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Lyu Y, Gao Y, Pang X, Sun S, Luo P, Cai D, Qin K, Wu Z, Wang B. Elucidating contributions of volatile organic compounds to ozone formation using random forest during COVID-19 pandemic: A case study in China. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2024; 346:123532. [PMID: 38365075 DOI: 10.1016/j.envpol.2024.123532] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 11/10/2023] [Accepted: 02/07/2024] [Indexed: 02/18/2024]
Abstract
Ozone has been reported to increase despite nitrogen oxides reductions during the COVID-19 pandemic, and ozone formation needs to be revisited using volatile organic compounds (VOCs), which are rarely measured during the pandemic. Here, a total of 98 VOCs species were monitored in an economy-active city in China from January 2021 to August 2022 to assess contributions to ozone formation during the pandemic. Total VOCs concentrations were 35.55 ± 21.47 ppb during the entire period, among which alkanes account for the largest fraction (13.78 ppb, 38.0%), followed by aromatics (6.16 ppb, 16.8%) and oxygenated VOCs (OVOCs, 5.69 ppb, 15.7%). Most VOCs groups (e.g., alkenes, OVOCs) and individual species (e.g., isoprene, methyl vinyl ketone) display obvious seasonal and diurnal variations, which are related to their sources and reactivities. No weekend effects of VOCs suggest limited influences from traffic emissions during pandemic. Aromatics and alkenes are the major contributors (39% and 33%) to ozone formation potential, largely driven by o/m/p-xylene (21%), ethylene (15%), toluene (9%). Secondary organic aerosol formation potential is dominated by toluene (>50%) despite its low proportion (5%). Further inclusion of VOCs and meteorology in the Random Forest model shows good ozone prediction performance (R2 = 0.77-0.86, RMSE = 11.95-19.91 μg/m3, MAE = 8.89-14.58 μg/m3). VOCs and NO2 contribute >50% of total importance with the largest difference in importance ratio of VOCs/NO2 in the summer and winter, implying ozone formation regime may vary. No seasonal variations in importance of meteorology are observed, while importance of other variables (e.g., PM2.5) is highest in the summer. This work identifies critical VOCs groups and species for ozone formation during the pandemic, and demonstrates the feasibility of machine learning algorithms in elucidation of ozone formation mechanisms.
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Affiliation(s)
- Yan Lyu
- College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China; School of Environment and Spatial Informatics, China University of Mining and Technology, Xuzhou, 221116, China; Shaoxing Research Institute, Zhejiang University of Technology, Shaoxing, 312077, China
| | - Yibu Gao
- College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China
| | - Xiaobing Pang
- College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China; Shaoxing Research Institute, Zhejiang University of Technology, Shaoxing, 312077, China.
| | - Songhua Sun
- Shaoxing Ecological and Environmental Monitoring Center of Zhejiang Province, Shaoxing, 312000, China
| | - Peisong Luo
- Shaoxing Ecological and Environmental Monitoring Center of Zhejiang Province, Shaoxing, 312000, China
| | - Dongmei Cai
- Department of Environment Sciences and Engineering, Fudan University, Shanghai, 200433, China
| | - Kai Qin
- School of Environment and Spatial Informatics, China University of Mining and Technology, Xuzhou, 221116, China
| | - Zhentao Wu
- College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China
| | - Baozhen Wang
- Green Intelligence Environmental School, Yangtze Normal University, Chongqing, 408100, China
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Li T, Mao H, Wang Z, Yu JZ, Li S, Nie X, Herrmann H, Wang Y. Field Evidence for Asian Outflow and Fast Depletion of Total Gaseous Mercury in the Polluted Coastal Atmosphere. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:4101-4112. [PMID: 36847858 DOI: 10.1021/acs.est.2c07551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Atmospheric mercury (Hg) cycling in polluted coastal atmosphere is complicated and not fully understood. Here, we present measurements of total gaseous mercury (TGM) monitored at a coastal mountaintop in Hong Kong downwind of mainland China. Sharp TGM peaks during cold front passages were frequently observed due to Asian pollution outflow with typical TGM/CO slopes of 6.8 ± 2.2 pg m-3 ppbv-1. Contrary to the daytime maximums of other air pollutants, TGM exhibited a distinct diurnal variation with a midday minimum. Moreover, we observed four cases of extremely fast TGM depletion after sunrise, during which TGM concentrations rapidly dipped to 0.3-0.6 ng m-3 accompanied by other pollutants on the rise. Simulated meteorological fields revealed that morning upslope flow transporting anthropogenically polluted but TGM-depleted air masses from the mixed layer caused morning TGM depletion at the mountaintop location. The TGM-depleted air masses were hypothesized to result mainly from fast photooxidation of Hg after sunrise with minor contributions from dry deposition (5.0%) and nocturnal oxidation (0.6%). A bromine-induced two-step oxidation mechanism involving abundant pollutants (NO2, O3, etc.) was estimated to play a dominant role, contributing 55%-60% of depleted TGM and requiring 0.20-0.26 pptv Br, an amount potentially available through sea salt aerosol debromination. Our findings suggest significant effects of the interaction between anthropogenic pollution and marine halogen chemistry on atmospheric Hg cycling in the coastal areas.
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Affiliation(s)
- Tao Li
- School of Environmental Science and Engineering, Shandong Key Laboratory of Environmental Processes and Health, Shandong University, Qingdao 266237, China
| | - Huiting Mao
- Department of Chemistry, College of Environmental Science and Forestry, State University of New York, Syracuse, New York 13210, United States
| | - Zhe Wang
- Division of Environment and Sustainability, Hong Kong University of Science and Technology, Kowloon, Hong Kong 999077, China
| | - Jian Zhen Yu
- Division of Environment and Sustainability, Hong Kong University of Science and Technology, Kowloon, Hong Kong 999077, China
| | - Shuwen Li
- Laboratory of Cloud-Precipitation Physics and Severe Storms (LACS), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
| | - Xiaoling Nie
- School of Environmental Science and Engineering, Shandong Key Laboratory of Environmental Processes and Health, Shandong University, Qingdao 266237, China
| | - Hartmut Herrmann
- School of Environmental Science and Engineering, Shandong Key Laboratory of Environmental Processes and Health, Shandong University, Qingdao 266237, China
- Atmospheric Chemistry Department (ACD), Leibniz Institute for Tropospheric Research (TROPOS), D-04318 Leipzig, Germany
| | - Yan Wang
- School of Environmental Science and Engineering, Shandong Key Laboratory of Environmental Processes and Health, Shandong University, Qingdao 266237, China
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Zhang Q, Shen Z, Zhang L, Zeng Y, Ning Z, Zhang T, Lei Y, Wang Q, Li G, Sun J, Westerdahl D, Xu H, Cao J. Investigation of Primary and Secondary Particulate Brown Carbon in Two Chinese Cities of Xi'an and Hong Kong in Wintertime. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:3803-3813. [PMID: 32150391 DOI: 10.1021/acs.est.9b05332] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Brown carbon (BrC), an aerosol carbonaceous matter component, impacts atmospheric radiation and global climate because of its absorption in the near-ultraviolet-visible region. Simultaneous air sampling was conducted in two megacities of Xi'an (northern) and Hong Kong (southern) in China in winter of 2016-2017. The aim of this study is to determine and characterize the BrC compounds in collected filter samples. Characteristic absorption peaks corresponding to aromatic C-C stretching bands, organo-nitrates, and C═O functional groups were seen in spectra of Xi'an samples, suggesting that the BrC was derived from freshly smoldering biomass and coal combustion as well as aqueous formation of anthropogenic secondary organic carbon. In Hong Kong, the light absorption of secondary BrC accounted for 76% of the total absorbances of BrC. The high abundance of strong C═O groups, biogenic volatile organic compounds (BVOCs) and atmospheric oxidants suggest secondary BrC was likely formed from photochemical oxidation of BVOCs in Hong Kong. Several representative BrC molecular markers were detected using Fourier transform ion cyclotron resonance mass spectrometry and their absorption properties were simulated by quantum chemistry. The results demonstrate that light absorption capacities of secondary anthropogenic BrC with nitro-functional groups were stronger than those of biogenic secondary BrC and anthropogenic primary BrC.
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Affiliation(s)
- Qian Zhang
- Key Laboratory of Northwest Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, China
- Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
| | - Zhenxing Shen
- Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
- Key Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
| | - Leiming Zhang
- Air Quality Research Division, Science and Technology Branch, Environment and Climate Change Canada, Toronto, Canada
| | - Yaling Zeng
- Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
| | - Zhi Ning
- Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong, China
| | - Tian Zhang
- Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
| | - Yali Lei
- Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
| | - Qiyuan Wang
- Key Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
| | - Guohui Li
- Key Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
| | - Jian Sun
- Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
| | - Dane Westerdahl
- Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong, China
| | - Hongmei Xu
- Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
| | - Junji Cao
- Key Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
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