天津重污染期间大气污染物浓度垂直分布特征

利用天津气象局255 m铁塔垂直4层观测平台(高度分别为3、40、120和220 m),对各层大气中的NOx、O3、SO2浓度(均以φ计)和PM2.5浓度(以ρ计)进行了连续观测,结合同步气象要素分析了2010年10月3—11日天津发生的一次重污染事件.结果表明:在此次重污染事件期间,一次及二次污染物浓度的垂直梯度变化差异显著,φ(NO)、φ(NO2)和ρ(PM2.5)随高度上升而降低,φ(NO)在3～120和120～220 m的递减率分别为58.0%和8.5%,ρ(PM2.5)在3～220 m递减率为13.0%;而φ(O3)和φ(SO2)平均值却随高度的上升而增加,其中φ(O3)在3～40、40～120和120～220 m的增长率分别为108.0%、19.1%和56.4%,φ(SO2)在3～220 m的增长率为25.0%.NOx主要来源于局地近地面污染源的排放;SO2主要来源于高架点源的排放,O3则来源于局地光化学过程积累;PM2.5受局地排放源和光化学过程的双重影响,垂直梯度变化最不显著.不利于扩散的气象条件使以局地排放为主的污染物积累升高及其伴随的光化学反应造成了天津此次重污染事件.

Vertical Distribution of Air Pollutants during Serious Air Pollution Event in Tianjin

In this study,vertical distributions of NOx,O3,SO2 and PM2.5 were observed continuously at four vertical platforms(3,40,120 and 220 m) in a 255 m meteorological observation tower in the Tianjin Meteorological Bureau.Corresponding meteorological data were also examined to interpret the characteristics of the vertical distributions of the four air pollutants.The results showed that a severe air pollution event occurred during the observation period from October 3rd to 11th,2010.Throughout the entire pollution process,the vertical distributions of primary and secondary pollutants differed significantly.The average rates of decrease of concentrations of NO from 3-120 m and from 120-220 m were 58.0% and 8.5%,respectively,while that of PM2.5 from 3-220 m was 13.0%.However,O3 and SO2 concentrations increased with height;the average rates of increase of concentrations of O3 from 3-40,40-120,and 120-220 m were 108.0%,19.1% and 56.4%,respectively,while that of SO2 from 3-220 m was 25.0%.Based on their vertical distribution characteristics,it was determined that NOx mainly came from local near-surface sources,SO2 was mainly from elevated point sources,O3 was attributed to the accumulation of local photochemical processes,and PM2.5 was influenced by both local sources and photochemical processes.Bad weather conditions not conducive for pollution dispersion finally resulted in a serious pollution event in Tianjin.