不同气团来源对广州细颗粒物理化特性的影响

利用2006年7月广州细颗粒物质量浓度、数谱分布与化学组成的观测数据与气团后向轨迹聚类分析结果,系统分析了不同气团来源对广州细颗粒物理化特性的影响。观测期间,广州气团来源可分成来自远海、近海、西面陆地和北面陆地4种类型。细颗粒物总数浓度水平在4种类型中基本相当。当气团来自远海时,二次转化影响较小,PM2.5质量浓度较低,颗粒物数浓度从大到小依次为老化爱根核模态新鲜爱根核模态度积聚模态;受到海洋气团的影响,Cl-在PM2.5中比例为4种类型中最大。气团来自近海时,颗粒物二次生成与老化现象突出,数谱峰值出现在积聚模态,而其他类型出现在爱根核模态;SO2-4、OC与NO-3之和在PM2.5中的比例大于50%,为4种类型中最高。气团来自西面陆地和北面陆地时,细颗粒物受陆地传输老化气团和本地来源影响均较明显。来自北面陆地时,250 nm以上颗粒物数浓度明显升高,是PM2.5平均浓度远高于其他类型的直接原因之一。

Impact of Air Mass History on the Physical and Chemical Properties of Fine Particles in Guangzhou

Based on the measurement of mass concentrations, number size distributions, and chemical compositions of fine particles in Guangzhou in July of 2006 and the cluster analysis of air mass backward trajectories, the impact of air mass history on the physical and chemical properties of fine particles were discussed systematically. During the measurement period, the air mass backward trajectories can be categorized into four main types: From the open sea, from the offing, from the western continent, and from the northern continent. Total particle number concentrations of the four types were comparable. With air mass from the open sea, the influence of secondary transformation was weak, mass concentrations of PM_2.5 were low, and the rank of size resolved particle number concentrations was: Aged Aitken mode>fresh Aitken mode >accommodation mode; under the impact of marine air mass, the contribution of Cl^- to PM_2.5 was the highest of the four types. With air mass from the offing, the effect of secondary transformation and aging process on fine particles was obvious: The average particle number size distribution peaked at the accommodation mode, different from the other types at the Aitken mode; the total contribution of SO₄^2-, OC, and NO₃^- to PM_2.5 was over 50%, highest among the four types. When the air mass came from the western or northern continent, the effects on the fine particles imposed by the aged air mass transported over the land and local sources were both noticeable. Concentrations of fine particles over 250m increased significantly with the air mass from north, which was one of the direct causes of the much higher PM_2.5 mass concentration of this type than the other three ones.