Effects of hydroperoxy radical heterogeneous loss on the summertime ozone formation in the North China Plain.

Hydroperoxy radical (HO) 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 (O) photochemical formation in the troposphere. Laboratory experiments and field observations have revealed efficient HO heterogeneous uptake on wet aerosols, but its impact on the O formation remains controversial. A severe and persistent O pollution episode has been simulated using the WRF-Chem model to evaluate the impacts of the HO heterogeneous loss on the O formation in the North China Plain (NCP) during the summertime of 2018. Comparisons between experimental simulations with the HO effective uptake coefficient of 0.2 and 0.0 shows that the HO heterogeneous loss decreases the daytime HO and maximum daily average 8-hour (MDA8) O 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 (5%) increase in the MDA8 O concentration due to decreased aerosol sink for the HO heterogeneous loss in the NCP. Our results reveal that decreased HO heterogeneous uptake does not constitute an important factor driving the O trend since 2013 in the NCP.