北京市冬春季大气颗粒物的粒径分布及消光作用

2004年1─5月，在北京市区连续监测了大气环境中ρ(PM₁₀₎，ρ(PM_2.5)，ρ(PM₁)和ρ(TSP)，以及大气能见度、地面气象要素.结果表明:春节期间颗粒物中细粒子所占的比例较高，ρ(PM₁)/ρ(PM_2.5)为0.81，ρ(PM10)/ρ(TSP)为0.61；而沙尘期其值分别为0.55和0.28.不同粒径的颗粒物质量浓度均呈在明显日变化，其夜间浓度峰值高于早晨交通繁忙时段.根据经验公式，将大气能见度换算为大气消光系数，并导出颗粒物消光系数.结果表明:颗粒物消光系数与颗粒物质量浓度呈显著正相关.进一步定义了颗粒物质量浓度消光比(CE_P)，用来表征颗粒物的污染特征.统计分析结果表明:当CE_P<103时，颗粒物质量浓度很低，PM_2.5所占比例较高，代表了有利于污染扩散的气象条件；当CE_P>167，颗粒物质量浓度高，但细粒子比(ρ(PM_2.5)/ρ(PM₁₀₎)稳定在0.5～0.7，湿度也稳定在20%～50%，代表了不利于污染扩散的气象条件. 

The Characteristic of Atmospheric Particle Size Distribution and Their Light Extinction Effect in Beijing during Winter and Spring Time

From January to May 2004, continuous measurements of mass concentration for atmospheric PM₁₀, PM_2.5, PM₁ and TSP, visibility and surface meteorological factors were carried out at a site in central urban Beijing. It was found thatfiner particles are at a higher ratio during the Spring Festival, namely, ρ(PM₁)/ρ(PM_2.5) is 0.81, ρ(PM₁₀₎/ρ(TSP)0.61; contrasted by those of 0.55 and 0.28 for a sandstorm time. The diurnal variations of concentrations for the above sized particles all showed a stronger peak at night than in morning rush hour. Visibility data was transformed into light extinction coefficients for both the atmosphere and particles using empirical equations. There are statistically strongpositive correlations between the PM concentration and the extinction coefficient of particles. Furthermore, the ratio of particle mass concentration to extinction coefficient (CE_P) was defined to study particle pollution properties.The result reveals that when CE_P is small (CE_P<103), PM mass concentration is low and fine particles are in the majority, which represents a favorable meteorological condition; while when CE_P become larger (CE_P>167), PM mass concentrations arehigh, ρ(PM_2.5)/ρ(PM₁₀₎is 0.5～0.7, and RH 20%～50%, which represents an unfavorable condition.