On Some Aspects of Nighttime Atmospheric Chemistry

Nighttime atmospheric chemistry is simulated in two different situations: an offshore oceanic environment, the Santa Barbara Channel region of the south central coast of California, and a dry environment, the Mojave Desert of California. In the marine case, conversion of NOₓ to peroxyacetyl nitrate (PAN) and HNO₃ is rapid; HNO₃ is formed by homogeneous hydrolysis of N₂O₅ and by nitrate radical reactions with organic gases, and the rate of HNO₃ production is limited by the abundance of O₃. Even in the desert case, predictions indicate that homogeneous hydrolysis of N₂O₅ dominates HNO₃ formation at night. The implications of recent studies concerning the unimolecular decomposition of NO₃ are discussed.