State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China; University of Chinese Academy of Sciences, Beijing, 100049, China; Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China.
Environ Pollut. 2019 Sep;252(Pt A):236-244. doi: 10.1016/j.envpol.2019.05.119. Epub 2019 May 23.
Current air quality models usually underestimate the concentration of ambient air sulfate, but the cause of this underestimation remains unclear. One reason for the underestimation is that the sulfate formation mechanism in the models is incomplete, and does not adequately consider the impact of the synergistic effects of high concentrations of multiple pollutants on sulfate formation. In this work, the roles of gaseous NO, NH and solution ionic strength in the formation of sulfate in the aqueous phase were quantitatively investigated using a glass reactor and a 30 m smog chamber, separately. The results showed that sulfate formation was enhanced to different degrees in the presence of gas-phase NO, NH and their coexistence as solutes in both liquid solution and aerosol water. NH enhances the aqueous oxidation of SO by NO mainly by accelerating the uptake of SO through increased solubility. More importantly, we found that high ionic strength in aerosol water could significantly accelerate the aqueous oxidation of SO, resulting in unexpectedly high S(VI) formation rates. We estimate that under severe haze conditions, heterogeneous oxidation of SO by NO on aerosols may be much shorter than that through gas phase oxidation by OH, aided by high ionic strengths in aerosols. Considering the existence of complex air pollution conditions with high concentrations of NO, NH and aerosol water, as expected in typical urban and suburban settings, the sulfate formation mechanisms revealed in the present work should be incorporated into air quality models to improve the prediction of sulfate concentrations.
目前的空气质量模型通常低估了环境空气中硫酸盐的浓度，但这种低估的原因仍不清楚。低估的一个原因是模型中硫酸盐形成机制不完整，没有充分考虑多种污染物高浓度对硫酸盐形成的协同作用的影响。在这项工作中，分别使用玻璃反应器和 30m 烟雾箱定量研究了气相 NO、NH 和溶液离子强度在水相硫酸盐形成中的作用。结果表明，在气相 NO、NH 及其共存作为液相和气溶胶水溶质的存在下，硫酸盐的形成都不同程度地得到了增强。NH 通过增加溶解度主要通过加速 SO 的吸收来增强 SO 的水相氧化。更重要的是，我们发现气溶胶水中的高离子强度可以显著加速 SO 的水相氧化，导致出乎意料的高 S(VI)形成速率。我们估计，在严重雾霾条件下，气溶胶上的 NO 对 SO 的非均相氧化可能比 OH 通过气相氧化的时间短得多，这得益于气溶胶中高的离子强度。考虑到存在复杂的空气污染条件，NO、NH 和气溶胶水的浓度较高，这在典型的城市和郊区环境中是可以预期的，因此，本工作中揭示的硫酸盐形成机制应被纳入空气质量模型，以提高硫酸盐浓度的预测。
