Underestimated benefits of NOx control in reducing SNA and O3 based on missing heterogeneous HONO sources

Substantial NOx emission mitigation is crucial for the synergistic reduction of particulate matter and ozone (O3) pollution in China. The traditional air quality model does not consider heterogeneous HONO chemistry, leading to uncertainties in estimating the benefits of NOx control. Previous studies have shown that the parameterization of heterogeneous HONO formation increases both the simulated value of sulfate–nitrate–ammonium (SNA) and that of O3, thus adding the heterogeneous reactions of HONO into air quality models inevitably leads to changes in the estimated benefits of NOx abatement. Here we investigated the changes in SNA and O3 concentrations from NOx emission reduction before and after adding heterogeneous HONO reactions in the Community Multi-Scale Air Quality (CMAQ) model. Including heterogeneous HONO reactions in the simulation improved the benefits of NOx reduction in terms of SNA control in winter. With 80