上海市大气颗粒物中水溶性离子的粒径分布特征

Characterization of major water-soluble ions in size-fractionated particulate matters in Shanghai

分析了上海市嘉定区不同粒径的大气颗粒物中9种水溶性离子(SO42-、NO3-、NH4+、K+、Na+、Cl-、Ca2+、Mg2+、F-)的分布特征.结果显示,SO42-、NO3-和NH4+含量很高,占9种离子总和的65%～81%.颗粒物的C/A值平均为1.08,说明颗粒物呈中性,略偏碱,这可能与缺少碳酸根等的测定有关.<1.5μm颗粒物中的离子占所有粒径段离子的52%～87%,表明离子主要集中在细颗粒物中.NH4+、K+呈单峰分布,峰值出现在<0.95μm的颗粒段;SO42-、NO3-、Ca2+、Cl-呈双峰分布,峰值分别出现在<0.95μm和3.0～7.2μm的粒径段,其中SO42-、NO3-的较高峰出现在<0.95μm的细颗粒段,Ca2+的较高峰出现在>3.0μm的颗粒段,Cl-则两峰高度相当;既有双峰分布又有单峰分布的离子是Na+、Mg2+和F-,3种离子的较高峰出现在>3.0μm的颗粒段.离子粒径分布与采样期间的气象条件、离子的形成机制和来源有关.

Size distributions of 9 water –soluble ions （SO42-、NO3-、NH4＋、K＋、Na＋、Cl - 、Ca2＋、Mg2＋、F - ） in atmospheric particles of Shanghai were determined. SO42-、NO3- and NH4＋ contributed 65%～81% of mass concentrations of the total ions. The average ratios of cations/anions （C/A） of the particles were 1.08, close to unity, indicating that particles were a bit more alkaline, which may be relative to the lack of determination of carbonate and so on. Mass concentrations of the ions focused in the particles with size of 1.5μm, which accounted for 52%～87% of those in the total suspended particles. Size distributions of NH4＋and K＋ showed mono-modals with the peak at the particle size of 0.95μm, SO42-、NO3-、Ca2＋、 Cl- appeared bi-modals with peaks at the particle sizes of 0.95μm and 3.0～7.2μm, respectively. SO42-、NO3- were preferably enriched in the particles with size of 0.95μm, while Ca2＋ in the particles with size of 3.0μm. Cl - appeared equal values in either of the two peaks. Na＋、Mg2＋ and F- showed both of bi-modals and mono-modals, and they were preferably enriched in the particles with size of 3.0μm. The size distributions of these ions depended on the meteorological conditions, formation mechanisms and sources.