Occurrence of atmospheric nitrous acid in the urban area of Beijing (China)

We used a pseudo steady state approach (PSS), which included homogeneous and heterogeneous reactions and direct emission, explaining on average about 83% and 48% of the observed HONO levels during the intensive winter and summer periods, respectively. The daytime unknown HONO production was on average 2.58 ppb h(-1) during the summer period. The HNO3 and fine particulate NO3- photolysis contributed weakly as HONO source. Including these sources in the PSS calculation, we explained about 53% of the observed HONO levels. The results showed that heterogeneous J(NO2) dependent processes on aerosol and ground surfaces, involving NO2 as HONO precursor, were HONO sources during the summer measurements. (C) 2013 Elsevier B.V. All rights reserved.