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

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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.