Effect of potential HONO sources on ROx budgets and SOA and PAN formation in North China in winter

Recent wintertime observations in north China found high concentrations of nitrous acid (HONO), secondary organic aerosols (SOA) and peroxyacetyl nitrate (PAN), especially during heavy haze periods, indicating stronger atmospheric oxidation capacity in winter haze days. Researchers speculated that HONO formation was enhanced in haze days through NO₂ heterogeneous reaction on aerosol surfaces, and high concentrations of HONO during daytime further improved SOA and PAN formation.

In this study, the WRF-Chem model updated with six potential HONO sources was used to quantify the impacts of potential HONO sources on the production and loss rates of RO_x ( OH+HO₂+RO₂) radicals, and on the concentrations of SOA and PAN in the Beijing-Tianjin-Hebei (BTH) region of China during wintertime of 2017. HONO simulations were greatly improved after considering the six potential sources, NO₂ heterogeneous reactions were the main sources of HONO. HONO photolysis was the key precursors of primary OH while the contribution of O₃ photolysis to OH could be neglected, the potential HONO sources remarkably accelerated RO_x cycles, significantly improved SOA and PAN simulations, especially in heavy polluted periods. The above results suggest that the potential HONO sources should be considered in regional and global chemical transport models when conducting relevant studies.