Halogens Enhance Haze Pollution in China.

Qinyi Li,Rafael P Fernandez,Carlos A Cuevas,Jose L Jimenez,Weihao Wang,Alfonso Saiz-Lopez,Xiao Fu,Alba Badia,Jianmin Chen,Xiang Peng,Yujing Mu,Tao Wang

doi:10.1021/acs.est.1c01949

Abstract

Severe and persistent haze events in northern China, characterized by high loading of fine aerosol especially of secondary origin, negatively impact human health and the welfare of ecosystems. However, current knowledge cannot fully explain the formation of this haze pollution. Despite field observations of elevated levels of reactive halogen species (e.g., BrCl, ClNO2, Cl2, HBr) at several sites in China, the influence of halogens (particularly bromine) on haze pollution is largely unknown. Here, for the first time, we compile an emission inventory of anthropogenic bromine and quantify the collective impact of halogens on haze pollution in northern China. We utilize a regional model (WRF-Chem), revised to incorporate updated halogen chemistry and anthropogenic chlorine and bromine emissions and validated by measurements of atmospheric pollutants and halogens, to show that halogens enhance the loading of fine aerosol in northern China (on average by 21%) and especially its secondary components (∼130% for secondary organic aerosol and ∼20% for sulfate, nitrate, and ammonium aerosols). Such a significant increase is attributed to the enhancement of atmospheric oxidants (OH, HO2, O3, NO3, Cl, and Br) by halogen chemistry, with a significant contribution from previously unconsidered bromine. These results show that higher recognition of the impact of anthropogenic halogens shall be given in haze pollution research and air quality regulation.

Highlights

Haze pollution has been threatening the health of millions of people in China for the past two decades
Haze pollution is characterized by an extremely high loading of fine aerosol, and especially that of secondary aerosol.[1]
secondary organic aerosol (SOA) comprises many oxidation products of various volatile organic compounds (VOCs) by oxidants, that is, OH, O3, and NO3.2 Sulfate is formed from the gaseous oxidation of SO2 by OH, aqueous reactions by H2O2, O3, and O2 catalyzed by transition metal ions (TMIs) in cloud droplets, and heterogeneous reactions on aerosol.[3−5] Nitrate is produced from NOx chemical processes involving OH and O3.6 Ammonium aerosol is determined by the availability of sulfuric acid, nitric acid (HNO3), ammonia (NH3), and aerosol pH

Summary

INTRODUCTION

Haze pollution has been threatening the health of millions of people in China for the past two decades. The presence of abundant VOCs and NOx species in the polluted region facilitates the reactions R1−R7 leading to an enhancement effect of halogens on oxidants; in the clean environment, reactions R8−R9 directly destroy O3 (the main source of OH radicals) and dominate the effect of halogens on oxidants, decreasing oxidation capacity. In the past few years, observational studies have reported elevated levels of halogen species in China. The majority of these reports focused on ClNO218−22 and a few on Cl223,24 and bromine species (BrCl, HOBr, Br2, and HBr).[25,26] A few modeling studies evaluated the impacts of chlorine chemistry on O3 and PM2.5.11,14 the overall impact of anthropogenic halogens ( bromine) on aerosols and haze pollution in China remains poorly understood.

MATERIAL AND METHOD

RESULTS AND DISCUSSION

■ ACKNOWLEDGMENTS

■ REFERENCES