Heterogeneous Oxidation of SO2 in Sulfate Production during Nitrate Photolysis at 300 nm: Effect of pH, Relative Humidity, Irradiation Intensity, and the Presence of Organic Compounds
Heterogeneous Oxidation of SO2 in Sulfate Production during Nitrate Photolysis at 300 nm: Effect of pH, Relative Humidity, Irradiation Intensity, and the Presence of Organic Compounds
复制标题
300 nm 硝酸盐光解过程中硫酸盐生产中 SO2 的非均相氧化：pH、相对湿度、辐照强度和有机化合物存在的影响
DOI：
10.1021/acs.est.9b01623
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发表时间：
2019-08-06
影响因子：
11.4
通讯作者：
Chan, Chak K.
中科院分区：
文献类型：
--
作者：
Gen, Masao;Zhang, Ruifeng;Chan, Chak K.
SO2的非均相氧化作用是造成我国灰霾期间硫酸盐高负荷的重要机制之一。我们早期的工作报道了SO2氧化过程中产生的OH和NO2在250 nm硝酸盐光解（环境。Sci.技术快报2019，6，86-91）。在这里，我们将这项工作扩展到在300 nm照射下硝酸盐光解过程中检查硫酸盐的产生，这可以额外产生NO2-或HNO 2，N（III）。流动池/原位拉曼实验表明，SO2的反应吸收系数γ（SO2）可表示为γ（SO2）= 1.64 × p（NO3-），其中p（N）（O3）（-）为硝酸盐的光解速率，范围为（1.0-8.0）× 10（-5）M·s（-1）。我们的动力学模型与p（NO3-）预测，N（III）是SO2氧化的主要贡献者，其次是NO2的贡献。此外，OH清除剂（例如，乙二醛或草酸）并不抑制硫酸盐的产生，这是因为减少了N（III）-消耗反应和由它们的存在维持的高颗粒pH。我们的计算表明，在典型的混浊条件下，硝酸盐的光解机制可以在pH 4-6和p（NO3-）= 10（-5）M s（-1）时产生类似于1 μ g m（-3）h（-1）的硫酸盐。本研究强调了在大气相关的光化辐射下，在颗粒硝酸盐光解的重要性，在SO2的活性氮（NO2-/HNO 2和NO2）的非均相氧化。然而，硝酸盐的光解速率常数需要更好地约束环境气溶胶。
Heterogeneous oxidation of SO2 is one of the promising mechanisms to account for high loading of sulfate during severe haze periods in China. Our earlier work reported on the SO2 oxidation by OH and NO2 produced during 250 nm nitrate photolysis (Environ. Sci. Technol. Lett. 2019, 6, 86-91). Here, we extend that work to examine sulfate production during nitrate photolysis at 300 nm irradiation, which can additionally generate NO2- or HNO2, N(III). Flow cell/in situ Raman experiments showed that the reactive uptake coefficient of SO2, ( )gamma(SO2), can be expressed as gamma(SO2) = 1.64 X p(NO3-), where p(N)(O3)(-) is the nitrate photolysis rate in the range of (1.0-8.0) x 10(-5) M s(-1). Our kinetic model with the p(NO3-) predicts that N(III) is the main contributor to the SO2 oxidation, followed by NO2 contribution. Furthermore, the addition of OH scavengers (e.g., glyoxal or oxalic acid) does not suppress the sulfate production because of the reduced N(III)-consuming reactions and the high particle pH sustained by their presence. Our calculations illustrate that under characteristic haze conditions, the nitrate photolysis mechanism can produce sulfate at similar to 1 mu g m(-3) h(-1) at pH 4-6 and p(NO3-) = 10(-5) M s(-1). The present study highlights the importance of in-particle nitrate photolysis in heterogeneous oxidation of SO2 by reactive nitrogen (NO2-/HNO2 and NO2) under atmospherically relevant actinic irradiation. However, the nitrate photolysis rate constant needs to be better constrained for ambient aerosols.