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The complex air pollution driven by both Ozone (O 3 ) and fine particulate matter (PM 2.5 ) significantly influences the air quality in the Sichuan Basin (SCB). Understanding the O 3 formation during autumn and winter is necessary to understand the atmospheric oxidative capacity. Therefore, continuous in-site field observations were carried out during the late summer, early autumn and winter of 2020 in a rural area of Chongqing. The total volatile organic compounds (VOCs) concentration reported by a Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) were 13.66 ± 9.75 ppb, 5.50 ± 2.64 ppb, and 9.41 ± 5.11 ppb in late summer, early autumn and winter, respectively. The anthropogenic VOCs (AVOCs) and biogenic VOCs (BVOCs) were 8.48 ± 7.92 ppb and 5.18 ± 2.99 ppb in late summer, 3.31 ± 1.89 ppb and 2.19 ± 0.93 ppb in autumn, and 6.22 ± 3.99 ppb and 3.20 ± 1.27 ppb in winter. A zero-dimensional atmospheric box model was employed to investigate the sensitivity of O 3 -precursors by relative incremental reactivity (RIR). The RIR values of AVOCs, BVOCs, carbon monoxide (CO), and nitrogen oxides (NO x ) were 0.31, 0.71, 0.09, and -0.36 for late summer, 0.24, 0.59, 0.22, and -0.38 for early autumn, and 0.30, 0.64, 0.33 and -0.70 for winter, and the results showed that the O 3 formation of sampling area was in the VOC-limited region, and O 3 was most sensitive to BVOCs (with highest RIR values, > 0.6). This study can be helpful in understanding O 3 formation and interpreting the secondary formation of aerosols in the winter., 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 © 2023. Published by Elsevier B.V.)

The ozone (O 3 ) pollution in China drew lots of attention in recent years, and the Sichuan Basin (SCB) was one of the regions confronting worsening O 3 pollution problem. Many previous studies have shown that regional transport is an important contributor to O 3 pollution. However, very few features of the O 3 profile during transport have been reported, especially in the border regions between different administrative divisions. In this study, we conducted tethered balloon soundings in SCB during the summer of 2020 and captured a nocturnal O 3 transport event during the campaign. Vertically, the O 3 transport occurred in the bottom of the residual layer, between 200 and 500 m above ground level. Horizontally, the transport pathway was directed from southeast to northwest based on the analysis of the wind field and air mass trajectories. The effect of transport in the residual layer on the surface O 3 concentration was related to the spatial distribution of O 3 . For cities with high O 3 concentrations in the upwind region, the transport process would bring clean air masses and abate pollution. For downwind lightly polluted cities, the transport process would slow down the decreasing or even increase the surface O 3 concentration during the night. We provided observational facts on the profile features of a transboundary O 3 transport event between two provincial administrative divisions, which implicated the importance of joint prevention and control measures. However, the sounding parameters were limited and the quantitative analysis was preliminary, more integrated, and thorough studies of this topic were called for in the future., 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 © 2023. Published by Elsevier B.V.)

The chemical composition of acid rain and its impact on lake water chemistry in Chongqing, China, from 2000 to 2020 were studied in this study. The regional acid rain intensity is affected jointly by the acid gas emissions and the neutralization of alkaline substances. The pH of precipitation experienced three stages of fluctuating decline, continuous improvement, and a slight correction. Precipitation pH showed inflection points in 2010, mainly due to the total control actions of SO 2 and NO x implemented in 2011. The total ion concentrations in rural areas and urban areas were 489.08 µeq/L and 618.57 µeq/L, respectively. The top four ions were SO 4 2- , Ca 2+ , NH 4 + and NO 3 - , which accounted for more than 90% of the total ion concentration, indicating the anthropogenic effects. Before 2010, SO 4 2- fluctuated greatly while NO 3 - continued to rise; however, after 2010, both SO 4 2- and NO 3 - began to decline rapidly, with the rates of -12.03 µeq/(L·year) and -4.11 µeq/(L·year). Because the decline rate of SO 4 2- was 2.91 times that of NO 3 - , the regional acid rain has changed from sulfuric acid rain to mixed sulfuric and nitric acid rain. The lake water is weakly acidic, with an average pH of 5.86, and the acidification frequency is 30.00%. Acidification of lake water is jointly affected by acid deposition and acid neutralization capacity of lake water. Acid deposition has a profound impact on water acidification, and nitrogen (N) deposition, especially reduced N deposition, should be the focus of future research., 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 © 2023. Published by Elsevier B.V.)

Nowadays, the fine particle pollution is still severe in some megacities of China, especially in the Sichuan Basin, southwestern China. In order to understand the causes, sources, and impacts of fine particles, we collected PM 2.5 samples and analyzed their chemical composition in typical months from July 2018 to May 2019 at an urban and a suburban (background) site of Chengdu, a megacity in this region. The daily average concentrations of PM 2.5 ranged from 5.6-102.3 µg/m 3 and 4.3-110.4 µg/m 3 at each site. Secondary inorganics and organic matters were the major components in PM 2.5 at both sites. The proportion of nitrate in PM 2.5 has exceeded sulfate and become the primary inorganic component. SO 2 was easier to transform into sulfate in urban areas because of Mn-catalytic heterogeneous reactions. In contrast, NO 2 was easily converted in suburbs with high aerosol water content. Furthermore, organic carbon in urban was much greater than that in rural, other than elemental carbon. Element Cr and As were the key cancer risk drivers. The main sources of PM 2.5 in urban and suburban areas were all secondary aerosols (42.9%, 32.1%), combustion (16.0%, 25.2%) and vehicle emission (15.2%, 19.2%). From clean period to pollution period, the contributions from combustion and secondary aerosols increased markedly. In addition to tightening vehicle controls, urban areas need to restrict emissions from steel smelters, and suburbs need to minimize coal and biomass combustion in autumn and winter., (Copyright © 2022. Published by Elsevier B.V.)

To study the emission characteristics of typical construction machinery in Chengdu, 12 construction machinery (excavators, bulldozers, loaders, and forklifts) under idling mode, moving mode, and working mode, were tested using a portable emission measurement system (PEMS). Under three operating modes, the typical construction machinery in the working mode was higher in the fuel-based average emission factors of PM 2.5 and NO x, while the fuel-based average emission factors of HC and CO were higher in idling mode. Integrated the results of investigation on ownership and activity levels of construction machinery, an exhaust emission inventory of typical construction machinery of Chengdu in 2018 was established according to the recommendation method. The annual emission of PM 2.5 , NO x , HC, and CO were 1.67 × 10 6 , 1.61 × 10 8 , 3.83 × 10 6 , and 1.26 × 10 7  kg, respectively, and the excavator contributed the maximum emissions, accounting for an average proportion of 43.95%. The emission of construction machinery in Chengdu exhibited a clear monthly trend, with the highest from April to October and the lowest from November to March. In addition, the exhaust emissions presented an obvious spot-like characteristics, and the high-value areas were mainly concentrated in the surrounding suburban counties such as Shuangliu Wenjiang etc. To reduce pollution from construction machinery and improve the quality of the atmospheric environment, more effective measures on housing construction and municipal construction should be taken in those districts in Chengdu., (Copyright © 2022. Published by Elsevier B.V.)

Integral to the urban ecosystem, greening trees provide many ecological benefits, but the active biogenic volatile organic compounds (BVOCs) they release contribute to the production of ozone and secondary organic aerosols, which harm ambient air quality. It is, therefore, necessary to understand the BVOC emission characteristics of dominant greening tree species and their relative contribution to secondary pollutants in various urban contexts. Consequently, this study utilized a dynamic enclosure system to collect BVOC samples of seven dominant greening tree species in urban Chengdu, Southwest China. Gas chromatography/mass spectrometry was used to analyze the BVOC components and standardized BVOC emission rates of each tree species were then calculated to assess their relative potential to form secondary pollutants. We found obvious differences in the composition of BVOCs emitted by each species. Ficus virens displayed a high isoprene emission rate at 31.472 μgC/(gdw (g dry weight)•hr), while Cinnamomum camphora emitted high volumes of D-Limonene at 93.574 μgC/(gdw•hr). In terms of the BVOC emission rates by leaf area, C. camphora had the highest emission rate of total BVOCs at 13,782.59 μgC/(m 2 •hr), followed by Cedrus deodara with 5466.86 μgC/(m 2 •hr). Ginkgo biloba and Osmanthus fragrans mainly emitted oxygenated VOCs with lower overall emission rates. The high BVOC emitters like F. virens, C. camphora, and Magnolia grandiflora have high potential for significantly contributing to environmental secondary pollutants, so should be cautiously considered for future planting. This study provides important implications for improving urban greening efforts for subtropical Chinese urban contexts, like Chengdu., (Copyright © 2021. Published by Elsevier B.V.)

Surface ozone (O 3 ) has become a critical pollutant impeding air quality improvement in many Chinese megacities. Chengdu is a megacity located in Sichuan Basin in southwest China, where O 3 pollution occurs frequently in both spring and summer. In order to understand the elevated O 3 during spring in Chengdu, we conducted sampling campaign at three sites during O 3 pollution episodes in April. Volatile organic compounds (VOCs) compositions at each site were similar, and oxygenated VOCs (OVOCs) concentrations accounted for the highest proportion (35%-45%), followed by alkanes, alkens (including acetylene), halohydrocarbons, and aromatics. The sensitivity of O 3 to its precursors was analyzed using an observation based box model. The relative incremental reactivity of OVOCs was larger than other precursors, suggesting that they also played the dominant role in O 3 formation. Furthermore, the positive matrix factorization model was used to identify the dominant emission sources and to evaluate their contribution to VOCs in the city. The main sources of VOCs in spring were from combustion (27.75%), industrial manufacturing (24.17%), vehicle exhaust (20.35%), and solvent utilization (18.35%). Discussions on VOCs and NO x reduction schemes suggested that Chengdu was typical in the VOC-limited regime, and VOC emission reduction would help to prevent and control O 3 . The analysis of emission reduction scenarios based on VOCs sources showed that the emission reduction ratio of VOCs to NO 2 needs to reach more than 3 in order to achieve O 3 prevention. Emission reduction from vehicular exhaust source and solvent utilization source may be more effective., (Copyright © 2021. Published by Elsevier B.V.)

To better understand the potential causes of visibility impairment in autumn and winter in Chengdu, relative humidity (RH), visibility, the concentrations of PM 2.5 and its chemical components were on-line measured continuously in Chengdu from Nov. 2016 to Jan. 2017. Six obvious haze episodes occurred in Chengdu, with the total time of haze episodes accounted for more than 90% of the total observation period, and higher NO 2 concentrations and RH were related to the high particle concentrations in haze episodes. The visibility decreased in a non-linear tendency under different RH conditions with the increase of PM 2.5 concentrations, which was more sensitive to RH under lower PM 2.5 concentrations. The threshold concentration of PM 2.5 got more smaller with the increase of RH. During the entire observation period, organic matter (OM) was the largest contributor (31.12% to extinction coefficient (b ext )), followed by NH 4 NO 3 and (NH 4 ) 2 SO 4 with 28.03% and 23.01%, respectively. However, with the visibility impairment from Type I (visibility > 10 km) to Type IV (visibility ≤2 km), the contribution of OM to b ext decreased from 38.12% to 26.77%, while the contribution of NH 4 NO 3 and (NH 4 ) 2 SO 4 to b ext increased from 19.09% and 20.20% to 34.29% and 24.35%, respectively, and NH 4 NO 3 became the largest contributor to b ext at Type IV. The results showed that OM and NH 4 NO 3 were the key components of PM 2.5 for visibility impairment in Chengdu, indicating that the control of precursors emissions of carbonaceous species and NH 4 NO 3 could effectively improve the visibility in Chengdu., (Copyright © 2019. Published by Elsevier B.V.)