长三角沙尘中气溶胶粒径分布及化学组分特征

基于PM、10nm~10μm气溶胶数谱、水溶性离子和气象要素数据，分析了2017年5月3日~8日一次沙尘远距离输送过程中长三角地区气溶胶粒径分布及其化学组成的污染特征.结果表明，此次沙尘伴随天气系统由北往南的传输过程中，PM的浓度逐渐降低，但是高浓度PM持续时间逐渐增加.沙尘在呼和浩特市影响时间为38h，而在南京的影响时间超过60h.沙尘期间气溶胶数浓度谱的峰值向大粒径段偏移，沙尘和非沙尘期间峰值分别位于33和26nm.表面积浓度谱在非沙尘期间为三峰型分布，但是在沙尘期间为四峰型分布.在沙尘期间PM_2.5和PM₁₀中水溶性离子的排序为Ca²⁺ > NH₄⁺ > SO₄^2- > NO₃^- > Mg²⁺ > Na⁺ > Cl^- > NO₂^- > K⁺ > F^-，非沙尘期间为NH₄⁺ > SO₄^2- > NO₃^- > Mg²⁺ > Ca²⁺ > Cl^- > NO₂^- > K⁺ > Na⁺ > F^-.沙尘期间不同水溶性离子的浓度变化不同，沙尘天PM_2.5和PM₁₀中Ca²⁺浓度分别是非沙尘天的9.5和13.7倍，Na⁺分别是非沙尘天的4.4倍和4.6倍.沙尘天PM_2.5和PM₁₀中Ca²⁺占总离子的比例分别为24.7%和24.9%，是非沙尘天的4.9和5.7倍.NO₃^-在PM₁₀中的占总离子的比例为18.7%，高于非沙尘天（13.9%），但是在PM_2.5中占总离子的比例仅为7.9%，低于非沙尘天（13.2%）.沙尘天F^-、Cl^-、SO₄^2-、NH₄⁺和K⁺离子在PM_2.5和PM₁₀中所占总离子的比例均低于非沙尘天.

Characteristics of aerosol size distribution and chemical components during a dust pollution episode in the Yangtze River Delta

Based on the measurement data of PM, aerosol number concentration (10nm~10μm), water-soluble ions (WSIs) and meteorological elements, the characteristics of aerosol size distribution and chemical components during a long-range transport of dust pollution episode in the Yangtze River Delta were analyzed from May 3 to 8, 2017. The results showed that the PM concentration gradually decreased when the dust transmitted from north to south accompanying with the synoptic system, but the duration time of high PM concentrations increased to the contrary. The impact time of the dust was 38h in Hohhot and exceeded 60h in Nanjing. The spectral distribution of number concentration shifted to larger particles on dust days, peaking at 26nm and 33nm on non-dust and dust days, respectively. The aerosol surface area concentration had a trimodal distribution on non-dust days and exhibited four peaks on dust days. The WSI concentrations in PM_2.5 and PM₁₀ on dust days ranked in the order of Ca²⁺ > NH₄⁺ > SO₄^2- > NO₃^- > Mg²⁺ > Na⁺ > Cl^- > NO₂^- > K⁺>F^-, and NH₄⁺ > SO₄^2- > NO₃^- > Mg²⁺ > Ca²⁺ > Cl^- > NO₂^- > K⁺ > Na⁺ > F^- on non-dust days. The mass concentration of Ca²⁺ and Na⁺ in PM_2.5, PM₁₀ on dust days were 9.5, 13.7 and 4.4, 4.6times higher than those on non-dust days, respectively. The proportion of Ca²⁺ to the total WSIs in PM_2.5 and PM₁₀ was 24.7% and 24.9% on dust days, which was 4.9 and 5.7times higher than those on non-dust days. The proportion of NO₃^- in PM₁₀ on dust days (18.7%) was higher than that on non-dust days (13.9%); but was only 7.9% for that in PM_2.5 on dust days, which was lower than that on non-dust days (13.2%). The proportions of F^-, Cl^-, SO₄^2-, NH₄⁺ and K⁺ in PM_2.5 and PM₁₀ on dust days were uniformly lower than those on non-dust days.