Development and field-deployment of an absorption spectrometer to measure atmospheric HONO and NO2

Field observations show daytime HONO levels in urban, rural and remote environments are greater than those expected at photostationary state, that is, balance between production by NO+OH reaction and loss by UV-photolysis and OH-oxidation. Studies have interpreted measurements of [HONO]Obs > [HONO]PSS - or equivalently, the rate of HONO loss exceeding that of production - as evidence of a missing, sunlight-driven HONO source. Formation rate inferred from assuming photostationarity indicate a significant source of HONO, which photolyzes to yield OH. Moreover, depending on the mechanism, it may represent a pathway by which deposited nitrogen oxides are repartitioned back into the atmosphere in reactive form.