Improving the representation of HONO chemistry in CMAQ and examining its impact on haze over China.

Shuping Zhang,Fengkui Duan,Jia Xing,Hong He,Arunachalam Sarav,Tao Ma,Haotian Zheng,Yujing Mu,Golam Sarwar,Dian Ding,Chaoyang Xue,Biwu Chu

doi:10.5194/acp-21-15809-2021

Abstract

We compare Community Multiscale Air Quality (CMAQ) model predictions with measured nitrous acid (HONO) concentrations in Beijing, China for December 2015. The model with the existing HONO chemistry in CMAQ severely under-estimates the observed HONO concentrations with a normalized mean bias of -97%. We revise the HONO chemistry in the model by implementing six additional heterogeneous reactions in the model: reaction of nitrogen dioxide (NO2) on ground surfaces, reaction of NO2 on aerosol surfaces, reaction of NO2 on soot surfaces, photolysis of aerosol nitrate, nitric acid displacement reaction, and hydrochloric acid displacement reaction. The model with the revised chemistry substantially increases HONO predictions and improves the comparison with observed data with a normalized mean bias of -5%. The photolysis of HONO enhances day-time hydroxyl radical by almost a factor of two. The enhanced hydroxyl radical concentrations compare favourably with observed data and produce additional sulfate via the reaction with sulfur dioxide, aerosol nitrate via the reaction with nitrogen dioxide, and secondary organic aerosols via the reactions with volatile organic compounds. The additional sulfate stemming from revised HONO chemistry improves the comparison with observed concentration; however, it does not close the gap between model prediction and the observation during polluted days.

Highlights

China has been suffering from haze pollution (Lelieveld et al, 2015) in which secondary particles contribute more than 70 % to the haze formation (Huang et al, 2014; Quan et al, 2014; Zheng et al, 2015; Guo et al, 2014)
The observed average concentration during the measurement period is 2.5 ppb; the ORI case only predicts an average concentration of 0.1 ppb, whereas the REV case predicts an average concentration of 2.3 ppb
Predicted OH concentrations with the existing HONO chemistry are lower than observed data almost by a factor of 2

Summary

Introduction

China has been suffering from haze pollution (Lelieveld et al, 2015) in which secondary particles contribute more than 70 % to the haze formation (Huang et al, 2014; Quan et al, 2014; Zheng et al, 2015; Guo et al, 2014). The mechanism for the formation of high levels of secondary particles is not yet clearly understood, and most current air quality models tend to underestimate particle concentrations compared with observed data in China. The gap between the model predictions and observed SO24− is persistent and still large (Zhang et al, 2019c)

Methods

Results

Conclusion