PNNL

Abstract

The nocturnal DOAS measurements of HONO and NO2 from three field experiments are presented. The observations show that [HONO]/[NO2] ratios between 10-30% relative humidity (RH) do not exceed 0.05, while values of up to 0.09 were observed at higher RH. These results are analyzed by interpreting the observed maximum [HONO]/[NO2] ratio at a given relative humidity as the pseudo steady state between the heterogeneous NO2 to HONO conversion and the HONO loss on surfaces. Theoretical condiderations show that the [HONO]/[NO2] ratio at the PSS is equal to the ratio of the heterogeneous NO2 to HONO conversion coefficient reactive HONO uptake coefficient, thus showing these processes depend on RH. This result has implications for the parameterizations of HONO formation in air pollution models.