Difference in PM2.5 Pollution and Transport Characteristics Between Urban and Suburban Areas

Abstract

Based on multi-source observation data, such as lidar ceilometer, aircraft AMDAR, and conventional sites, combined with numerical simulation (CAMx-PSAT), this study took the typical cities of the Beijing-Tianjin-Hebei region-Beijing (BJ) urban area and suburbs (Miyun) and Shijiazhuang (SJZ) urban area and suburbs (Pingshan) as the case study areas. The differences in boundary layer height between urban areas and suburbs (ΔPBLH), surface PM2.5 mass concentration (ΔSurf_PM2.5), vertical PM2.5 mass concentration (ΔVert_PM2.5), and transmission flux intensity and height distribution characteristics were analyzed. The results showed:due to factors such as anthropogenic heat sources, short-wave radiation, and thermal turbulence, the annual average planetary boundary layer height in urban areas was 8%-29% higher than that in the suburbs, and in different seasons, the monthly average planetary boundary layer height in urban areas was 2% (April in SJZ)-47% (July in BJ) higher than that in the suburbs. Due to the combined effects of anthropogenic emissions, inversions, and atmospheric turbulence, the annual averageρ(PM2.5) in urban areas between 0-1260 m was higher than that in suburbs by 0.1 (SJZ)-29.7 (BJ) μg·m-3 and decreased with the increase in height. The annual average total net flux intensity in urban areas was much greater than that in suburbs, with outflows in urban areas and inflows in suburbs; due to the urban low pressure and the suburban high pressure, suburban thermal circulation was formed. The annual average total net flux intensity in BJ (44.77 t·d-1) was greater than that in SJZ (34.44 t·d-1). Affected by wind speed and PM2.5 mass concentration, between 0-1260 m, the fluxes in urban areas and suburbs and surrounding areas showed an obvious trend of increasing net flux intensity with the increase in height above the ground. Furthermore, the transmission exchange between urban areas and suburbs and surrounding areas in January and April had the most obvious impact on the environment. The intensity of the maximum net flux in the lower urban areas and the suburbs in different seasons was significantly different, and the difference between the two was 2.23-4.48 times; however, the height characteristic difference in the intensity of the maximum net flux was small, mainly located at 611-1260 m.