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Oxygenated volatile organic compound (OVOC) emissions play a critical role in tropospheric ozone (O3) formation. This paper aims to establish an emission inventory and source profile database for OVOCs in Beijing, utilizing revised and reconstructed data from field measurements and existing literature. The study also assesses their potential impact on the O3 base on the ozone formation potential (OFP). Results indicate that OVOC emissions in Beijing predominantly originate from natural and residential sources, encompassing commercial solvent usage, cooking, residential combustion, construction adhesives, and construction coatings. OVOCs contributed 5.6% to OFP, which is significantly less than their emission contribution of 20.1%. Major OFP contributors include plant sources (26.2%), commercial solvent use (21.0%), cooking (20.5%), and construction adhesives (8.4%). The primary OVOC species contributing to OFP for OVOCs are acetaldehyde, methanol, hexanal, ethanol, and acetone, collectively contributing 59.0% of the total OFP. Natural sources exhibit significant seasonal variability, particularly in summer when plant emissions peak, constituting 78.9% of annual emissions and significantly impacting summer ozone pollution (OFP of 13,954 t). Conversely, emissions from other OVOC sources remain relatively stable year-round. Thus, strategies to mitigate summer ozone pollution in Beijing should prioritize plant sources while comprehensively addressing residential sources in other seasons. District-specific annual OVOC emissions are from Fangshan (3967 t), Changping (3958 t), Daxing (3853 t), and Chaoyang (3616 t), which reflect year-round forested areas in these regions and high populations. [ABSTRACT FROM AUTHOR]

A comprehensive chlorine heterogeneous chemistry is incorporated into the Community Multiscale Air Quality (CMAQ) model to evaluate the impact of chlorine-related heterogeneous reaction on diurnal and nocturnal nitrate formation and quantify the nitrate formation from gas-to-particle partitioning of HNO3 and from different heterogeneous pathways. The results show that these heterogeneous reactions increase the atmospheric Cl2 and ClNO2 level, leading to an increase of the nitrate concentration by ~10% in the daytime. However, these reactions also lead to a decrease the nocturnal nitrate by ~20%. Sensitivity analyses of uptake coefficients show that the empirical uptake coefficient for the O3 heterogeneous reaction with chlorinated particles may lead to the large uncertainties in the predicted Cl2 and nitrate concentrations. The N2O5 uptake coefficient with particulate Cl- concentration dependence performs better to capture the concentration of ClNO2 and nocturnal nitrate concentration. The reaction rate of OH and NO2 in daytime increases by ~15% when the heterogeneous chlorine chemistry is incorporated, resulting more nitrate formation from HNO3 gas-to-particle partitioning. By contrast, the contribution of the heterogeneous reaction of N2O5 to nitrate concentrations decreases by about 27% in the nighttime when its reactions with chloriated particles are considered. However, the generated gas-phase ClNO2 from the heterogeneous reaction of N2O5 and chlorine-containing particles further decompose to increase the nitrate by 6%. In general, this study highlights the potential of significant underestimation of daytime and overestimation of nighttime nitrate concentrations for chemical transport models without proper chlorine chemistry in the gas and particle phases. [ABSTRACT FROM AUTHOR]

Water-soluble inorganic ions (WSI), a major component of PM 2.5 , often increased rapidly during the haze event in Beijing. Sulfate (SO 4 2−), Nitrate (NO 3 −), and Ammonium (NH 4 +) are three main components of WSI. Since year 2015, sulfate concentrations in PM 2.5 has gradually decreased owing to the effective control of SO 2 emissions. However, the contribution of nitrate to PM 2.5 has significantly increased during haze events in Beijing at the same time. In this study, a highly time-resolved online analyzer (Monitor for Aerosols and Gases, MARGA) was employed to measure the WSI in PM 2.5 in Beijing from 5 February to 15 November 2017. Three typical haze events during this sampling period were investigated. During heavy pollution episodes in winter, nitrate concentrations increased from 7.5 μg/m3 to 45.6 μg/m3 (45.0% of WSI), while sulfate increased from 4.2 μg/m3 to 20.1 μg/m3 (19.8% of WSI). This indicated that nitrate is more important than sulfate as a driver for the growth of PM 2.5 during the period of heavy air pollution in winter. Nitrate also dominates the increase of WSI in the pollution episodes in autumn, with an average concentration of 52.5 μg/m3, and contributed up to 67% of WSI. The average concentration ratio of NH 4 + to SO 4 2− was higher in autumn (1.02) than that in summer (0.74) and close to that in winter (1.00). This is mainly because the emission control of coal combustion in Beijing and surrounding areas results in an NH 3 -rich and SO 2 -lean atmosphere, which promoted the formation of ammonium nitrate. Our study indicates that nitrate has become the most important component of WSI in PM 2.5 and is driving the rapid growth of PM 2.5 concentrations during heavy pollution episodes in Beijing. Therefore, more efforts shall be made to reduce the nitrogen oxide and ammonia emissions in Beijing and surrounding areas. Unlabelled Image • Nitrate become the main component of PM 2.5 than sulfate during the haze events in Beijing. • High NOx emission, low temperature and low aerosol acidity are the key factors to promote nitrate formation in Beijing. • Molar ratio of NH 4 + to SO 4 2- increased from 1.5 (before 2013) to 3.33 (2017) due to ammonia-rich atmosphere in Beijing. [ABSTRACT FROM AUTHOR]

The national Air Pollution Prevention and Control Action Plan required significant decreases in PM 2.5 levels over China. To explore more effective emission abatement strategies in industrial cities, a case study was conducted in Baotou to evaluate the current national control measures. The total emissions of SO 2, NO X , PM 2.5 and NMVOC (non-methane volatile organic compounds) in Baotou were 211.2 Gg, 156.1 Gg, 28.8 Gg, and 48.5 Gg, respectively in 2013, and they would experience a reduction of 30.4%, 26.6%, 15.1%, and 8.7%, respectively in 2017 and 39.0%, 32.0%, 24.4%, and 12.9%, respectively in 2020. The SO 2 , NO X and PM 2.5 emissions from the industrial sector would experience a greater decrease, with reductions of 37%, 32.7 and 24.3%, respectively. From 2013 to 2020, the concentrations of SO 2 , NO 2 , and PM 2.5 are expected to decline by approximately 30%, 10% and 14.5%, respectively. The reduction rate of SNA (sulfate, nitrate and ammonium) concentrations was significantly higher than that of PM 2.5 in 2017, implying that the current key strategy toward controlling air pollutants from the industrial sector is more powerful for SNA. Although air pollution control measures implemented in the industrial sector could greatly reduce total emissions, constraining the emissions from lower sources such as residential coal combustion would be more effective in decreasing the concentration of PM 2.5 from 2017 to 2020. These results suggest that even for a typical industrial city, the reduction of PM 2.5 concentrations not only requires decreases in emissions from the industrial sector, but also from the low emission sources. The seasonal variation in sulfate concentration also showed that emission from coal-burning is the key factor to control during the heating season. [ABSTRACT FROM AUTHOR]

Due to the implementation of different air pollution control measures in the Beijing-Tianjin-Hebei (BTH) region during 2013-2017, the air quality exhibited varied improvements in each province, indicating substantial changes in the interprovincial regional transport of PM 2.5 . In this study, we investigated these changes by using the Community Multiscale Air Quality (CMAQ) model coupled with the integrated source apportionment method (ISAM) during this period. The results showed that the concentrations of primary particles, SO 4 2- , and NO 3 - decreased by 41.5, 40.8, and 1.8%, respectively due to the air pollutants emission reduction. Local air pollutant emissions were the predominant contributors of PM 2.5 for each region in BTH, accounting for 41.3-47.6, 38.1-40.6, 50.6-53.6, and 54.0-57.1% of PM 2.5 in Beijing, Tianjin, and northern and southern Hebei, respectively. Total PM 2.5 has been mitigated by 7.1-12.3 and 5.1-11.7 μg/m 3 from local and regional emission reduction, respectively in the BTH. Moreover, diverse local meteorological conditions variation increased the PM 2.5 concentration by 5.3 μg/m 3 in Tianjin and decreased it by 7.6, 2.0, and 4.9 μg/m 3 in Beijing, and northern and southern Hebei, respectively. Estimation by integrated exposure-response function revealed that the number of premature deaths attributable to PM 2.5 exposure decreased by approximately 3000 in the BTH region during 2013-2017. Additional policies that focus on PM 2.5 -O 3 coordinated control and stringent regional joint air pollution regulation are required to substantially reduce the health impacts, especially in southern Hebei., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

China issued a series of control measures to mitigate PM 2.5 pollution, including long-term (i.e., Air Pollution Prevention and Control Action Plan, APPCAP) and short-term (emergency measures in autumn and winter) acts. However, the O 3 concentration increased significantly as PM 2.5 levels sharply decreased when these measures were implemented. Therefore, the policy-driven positive/negative health effects of PM 2.5 /O 3 need to be comprehensively estimated. The health impact function (HIF) is applied to evaluate the health burden attributable to long- and short-term PM 2.5 and O 3 exposure. The results show that the PM 2.5 concentration decreased by 42.95% in 74 cities, whereas O 3 pollution is increased by 17.56% from 2013 to 2018. Compared with 2013, the number of premature deaths attributable to long- and short-term PM 2.5 exposure decreased by almost 5.31 × 10 4 (95% confidence interval [CI]: 2.87 × 10 4 -4.71 × 10 4 ) (10.13%) and 3.00 × 10 4 (95% CI: 1.66 × 10 4 -4.39 × 10 4 ) (72.49%), respectively, in 2018. In contrast, O 3 -attributable deaths, increased by 1.98 × 10 4 (95% CI: 0.31 × 10 4 -3.59 × 10 4 ) (130.57%) and 0.91 × 10 4 (95% CI: 0.50 × 10 4 -1.33 × 10 4 ) (76.16%) for long- and short-term exposure, respectively. The number of avoidable deaths attributed to PM 2.5 reduction is larger than the level of premature deaths related to increasing O 3 . Although annual mean PM 2.5 concentrations have fallen rapidly, the benefits of reducing long-term exposure are limited, whereas the deaths associated with acute exposure decrease more significantly due to the reduction of heavy-pollution days by implementing emergency measures. The results show appreciable effectiveness in protecting human health and illustrate that synchronous control of PM 2.5 and O 3 pollution should be emphasized., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)