广州城区秋季大气PM_(2.5)中主要水溶性无机离子分析

Major Inorganic Water-soluble Ions in Fine Particles Collected in Autumn in Urban Guangzhou

分别在广州市中心城区高楼顶(距地50m)和交通干线路边(距地1.2m),于2006年秋季连续一周采集了大气PM2.5样品,对比分析了SO42-、NO3-、Cl-、F-、Na+、NH4+、Ca2+、K+、Mg2+等9种水溶性无机离子含量。结果表明,楼顶相对充分混合大气中PM2.5的质量浓度范围59.5～129.5μg/m3,均值为83.7μg/m3;交通干线路边大气PM2.5的质量浓度范围为108.4～132.2μg/m3,均值为121.1μg/m3。9种离子总浓度平均达到50.9(楼顶)和44.1(路边)μg/m3,占PM2.5质量浓度的60.8%(楼顶)和36.4%(路边)。SO42-和NO3-为水溶性无机离子主要组成,其占PM2.5质量浓度的比例均是楼顶高于路边,显示二次气溶胶对楼顶充分混合大气中PM2.5有较大贡献,而路边样品中一次来源贡献相对较大。计算表明采样期间海盐对广州大气PM2.5中的水溶性组分贡献较小。NH4+当量浓度远小于SO42-和NO3-的当量浓度,中和度远<1,反映PM2.5酸性较强,且楼项PM2.5粒子酸性高于路边样品。

On a rooftop 50m above ground and at a roadside 1.2m above ground in urban Guangzhou, PM25 samples were collected consecutively for a week in autumn of 2006 for comparison of major inorganic water-soluble ions including SO4^2-, NO3^-, Cl^-, F^-, Na^＋, NH4^＋, Ca^2＋, K^＋ and Mg^2＋ . Results showed that PM25 mass concentrations on the rooftop ranged 59.5-129.5 μg/ma with an average of 83.7μg/m^3, while those at the roadside ranged 108.4-132.2μg/m^3 with average of 121.1μg/m^3. In average, 9 ions/anions had a sum of 50.9μg/m^3 and 44.11μg/m^3, accounting for 60.8% and 36.4% in total mass of PM25 respectively for the rooftop and roadside samples. SO4^2- and NO3^- were major constituents among major water soluble ions, and their shares in PM25 were both higher on the rooftop than at the roadside, indicating that contributions from secondary formation were larger on the rooftop where air was well mixed, and that roadside PM25 instead had a relatively larger contribution from primary sources. Calculated sea salt contribution to water soluble fraction of PM25 was trivial. The equivalent concentrations of NH4^＋ were less than those of SO4^2- and NO3^- with neutralization ratio much lower than 1.0, indicating high particle acidity, which was higher on the rooftop than at the roadside.