北京地区基于化学组分的气溶胶吸湿性研究

Study on the hygroscopicity of aerosols in Beijing based on chemical compositions

吸湿性是气溶胶的重要理化特性之一,对气溶胶颗粒的尺寸、化学组分、相态及表面形态有重要影响.现阶段在北京地区开展了大量的气溶胶吸湿性研究,但这些研究很多是利用吸湿性串联差分迁移率分析仪或加湿浊度计对1~2个季节中的代表时段开展研究.本研究基于对北京城市站点气溶胶化学组分的长期在线观测探索其吸湿性的季节变化特征和影响因素.结果表明:北京地区气溶胶的吸湿性在不同季节和不同污染状况存在明显差异,吸湿性参数κ夏、秋两季(0.40、0.38)大幅高于冬、春两季(0.23、0.27),各季节污染条件下κ均高于清洁条件,其中,夏季差距最小、冬季最大.观测期间各季节κ呈现一定的日变化特征.夏季κ呈现上午单峰特征,秋季κ呈现下午单峰特征.除冬季外,其他季节白天气溶胶吸湿性均高于夜晚时段,存在明显的昼夜差异.

Hygroscopicity is one of the important physicochemical properties of atmospheric aerosols,which has significant influences on the size,chemical composition,phase state and surface morphology of aerosol particles.Currently,a large number of studies on aerosol hygroscopicity have been conducted in the Beijing area.However,many of these studies are based on hygroscopicity tandem differential mobility analyzers or humidified nephelometer,focusing on representative periods of one to two seasons.In this study,based on online observations of aerosol chemical composition at an urban site in Beijing,we investigated the seasonal variations and influencing factors of aerosol hygroscopicity.The results indicate that aerosol hygroscopicity in the Beijing area exhibits significant differences among different seasons and pollution conditions.The hygroscopicity parameterκis substantially higher in summer and autumn(0.40,0.38)than in winter and spring(0.23,0.27).Under polluted conditions,the hygroscopicity parameterκin all seasons is higher than under clean conditions,with the smallest difference in summer and the largest difference in winter.During the observation period,κshows diurnal variations.In summer,the daily maximumκis presented in the morning;while in autumn,it occurred in the afternoon.Except for winter,κshows higher level in daytime than in nighttime.