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.