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Wan F, Hao Y, Huang W, Wang X, Tian M, Chen J. Hindered visibility improvement despite marked reduction in anthropogenic emissions in a megacity of southwestern China: An interplay between enhanced secondary inorganics formation and hygroscopic growth at prevailing high RH conditions. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 895:165114. [PMID: 37379922 DOI: 10.1016/j.scitotenv.2023.165114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Revised: 06/19/2023] [Accepted: 06/23/2023] [Indexed: 06/30/2023]
Abstract
The PM2.5-bound visibility improvement remains challenging in China despite vigorous control on anthropogenic emissions in recent years. One critical issue could exist in the distinct physicochemical properties especially of secondary aerosol components. Taken the COVID-19 lockdown as an extreme case, we focus on the relationship between visibility, emission cuts, and secondary formation of inorganics with changing optical and hygroscopic behaviors in Chongqing, a representative city characterized with humid weather and poor diffusion conditions in Sichuan Basin, southwest of China. It is found that the increased secondary aerosol abundance (e.g., PM2.5/CO and PM2.5/PM10 as a proxy) with enhanced atmospheric oxidative capacity (e.g., O3/Ox, Ox = O3 + NO2), combined with insignificant meteorological dilution effect, might partly offset the benefit on the improved visibility from substantial reduction in anthropogenic emissions during the COVID-19 lockdown. This is in line with the efficient oxidation rates of sulfur and nitrogen (i.e., SOR, NOR), increasing more significantly with PM2.5 and relative humidity (RH) in comparison to O3/Ox. The resulted larger fraction of nitrate and sulfate (i.e., fSNA) would promote the optical enhancement (i.e., f(RH)) and mass extinction efficiency (MEE) of PM2.5, especially under highly humid conditions (e.g., RH > 80 %, with approximately half of the occurrence frequency). This could further facilitate secondary aerosol formation via aqueous-phase reaction and heterogeneous oxidation, likely due to enhanced water uptake and enlarged size/surface area upon hydration. In combination of gradually increased atmospheric oxidative capacity, this positive feedback would in turn inhibit the visibility improvement particularly at high RH environment. Considering the current air pollution complex status over China, further work on the formation mechanisms of major secondary species (e.g., sulfate, nitrate, and secondary organics), size-resolved chemical and hygroscopic properties, together with their interactions are highly recommended. Our results are hoping to assist in the atmospheric pollution complex mitigation and prevention in China.
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Affiliation(s)
- Fenglian Wan
- College of Environment and Ecology, Chongqing University, Chongqing, China
| | - Yuhang Hao
- College of Environment and Ecology, Chongqing University, Chongqing, China
| | - Wei Huang
- National Meteorological Center, China Meteorological Administration, Beijing, China
| | - Xinyu Wang
- College of Environment and Ecology, Chongqing University, Chongqing, China
| | - Mi Tian
- College of Environment and Ecology, Chongqing University, Chongqing, China
| | - Jing Chen
- College of Environment and Ecology, Chongqing University, Chongqing, China; Key Laboratory of Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing University, Chongqing, China.
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Tian P, Zhang N, Li J, Fan X, Guan X, Lu Y, Shi J, Chang Y, Zhang L. Potential influence of fine aerosol chemistry on the optical properties in a semi-arid region. ENVIRONMENTAL RESEARCH 2023; 216:114678. [PMID: 36341796 DOI: 10.1016/j.envres.2022.114678] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 10/21/2022] [Accepted: 10/24/2022] [Indexed: 06/16/2023]
Abstract
The current understanding regarding the potential influence of aerosol chemistry on the optical properties does not satisfy accurate evaluation of aerosol radiative effects and precise determination of aerosol sources. We conducted a comprehensive study of the potential influence of aerosol chemistry on the optical properties in a semi-arid region based on various observations. Organic matter was the main contributor to the scattering coefficients followed by secondary inorganic aerosols in all seasons. We further related aerosol absorption to elemental carbon, organic matter, and mineral dust. Results showed that organic matter and mineral dust contributed to >40% of the aerosol absorption in the ultraviolet wavelengths. Therefore, it is necessary to consider the absorption of organic matter and mineral dust in addition to that of elemental carbon. We further investigated the potential influence of chemical composition, especially of organic matter and mineral dust on the optical parameters. Mineral dust contributed to higher absorption efficiency and lower scattering efficiency in winter. The absorption Ångström exponent (AAE) was mostly sensitive to organic matter and mineral dust in winter and spring, respectively; it was relatively high (i.e., 1.68) in winter and moderate (i.e., 1.42) in spring. Unlike in the other seasons, mineral dust contributed to higher mass absorption efficiency in winter. This work reveals the complexity of the relationship between aerosol chemistry and optical properties, and especially the influence of organic matter and mineral dust on aerosol absorption. The results are highly important regarding both regional air pollution and climate.
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Affiliation(s)
- Pengfei Tian
- Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China
| | - Naiyue Zhang
- Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China
| | - Jiayun Li
- Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China.
| | - Xiaolu Fan
- Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China
| | - Xu Guan
- Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China
| | - Yuting Lu
- Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China
| | - Jinsen Shi
- Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China; Collaborative Innovation Center for Western Ecological Safety, Lanzhou University, Lanzhou, 730000, China
| | - Yi Chang
- Gansu Province Environmental Monitoring Center, Lanzhou, 730020, China
| | - Lei Zhang
- Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, China; Collaborative Innovation Center for Western Ecological Safety, Lanzhou University, Lanzhou, 730000, China
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