南京霾天颗粒物数浓度特征及其受气象条件影响分析

2013年12月,我国中东部地区爆发持续性霾污染过程。本研究利用空气动力学粒径谱仪和气溶胶粒径谱仪在线观测这次霾污染过程中13.6~20 000 nm颗粒物数浓度,结合气象参数和颗粒物化学组分对南京霾天颗粒物数浓度分布特征,及其与气象条件相关性进行分析。结果表明,霾天颗粒物主要分布在积聚模态,且500~1 000 nm和1 000~2 500 nm粒径段颗粒物数浓度的增多是造成霾天能见度低的主要原因;随着相对湿度的增大,13.6~100 nm粒径段颗粒物数浓度逐渐降低,而大于100 nm颗粒物数浓度升高;500~1 000 nm和1 000~2 500 nm粒径段颗粒物数浓度受相对湿度的影响尤为明显,并且这2个粒径段颗粒物受气态污染物(SO2,NOX)的二次转化影响较大。霾污染期间南京大气颗粒物主要来自南京东南和西北方向的污染源排放,颗粒物数浓度总体上与风速呈负相关关系;温度对颗粒物数浓度的影响主要集中在13.6~100 nm粒径段;边界层的高度与粒径100 nm颗粒物呈负相关性,边界层的抬升反而利于超细粒子的生成和增长;逆温层的强度对超细粒子的作用更为明显。

Characteristics of the particulate number concentration and association with meteorological conditions during winter haze episode in Nanjing

A lasting haze pollution event occurred in the central and East China in December, 2013. A field study on size distribution, number concentrations of aerosol particle with the diameter between 13.6-20 000 nm has been conducted by using Aerodynamic Particle Sizer (APS) and Scanning Mobility Particle Sizer (SMPS) during the haze period in Nanjing. Besides, the main meteorological parameters and chemical composition of particles, were also collected simultaneously. Results indicated that the particles in haze day are mainly accumulation mode, and the increasing of the particles between 500-1 000 nm and 1 000-2 500 nm was the main reason of the low visibility in haze days. With the increasing of relative humidity, the number concentrations of particles, as a function of the diameter, gradually reduced for particles in 13.6-100 nm (ultrafine particle), but increased for particles above 100 nm. The number concentrations of particles between 500-1 000 nm and 1 000-2 500 nm in diameter were obviously influenced by relative humidity and the secondary transformation of the gaseous contaminants (SO₂,NO_X). During the haze days, the number concentrations of particles were mainly influenced by the emission from southeasterly and northeasterly wind, and negatively related with wind speed. The influence of temperature on the particle number concentrations was obviously in 13.6 nm and 100 nm in diameter. The boundary layer height negatively correlated with the ultrafine particle. The intensity of inversion layer particularly impacted on the ultrafine particle.