A photochemical model and sensitivity study of the triple-oxygen isotopic (Δ¹⁷O) composition of NO_y, HO_x, and H₂O₂ in a polluted boundary layer

Abstract. We present a photochemical model developed for the explicit calculation of triple oxygen isotopic compositions (Δ¹⁷O) of major atmospheric species. While we focus on the Δ¹⁷O of HNO₃ and aerosol nitrate (NO⁻₃) and its precursors such as NO, NO₂ and N₂O₅, the general implementation given here also provides Δ¹⁷O predictions for other important atmospheric compounds such as OH, H₂O₂, and HO₂. Through the use of a simple aerosol surface area model, we calculate the Δ¹⁷O composition of aerosol nitrate produced as a function of aerosol size and aerosol surface type. We explore the sensitivity of the Δ¹⁷O of atmospheric species through a series of sensitivity studies and show that the Δ¹⁷O of atmospheric compounds is affected to various degrees by environmental factors such as temperature, relative humidity, ozone concentration, NO_x flux, and total ozone column density. In addition, we find that Δ¹⁷O of these species is sensitive to photochemical conditions such as cloud albedo, latitude, and time of year. We compare the Δ¹⁷O calculation outputs to previous methods and find significant differences in the Δ¹⁷O of NO₂. We describe the origins of these and suggest studies that may help to resolve these differences.