Sulfate Formation Enhanced by a Cocktail of High NOx, SO2, Particulate Matter, and Droplet pH during Haze-Fog Events in Megacities in China: An Observation-Based Modeling Investigation.
Sulfate Formation Enhanced by a Cocktail of High NOx, SO2, Particulate Matter, and Droplet pH during Haze-Fog Events in Megacities in China: An Observation-Based Modeling Investigation.
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DOI：
10.1021/acs.est.6b00768
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发表时间：
2016-07
影响因子：
11.4
通讯作者：
Jian Xue;Z. Yuan;S. Griffith;Xin Yu;A. Lau;J. Yu
中科院分区：
文献类型：
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作者：
Jian Xue;Z. Yuan;S. Griffith;Xin Yu;A. Lau;J. Yu
近年来，在中国的一些特大城市，持续一到几天的雾事件经常与高水平的气溶胶负荷有关，其特征是高硫酸盐（高达30 μg m(-3)），因此被称为雾霾事件。伴随的污染特征包括高气相SO2（高达71 ppbv）和NO2（高达69 ppbv）的混合比，高水相pH（5-6）和较小的雾滴（低至2 μm），这是由于化石燃料燃烧和建筑活动提供大量Ca（2+）的强烈排放造成的。在这项工作中，我们使用基于观测的二次无机气溶胶（OBM-SIA）模型来模拟中国特大城市遇到的雾霾事件条件下硫酸盐的形成途径。OBM分析发现，在典型的雾霾水pH为5.6时，溶解的NO2氧化S（IV）是最重要的途径，其次是SO2在气溶胶表面的非均相反应。由于高NOx条件抑制H2O2的形成，H2O2对S（IV）的水相氧化是一个非常次要的形成途径。模型结果表明，高雾水pH值、高浓度NO2、SO2和PM以及小雾滴的独特组合能够极大地促进硫酸盐的形成。这样的雾霾天气可能会导致夜间硫酸盐的快速生成，随后在早晨雾消散后，PM2.5就会很高。硫酸盐的形成被模拟为对雾水pH、PM和前驱气体NO2和SO2高度敏感。这些对主要影响因素的见解表明，减少道路粉尘和氮氧化物排放可以减少雾霾天气期间中国大城市的PM2.5负荷。
In recent years in a few Chinese megacities, fog events lasting one to a few days have been frequently associated with high levels of aerosol loading characterized by high sulfate (as high as 30 μg m(-3)), therefore termed as haze-fog events. The concomitant pollution characteristics include high gas-phase mixing ratios of SO2 (up to 71 ppbv) and NO2 (up to 69 ppbv), high aqueous phase pH (5-6), and smaller fog droplets (as low as 2 μm), resulting from intense emissions from fossil fuel combustion and construction activities supplying abundant Ca(2+). In this work, we use an observation-based model for secondary inorganic aerosols (OBM-SIA) to simulate sulfate formation pathways under conditions of haze-fog events encountered in Chinese megacities. The OBM analysis has identified, at a typical haze-fogwater pH of 5.6, the most important pathway to be oxidation of S(IV) by dissolved NO2, followed by the heterogeneous reaction of SO2 on the aerosol surface. The aqueous phase oxidation of S(IV) by H2O2 is a very minor formation pathway as a result of the high NOx conditions suppressing H2O2 formation. The model results indicate that the unique cocktail of high fogwater pH, high concentrations of NO2, SO2, and PM, and small fog droplets are capable of greatly enhancing sulfate formation. Such haze-fog conditions could lead to rapid sulfate production at night and subsequently high PM2.5 in the morning when the fog evaporates. Sulfate formation is simulated to be highly sensitive to fogwater pH, PM, and precursor gases NO2 and SO2. Such insights on major contributing factors imply that reduction of road dust and NOx emissions could lessen PM2.5 loadings in Chinese megacities during fog events.