Abstract：Using the air pollutant monitoring data and meteorological observation data in summer and winter during 2017~2019 in Tianjin, the effects of atmospheric vertical diffusion conditions on PM2.5 and O3 were studied based on the vertical observation of Tianjin Meteorological Tower. The results showed that the mass concentration of near-surface PM2.5 decreased with height, while the concentration of O3 increased with height. Influenced by the seasonal and diurnal variation of atmospheric turbulence intensity, there was a significant correlation between the PM2.5 mass concentration on the ground and at 120m height, but insignificant correlation between the PM2.5 mass concentration on the ground and at 200m height in winter. In summer, the correlation coefficient of PM2.5 mass concentration at 120m and 200m height was 0.72 and the PM2.5 mass concentration at 120m and 200m height were even higher than the ground in the afternoon. In summer, the difference of O3 mass concentration at different heights is lower than that in winter, and the O3 mass concentration were close to the ground at 120m height. Atmospheric stability, temperature inversion intensity, and temperature decline rate were taken as atmospheric vertical diffusion indexes, which had certain indicator effects on the vertical gradient of PM2.5 and O3. The correlation coefficient between TKE and PM2.5 mass concentration was -0.65 in winter, and that between TKE and ΔPM2.5 in summer was -0.39. The correlation coefficients between TKE and O3 concentration were 0.46 and 0.53, in summer and winter respectively. The correlation coefficients between TKE and ΔO3 concentration were 0.73 and 0.70, in summer and winter respectively. The weak downdraft has an obvious influence on the increase of O3 concentration. The correlation coefficients between the vertical velocity at 40m height and O3 concentration were -0.54 and -0.61 in winter and summer, respectively. Through the analysis of a typical PM2.5 heavy pollution process and typical O3 pollution processes, it is found that the changes of atmospheric stability, temperature decline rate and TKE were closely related to the generation, extinction, maintenance and variation of PM2.5 pollutants. The formation of O3 pollution near the surface was closely related to favorable photochemical reactions. In addition, the transport influence of downdraft should also be paid attention to during O3 pollution processes.
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