Effects of Hydroperoxy Radical Heterogeneous Loss on the Summertime Ozone Formation in the North China Plain

Hydroperoxy radical (HO2) is a crucial oxidant participating in the oxidation of nitrogen oxide to nitrogen dioxide which constitutes one of the most important pathways for the ozone (O3) photochemical formation in the troposphere. Laboratory experiments and field observations have revealed efficient HO2 heterogeneous uptake on wet aerosols, but its impact on the O3 formation remains controversial. A severe and persistent O3 pollution episode has been simulated using the WRF-Chem model to evaluate the impacts of the HO2 heterogeneous loss on the O3 formation in the North China Plain (NCP) during the summertime of 2018. Comparisons between experimental simulations with the HO2 effective uptake coefficient of 0.2 and 0.0 shows that the HO2 heterogeneous loss decreases the daytime HO2 and maximum daily average 8-hour (MDA8) O3 concentrations by about 5% and 1% in the NCP, respectively. Emission mitigation from 2013 to 2018 is found to contribute a 2.1 μg m-3 (5%) increase in the MDA8 O3 concentration due to decreased aerosol sink for the HO2 heterogeneous loss in the NCP. Our results reveal that decreased HO2 heterogeneous uptake does not constitute an important factor driving the O3 trend since 2013 in the NCP.