2015—2017年唐山市PM2.5重污染生消气象条件分析

Meteorological conditions for formation and dissipation of PM2.5 heavy pollution in Tangshan from 2015 to 2017

利用2015—2017年唐山市空气质量日空气质量指数、小时PM 2.5浓度和气象数据,分析了唐山市重污染特征及PM 2.5重污染生成、消散气象条件。结果表明:2015—2017年唐山市重污染天数为减少趋势,年平均重污染天数36 d。冬季发生重污染天数最多,秋季次之。重污染天气中首要污染物为PM 2.5、PM 10和O 3,PM 2.5为首要污染物占比87%,PM 10占比6%,O 3占比7%。小时PM 2.5浓度与相对湿度、总云量、24 h变温正相关,与风速、气温、风向、1 h降水负相关。冬季相关性最好,其次是秋季和春季。90%PM 2.5重污染相对湿度均为50%以上,冬季和秋季高达98%;风速大于4 m·s^-1时,有0.7%的PM 2.5达到重污染;降水对PM 2.5有一定清除作用。升温、湿度增加和负变压有助于污染天气形成,生成过程中平均风速为1.8 m·s^-1,主导风向为SW,其次是S、W。降温、湿度下降、正变压、降水有助于污染天气消散,消散过程中平均风速为3.1 m·s^-1,主导风向为E,其次是NE、N。各方位3 m·s^-1的风具有清除能力,偏北风具有较好清除能力,风速较其他方向风速小。

Based on observational data of daily air quality index(AQI),hourly PM 2.5 concentration,and meteorological parameters in Tangshan from 2015 to 2017,we analyzed the characteristics of heavy air pollution and meteorological conditions for formation and dissipation of PM 2.5 pollution.The results show that the day number of heavy air pollution exhibits a decreasing trend from 2015 to 2017,with an annual mean value of 36 d.Heavy air pollution events occur most frequently during winter,followed by autumn.The primary air pollutant during heavy pollution events include PM 2.5,PM 10,and O 3,accounting for 87%,6%,and 7%,respectively.The hourly PM 2.5 concentration has a positive correlation with relative humidity,total cloud fraction,and 24-h temperature change,and has a negative correlation with wind speed,air temperature,wind direction,and hourly precipitation.Such correlation is highest in winter,followed by autumn and spring.The relative humidity is higher than 50%for 90%of heavy PM 2.5 pollution events,and almost 98%in winter and autumn.The proportion of heavy PM 2.5 pollution events in the presence of wind speed larger than 4 m·s^-1 is 0.7%,and precipitation has a scavenging effect on air pollution to some degree.Pollution events tend to occur under conditions of increasing air temperature and humidity and negative pressure change.The average wind speed during the formation process of air pollution is 1.8 m·s^-1,with the dominant wind direction of the southwest,followed by southerly and westerly winds.The reduction of air temperature and humidity and positive pressure change favor the dissipation of air pollution,and the average wind speed reaches 3.1 m·s^-1 during the dissipation periods,predominantly controlled by easterly winds and then northeasterly and northerly winds.Wind speed larger than 3 m·s^-1 has a scavenging effect on air pollution,and northerly winds perform better than other wind direction despite lower wind speed.