TY - JOUR
T1 - Unraveling a New Chemical Mechanism of Missing Sulfate Formation in Aerosol Haze
T2 - Gaseous NO2 with Aqueous HSO3 -/SO3 2-
AU - Yang, Jinrong
AU - Li, Lei
AU - Wang, Shixian
AU - Li, Hui
AU - Francisco, Joseph S.
AU - Zeng, Xiao Cheng
AU - Gao, Yi
N1 - Funding Information:
We thank Pan Guo, Hao Li, Yongchun Liu, and Jie Zhong for valuable discussions. Y.G. is grateful for funding support from the National Natural Science Foundation of China (11574340, 21773287). This work was also supported by a China Postdoctoral Science Foundation-funded project (2018M640051, 2019T120041). The computational resources utilized in this research were provided by the Shanghai Supercomputer Center and the National Supercomputing Center in Tianjin. X.C.Z. and J.S.F. are grateful for support from the University of Nebraska Holland Computing Center.
Publisher Copyright:
© 2019 American Chemical Society.
PY - 2019/12/11
Y1 - 2019/12/11
N2 - A source of missing sulfate production associated with high-level fine-particle pollution in the megacities of China is believed to stem from the oxidation of a notable fraction of sulfur dioxide (SO2) by nitrogen dioxide (NO2) in aqueous aerosol environments, suggesting that an unknown reaction pathway exists for aqueous sulfur oxidation. At weakly acidic aerosols, the dissolved SO2 mainly exists in the form of HSO3 -, whereas at neutral aerosols, SO3 2- becomes the main form. Herein, by using both ab initio molecular metadynamics simulations and high-level quantum mechanical calculations, we show a hitherto unreported chemical mechanism for the formation of sulfate through the reaction between HSO3 -/SO3 2- anions at the surface/in the interior of a water nanodroplet and gas-phase NO2 molecules. For weakly acidic aerosols, contrary to the conventional high-barrier electron-transfer pathway in the gas phase, HSO3 - at the water nanodroplet surface can transfer an electron to NO2 with a low free-energy barrier of 4.7 kcal/mol through a water bridge. For neutral aerosols, the electron-transfer pathway between SO3 2- in the interior of the water nanodroplet and NO2 needs to overcome a lower free-energy barrier of 3.6 kcal/mol to form SO3 -, with the assistance of the hydrogen-bonding network of water molecules. This new reaction pathway for the sulfate formation from HSO3 -/SO3 2- via water nanodroplets and gaseous NO2 provides a new perspective on the growth of haze particles from pre-existing aqueous aerosols and suggests that new control strategies are needed to address haze pollution.
AB - A source of missing sulfate production associated with high-level fine-particle pollution in the megacities of China is believed to stem from the oxidation of a notable fraction of sulfur dioxide (SO2) by nitrogen dioxide (NO2) in aqueous aerosol environments, suggesting that an unknown reaction pathway exists for aqueous sulfur oxidation. At weakly acidic aerosols, the dissolved SO2 mainly exists in the form of HSO3 -, whereas at neutral aerosols, SO3 2- becomes the main form. Herein, by using both ab initio molecular metadynamics simulations and high-level quantum mechanical calculations, we show a hitherto unreported chemical mechanism for the formation of sulfate through the reaction between HSO3 -/SO3 2- anions at the surface/in the interior of a water nanodroplet and gas-phase NO2 molecules. For weakly acidic aerosols, contrary to the conventional high-barrier electron-transfer pathway in the gas phase, HSO3 - at the water nanodroplet surface can transfer an electron to NO2 with a low free-energy barrier of 4.7 kcal/mol through a water bridge. For neutral aerosols, the electron-transfer pathway between SO3 2- in the interior of the water nanodroplet and NO2 needs to overcome a lower free-energy barrier of 3.6 kcal/mol to form SO3 -, with the assistance of the hydrogen-bonding network of water molecules. This new reaction pathway for the sulfate formation from HSO3 -/SO3 2- via water nanodroplets and gaseous NO2 provides a new perspective on the growth of haze particles from pre-existing aqueous aerosols and suggests that new control strategies are needed to address haze pollution.
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U2 - 10.1021/jacs.9b08503
DO - 10.1021/jacs.9b08503
M3 - Article
C2 - 31722172
AN - SCOPUS:85075675061
VL - 141
SP - 19312
EP - 19320
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 49
ER -