天津大气扩散条件对污染物垂直分布的影响研究

利用2017~2019年夏、冬季天津市大气污染物监测和气象观测数据,基于天津气象铁塔垂直观测,针对大气垂直扩散条件对PM_2.5和O₃的影响进行研究.结果显示:近地面PM_2.5浓度随高度的升高而下降,O₃浓度则随高度的升高而上升,受大气垂直扩散条件的季节和日变化影响,冬季,地面与120m PM_2.5质量浓度相关明显,与200m PM_2.5质量浓度无明显相关.夏季,120m和200m PM_2.5质量浓度相关系数为0.72,午后通常出现120m和200m PM_2.5质量浓度高于地面的情况.夏季,不同高度O₃浓度差异小于冬季,地面与120m高度O₃浓度接近.以大气稳定度、逆温强度和气温递减率作为大气垂直扩散指标,对地面PM_2.5和O₃垂直分布具有指示作用.冬季,TKE与PM_2.5质量浓度相关系数为到-0.65,夏季,TKE与ΔPM_2.5相关系数为-0.39.夏、冬季TKE与地面O₃浓度的相关系数分别为0.46和0.53,与ΔO₃的相关系数分别为0.73和0.70.弱下沉运动对地面O₃浓度影响较强,40m高度垂直运动速度与地面O₃浓度的相关系数在冬、夏季分别为-0.54和-0.61.对冬季典型PM_2.5重污染过程的分析发现,雾霾的生消维持和PM_2.5浓度的变化与大气稳定度、气温垂直递减率和TKE的变化有直接关系.对夏季典型O3污染过程的分析发现,近地面的O₃污染的形成与有利光化学反应的气象条件密切相关,同时,垂直向下输送和有利垂直扩散条件对O₃污染的形成和爆发影响明显.

Effects of atmospheric diffusion conditions on vertical distribution of pollutants in Tianjin

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 PM_2.5 and O₃ were studied based on the vertical observation of Tianjin Meteorological Tower. The results showed that the mass concentration of near-surface PM_2.5 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 PM_2.5 mass concentration on the ground and at 120m height, but insignificant correlation between the PM_2.5 mass concentration on the ground and at 200m height in winter. In summer, the correlation coefficient of PM_2.5 mass concentration at 120m and 200m height was 0.72 and the PM_2.5 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 PM_2.5 and O₃. The correlation coefficient between TKE and PM_2.5 mass concentration was -0.65 in winter, and that between TKE and ΔPM_2.5 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 PM_2.5 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 PM_2.5 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.