北京市区大气气溶胶散射系数亲水增长的观测研究

An experimental study on the influence of relative humidity on the atmospheric aerosol scattering coefficient at an urban site in beijing

中文关键词:  湿度调节装置,气溶胶散射系数, 亲水增长因子

英文关键词:humidifier, aerosol scattering coefficient, hygroscopic growth factor

中文摘要:

      利用自制的“进样气流湿度调节”装置，在2005年12月7—22日在中国气象局科技大楼测点（记为CAMS）对北京市区冬季气溶胶散射系数随湿度的变化关系进行了观测试验，结果显示，观测期间北京市区气溶胶散射系数亲水增长因子（定义为一定湿度下的气溶胶散射系数与“干”气溶胶散射系数的比值）在湿度从低到高的变化过程中，主要表现出“平滑连续”的增长特点。总体上，当相对湿度从小于40％增大到大约93％时，平均气溶胶散射系数亲水增长因子可达2.10，而在相对湿度80％时的平均散射系数亲水增长因子f(RH=80％±1%)大约为1.26±0.15。按照污染情况和天气过程把观测期间划分为“相对污染”时段和“清洁”时段，则在“相对污染”情况时，北京市区CAMS测点的气溶胶散射系数增长因子f(RH=80%)大约为1.48，而在“清洁”时段约为1.2。与国外有关观测相比，北京冬季“清洁”时段气溶胶的散射系数亲水增长因子f(RH=80%)在数值上与生物质燃烧型和扬尘类型气溶胶的亲水增长相似。反映了在不同天气背景下北京市区的气溶胶类型有不同的特点。

英文摘要:

      The humidity-controlled aerosol measurement system was developed to study the hygroscopic properties of aerosols. The system included a humidity-controlled inlet to humidify the sample air, and two nephelometers to simultaneously measure the aerosol scattering coefficients under “dry” and “wet’ conditions. During the measurement, the air passed through the inlet and was humidified by the water vapor diffusing through the wall of the membrane tube. The method used to adjust the amount of water vapor, was called the “combination of water vapor addition and/or thermal control” method, was realized by controlling the temperature of water out of the membrane tube. Using this system, the experimental study on the hygroscopic growth of aerosol scattering coefficients at an urban site (CAMS) in Beijing city was conducted from December 7 to 22, 2005. The instrument was installed on the roof of a building on the campus of Chinese Meteorological Administration in the northwest of Beijing urban area, and the inlet of the instrument was about 50 m above the ground. The preliminary analysis of the measurements indicate that: overall, the hygroscopic growth factor of the scattering coefficient f(RH) increased continuously when the RH increased. the average growth factor f(RH) of the aerosols for the whole measurement period could reach to 2.1 when RH increased from less than 40% to 93％. The average hygroscopic growth factor at relative humidity of 80%, f(RH=80％±1%), was about 1.26 ±0.15. Further calculation shows that the hydroscopic growth factor f(RH) was relatively higher when the air was relatively polluted, where, the f(RH) at RH=80% was about 1.48, however, when the air was clean, the growth factor f(RH) at RH=80% was about 1.2. The growth factor f(RH) for relatively polluted case was lower than the result reported by Carrico (Carrico et al.,2003), f(RH=82%)＝2.22±0.20, for polluted aerosol type during the Ace-Asia experiment, but the behavior of the hydroscopic growth under clean air conditions was similar to those influenced by burning biomass or blowing dust as reported (Carrico et al., 2003; Kotchenruther et al, 1998). These results reflect the different characteristics of aerosol types at Beijing urban area under the different air conditions in the winter.