Preprints
https://doi.org/10.5194/egusphere-2022-178
https://doi.org/10.5194/egusphere-2022-178
 
08 Apr 2022
08 Apr 2022
Status: this preprint is open for discussion.

A comprehensive study about the in-cloud processing of nitrate through coupled measurements of individual cloud residuals and cloud water

Guohua Zhang1,2,3, Xiaodong Hu1,2,4, Wei Sun1,2,4, Yuxiang Yang1,2, Ziyong Guo1,2,4, Yuzhen Fu1,2, Haichao Wang5, Shengzhen Zhou5, Lei Li6, Mingjin Tang1,2,3, Zongbo Shi7, Duohong Chen8, Xinhui Bi1,2,3, and Xinming Wang1,2,3 Guohua Zhang et al.
  • 1State Key Laboratory of Organic Geochemistry and Guangdong Provincial Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou 510640, PR China
  • 2CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China
  • 3Guangdong-Hong Kong-Macao Joint Laboratory for Environmental Pollution and Control, Guangzhou Institute of Geochemistry, CAS, Guangzhou 510640, PR China
  • 4University of Chinese Academy of Sciences, Beijing 100049, PR China
  • 5School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou 519082, PR China
  • 6Institute of Mass Spectrometer and Atmospheric Environment, Jinan University, Guangzhou 510632, PR China
  • 7School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, U.K.
  • 8State Environmental Protection Key Laboratory of Regional Air Quality Monitoring, Guangdong Environmental Monitoring Center, Guangzhou 510308, PR China

Abstract. While the formation and evolution of nitrate in airborne particles are extensively investigated, little is known about the processing of nitrate in clouds. Here we present a detailed investigation on the in-cloud formation of nitrate, based on the size-resolved mixing state of nitrate in the individual cloud residual and cloud-free particles obtained by single particle mass spectrometry, and also the mass concentrations of nitrate in the cloud water and PM2.5 at a mountain site (1690 m a.s.l.) in southern China. The results show a significant enhancement of nitrate mass fraction and relative intensity of nitrate in cloud water and the cloud residual particles, respectively, reflecting a critical role of in-cloud processing in the formation of nitrate. We first exclude the gas phase scavenging of HNO3 and the facilitated activation of nitrate-containing particles as the major contribution for the enhanced nitrate, according to the size distribution of nitrate in individual particles. Based on regression analysis and theoretical calculations, we then reveal a critical role of in-cloud formation of nitrate via N2O5 hydrolysis, even during the daytime, attributed to the diminished light in clouds. Nitrate is highly related (R2 = ~0.6) to the variation of [NOx][O3], temperature and droplet surface area in clouds. Accounting for droplet surface area greatly enhances the predictability of the observed nitrate compared with using [NOx][O3] and temperature. The substantial contribution of N2O5 hydrolysis to nitrate in clouds during the daytime was reproduced by a multiphase chemical box model. Assuming that the photolysis rate is 30 % of the default setting, the overall contribution of N2O5 hydrolysis pathway to nitrate formation increases by ~20 % in clouds. Given that N2O5 hydrolysis acts as a major sink of NOx in the atmosphere, further model updates would improve our understanding about the processes contributing to nitrate production in cloud and the cycling of odd nitrogen.

Guohua Zhang et al.

Status: open (until 20 May 2022)

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  • RC1: 'Comment on egusphere-2022-178', Anonymous Referee #1, 29 Apr 2022 reply

Guohua Zhang et al.

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Short summary
We show a significant enhancement of nitrate mass fraction in cloud water and relative intensity of nitrate in the cloud residual particles, and highlight that hydrolysis of N2O5 serves as the critical route for the in-cloud formation of nitrate, even during the daytime. Given that N2O5 hydrolysis acts as a major sink of NOx in the atmosphere, further model updates may improve our understanding about the processes contributing to nitrate production in cloud and the cycling of odd nitrogen.