Effect of COVID-19 lockdown on the characterization and mixing state of carbonaceous particles in the urban atmosphere of Liaocheng,the North China Plain |
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| Affiliation: | 1. School of Geography and the Environment, Liaocheng University, Liaocheng, 252000, China;2. Key Laboratory of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai, 200241, China;1. Key Laboratory of Low-grade Energy Utilization Technologies and Systems (Chongqing University), Ministry of Education, Chongqing, 400044, China;2. Dongfang Boiler Group Co., Ltd, Chengdu, 611731, China;3. Geely Baikuang Group Co., Ltd, Guangxi, 533000, China;1. School of Energy Science and Engineering, Harbin Institute of Technology, Harbin, 150001, China;2. China Construction Eco-Environmental Protection Technology Co., Ltd., Suzhou, 215100, China;1. School of Chemistry and Chemical Engineering, Chongqing University of Science and Technology, Chongqing, 401331, China;2. Provincial and Ministerial Co-Constructive of Collaborative Innovation Center for MSW Comprehensive Utilization, School of Metallurgy and Materials Engineering, Chongqing University of Science and Technology, Chongqing, 401331, China;1. School of Pharmacy, Jilin Medical University, Jilin, 132013, Jilin Province, China;2. College of Life Science, Jilin University, Changchun, 130012, Jilin Province, China;3. Department of Pharmaceutics, School of Pharmaceutical Science, Peking University, Beijing, 100191, China;4. College of Pharmaceutical Sciences, Yanbian University, Yanji, 133002, Jilin Province, China |
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| Abstract: | To investigate the effect of COVID-19 control measures on aerosol chemistry, the chemical compositions, mixing states, and formation mechanisms of carbonaceous particles in the urban atmosphere of Liaocheng in the North China Plain (NCP) were compared before and during the pandemic using a single particle aerosol mass spectrometry (SPAMS). The results showed that the concentrations of five air pollutants including PM2.5, PM10, SO2, NO2, and CO decreased by 41.2%–71.5% during the pandemic compared to those before the pandemic, whereas O3 increased by 1.3 times during the pandemic because of the depressed titration of O3 and more favorable meteorological conditions. The count and percentage contribution of carbonaceous particles in the total detected particles were lower during the pandemic than those before the pandemic. The carbonaceous particles were dominated by elemental and organic carbon (ECOC, 35.9%), followed by elemental carbon-aged (EC-aged, 19.6%) and organic carbon-fresh (OC-fresh, 13.5%) before the pandemic, while EC-aged (25.3%), ECOC (17.9%), and secondary ions-rich (SEC, 17.8%) became the predominant species during the pandemic. The carbonaceous particle sizes during the pandemic showed a broader distribution than that before the pandemic, due to the condensation and coagulation of carbonaceous particles in the aging processes. The relative aerosol acidity (Rra) was smaller before the pandemic than that during the pandemic, indicating the more acidic particle aerosol during the pandemic closely related to the secondary species and relative humidity (RH). More than 95.0% and 86.0% of carbonaceous particles in the whole period were internally mixed with nitrate and sulfate, implying that most of the carbonaceous particles were associated with secondary oxidation during their formation processes. The diurnal variations of oxalate particles and correlation analyses suggested that oxalate particles before the pandemic were derived from aqueous oxidation driven by RH and liquid water content (LWC), while oxalate particles during the pandemic were originated from O3-dominated photochemical oxidation. |
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| Keywords: | Carbonaceous particles Oxalate particles Mixing state COVID-19 lockdown Single particle aerosol mass spectrometry (SPAMS) |
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