PNNL

Abstract

Nitrous acid is an important precursor for OH radicals in the polluted troposphere. The heterogeneous conversion of NO2 to HONO, howver, is currently not well understood. Simultaneous measurements of HONO and NO2 in Phoenix in summer 2001 using long path differential optical absorption spectroscopy show raios of chemically formed secondary [HONO] to [NO2] that rarely exceeded 3%. During tow nocturnal dust storm events, however, a significant increase of this ratio was observed. The unprecedented high values of secondary [HONO]\[NO2] near 19% suggest a highly efficient NO2 to HONO conversion process on mineral dust particles. The particle composition in Phoenix is similar to other mineral dusts, implying that the enhanced NO2 conversion could be an important HONO, and therefore also OH, source in regions where pollution and dust storms coincide.