Abstract
Located in East Asia, the North China Plain (NCP) has a severe air pollution problem. In this study, variations in visibility, particulate matter (PM), gaseous pollutants, vertical meteorological parameters, and different types of aerosols and their optical properties were evaluated during an air pollution episode that occurred from 10 to 15 January 2019 in Tianjin over the NCP. The visibility was <10 km for approximately 96 h, and the concentrations of PM with an aerodynamic diameter of <2.5 μm (PM2.5) and <10 μm (PM10) increased to 300 and 400 μg/m3, respectively. Because of the conversion of SO2 to sulphate aerosol particles, the sulphur dioxide (SO2) concentration decreased to a minimum of 10 μg/m3. The continual deterioration of visibility was related to the high relative humidity and the boundary layer of <0.1 km. The southwest airflow (3.0–4.0 m/s) transported various pollutants from Hebei Province to the NCP. Higher mixing ratios of sulphate aerosols, organic aerosols, and black carbon aerosols were distributed over a 0.5-km-diameter area, and the maximum concentrations were approximately 90, 250–300, and 20 μg/kg, respectively. Higher mixing ratios of dust aerosols and sea salt aerosols were distributed within 1.5 km and 1.0–2.5 km, respectively, and their maximum concentrations were approximately 15 and 9 μg/kg, respectively. The findings are valuable for analysing the relationship between air quality and pollutant transport in the NCP.
Highlights
Aerosols can directly alter the energy balance of the earth–atmosphere system by absorbing and scattering solar radiation (Ackerman and Toon, 1981; Charlson et al, 1992; Hansen et al, 1997)
With the further evolution of pollution, the PM2.5 concentration increased to approximately 200 μg/m3 at 0000 China Standard Time (CST) on 11 January, reaching approximately 250 μg/m3 on 12 January
Compared with the influence of fine mode particles, the significant increase of PM10 mass concentration reflects the important contribution of coarse particles to aerosol pollution in Tianjin
Summary
Aerosols can directly alter the energy balance of the earth–atmosphere system by absorbing and scattering solar radiation (Ackerman and Toon, 1981; Charlson et al, 1992; Hansen et al, 1997). We synchronously observed near-surface and boundary-layer meteorological factors and aerosols in the vertical direction to examine mechanisms through which aerosols with different chemical compositions affect regional air quality, causing severe pollution. Data collected from six meteorological stations in Tianjin, comprising the hourly mass concentrations of four crucial particles and gaseous pollutants, namely PM2.5 (PM with an aerodynamic diameter of ≤2.5 μm), PM10 (PM with an aerodynamic diameter of ≤10 μm), SO2, and NO2, were obtained from the website of the China National Environmental Monitoring Centre (http://www.cnemc.cn). Potential source contribution function (PSCF) and concentration weighted trajectory (CWT) analyses of the study area (33.5°N–56.0°N, 85.0°E–117.5°E) were performed.
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