广州雾霾期间气溶胶水溶性离子的日变化特征及形成机制

为研究雾霾天气下SO42-、NO3-和NH4+的形成机制,2013年4月18~23日,使用6级Anderson大流量采样器采集了不同粒径段的气溶胶样品,并利用离子色谱对其中的水溶性无机离子进行了分析.结果表明,广州雾霾期间PM3和PM10中总水溶性无机离子平均浓度分别为(32.7±13.3)μg/m3和(39.4±15.7)μg/m3.SO42-、NO3-和NH4+是最主要的水溶性离子,它们在PM3和PM10中占总离子质量分数分别为76%和71%.3种离子主要集中在0.49~1.5μm的液滴模态,该模态中NH4+主要以(NH4)2SO4和NH4NO3的形式存在,而凝聚模态的NH4+则主要以(NH4)2SO4和NH4HSO4的形式存在.液滴模态的SO42-主要来自雾内或颗粒表面的液相氧化反应,NO3-主要来自夜间N2O5在颗粒表面的水解反应,NH4+主要来自NH3在颗粒上进行的非均相中和反应,而这3种离子在该模态的日变化特征则很好的反映了以上的形成机制.受太阳辐射的影响,3种离子的浓度在凝聚模态均表现为白天高于夜晚.

Diurnal variations and formation mechanisms of water-soluble inorganic ions in aerosols during a haze-fog period in Guangzhou

To investigate the formation mechanism of SO42-, NO3? and NH4+ during a haze-fog period (18~23 April 2013) in Guangzhou, China, particulate matter smaller than 10 μm was collected with an Anderson sampler equipped with a six-stage cascade impactor. Size-resolved mass concentrations of water soluble inorganic ions were quantitatively analyzed. During the haze-fog episode, the average mass concentrations of the total water soluble inorganic ions in PM3 and PM10 were (32.7±13.3)μg/m3 and (39.4±15.7)μg/m3, respectively. NH4+, NO3? and SO42? were found to be the dominant species, accounting for 76% and 71% of the total inorganic ions in PM3 and PM10, respectively. These ions were principally present in the size range of 0.49~1.5μm (i.e. droplet mode). Ammonium was mainly in the forms of (NH4)2 SO4 and NH4NO3 in the droplet mode, while present in the forms of (NH4)2 SO4 and NH4 HSO4 in the condensation mode (<0.49μm). Further analysis on the diurnal variation of these ions suggested that SO42- in droplet mode was mainly formed through in-fog processes and/or aqueous-phase reactions, while NO3- through the hydrolysis of N2O5, and NH4+ by heterogeneous neutralization. In addition, it was found that condensation mode SO42-, NO3? and NH4+ had higher mass concentration in the daytime than at night due to the influence of solar radiation.