CO. Overall, quantification of the concentration and trends of VOCs and trace gases in a major city in Texas offers vital information for general air quality management and supports strategies for reducing O₃ pollution. The SAFS campaign VOC results will also add to the growing body of literature on urban sources and concentrations of VOCs in major urban areas.

Characteristics of volatile organic compounds in the metropolitan city of Seoul, South Korea: Diurnal variation, source identification, secondary formation of organic aerosol, and health risk

Atmospheric volatile organic compounds (VOCs) in Seoul, the capital of South Korea, have attracted increased attention owing to their emission, secondary formation, and human health risk. In this study, we collected 24 hourly samples once a month at an urban site in Seoul for a year (a total of 288 samples) using a sequential tube sampler. Analysis results revealed that toluene (9.08 ± 8.99 μg/m³) exhibited the highest annual mean concentration, followed by ethyl acetate (5.55 ± 9.09 μg/m³), m,p-xylenes (2.79 ± 4.57 μg/m³), benzene (2.37 ± 1.55 μg/m³), ethylbenzene (1.81 ± 2.27 μg/m³), and o-xylene (0.91 ± 1.47 μg/m³), indicating that these compounds accounted for 77.8-85.6% of the seasonal mean concentrations of the total (Σ₅₉) VOCs. The concentrations of the Σ₅₉ VOCs were statistically higher in spring and winter than in summer and fall because of meteorological conditions, and the concentrations of individual VOCs were higher during the daytime than nighttime owing to higher human activities during the daytime. The conditional bivariate probability function and concentration weighted trajectory analysis results suggested that domestic effects (e.g., vehicular exhaust and solvents) exhibited a dominant effect on the presence of VOCs in Seoul, as well as long-range atmospheric transport of VOCs. Further, the most important secondary organic aerosol formation potential (SOAFP) compounds included benzene, toluene, ethylbenzene, and m,p,o-xylenes, and the total SOAFP of nine VOCs accounted for 5-29% of the seasonal mean PM_2.5 concentrations. The cancer and non-cancer risks of the selected VOCs were below the tolerable (1 × 10^-4) and acceptable (Hazard quotient: HQ < 1) levels, respectively. Overall, this study highlighted the feasibility of the sequential sampling of VOCs and hybrid receptor modeling to further understand the source-receptor relationship of VOCs.

Health Risk-Oriented Source Apportionment of Hazardous Volatile Organic Compounds in Eight Canadian Cities and Implications for Prioritizing Mitigation Strategies

Traditionally, environmental authorities make regulatory policies for controlling volatile organic compound (VOC) pollution based on the mitigation of dominant VOC sources. However, the emission from each VOC source has a unique combination of VOC species of different toxicities. Without quantitatively assessing the health risk associated with each source, the effectiveness of the mitigation policy could be undermined. To address this shortcoming, we developed a new health risk-oriented source apportionment method that can provide quantitative health risk assessment and source-specific mitigation strategies for hazardous VOCs. We estimated that the integrated inhalation cancer risk (ICR) of hazardous VOCs was 7.7 × 10^-5 in Western Canada, indicating a 100% likelihood of exceeding Health Canada's acceptable risk level (1.0 × 10^-5). Anthropogenic sources were responsible for 56.3-73.8% of cancer risks across eight Canadian cities except for the regional background island, where natural sources contributed over 77% to the integrated ICR. Thus, substantial environmental and health cobenefits could be achieved via reducing the ambient levels of benzene and 1,3-butadiene by 39.3-75.7 and 14-69.3%, respectively, and mitigating emissions from fuel combustion (by 31.3-54.1%), traffic source (3.0-36.8%), and other anthropogenic sources (5.3-20.1%) in Western Canada. Our study has significant implications for prioritizing air pollution mitigation policies, especially for quantitative reduction of hazardous air pollutants.

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.

In Situ Measurement of NO, NO2, and H2O in Combustion Gases Based on Near/Mid-Infrared Laser Absorption Spectroscopy

In this study, a strategy was developed for in situ, non-intrusive, and quantitative measurement of the oxides of nitrogen (NO and NO₂) to describe emission characteristics in gas turbines. The linear calibration-free wavelength modulation spectroscopy (LCF-WMS) approach combined with the temperature profile-fitting strategy was utilized for trace NO and NO₂ concentration detection with broad spectral interference from gaseous water (H₂O). Transition lines near 1308 nm, 5238 nm, and 6250 nm were selected to investigate the H₂O, NO, and NO₂ generated from combustion. Experiments were performed under different equivalence ratios in a combustion exhaust tube, which was heated at 450-700 K, with an effective optical length of 1.57 m. Ultra-low NO_x emissions were captured by optical measurements under different equivalence ratios. The mole fractions of H₂O were in agreement with the theoretical values calculated using Chemkin. Herein, the uncertainty of the TDLAS measurements and the limitation of improving the relative precision are discussed in detail. The proposed strategy proved to be a promising combustion diagnostic technique for the quantitative measurement of low-absorbance trace NO and NO₂ with strong H₂O interference in real combustion gases.

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 L_OH 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.

A comprehensive investigation on volatile organic compounds (VOCs) in 2018 in Beijing, China: Characteristics, sources and behaviours in response to O3 formation

Observations of volatile organic compounds (VOCs) are a prerequisite for evaluating the effectiveness of government efforts targeting VOC pollution. Here, based on the one-year online VOC measurement in 2018 in Beijing, systematic analyses and model simulation were conducted to illuminate VOC characteristics, emission sources, regional hotspots and behaviours in response to O₃ formation. The observed mean VOC concentration in 2018 was 29.12 ± 17.64 ppbv declined distinctly compared to that in 2015 and 2016. Vehicle exhaust (39.95%), natural gas/liquefied petroleum gas (22.04%) and industrial sources (20.64%) were the main contributors to VOCs in Beijing. Regional transport, mainly from the south-south-east (SSE) and south-south-west (SSW), quantitatively contributed 36.65%-55.06% to VOCs based on our developed method. O₃ sensitivity tended to be in the transition regime in summer identified by ground-based and satellite observations. Strong solar radiation along with high temperature and low humidity aggravated O₃ pollution that was further intensified by regional transport from southern polluted regions. The model simulation determined that turning off CH₃CHO related reactions brought about the most predominantly short-term and long-run O₃ reduction, indicating that control policies in VOC species should be tailored, instead of one-size-fits-all. Overall, region-collaborated and active VOC-species-focused strategies on VOC controls are imperative.

Multiply improved positive matrix factorization for source apportionment of volatile organic compounds during the COVID-19 shutdown in Tianjin, China

Ambient concentrations of volatile organic compounds (VOCs) vary with emission rates, meteorology, and chemistry. Conventional positive matrix factorization (PMF) loses information because of dilution variations and chemical losses. Multiply improved PMF incorporates the ventilation coefficient, and total solar radiation or oxidants to reduce the effects of dispersion and chemical loss. These methods were applied to hourly speciated VOC data from November 2019 to March 2020 including during the COVID-19 shutdown. Various comparisons were made to assess the influences of these fluctuation drivers by time of day. Dispersion normalized PMF (DN-PMF) reduced the dispersion variations. Dispersion-radiation normalized PMF (DRN-PMF) reduced the impact of chemical loss, especially at night, which was better than Dispersion-O_x normalized PMF (DON-PMF). The conditional bivariate probability function (CBPF) plots of DRN-PMF results were consist with actual source locations. The DN-PMF, DRN-PMF, and DON-PMF results were consistent between 10:00 and 15:00, suggesting dispersion was significantly more influential than photochemical reactions during these times. The DRN-PMF results indicated that the highest VOC contributors during the COVID-19 shutdown were liquefied petroleum gas (LPG) (28.8%), natural gas (25.2%), and pulverized coal boilers emissions (19.6%). Except for petrochemical-related enterprises and LPG, the contribution concentrations of all other sources decreased substantially during the COVID-19 shutdown, by 94.7%, 90.6%, and 86.8% for vehicle emissions, gasoline evaporation, and the mixed source of diesel evaporation and solvent use, respectively. Controlling the use of motor vehicles and related volatilization of diesel fuel and gasoline can be effective in controlling VOCs in the future.

Diffusion simulation, health risks, ozone and secondary organic aerosol formation potential of gaseous pollutants from rural comprehensive waste treatment plant

Comprehensive waste treatment plants (CWTPs) are significant sources of gaseous pollutants such as odors, volatile organic compounds (VOCs) and nitrogen oxides (NOx), polluting the environment and endangering human health. This study conducted on-site investigations on gaseous pollutants emissions from different areas of a CWTP. A total of 10 pollutants were identified of which ammonia (11.32 mg/m³ in average) was the main odorous substance, and benzene (19.51 mg/m³ in average) and toluene (42.07 mg/m³ in average) were the main VOCs. The feeding workshop (FW) was considered the main source of gaseous pollutants. The Gaussian plume model demonstrated that the pollution became more serious after spreading in the southeast downwind direction. Occupational exposure risks of on-site workers were mainly attributed to hydrogen sulfide, ammonia, benzene, and toluene, as their hazard index (HI) and lifetime cancer risk (CR) exceeded the recommended occupational safety limits. The gaseous pollutants diffused from CWTP may still pose a potential health risk to residents within a range of up to 7.5 km. The emulation and quantification of ozone formation potential by methods of Propyl-Equiv and MIR demonstrated that the contribution rate of toluene presented in each stage of CWTP exceed 80 %. Toluene was also the largest contributor to secondary organic aerosol with the contribution rate reached 56.34-85.14 %, followed by benzene (14.72-38.52 %). This research provides a basis for the reduction and control of gaseous pollutants in the treatment and disposal of rural domestic waste.

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

Frequent ozone and fine particulate matter (PM_2.5) pollution have been occurring in the Guanzhong Plain in China. To effectively control the tropospheric ozone and PM_2.5 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 (L_OH) 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 L_OH 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.

Cancer risk assessment for exposure to hazardous volatile organic compounds in Calgary, Canada

Oil and natural gas (O&G) extraction operations emit hazardous volatile organic compounds (VOCs) in quantities that have adverse effects on human health. Our current understanding of the exposure risks associated with upstream O&G exploitations remains limited, and very few quantitative on-site remediation strategies have been proposed. To this end, we assessed the health risks associated with the emission of hazardous VOCs and presented a set of remediation goals for the city of Calgary, which is a major center of the Canadian oil industry. Results from probabilistic risk assessment (PRA) suggested that although VOCs had a negligible impact on chronic non-cancer-associated risk, inhalation-associated cancer risk remained a significant concern. Carbon tetrachloride, benzene, and 1,3-butadiene were the dominant VOCs, representing 88% of the integrated inhalation cancer risk (= 7.8 × 10^-5); background, solid fuel combustion, and O&G extraction were among the primary sources that posed the greatest threat to human health. Results of a Monte Carlo simulation revealed that the probability of developing cancer due to inhalation of hazardous VOCs was ∼13.1% on clean air days and 45.9% on days with significant levels of air pollution. Preliminary remediation goals (PRGs) included reductions of 24.2-65.1% and 11.4-50.9% targeting priority VOCs and their sources, respectively. Taken together, our findings suggest that stringent control of the sources of VOCs, particularly fossil fuel combustion, is an urgent priority. PRA coupled with PRGs provides informative risk assessments and suggests quantitative remediation strategies that can be applied toward improved management of hazardous pollutants.

Air quality characteristics in Wuhan (China) during the 2020 COVID-19 pandemic

Understanding the relationship between air quality, pollution emission control measures, and meteorological conditions is important for developing effective air quality improvement policies. In this study, we used pollution monitoring and meteorological data from January to May 2020 to analyze the air quality characteristics during the COVID-19 lockdown in Wuhan, which lasted from January 23 to April 8, 2020. Compared with the same period in 2019, the air quality in 2020 was significantly better. The total excellent and good air quality rates increased by 17.58%-90.08% in 2020; concentrations of NO₂, particulate matter with a diameter <10 μm (PM₁₀) and <2.5 μm (PM_2.5), and total volatile organic compounds (TVOCs) also decreased by 38.23%, 30.25%, 32.92%, and 39.80%, respectively. Moreover, the number of days with NO₂, PM₁₀, and PM_2.5 as the primary pollutants decreased by approximately 10%, 9%, and 15%, respectively. We compared the wind direction, wind speed, temperature, and relative humidity in January-April 2020, 2019, 2018, and 2017 and found no obvious correlation between meteorological factors and improved air quality during the 2020 lockdown. The implementation of strict lockdown measures, such as home quarantining, traffic restrictions, and non-essential enterprise shutdowns, was the dominant cause for the substantial air quality improvement during the 2020 COVID-19 lockdown in Wuhan.

Efficient combustion of chlorinated volatile organic compounds driven by natural sunlight

Catalytic combustion of chlorinated volatile organic compounds (CVOCs) driven by natural sunlight is the promising CVOCs elimination method, which has not been realized. In this work, we designed a new sunlight-driven catalytic system for CVOCs combustion based on a scalable CuMnCeO_x gel and a new photothermal conversion device. The CVOCs elimination rate of CuMnCeO_x gel was reached to 99% at 250 °C, 25 times higher than that of CuMnCeO_x in bulk form. Further, the new photothermal conversion device could heat the CuMnCeO_x gel to 300 °C under one standard solar irradiation and this joint showed a stable one standard sunlight-driven CVOCs combustion at the rate of 6.8 mmol g^-1 h^-1, which was more than 7.8 times higher than the state of the art of photocatalytic CVOCs decomposition. Moreover, the new sunlight-driven thermal catalytic system was able to stable full oxidize the CVOCs in the concentration from 0.1 to 1000 ppm. Therefore, the natural sunlight-driven thermal CVOCs combustion system with high activity and zero secondary pollution shows the potential for large-scale industrial applications.

Air pollution episodes during the COVID-19 outbreak in the Beijing-Tianjin-Hebei region of China: An insight into the transport pathways and source distribution

Although anthropogenic emissions decreased, polluted days still occurred in the Beijing-Tianjin-Hebei (BTH) region during the initial outbreak of the coronavirus disease (COVID-19). Analysis of the characteristics and source distribution of large-scale air pollution episodes during the COVID-19 outbreak (from 23 January to April 8, 2020) in the BTH region is helpful for exploring the efficacy of control measures and policy making. The results indicated that the BTH region suffered two large-scale air pollution episodes (23-28 January and 8-13 February), which were characterized by elevated PM_2.5, SO₂, NO₂, and CO concentrations, while the O₃ concentration decreased by 1.5%-33.9% (except in Shijiazhuang, where it increased by 16.6% during the second episode). These large-scale air pollution episodes were dominated by unfavorable meteorological conditions comprising a low wind speed and increased relative humidity. The transport pathways and source distribution were explored using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT), potential source contribution function (PSCF), and concentration weighted trajectory (CWT) models. The air pollution in the BTH region was mainly affected by local emission sources during the first episode, which contributed 51.6%-60.6% of the total trajectories in the BTH region with a PM_2.5 concentration ranging from 146.2 μg/m³ to 196.7 μg/m³. The short-distance air masses from the southern and southwestern areas of the BTH region were the main transport pathways of airflow arriving in the BTH region during the second episode. These contributed 51.9%-57.9% of the total trajectories and originated in Hebei, Henan, central Shanxi, and Shaanxi provinces, which were the areas contributing the most to the PM_2.5 level and exhibited the highest PSCF and CWT values. Therefore, on the basis of local emission reduction, enhancing regional environmental cooperation and implementing a united prevention and control of air pollution are effective mitigation measures for the BTH region.

Optimization of a volatile organic compound control strategy in an oil industry center in Canada by evaluating ozone and secondary organic aerosol formation potential

Volatile organic compounds (VOCs) play a vital role in the formation of photochemical smog and haze in large urban environments. Previous source apportionment studies have focused on the contribution of different sources to VOC concentration with a view to pinpointing the major culprits for effective emission mitigation. However, different VOC sources may have different ozone (O₃) and secondary organic aerosol (SOA) formation potentials. From a control perspective, it would be more rational to consider the role of individual VOC sources in secondary pollution; therefore, here, we propose a tiered source identification method that considers the formation potentials of O₃ and SOA, which we applied in Calgary, Alberta, a site under the influence of multiple competing VOC sources. The pollution characteristics, secondary pollutant formation potential, and geographical origin of VOC sources were investigated over a five-year period. Seven major sources were identified using the positive matrix factorization (PMF) model, among which vehicle exhausts and solid fuel combustion were the dominant VOC sources responsible for O₃ (60%) and SOA (63%) formation. Combustion of both liquid fuel (gasoline and diesel) and solid fuel (wood and coal) has exceeded the contribution of oil and gas production and become the top contributor to O₃ and aerosol pollution in Calgary. This finding is consistent with the significant reduction (32.2-99.8%) in oil and gas production in Calgary over the period of 2013-2017. The source apportionment results show that the primary VOC source has shifted from conventional oil and gas extraction to a mixture of vehicle exhausts and oil and gas extraction, indicating the effectiveness of emission control measures taken in the energy sectors. Moreover, regionally transported VOCs from combustion sources in southeastern British Columbia have greatly increased the VOC level and secondary pollutant formation in Calgary. To effectively alleviate secondary pollution problems, the performance of joint pollution control measures has been suggested by the governments of both Alberta and British Columbia. These findings reveal that the tiered source identification strategy combining the traditional receptor model with socioeconomic factors, emission inventory, and source region analysis is a robust and promising tool for the interpretation of source apportionment results and optimization of secondary pollution control.