Science Inventory

Impact and pathway of halogens on atmospheric oxidants in coastal city clusters in the Yangtze River Delta region in China

Citation:

Chen, H., P. Liu, Q. Wang, R. Huang, AND G. Sarwar. Impact and pathway of halogens on atmospheric oxidants in coastal city clusters in the Yangtze River Delta region in China. Atmospheric Pollution Research. Turkish National Committee for Air Pollution Research and Control, Izmir, Turkey, 15(2):N/A, (2024). https://doi.org/10.1016/j.apr.2023.101979

Impact/Purpose:

Traditionally, air quality models employ emissions and chemistry of VOC, NOx, SO2, CO, NH3, and PM. Halogens are not typically included in most air quality models. Recent studies suggest that halogens emitted from natural and anthropogenic sources can impact air quality. In this study, both natural and anthropogenic halogen emissions are estimated over China and their impacts on air quality are examined using the CMAQ model.

Description:

Halogens (chlorine, bromine, and iodine) are known to profoundly influence atmospheric oxidants (hydroxyl radical (OH), hydroperoxyl radical (HO¿), ozone (O¿), and nitrate radical (NO¿)) in the troposphere and sub- sequently affecting air quality. However, their impact on atmospheric oxidation and air pollution in coastal areas in China is poorly characterized. In this study, we use the WRF-CMAQ (Weather Research and Forecasting- Community Multiscale Air Quality) model with full halogen chemistry and process analysis to assess the in- fluences and pathways of halogens on atmospheric oxidants in the Yangtze River Delta (YRD) region, a typical coastal city cluster in China. Halogens cause the annual OH radical increase by up to 16.4% and NO¿ decrease by up to 45.3%. O¿ increases by 2.0% in the YRD but decreases by 3.3% in marine environment. Halogen induced changes in atmospheric oxidants lead to a general increase of atmospheric oxidation capacity by 5.1% (maximum 48.4%). The production rate of OH (POH) in the YRD is enhanced by anthropogenic chlorine through both increased HO¿ pathway and hypohalous acid photolysis pathway, while POH over ocean is enhanced by oceanic halogens through converting HO¿ into hypohalous acid. Anthropogenic chlorine enhances both O¿ and NO¿ production (PNO¿) rates through influencing their precursors while oceanic halogens reduce PNO¿ and directly destroy ozone. Iodine contributed most (on average of 91% in oceanic halogens) in reducing production rates of potential effects of halogens on air quality need to be considered in air lity policies and regulations in the YRD region.