Comparison of the ozone formation mechanisms and VOCs apportionment in different ozone pollution episodes in urban Beijing in 2019 and 2020: Insights for ozone pollution control strategies

Field experiment and simulation for catalytic decomposition of ozone by exterior wall coatings with self-purifying materials

In recent years, ozone has become one of the key pollutants affecting the urban air quality. Direct catalytic decomposition of ozone emerges as an effective method for ozone removal. Field experiments were conducted to evaluate the effectiveness of exterior wall coatings with ozone decomposition catalysts for ozone removal in practical applications. ANSYS 2020R1 software was first used for simulation and analysis of ozone concentration and flow fields to investigate the decomposition boundary of these wall coatings. The results show that the exterior wall coatings with manganese-based catalysts can effectively reduce the ozone concentration near the wall coating. The ozone decomposition efficiency is negatively correlated with the distance from the coating and the decomposition boundary range is around 18 m. The decomposition boundary will increase with the increase of temperature, and decrease with the increase of the wind speed and the relative humidity. These results underscore the viability of using exterior wall coatings with catalysts for controlling ozone pollution in atmospheric environments. This approach presents a promising avenue for addressing ozone pollution through self-purifying materials on building external wall.

Insights into the source characterization, risk assessment and ozone formation sensitivity of ambient VOCs at an urban site in the Fenwei Plain, China

The ground-level O3 concentration has shown a deteriorating trend in the Fenwei Plain of China, which poses a greater challenge for formulating control strategies of O3 precursor (VOCs). To accurately control VOCs sources and effectively reduce O3 concentration from a seasonal perspective, online monitoring of 114 VOCs was conducted at Yuncheng Middle School Station from January 1, 2021 to December 31, 2021. The VOCs concentration showed a seasonal variation with the highest in winter and the lowest in summer. During the four seasons, alkanes (34.5-41.7 %) and OVOCs (36.6-46.9 %) were the most abundant species. The emission ratios of specific VOCs species indicated that vehicular exhaust, industrial source, and combustion were the major VOCs sources. The Positive Matrix Factorization (PMF) model identified that industrial source and secondary conversion were the main contributors in summer, while combustion and LPG/NG contributed more significantly in winter. The 2021-based VOCs emission inventory showed that the total VOCs emissions in the central urban area of Yuncheng was 8128.8 t, in which industrial process was the largest contributor. Alkanes, aromatics, and OVOCs accounted for 31.0 %, 25.8 %, and 25.7 % of the annual VOCs emission, respectively. In addition, the calculated relative incremental reactivity (RIR) values of O3 precursors demonstrated that alkenes and aromatics were the most sensitive groups to O3 formation during the four seasons. The ambient VOCs posed the non-carcinogenic risk across all seasons, which can be attributed to acrolein and three main sources (industrial source, secondary conversion, and combustion). However, ambient VOCs exposed to definite carcinogenic risks due to the appearance of 1,2-dichloroethane, 1,2-dichloropropane, and benzene, and the main risks arose from industrial source, vehicular exhaust, and solvent usage. These findings emphasize the necessity of undertaking scientific and systematic measures for priority species and control sources of VOCs emission.

A modeling approach to dynamically estimating local photochemistry process and its contribution to surface O3 pollution

Ozone (O3) pollution in city level is a complex issue that arises not only from local photochemistry process but also involves mid- or long-range O3 transport. In this study, we developed a modeling approach to dynamically quantifying local photochemical process (indicated as Chem_O3) and estimating its role in surface O3 pollution in city level. The work was conducted on North BTH of China for summer of 2022 and mainly focused on the urban areas, in which surface O3 usually as the most dominant air pollutants to harm population health. The method was constructed via establishing the hourly response of locally-formed O3 to locally-released NOx (RO3-NO2, ppb·ppb-1) based on ISAM simulations and then combining RO3-NO2 and ambient NO2 levels to quantify time-varying Chem_O3. The results showed that the monthly mean of Chem_O3 and its proportion to actual O3 (Chem%) was 17.9-26.0 ppb and 46.7%-62.6% in major urban areas of North BTH, following the order of mega-city > industrialized city > normal city > forest city. Moreover, daily Chem% presented the different trend with daily O3 in these study areas, slight-positive for mega-cities, but moderate or strong-negative for most other cities. Specially, our developed method could additionally disentangling O3 physical transport among the studied cities, and we found the inflow of O3 was much lower than the outflow of O3 for two mega-cities, while it was opposite in other cities. We think this method could clearly point out the role of local photochemistry control in O3 reduction, which could help city environment managers to develop scientific and effective policy strategies to cope with ozone-related problems.

Implications of photochemical losses of VOCs: An integrated approach for source apportionment, ozone formation potential and health risk assessment

The increasing ozone (O3) concentration has received significant attention recently, yet the health risks posed by volatile organic compounds (VOCs) cannot be ignored. Accurately identifying the primary sources of VOCs contributing to health risks and O3 formation has been challenging due to their high reactivity with oxidants in ambient air. This study conducted field measurements of VOCs seasonally and diurnally in an urban area of central Taiwan, aiming to elucidate the effects of photochemical loss of VOCs on the source apportionment of O3, as well as health risks of VOCs under different levels of O3. The results revealed that O3 formation was sensitive to VOCs, which was diagnosed using the regional threshold of the observed VOCs/NOX ratio and was further supported by a significant positive correlation between O3 concentrations and initial O3 formation potential. The dispersion normalized positive matrix factorization model, applied to initial mixing ratios of VOCs, identified six VOC sources, with the synthetic rubber industry and solvent usage being prominent contributors to O3 formation potential. A source-attributed health risk assessment approach was developed that incorporates the effects of photochemical losses and observed mixing ratios of VOCs, enabling a more accurate evaluation of health risks from different sources. Non-carcinogenic risks associated with VOC sources remained within acceptable thresholds, while the carcinogenic risks posed by vehicle exhaust and solvent usage were above acceptable levels, particularly on O3 non-polluted days. This study highlights the importance of establishing concurrent control strategies for VOCs and O3 to effectively mitigate air pollution and improve public health.

Predicting plateau atmospheric ozone concentrations by a machine learning approach: A case study of a typical city on the southwestern plateau of China

Atmospheric ozone (O3) has been placed on the priority control pollutant list in China's 14th Five-Year Plan. Due to their unique meteorological conditions, plateau regions contain high concentrations of atmospheric O3. However, traditional experimental methods for determining O3 concentrations using automatic monitoring stations cannot predict O3 trends. In this study, two machine learning models (a nonlinear auto-regressive model with external inputs (NARX) and a temporal convolution network (TCN)) were developed to predict O3 concentrations in a plateau area in the Kunming region by considering the effects of meteorological parameters, air quality parameters, and volatile organic compounds (VOCs). The plateau O3 prediction accuracy of the machine learning models was found to be much higher than those of numerical models that served as a comparison. The O3 values predicted by the machine learning models closely matched the actual monitoring data. The temporal distribution of plateau O3 displayed a high all-day peak from February to May. A correlation analysis between O3 concentrations and feature parameters demonstrated that humidity is the feature with the highest absolute correlation (-0.72), and was negatively correlated with O3 concentrations during all test periods. VOCs and temperatures were also found to have high positive correlation coefficients with O3 during periods of significant O3 pollution. After negating the effects of meteorological parameters, the predicted O3 concentrations decreased significantly, whereas they increased in the absence of NOx. Although individual VOCs were found to greatly affect the O3 concentration, the total VOC (TVOC) concentration had a relatively small effect. The proposed machine learning model was demonstrated to predict plateau O3 concentrations and distinguish how different features affect O3 variations.

The Characteristics, Sources, and Health Risks of Volatile Organic Compounds in an Industrial Area of Nanjing

This study investigates the chemical complexity and toxicity of volatile organic compounds (VOCs) emitted from national petrochemical industrial parks and their effects on air quality in an industrial area of Nanjing, China. Field measurements were conducted from 1 December 2022, to 17 April 2023, focusing on VOC concentrations and speciations, diurnal variations, ozone formation potential (OFP), source identification, and associated health risks. The results revealed an average total VOC (TVOC) concentration of 15.9 ± 12.9 ppb and an average OFP of 90.1 ± 109.5 μg m-3. Alkanes constituted the largest fraction of VOCs, accounting for 44.1%, while alkenes emerged as the primary contributors to OFP, comprising 52.8%. TVOC concentrations peaked before dawn, a pattern attributed to early morning industrial activities and nighttime heavy vehicle operations. During periods classified as clean, when ozone levels were below 160 μg m-3, both TVOC (15.9 ± 12.9 ppb) and OFP (90.4 ± 110.0 μg m-3) concentrations were higher than those during polluted hours. The analysis identified the key sources of VOC emissions, including automobile exhaust, oil and gas evaporation, and industrial discharges, with additional potential pollution sources identified in adjacent regions. Health risk assessments indicated that acrolein exceeded the non-carcinogenic risk threshold at specific times. Moreover, trichloromethane, 1,3-butadiene, 1,2-dichloroethane, and benzene were found to surpass the acceptable lifetime carcinogenic risk level (1 × 10-6) during certain periods. These findings highlight the urgent need for enhanced monitoring and regulatory measures aimed at mitigating VOC emissions and protecting public health in industrial areas. In the context of complex air pollution in urban industrial areas, policymakers should focus on controlling industrial and vehicle emissions, which can not only reduce secondary pollution, but also inhibit the harm of toxic substances on human health.

Volatile organic compounds (VOCs) emissions from internal floating-roof tank in oil depots in Beijing: Influencing factors and emission reduction strategies analysis

The internal floating-roof tank is the main type of storage tank for refined oil products. The volatile organic compounds (VOCs) emission from the internal floating-roof tank plays a dominant role in the unorganized emission source of the oil depot. In this study, we selected six typical oil depots in Beijing to investigate VOC emission characteristics from the tank top vent hole using infrared imaging technology and flame ionization detector (FID). The results reveal that infrared thermal imager is efficient in quickly identifying the emission level of the tank discharge point. The ambient temperature and wind speed have a direct effect on sealing loss, the turnover can greatly influence the wall hanging loss, and the concentration of VOCs emitted from the tank top vent hole is negatively correlated with liquid height. Furthermore, the influence of accessories type of the internal floating-roof tank on the concentration of VOCs emission from the top vent hole is also studied when other parameters remain unchanged, and find the floating deck type and sealing mode have a significant influence on their VOCs emissions, of which the combination of pontoon type floating deck and secondary seal are effective in controlling the concentration of VOCs emitted from the tank top vent hole. Finally, based on our experimental results, several feasible emission reduction strategies are proposed in terms of source prevention and process control in order to achieve the fine management of the whole process. This paper provides important technical support and policy thoughts for VOCs emission control during oil storage.

Significance of Volatile Organic Compounds to Secondary Pollution Formation and Health Risks Observed during a Summer Campaign in an Industrial Urban Area

The chemical complexity and toxicity of volatile organic compounds (VOCs) are primarily encountered through intensive anthropogenic emissions in suburban areas. Here, pollution characteristics, impacts on secondary pollution formation, and health risks were investigated through continuous in-field measurements from 1-30 June 2020 in suburban Nanjing, adjacent to national petrochemical industrial parks in China. On average, the total VOCs concentration was 34.47 ± 16.08 ppb, which was comprised mostly by alkanes (41.8%) and halogenated hydrocarbons (29.4%). In contrast, aromatics (17.4%) dominated the ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) with 59.6% and 58.3%, respectively. Approximately 63.5% of VOCs were emitted from the petrochemical industry and from solvent usage based on source apportionment results, followed by biogenic emissions of 22.3% and vehicle emissions of 14.2%. Of the observed 46 VOC species, hexachlorobutadiene, dibromoethane, butadiene, tetrachloroethane, and vinyl chloride contributed as high as 98.8% of total carcinogenic risk, a large fraction of which was ascribed to the high-level emissions during ozone pollution episodes and nighttime. Therefore, the mitigation of VOC emissions from petrochemical industries would be an effective way to reduce secondary pollution and potential health risks in conurbation areas.