The effects of nitrate on the heterogeneous uptake of sulfur dioxide on hematite
Author:
Kong L. D., Zhao X., Sun Z. Y., Yang Y. W., Fu H. B., Yang X., Zhang S. C., Chen J. M., Wang L.ORCID, Cheng T. T.
Abstract
Abstract. Nitrate is often found to be associated with atmospheric particles. Surface nitrate can change the hygroscopicity of these particles, and thus impact their chemical reactivity. However, the influence of nitrate on the heterogeneous reactions of atmospheric trace gases is poorly understood. In this work, the effects of nitrate on heterogeneous conversion of SO2 with hematite at 298 K were investigated using an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and a White cell coupled with Fourier transform infrared spectroscopy (White cell-FTIR). It is found that nitrate participates in the heterogeneous reactions of SO2, accelerates the formation rate of sulfate, and leads to the formation of surface-adsorbed HNO3 and gas-phase N2O and HONO, revealing that nitrate has a significant impact on the heterogeneous conversion of SO2 to sulfate. The results indicate that small amounts of nitrate significantly enhance the reactivity of hematite-nitrate mixtures and favor the enhancement in SO2 uptake and an increase in the amount of sulfate on hematite. For mixtures, the sample containing 24% nitrate exhibits the highest sulfate formation rate, and its corresponding average sulfate formation rate is about 5 times higher than that of hematite alone. No uptake of SO2 and formation of sulfate are observed on the pure nitrate. Evidence presented herein implies a significant contribution of the unreleased HNO3 and HONO in the particles for the conversion of SO2 and the enhanced formation of sulfate in the atmosphere. A possible mechanism for the influence of nitrate on the heterogeneous conversion of SO2 on hematite is proposed, and atmospheric implications based on these results are discussed.
Publisher
Copernicus GmbH
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