Heterogeneous conversion of NO2 on secondary organic aerosol surfaces: A possible source of nitrous acid (HONO) in the atmosphere?

Abstract

The heterogeneous conversion of NO₂ on different secondary organic aerosols (SOA) was investigated with the focus on a possible formation of nitrous acid (HONO). In one set of experiments different organic aerosols were produced in the reactions of O₃ with alpha-pinene, limonene or catechol and OH radicals with toluene or limonene, respectively. The aerosols were sampled on filters and exposed to humidified NO₂ mixtures under atmospheric conditions. The estimated upper limits for the uptake coefficients of NO₂ and the reactive uptake coefficients NO₂  -> HONO are in the range of 10^-6 and 10^-7, respectively. The integrated HONO formation for 1 h reaction time was 13 cm^-2 geometrical surface and HONO were in the range of 7 x 10^-7 - 9 x 10^-6. The results from the present study show that heterogeneous formation of nitrous acid on secondary organic aerosols (SOA) is unimportant for the atmosphere.