天津大气稳定度和逆温特征对PM2.5污染的影响

利用气象铁塔资料分析了逆温频率和强度，采用温差-风速法计算了天津地区大气稳定度，探讨了其相互关系及对PM_2.5浓度月均值和超标日的影响，并对一次重污染过程中大气稳定度和逆温分布特征进行了分析.结果表明，2015年9月~2017年8月A，B，C，D，E和F类大气稳定度发生频率依次为6.7%，11.4%，22.4%，46.1%，11.1%和2.2%，秋冬季节稳定类天气（E，F类）较多，全年白天各时段均以不稳定类大气为主，夜间大气稳定度以中性为主，秋冬季夜间稳定类高达30%~40%.观测期内冬季逆温频率最高，5：00~8：00和21：00~23：00超过90%，冬季逆温强度也最高.随着稳定类大气层结日数的增多，PM_2.5月均值和污染日数均有所增大，同时逐月PM_2.5均值、污染日发生频率均与逆温发生频率呈正相关关系.2016年12月16~21日的一次重污染天气过程显示，PM_2.5受到大气稳定度和逆温发展的影响，霾形成、雾-霾交替和消散等阶段大气稳定度和逆温特征具有显著的不同.大气持续趋于稳定及逆温强度的逐渐增大，对污染生成和维持起了非常重要的作用，污染过程中大气稳定度和逆温特征的精细化分析有助于提升重污染天气预报预警水平.

Atmospheric stability and inverse temperature characteristics of Tianjin and its effect on PM2.5 pollution

Temperature-velocity method was used to calculate the atmospheric stability in Tianjin and the frequency and intensity of the inversion of temperature were analysed based on the meteorological tower. In addition, we investigated the relationship between atmospheric stability and the temperature inversion, which had an influence on the monthly averaged mass concentration of PM_2.5. The characteristics of atmospheric stability and temperature inversion were analysed during a heavy haze period. The results showed that the frequencies of atmospheric stability were 6.7%, 11.4%, 22.4%, 46.1%, 11.1% and 2.2%, respectively, from September 2015 to August 2017. The stagnant meteorological conditions occurred frequently during fall and winter. The unstable and neutral atmospheric stability dominated the daytime and nighttime of all year, respectively. The stable atmosphere contributed 30%~40% during nighttime in fall and winter. During the observation period, the frequency of temperature inversion was the highest in winter, which up to more than 90% during 5:00~8:00and 21:00~23:00. The intensity of temperature inversion was also the highest in winter. With the increase of the number of days of stable atmosphere, the monthly averaged mass concentration of PM_2.5 and the number of polluted days increased. Meanwhile, the monthly averaged mass concentration of PM_2.5 and the frequency of polluted day were all positively correlated with the frequency of inversion temperature. A heavy pollution process from December 16, 2016 to December 21, 2016 showed that the mass concentration of PM_2.5 was effected by the atmospheric stability and the evolution of inversion temperature. The characteristics of atmospheric stability and temperature inversion during the formation of haze, fog-haze alternation and dissipation of haze had obvious difference. As the atmosphere continues to stabilize and the inversion temperature increases, it plays a very important role in the generation and maintenance of pollution. Fine analysis of atmospheric stability and inversion characteristics in the process of pollution will help to improve the prediction and warning level of heavy pollution weather.