北京冬、夏季颗粒物及其离子成分质量浓度谱分布

Mass Size Distribution of Beijing Particulate Matters and Its Inorganic Water-Soluble Ions in Winter and Summer

为认识北京大气颗粒物的重要特性之一的粒径谱分布,利用多级撞击式颗粒物采样器MOUDI对北京城区夏季和冬季大气颗粒物进行了4次为期1周的采样,采样时间分别是2001-07、2002-03、2002-07和2003-01.通过分析获得了颗粒物及其离子成分的质量浓度谱分布;发现北京城区颗粒物中细粒子占PM10的40%~60%,已经成为PM10的主要组成部分;但是细粒子和粗粒子的质量浓度与PM10都有很强的相关性(R2>80%),仍然可以通过控制粗粒子的浓度来降低PM10的浓度;在细粒子浓度高于70μg·m-3时,硫酸盐、硝酸盐和铵盐在细粒子中所占比例之和大于70%,是颗粒物浓度升高的主要因素;并且观测到颗粒物的质量粒径谱分布在积聚模态存在2个亚模态以及积聚模态出现在1·0~1·8μm的粒径段的谱分布;对于积聚模态峰值出现在1·0~1·8μm粒径段的原因,进行了初步分析.

To understand one of the important characteristics of Beijing particulate matter pollution, the mass size distribution of particulate matters and its water-soluble ions, the particle samples were collected by a MOUDI cascade impactor in Beijing during July 2001, March 2002, July 2002 and January 2003 and every sampling period lasted a week. By analysis, the results indicate that there is “two modes' in the diameter range of the fine particle, one called “condensation mode' and another called “droplet mode', and the reasons of the peak of the accumulation mode appearing in the diameter range of 1～1.8μm was discussed in this paper. And there was a relatively strong correlation between PM- 1.8 and PM- 10(R^2>80%), the same to PM- (1.8～10) (PM- 10 minus PM- 1.8); the ratio of PM- 1.8/PM- 10 varietied between 40% and 60% during the sampling periods; as a result, the mass concentration of PM- 10 can be decreased by decreasing the concentration of coarse particles; sulfate, nitrate and ammonium are the main component of the inorganic water-soluble ions and the percentage of these three ions in PM- 1.8 was above 70% when the concentration of fine particle was more than 70μg·m~ -3 and they are the main reason increasing particle concentration.