Sources of atmospheric nitrous acid (HONO) in the European High Arctic

The atmospheric concentrations of nitrous acid (HONO) have been measured from 15 to 25 April 2010 at Ny-Ålesund (Svalbard). The results were discussed from the stand point of diurnal variations and meteorological effects. No clear diurnal cycle for the HONO concentrations was observed during our measurements. HONO concentration showed strong and significant correlation with both nitrogen dioxide (NO2) and relative humidity (RH), suggesting the importance of heterogeneous processes as HONO source. The strong correlation between HONO and HONO to NO2 ratio suggested the occurrence of heterogeneous conversion from NO2 to HONO, or HONO direct emission processes, or both. We used a pseudo steady state approach, including homogeneous and heterogeneous reactions and the emissive fluxes of HONO from the snow surface. It allowed accounting for all observed HONO concentrations only from small period. Except on them, about 28 % of the measured HONO was explained. The results showed that the heterogeneous conversion of NO2 on humid surface was a major HONO source, especially during the night. However, the results indicated the occurrence of a daytime HONO source whose strength was enough to compete with the HONO photolysis.