广州城区秋季大气PM_(2.5)中主要水溶性无机离子分析

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。

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

On a rooftop 50m above ground and at a roadside 1.2m above ground in urban Guangzhou, PM_(2.5) samples were collected consecutively for a week in antumn of 2006 for comparison of major inorganic water-soluble ions including SO_4~(2-), NO_3~-, Cl~-, F~-, Na~+, NH_4~+, Ca~(2+), K~+ and Mg~(2+). Results showed that PM_(2.5) mass concentrations on the rooftop ranged 59.5～129.5 μg/m~3 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 44.1μg/m~3, accounting for 60.8% and 36.4% in total mass of PM_(2.5) respectively for the rooftop and roadside samples. SO_4~(2-) and NO_3~- were major constituents among major water soluble ions, and their shares in PM_(2.5) 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 PM_(2.5) instead had a relatively larger contribution from primary sources. Calculated sea salt contribution to water soluble fraction of PM_(2.5) was trivial. The equivalent concentrations of NH_4~+ were less than those of SO_4~(2-) and NO_3~- with neutralization ratio much lower than 1.0, indicating high particle acidity, which was higher on the rooftop than at the roadside.