UCLA

OH radicals are crucial for the formation of secondary organic aerosol (SOA) and ozone in the atmosphere. HONO photolysis is one of the main sources of OH radicals, especially in winter. HONO chemistry in polluted areas has been a widely discussed in the last five dec-ades. However, HONO chemistry is often absent or simplified in air quality models, making its impact on OH radical chemistry uncertain. In this thesis, I investigated the formation of HONO over snow in a polluted rural area.The platform for atmospheric chemistry and vertical transport in one dimension (PACT-1D) model was used to calculate a 4-day cycle (Jan. 18th -Jan. 21st,2014) of atmospheric composi-tion and HONO figures. The model output was compared with observational data from the Uintah Basin Winter Ozone Study 2014(UBWOS 2014). Modeled HONO mixing ratios compared well with observation. HONO fluxes from surface chemistry in the model shows good agreement of shape and magnitude. In conclusion, PACT-1D model calculations show that chemical HONO formation on the snow explain the observed HONO mixing ratios.