北京夏季高温高湿和降水过程对大气颗粒物谱分布的影响

2004-07-13～2004-08-23使用TDMPS-APS系统在线测量颗粒物的数浓度谱分布,并于07-16～07-18选取了高温闷热夜晚、日间高温高湿和雨后晴朗干洁3种天气条件,使用多级串联撞击式采样器(MOUDI)测量颗粒物的质量浓度谱分布,结果表明,高温高湿天气条件下颗粒物的污染、尤其细粒子污染严重,导致很低的能见度(2.5km);PM_1.8和PM₁₀的质量浓度分别为170.68μg/m³和249.35μg/m³,细粒子质量浓度占PM10的68%;粒径为50～100nm颗粒物的数浓度最高,为2×10⁴～3×10⁴个/cm³;降雨过程对粗粒子和细粒子均有去除作用,对细粒子的去除作用尤为明显;降雨后PM₁₀和PM_1.8浓度分别比降雨前降低3倍和6倍;降雨过后的晴朗干洁天气有利于新粒子(3～20nm)的生成,生成的新粒子快速长大到50～100nm;随着污染物的累积,以后几天内又变为污染天气.

Effects of High Temperature, High Relative Humidity and Rain Process on Particle Size Distributions in the Summer of Beijing

On-line measurements of particle number size distribution were conducted during 2004-07-13 - 2004-08-23 by using TDMPS-APS system in Beijing; in between the size distributions of particle mass and chemical compositions were measured by using MOUDI cascade impactor under three kinds of weather conditions: (1) high temperature and high relative humidity night, (2) high temperature and high relative humidity day, and (3) clear days. The results indicate that particulate matter, especially fine particle pollution becomes severe under high temperature and high relative humidity conditions, which results in low visibility (2.5km); the average concentrations of PM1.8 and PM10 are 170.68 microg/m3 and 249.35 microg/m3, respectively, PM1.8 accounts for 68% of PM10; number concentration mainly concentrates in the range of 50 - 100nm, about 2 x 10(4) - 3 x 10(4)cm(-3); rain process has a great effect on scavenging particles, especially fine particles. After the rain process PM10 is 3 times lower and PM1.8 is 6 times lower than the values before the rain; in the following clear day, new particle formation is observed, the newly formed particles (3 - 20nm) grow to 50 - 100nm rapidly. After that, the pollutants start to accumulate and it becomes heavy polluted in few days.