秋季南通近海大气气溶胶水溶性离子粒径分布特征

2012年10~11月在南通近海设立观测点,利用Anderson分级采样器采集大气气溶胶样品,用离子色谱仪(Metrohm IC)分析其中10种水溶性离子组成.结果表明,南通秋季近海PM10和PM2.1中水溶性离子浓度分别为59.70,45.96mg/m3.PM2.1中主要离子质量浓度排列依次为SO42->NO3->NH4+>Ca2+. SO42-,NO3-和NH4+占PM10中离子浓度的80%以上,二次离子为近海区域气溶胶的主要成分.SO42,NH4+和NO3-均表现出单峰型分布,峰值区间均为0.43~1.1mm,Ca2+,Na+和Cl-表现为双峰型.Ca2+高浓度峰值出现4.7~5.8mm粒径段内;Na+和Cl-峰值出现在0.43~1.1mm和3.3~5.8mm内,但最大峰值浓度区间不一致.PM10中nss-SO42-/SO42-比值均高于90%,陆地源对近海硫酸盐的影响显著.nss-SO42-/NO3-的比值在<2.1μm的粒径段内均大于1,表明该区域固定源是大气细粒子中离子的重要贡献源,但移动源对粗粒子的影响值得重视.个例分析显示,稳定的天气系统,高污染排放内陆地区的污染物传输,是造成10月27日的严重污染过程的主要原因.

Size distribution of water-soluble ions in aerosol from an offshore site of Nantong in autumn

Size fractionated aerosol particles were collected with an Anderson cascade sampler at an offshore site of Nantong in October and November, 2012. Ten types of water-soluble ions were analyzed by ion chromatography (IC, Metrohm Inc. Swiss). Results show that the mass concentrations of all the ions in PM10 and PM2.1 were 59.70mg/m3and 45.96mg/m3, respectively. The descending order of mass concentration for major ionic species in PM2.1 was: SO42->NO3->NH4+>Ca2+. SO42-, NH4+ and NO3- were found to contribute about 80% of total ionic concentrations in PM10, indicating that the secondary ionic species were major component in aerosol. SO42-, NH4+ and NO3- were unimodally distributed in particles, with a peak value in size-bin of 0.43~1.1mm. Ca2+, Na+ and Cl- exhibited bimodal distribution. Ca2+ showed the dominant peak at 4.7~3.3mm, while Cl- and Na+ exhibited the peak values in the size ranges of 0.43~1.1mm and 3.3~5.8mm. However, the maximum concentrations of Cl- and Na+ were located in different size ranges. The value of nss-SO42-/SO42 was higher than 90% in PM10, indicating that the terrestrial sources exert significant influence upon the sulfate aerosols of the offshore site. The ratios of nss-SO42-/NO3- were all higher than 1.0 for aerosol particles less than 2.1mm in diameter, indicating that the stationary sources were more important for ions in fine particles than vehicle emission in this region. The influence of vehicle emission on coarse particles should also be paid attention. Case study showed that the stable weather system and the transport of pollutants from inland regions with high pollutant emissions can explain the severe pollution episode occurred in October 27th.