Highest Ozone Formation Potential Research Articles

Non-exhaust gas and particle emissions of light-duty vehicles – Quantification under driving conditions in a sealed cabin

Non-exhaust emissions have emerged as a pivotal contributor to vehicle emissions, as regulatory efforts persist in curtailing exhaust emissions. This research focused on the running-loss evaporative volatile organic carbon (VOC) and non-exhaust particle (NEP) emission factors (EFs) of a light-duty vehicle in the sealed housing. VOC concentrations demonstrated an upward trend with elevated vehicle temperatures and extended driving durations. Normalized over driving distance, the hot-start WLTC test exhibited the highest VOC EFs, about 617 μg/km, and the highest ozone formation potential (OFP) value of 1.75 mgO3/km. Toluene and xylene were the main pollutants contributing to the OFP value across all tests. Evaluating EFs of various evaporative emission forms in mg/h, the BTEXs EF of running-loss tests was recorded at 10.2 mg/h, comparable to diurnal-breathing tests but significantly lower than hot-soak tests. Additionally, particles within the 10–23 nm range consistently dominated total NEP above 10 nm. Particle number (PN) concentrations of 10–23 nm particles exhibited a sharp increase under intense driving conditions and a slow decrease under other driving conditions. The results suggested a continuous consumption of smaller particles, leading to their coalescence into larger particles. The EF of NEP above 23 nm in the US06_4 test was 1.72 × 1012 #/km, surpassing the current exhaust particle emission limit. Consequently, NEP has been a major vehicle particle source of greater concern than exhaust particles.

Composition Characteristics of VOCs in the Atmosphere of the Beibei Urban District of Chongqing: Insights from Long-Term Monitoring

Reducing anthropogenic volatile organic compounds (VOCs) is the most effective way to mitigate O3 pollution, which has increased over the past decades in China. From 2012 to 2017, special stainless-steel cylinders were used to collect ambient air samples from the urban area of Beibei district, Chongqing. Three-step pre-concentration gas chromatography–mass spectrometry was used to detect the collected air samples. The composition, concentration, photochemical reactivity, and sources of VOCs in Beibei were analyzed. During the observation period, the annual average VOC concentration was 31.3 ppbv, which was at an intermediate range compared to other cities in China. Alkanes (36.8%) and aromatics (35.6%) were the most abundant VOC groups, followed by halo-hydrocarbons (14.4%) and alkenes (12.6%). The overall trend of seasonal distribution of VOC concentration was high in summer and autumn, and low in winter and spring, with a statistically significant difference between summer and winter concentrations. The ozone formation potential (OFP) showed that alkenes were the most active species, followed by aromatics and alkanes, and summer was the season with the highest OFP (131.6 ppbv). Three major emission sources were identified through principal component analysis (PCA), i.e., vehicle exhaust emissions (66.2%), fuel oil evaporation (24.8%), and industrial sources (9.0%). To ameliorate the air quality within the study area, concerted efforts should be directed towards curtailing traffic emissions and mitigating the release of alkenes, particularly emphasizing more stringent interventions during the summer season.

The development and application of a novel helicopter-based airborne platform for near-surface monitoring and sampling of atmospheric pollutants

This study presents a novel approach utilising helicopters as platforms for real-time monitoring of air pollutants and routine canister sampling to enhance our understanding of air pollution in the Greater Bay Area (GBA). By employing this method, local spatial and vertical distribution of various air pollutants (including CO, NO, NO2, O3, PM2.5 and VOCs) in Hong Kong could be obtained within hours for fast snapshots of air pollution.The investigation involved hovering ascent and descent operations above Tap Mun Island, revealing no indication of self-contamination from engine exhaust during the hovering process. The analysis of air pollutant spatial distribution in and around Hong Kong through multiple trips showed higher concentrations of O3 and PM2.5 in the northern region on days with episodic pollution, while urban areas exhibited elevated levels of NO2 and CO concentration. In contrast, Tap Mun Island as the background area demonstrated relatively low pollutant concentrations. The vertical distribution of concentrations of VOC species with high ozone formation potential revealed minor variations at sampling altitudes of 500 ft and 1000 ft over the waters around Hong Kong. The novel monitoring protocol using helicopters as platforms proves to be an effective approach for pollution episode investigations, offering valuable insights in the formation mechanisms and transport pathways of O3. The findings of the heterogenous spatial distribution of O3 and its precursors underscore the significance of ongoing monitoring efforts and policy development to combat air pollution in the dynamic GBA and similar regions worldwide.

Estimation of air pollution removal capacity by urban vegetation from very high-resolution satellite images in Lithuania

In cities, particulate matter (PM10), carbon dioxide (CO2), nitrogen dioxide (NO2), and ground-level ozone (O3) are some of the most significant air pollutants that have negative effects on human health, vegetation, and biodiversity. The city of Kaunas (Lithuania) represents the geographical region of north-eastern Europe and the Humid continental climate zone. By using a satellite-based approach with Worldview-3 (WV-3) satellite imagery at the very-high spatial and spectral resolution, we have detected and classified the most common tree species (a total of 284,305 trees) in Kaunas with an overall accuracy of about 88% e.g., Acer spp. (10%), Aesculus hippocastanum (11%), Pinus spp. (9%), Quercus spp. (24%), and Tilia spp. (5%) in both private (e.g., residential gardens) and public areas over a large study area (56 km2). The green cover of Kaunas city represents 64% of the total study area. In 2022, the 284,305 trees detected in Kaunas city center and surrounding areas have removed approximately 2084 tons of NO2, 217 tons of PM10, and 22,938 tons of CO2 while dominant trees formed more O3 than they absorbed (1204 tons released) mainly due to the high ozone formation potential of Quercus spp.

Ozone Pollution Characteristics and Sensitivity During the Ozone Pollution Days in Summer 2021 of Xinxiang City

This study was based on the observation of volatile organic compounds (VOCs), conventional gaseous air pollutants, and meteorological parameters observed at the Xinxiang Municipal Party School site from June to August 2021. The ozone (O3) characteristics and sensitivity of O3 pollution days and the control strategy of its precursors were studied using an observation-based model (OBM). It was found that the meteorological conditions were characterized by high temperature, low humidity, and low pressure in O3-pollution days. The concentrations of O3 and its precursors all increased in the O3 pollution days. Oxygenated volatile organic compounds (OVOCs) and alkanes were the highest-concentration components of VOCs on O3 pollution days in Xinxiang, and OVOCs had the highest ozone formation potential (OFP) and hydroxyl (·OH) reactivity. According to the relative incremental reactivity (RIR) analysis, during the O3 pollution days in Xinxiang, O3sensitivity was in the VOCs-limited regime in June and in the transitional regime in July and August. Ozone production was more sensitive to alkenes and OVOCs. The RIR values of the precursors in June changed throughout the day, but O3 sensitivity remained the VOCs-limited regime. In July and August, O3 sensitivity was the VOCs-limited regime in the morning, transitional regime at noon, transitional and NOx-limited regime, respectively in the afternoon. By simulating different precursor-reduction scenarios, the results showed that the reduction of VOCs was always beneficial to the control of O3, whereas the reduction of NOx had little effect on the control of O3 and a risk of increasing O3.

Real-time measurements of non-methane volatile organic compounds in the central Indo-Gangetic basin, Lucknow, India: source characterisation and their role in O3 and secondary organic aerosol formation

Abstract. Lucknow is the capital of India's largest state, Uttar Pradesh, one of South Asia's most polluted urban cities. Tropospheric photochemistry relies on non-methane volatile organic compounds (NMVOCs), which are ozone and secondary organic aerosol precursors. Using the proton-transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at an urban background site in Lucknow, the chemical characterisation of NMVOCs was performed in real time from December 2020 to May 2021. About ∼ 173 NMVOCs from m/z 31.018 to 197.216 were measured during the study period, including aromatics, non-aromatics, oxygenates, and nitrogen-containing compounds. The campaign daily mean concentrations of the NMVOCs were 125.5 ± 37.5 ppbv. The NMVOC daily average concentrations were about ∼ 30 % higher during the winter months (December–February) than in summer (March–May). The oxygenated volatile organic compounds and aromatics were the dominant VOC families, accounting for ∼ 57 %–80 % of the total NMVOC concentrations. Acetaldehyde, acetone, and acetic acid were the major NMVOC species, 5–15 times higher than the other species. An advanced multi-linear engine (ME-2) model was used to perform the NMVOC source apportionment using positive matrix factorisation (PMF). It resolves the five main sources contributing to these organic compounds in the atmosphere. They include traffic (23.5 %), two solid fuel combustion factors, SFC 1 (28.1 %) and SFC 2 (13.2 %), secondary volatile organic compounds (SVOCs) (18.6 %), and volatile chemical products (VCPs) (16.6 %). Aged and fresh emissions from solid fuel combustion (SFCs 1 and 2) were the dominant contributors to the total NMVOCs, and compounds related to these factors had a high secondary organic aerosol (SOA) formation potential. Interestingly, the traffic factor was the second-highest contributor to the total NMVOCs, and compounds related to this factor had a high ozone formation potential. Significant differences in the composition of the two solid fuel combustions indicate the influence of local emissions and transport of regional pollution to the city. The high temperature during summer leads to more volatilisation of oxygenated VOCs, related to the VCP factor. The study is the first attempt to highlight the sources of NMVOCs and their contribution to secondary pollutant (SOA and O3) formation in the city of Lucknow during winter and summer. The insights from the study would help various stakeholders to manage primary and secondary pollutants within the city.

Analysis of VOC emissions and O3 control strategies in the Fenhe Plain cities, China

Long-term continuous hourly measurements of ambient volatile organic compounds (VOCs) are scarce at the regional scale. In this study, a one-year hourly measurement campaign of VOCs was performed in Lvliang, Linfen, and Yuncheng in the heavily polluted Fenhe Plain region in China. The VOC average (±standard deviation, std) concentrations in Lvliang, Linfen, and Yuncheng were 44.4 ± 24.9, 45.7 ± 24.9, and 37.5 ± 25.0 ppbv, respectively. Compared to published data from the past two decades in China, the observed VOCs were at high concentration levels. VOCs in the Fenhe Plain cities were significantly impacted by industrial sources according to calculated emission ratios but were less affected by liquefied petroleum gas and natural gas (LPG/NG) and traffic emissions than those in megacities abroad. The emission inventories and observation data were combined for verification and identification of the key VOC species and sources controlling ozone (O3). Industrial emissions were the largest source of VOCs, accounting for 65%–79% of the total VOC emissions, while the coking industry accounted for 45.2%–66.0%. The emission inventories significantly underestimated oxygenated VOC (OVOC) emissions through the verification of VOC emission ratios. O3 control scenarios were analyzed by changing VOC/NOX reduction ratios through a photochemical box model. O3 control strategies were formulated considering local pollution control plans, emission inventories, and O3 formation regimes. The O3 reduction of reactivity-control measures was comparable with emission-control measures, ranging from 16% to 41%, which was contrary to the general perception that ozone formation potential (OFP)-based measures were more efficient for O3 reduction. Sources with high VOC emissions are accompanied by high OFP on the Fenhe Plain, indicating that the control of high-emission sources can effectively mitigate O3 pollution on this region.

Distribution characteristics, source apportionment, and chemical reactivity of volatile organic compounds in two adjacent areas in Shanxi, North China

To determine the pollution characteristics, source apportionment, and chemical reactivity of volatile organic compounds (VOCs) in two adjacent areas, VOC samples were collected using 3.2-L stainless steel canisters between 2017 and 2018 in Taiyuan and Yuci areas. The concentrations of 48 VOCs were determined using a gas chromatography-mass selective detector/flame ionization detector. The average concentrations of the 48 VOCs (total VOCs [TVOCs]) in the Taiyuan and Yuci areas were 30.09 and 24.08 ppbv, respectively; the highest concentrations were recorded for ethane, which accounted for 21.40% and 25.49% of the TVOCs detected in the Taiyuan and Yuci areas, respectively. Alkanes accounted for the highest proportion of the TVOCs, followed by alkenes, alkynes, and aromatics. Through positive matrix factorization, six source categories were identified in Taiyuan and Yuci, namely gasoline evaporation (24.38%), petrochemical industrial sources (15.46%), biogenic emissions and LPG usage (8.75%), combustion sources (28.33%), solvent use (12.95%), and vehicle exhaust (10.13%). The backward trajectory and weighted potential source contribution function analysis results indicated that Taiyuan and Yuci were potential source areas for each other in September, and that Taiyuan was the potential source area of Yuci in November and December. Among the TVOCs detected in the Taiyuan and Yuci areas, alkenes contributed the most to ozone formation potential (OFP), followed by aromatics and alkanes; alkynes contributed the least to OFP. Aromatics contributed the most to secondary organic aerosol formation potential (SOAFP), accounting for 92.80% and 92.37% of the SOAFP in the Taiyuan and Yuci areas, respectively. These results indicate that the TVOCs in the Taiyuan and Yuci areas must be controlled, particularly aromatics with high SOAFP and alkenes with high OFP. Our results help to clarify the migration, transformation, and sources of ambient VOCs in adjacent areas; they also provide fundamental data on pollution control and the prevention of regional organic air pollution.

Carbonyls from commercial, canteen and residential cooking activities as crucial components of VOC emissions in China

Cooking in China supply the large population with nutrition and, as a commercial activity, it also promotes the economic growth of Chinese society. The specific cooking styles in China can produce complex volatile organic compound (VOC) emissions. The resulting adverse effects on the environment and human health of carbonyls from cooking should not be ignored. We quantitatively evaluated the contribution of carbonyls to common VOCs (carbonyl/VOC ratio) from cooking activities in China through the establishment and comparison of the source profiles, emission factors (EFs), emission amount and ozone formation potential (OFP). It was found that carbonyls are crucial components of VOCs from commercial, canteen and residential cooking activities (COC, CAC and REC, respectively). The carbonyl/VOC ratio from cooking activities in China had EFs, emissions, and a total OFP of 22–65 %, 23–34 %, and 49–104 %, respectively. The high OFP was due to the high OFP emissions intensity (OFPEI) and maximum incremental reactivity (MIR) values of carbonyls. This indicates that to alleviate O3 pollution, OFP-based control measures that target carbonyls might be more efficient than measures that target common VOCs. Priority should be given to emission controlling COC emissions, specifically those from medium- and large-scale catering. Formaldehyde, acetaldehyde, and hexanal were the key carbonyl species that form O3 in the environment. Our findings imply that cooking-emitted carbonyls should not be overlooked in investigations of O3 formation and that these compounds should be subject to strict regulations.

Volatile organic compounds emission in the rubber products manufacturing processes

Volatile organic compounds (VOCs) emission from rubber products manufacture processes, mixing, shaping and vulcanization were investigated in four rubber products factories in China. The source emission air was passively sampled by pre-vacuumized stainless steel canister and analyzed by gas chromatography-mass spectrometry-flame ionization detection (GC/MS-FID). The species profile of 107 VOCs in the emission processes were obtained. We calculated the photochemical ozone formation potential (OFP) and carcinogenic risk (CR) of the VOCs for each manufacture process. The results showed that mixing process mainly released dichloromethane (14.53%), carbon disulfide (CS2) (6.88%), styrene (5.72%), 4-methyl-2-pentanone (5.22%) and naphthalene (3.69%) for solvents used and raw rubber degradation in the process. The C6–C8 alkanes, especially heptane and isomers of heptane (44.71%), were dominated in shaping process. The major species released from vulcanization process were carbon disulfide (29.72%), naphthalene (8.17%), acetone (7.73%) and dichloromethane (4.26%). VOCs emitted from vulcanization process had the highest OFP, which contributed by naphthalene, m/p-xylene, o-xylene and carbon disulfide. VOCs emission from mixing process had the highest CR, and 1,2-dibromoethane, 1,2-dichlorethane and 1,3-butadiene were the main contributors to CR. We also estimated the total VOCs emissions into the atmosphere from tires manufacturing in China, which were 7.58 × 105 t in 2018 and contributed about 9% of total industry processes VOCs emissions.

Mass Concentration, Source and Health Risk Assessment of Volatile Organic Compounds in Nine Cities of Northeast China.

From April 2008 to July 2009, ambient measurements of 58 volatile organic compounds (VOCs), including alkanes, alkenes, and aromatics, were conducted in nine industrial cities (Shenyang, Fushun, Changchun, Jilin, Harbin, Daqing, Huludao, Anshan and Tianjin) of the Northeast Region, China (NRC). Daqing had the highest concentration of VOCs (519.68 ± 309.88 μg/m3), followed by Changchun (345.01 ± 170.52 μg/m3), Harbin (231.14 ± 46.69 μg/m3), Jilin (221.63 ± 34.32 μg/m3), Huludao (195.92 ± 103.26 μg/m3), Fushun (135.43 ± 46.01 μg/m3), Anshan (109.68 ± 23.27 μg/m3), Tianjin (104.31 ± 46.04 μg/m3), Shenyang (75.2 ± 40.09 μg/m3). Alkanes constituted the largest percentage (>40%) in concentrations of the quantified VOCs in NRC, and the exception was Tianjin dominated by aromatics (about 52.34%). Although alkanes were the most abundant VOCs at the cities, the most important VOCs contributing to ozone formation potential (OFP) were alkenes and aromatics. Changchun had the highest OFP (537.3 μg/m3), Tianjin had the lowest OFP (111.7 μg/m3). The main active species contributing to OFP in the nine cities were C2~C6 alkanes, C7~C8 aromatic hydrocarbons, individual cities (Daqing) contained n-hexane, propane and other alkane species. Correlation between individual hydrocarbons, B/T ratio and principal component analysis model (PCA) were deployed to explore the source contributions. The results showed that the source of vehicle exhausts was one of the primary sources of VOCs in all nine cities. Additionally, individual cities, such as Daqing, petrochemical industry was founded to be an important source of VOCs. The results gained from this study provided a large of useful information for better understanding the characteristics and sources of ambient VOCs incities of NRC. The non-carcinogenic risk values of the nine cities were within the safe range recognized by the U.S. Environmental Protection Agency (HQ < 1), and the lifetime carcinogenic risk values of benzene were 3.82 × 10−5~1.28 × 10−4, which were higher than the safety range specified by the US Environmental Protection Agency (R < 1.00 × 10−6). The results of risk values indicated that there was a risk of cancer in these cities.

Assessing the impact of episodic flare emissions on ozone formation in the Houston-Galveston-Brazoria area of Texas

Ozone formation due to episodic industrial emissions was modeled for the Houston-Galveston-Brazoria (HGB) region in Texas. A total of more than 1000 synthetic emission scenarios were modeled, accounting for different sources, emission magnitudes, emission compositions, duration and timing of the emission events, meteorology at the time of the emissions, and location of the emission source. Episodic emissions consistent with the characteristics of flaring resulted in the greatest amount of ozone formation. An index, based on incremental reactivity, for characterizing the ozone formation potential of flaring emissions was developed using the synthetic scenarios and was applied to the ~4500 flares that report emissions in the state of Texas. The flares with the highest ranking index in the HGB were identified and additional modeling was performed on the ozone formation potential of these flares. If these flares are modeled with their annual average emission rates, the maximum increase in maximum daily 8-h average ozone (MDA8) formation associated with flaring emissions is <1 ppb. If, however, it is assumed that emissions from flaring are episodic, rather than continuous, and temporal patterns consistent with previous data collection on flare emission variability in the HGB are applied, MDA8 enhancements associated with flaring emissions are >10 ppb for multiple scenarios. This analysis suggests that, for flares emissions that have high ozone formation potential, the temporal patterns of flare emissions should be accounted for in developing ozone mitigation plans.

Assessment of carbonyl and PAH emissions in an automotive diesel engine fueled with butanol and renewable diesel fuel blends

A comparative experimental study assessing the unregulated emissions of carbonyl compounds, polycyclic aromatic hydrocarbons (PAHs) in solid particle and gaseous phase and the contribution to ozone formation potential, was carried out for an automotive diesel engine operating under two representative urban driving conditions with butanol and renewable diesel. Both renewable fuels were blended with ultra-low sulfur diesel (ULSD) fuel to replace 13% of aromatic compounds in the reference fuel (Butanol at 13%v/v –Bu13- and Renewable diesel –RD- at 13% v/v –RD13-) and in the case of RD, an additional concentration of 20% v/v was tested (RD20). The particle and gas phase sampling procedure for PAHs characterization was carried out without any air dilution. A total of 18 PAHs (16 requested by the US EPA + benzo[e]pyrene and dibenzo[a,l]pyrene which is acknowledged for its significant carcinogenic potential) were determined. Independently of the engine operating mode, Bu13 exhibited the highest carbonyl compound emissions among all tested fuels (M1:18.8 mg/kWh of formaldehyde, M2: 18.2 mg/kWh of acetaldehyde) and the highest ozone formation potential (307 mg O3/kWh). Both RD blends exhibited similar carbonyl emissions (RD13 = 7.0 mg/kWh, RD20 = 8.3 mg/kWh) compared to ULSD (10.2 mg/kWh). Independently of the fuel and engine operating mode, most of the PAHs were present in the gas-phase, with predominance of those between 3 and 4 rings (up to 70%). No trend was observed on PAHs emissions with the addition of butanol or RD to the ULSD. It was observed that some local combustion conditions might increase the emissions of PAHs for both renewable fuels, mainly those of lower molecular weight.

Emission characteristics and reactivity of volatile organic compounds from typical high-energy-consuming industries in North China

To effectively reduce the compound pollution of fine particulate matter (PM2.5) and ozone (O3), volatile organic compound (VOC) emission sources are being extensively studied. Studies on VOC emission characteristics have mainly focused on solvent-using and technological sources, while research on the combustion processes of high-energy-consuming industries remains limited. Here, we investigate the emission characteristics of 102 VOC species emitted from eight sources (sintering, pelletizing, steel smelting, a coke oven chimney, the topside of a coke oven, thermal power, and two types of cement kilns) used in four types of high-energy-consuming industries. Our results show significant differences among these sources. The average VOC mass concentrations varied from 0.14 to 7.08 mg/m3. Alkanes had the highest percentage contribution to VOCs from sintering (45.9%) and thermal power (44.6%), while aromatics had the highest percentage contribution from steel smelting (47.8%) and the topside of the coke oven (52.9%). Alkenes were abundant in the coke oven chimney (49.1%), and oxygenated VOCs accounted for 65.3% of the total VOCs from pelletizing. We also observed notable differences between the two types of cement kilns. In general, ethane, ethene, benzene, propane, acetaldehyde, and chloromethane were the dominant VOC species in all sources. The differences between the sources were due to factors such as the applied raw materials, calcination temperature, and end-of-pipe treatment. By reviewing studies from the past 20 years, we found that differences in the number of VOC species and the implementation of ultra-low emissions affect VOC emission characteristics. The coke oven chimney and cement kiln chimney-1 had the highest ozone formation potential and secondary organic aerosol potential, respectively. The VOC emissions from coking, iron and steel, thermal power, and cement industries were 1162.1, 289.9, 311.0, and 470.2 Gg, respectively. Our results highlight the need for more effective control measures to minimize VOC emissions from high-energy-consuming industries.

Segment-based Volatile Organic Compound Emission Characteristics from Different Types of Coking Plants in China

ABSTRACT The source profiles, emission factors, and chemical reactivity of volatile organic compounds (VOCs) generated by two typical coking plants, one employing a non-recovery process and the other, a mechanical process, in Shanxi Province, a major coking hub in China, were determined for different segments of coke production during normal operations. The primary components in the stack flue gas were ethylene, 1-butene, benzene, acetylene, and 2,2-dimethylbutane for the non-recovery plant and styrene, benzene, and ethylene for the mechanical plant. The fugitive emissions were also monitored at the mechanical plant, and the most abundant species leaking from the oven were benzene, toluene, ethane, m-xylene, and ethylene, whereas those leaking from byproducts were benzene, propane, ethane, ethylene, n-pentane, n-butane, isobutene, 1-butene, toluene, and propylene. The stack flue gas at the non-recovery and mechanical coking plants exhibited VOC emission factors of 96 g Mg–1-coke and 0.4 g Mg–1-coke, respectively; thus, VOCs released by the former merit greater concern. Since the highest ozone formation potential (OFP) was observed for the stack flue gas at the non-recovery plant (80.26 mg m–3), followed by fugitive oven emissions at the mechanical plant (7.22 mg m–3), controlling these VOCs will significantly reduce their conversion into ozone. Overall, replacing non-recovery coking plants with mechanical coking plants will decrease VOC emissions and improve the ambient air quality in China.

Spatial trends, health risk assessment and ozone formation potential linked to BTEX

The current study set out to examine BTEX species comprehensively in order to assess their spatiotemporal distribution, carcinogenic and non-carcinogenic health risk assessment, and ozone formation potential (OFP), source identification, and sensitivity and uncertainty analysis in the capital city of Qom, Iran. Data were gathered from 16 sampling stations in the winter and spring seasons. The average BTEX levels of both sampling periods were 22.49 for toluene, 15.2 for benzene, 12.38 for xylene, and 5.69 for ethylbenzene. Higher concentrations were observed in the city center and in the proximity of a power plant. Pollution source identification was carried out using principal component analysis (PCA). PCA and the T/B ratio both indicated that industrial sources are the primary pollution source in the spring, while, in the winter, BTEX levels were driven by traffic sources. The highest OFP was determined to be from xylene, followed by toluene, ethylbenzene, and benzene. Among the BTEX species, benzene had the highest cancer and non-cancer risk above and under the United States Environmental Protection Agency’s standard, respectively. Pollutant concentration was the most sensitive parameter followed by body weight, inhalation rate, and exposure frequency.

Unveiling tropospheric ozone by the traditional atmospheric model and machine learning, and their comparison:A case study in hangzhou, China

Tropospheric ozone in the surface air has become the primary atmospheric pollutant in Hangzhou, China, in recent years. Previous analysis is not enough to decode it for better regulation. Therefore, we use the traditional atmospheric model, Weather Research and Forecasting coupled with Community Multi-scale Air Quality (WRF-CMAQ), and machine learning models, Extreme Learning Machine (ELM), Multi-layer Perceptron (MLP), Random Forest (RF) and Recurrent Neural Network (RNN) to analyze and predict the ozone in the surface air in Hangzhou, China, using meteorology and air pollutants as input. We firstly quantitatively demonstrate that the dew-point deficit, instead of temperature and relative humidity, is the predominant meteorological factor in shaping tropospheric ozone. Urban heat island, daily direct solar radiation time, wind speed and wind direction play trivial role in impacting tropospheric ozone. NO2 is the primary influential factors both for hourly ozone and daily O3-8 h due to the titration effect. The most environmental-friendly way to mitigate the ozone pollution is to lower the volatile organic compounds (VOCs) with the highest ozone formation potentials. We deduce that the tropospheric ozone formation process tends to be not only non-linear but also non-smooth. Compared with the traditional atmospheric models, machine learning, whose characteristics are rapid convergence, short calculating time, adaptation of forecasting episodes, small program memory, higher accuracy and less cost, is able to predict tropospheric ozone more accurately.

Speciated VOCs Emission Inventory and Ozone Formation Potential in Sichuan Province

Based on the measured data in the literature, VOCs (volatile organic compounds) source profiles were revised and reconstructed without OVOCs (oxygenated volatile organic compounds) species to obtain the normalized VOCs source profiles. Using the 2015 Sichuan emission inventory, source profiles based on the 1 km×1 km gridded speciated VOCs emission inventory were developed, and the ozone formation potentials of the species were estimated to assess the environmental impact on ozone formation. The established VOCs source profile database consists of 45 source profiles and 519 species. Since the source profiles were established based on the revision and reconstruction of pollution sources, such as biomass burning and transportation, that are rich in OVOCs, the source profile database is better applicable to establishing the speciated VOCs emission inventory and source apportionment. The speciated VOCs emission inventory showed that the total anthropogenic emission of VOCs in Sichuan Province was 773.8 kt, of which the emissions of alkanes, olefins, alkynes, aromatics, OVOCs, halohydrocarbons, and other VOCs accounted for 21.6%, 10.0%, 1.7%, 28.0%, 26.2%, 4.2%, and 8.3% of the total respectively. The total OFP (Ozone formation potential) was 2584.9 kt, of which the OFPs of the VOCs groups mentioned above accounted for 6.9%, 26.1%, 0.5%, 42.3%, 23.2%, 0.4%, and 0.5% respectively. The main VOCs species emitted in all cities of Sichuan Province were aromatics, OVOCs, and alkanes; however, there were some significant regional differences:transportation in Chengdu, Ya'an, Aba, Ganzi, and Liangshan made a greater contribution to VOCs emissions, with alkane emissions accounting for a higher proportion in the total VOCs emission. As a heavy industrial city, Panzhihua suffered most from emissions from industrial processes, which contain a relatively high proportion of alkanes. Solvent use in Deyang, Meishan, Suining, and Ziyang made a great contribution to the VOCs emissions, and the OVOCs emission was relatively high. Emissions of VOCs and species with relatively high OFPs in Sichuan Province were mainly distributed in the Sichuan Basin, which has a dense population and highly developed industry, as well as some areas in Liangshan and Panzhihua. The main source of m-xylene and toluene was solvent use; therefore, m-xylene and toluene were relatively concentrated in developed urban areas. In addition, biomass burning contributed greatly to the emissions of ethene and formaldehyde; therefore, ethene and formaldehyde were mainly distributed in the cultivated areas of agriculturally advanced Eastern Sichuan and Southern Sichuan.

Source Profiles and Chemical Reactivity of Volatile Organic Compounds from Surface Coating of Aluminum Products in Foshan, China

Volatile organic compounds (VOCs) samples were collected and analyzed for the surface coating processes of aluminum products in Foshan. The concentration levels of VOCs from solvent-based coating (63.90-149.67 mg·m-3) are much higher than that from water-based, electrophoretic, and powder coating (2.99-21.93 mg·m-3). With respect to the VOC composition, aromatics are the main VOC group of solvent-based coating emission, ranging from 52.32%-71.55%. Typical species include toluene, ethylbenzene, xylene, and ethyl acetate. The VOCs emitted from water-based coating are mainly oxygenated VOCs, such as ethyl acetate (48.59%) and tetrahydrofuran (8.43%), while the percentage of aromatics (11.32%) is lower than that of solvent-based coating. Isopropanol is the most abundant species of electrophoretic coating emissions, accounting for up to 81.19% of the VOCs. The major VOC compounds of powder coating processes are acetone (30.25%), propane (15.48%), ethylene (12.15%), ethane (9.35%), and n-butane (5.16%). The calculation of the ozone formation potential (OFP) shows that the solvent-based coating has the highest OFP (3.89 g·g-1), followed by powder coating (2.53 g·g-1), while water-based and electrophoretic coating have lower OFPs (1.31 and 0.85 g·g-1, respectively). The most important contributor to OFP of solvent-based coating are aromatics, especially C7-C10 aromatics. The major contributors of water-based coating are ethyl acetate, m/p-xylenes, and toluene, with contributions of 23.24%, 21.76%, and 17.07%, respectively. The key reactive components of powder coating are ethylene, propene, and 1-butene; the sum of alkenes accounts for 71.11% of the OFP. With respect to the contribution of VOCs emitted from electrophoretic coating to the OFP, the percentage of isopropanol (65.08%) is significantly larger than that of other species (<6%).

Vertical stratification of volatile organic compounds and their photochemical product formation potential in an industrial urban area

High emissions of volatile organic compounds (VOCs) from the petrochemical industry and vehicle exhaust may contribute to high ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP). In this study, the vertical profiles of VOCs were created for the southern Taiwan industrial city of Kaohsiung. Vertical air samples were collected up to 1000 m using an unmanned aerial vehicle (UAV). In Renwu District, VOC distribution was affected by the inversion layer up to 200 m height. Total VOCs (36–327 ppbv), OFP (66–831 ppbv) and SOAFP (0.12–5.55 ppbv) stratified by height were the highest values at 300 m. The VOCs originated from both local and long-distance transport sources. These findings can be integrated into Kaohsiung's future air quality improvement plans and serve as a reference for other industrialized areas worldwide.