Light-induced nitrous acid (HONO) production from NO2 heterogeneous reactions on household chemicals
2014
Gómez Alvarez, Elena | Sörgel, Matthias | Gligorovski, Sasho | Bassil, Sabina | Bartolomei, Vincent | Coulomb, Bruno | Zetzsch, Cornelius | Wortham, Henri
Nitrous acid (HONO) can be generated in various indoor environments directly during combustion processes or indirectly via heterogeneous NO2 reactions with water adsorbed layers on diverse surfaces. Indoors not only the concentrations of NO2 are higher but the surface to volume (S/V) ratios are larger and therefore the potential of HONO production is significantly elevated compared to outdoors. It has been claimed that the UV solar light is largely attenuated indoors.Here, we show that solar light (λ > 340 nm) penetrates indoors and can influence the heterogeneous reactions of gas-phase NO2 with various household surfaces. The NO2 to HONO conversion mediated by light on surfaces covered with domestic chemicals has been determined at atmospherically relevant conditions i.e. 50 ppb NO2 and 50% RH. The formation rates of HONO were enhanced in presence of light for all the studied surfaces and are determined in the following order: 1.3·109 molecules cm−2 s−1 for borosilicate glass, 1.7·109 molecules cm−2 s−1 for bathroom cleaner, 1.0·1010 molecules cm−2 s−1 on alkaline detergent (floor cleaner), 1.3·1010 molecules cm−2 s−1 for white wall paint and 2.7·1010 molecules cm−2 s−1 for lacquer.These results highlight the potential of household chemicals, used for cleaning purposes to generate HONO indoors through light-enhanced NO2 heterogeneous reactions.The results obtained have been applied to predict the timely evolution of HONO in a real indoor environment using a dynamic mass balance model. A steady state mixing ratio of HONO has been estimated at 1.6 ppb assuming a contribution from glass, paint and lacquer and considering the photolysis of HONO as the most important loss process.
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