长三角一次重污染事件中气溶胶粒径谱及水溶性离子分布特征

Distribution Characteristics of Aerosol Size and Water-soluble Ions During a Heavy Pollution Event in Yangtze River Delta

使用宽范围颗粒粒径谱仪(Wide-range panticle spectrometer,WPS)、Andersen-Ⅱ型9级撞击采样器和离子色谱仪对南京2011年4月29日至5月8日城市大气中10 nm^10μm气溶胶数浓度谱、质量浓度及水溶性离子浓度进行观测,观测过程涵盖了生物质燃烧、新粒子生成事件(New particle formation event,NPF)、沙尘远距离输送造成的重污染事件、短时降水过程以及晴好天气。结果表明:5月1日至5日长江三角洲发生的大范围重污染事件是由生物质燃烧以及起源于我国北方甘肃、内蒙古等地的强沙尘天气远距离输送共同造成的。NPF中核模态和爱根核模态的浓度较高,可达104个/cm3;沙尘天粗模态粒子的浓度最高,可达50个/cm3。降水对大于1μm的粗粒子的清除作用较强,而对于100 nm^1μm的积聚模态粒子的清除作用较小。不同天气过程中气溶胶数浓度谱分布不同。气溶胶数浓度谱在NPF期间为单峰型分布,而在沙尘天、雨天和晴天均为双峰型分布。不同天气条件下气溶胶质量浓度谱均为三峰型分布,峰值分别位于0.6μm、3.0μm和9.5μm。不同种类水溶性离子质量浓度谱不同。不同污染过程对气溶胶质量浓度和化学组分的影响不同。生物质燃烧对小于1μm的水溶性离子的影响较大,但是对质量浓度的贡献较小。沙尘对大于2.1μm的质量浓度影响较大,对水溶性离子浓度几乎没有影响。

The aerosol number concentration ranging from 10 nm to 10 μm, aerosol mass concentration and wa-ter-soluble ions were measured by using the Wide-Range Particle Spectrometer（WPS）, Anderson-Ⅱ-type 9 crash sampler and IC chromatography in Nanjing from April 29 to May 8, 2011. Episodes including the biomassburning, new particle formation event（NPF）, dust storm, rainfall and sunny days occurred during the observationperiods. Results show that the regional and heavy pollution episode in the Yangtze River Delta during May 1 to5 was caused by dust storm processes originated from the north China, such as Gansu and Inner Mongolia, andbiomass burning processes. The aerosol number concentration in nucleation mode and Aitken mode were thehighest in NPF event, and could reach 10^4/cm^-3. While the coarse mode aerosol had the highest number concen-tration in dust storm episode, and reached up to 50/cm^-3. The precipitation process had greater scavenging effectson coarse mode aerosol particles（〉1μm）, and had small scavenging effects on accumulation mode particles（100 nm^1 μm）. The spectral distributions of aerosol number concentration were different under different weath-er conditions, exhibiting unimodal on NPF days, and bimodal in episodes of dust storm, rainfall days and sunnydays. The spectral distributions of aerosol mass concentrations were trimodal under different weather conditions,with peaks at 0.6 μm, 3.0 μm and 9.5 μm, respectively. The spectral distributions of different water-solubleions were different. The different pollution events had different effects on the mass concentration and water-solu-ble ions of aerosol. The biomass burning process mainly affected the water-soluble ions of aerosol particles small-er than 1 μm, and had little impacts on mass concentration. On the contrary, dust storm process mainly affectedthe mass concentration of particles larger than 2.1μm, and had little impacts on water-soluble ions.