THE DIURNAL-VARIATION OF HYDROGEN, NITROGEN, AND CHLORINE RADICALS - IMPLICATIONS FOR THE HETEROGENEOUS PRODUCTION OF HNO2
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In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained through sunrise and sunset in the lower stratosphere during SPADE are compared to results from a photochemical model constrained by observed concentrations of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N 2 O 5 on sulfate aerosols agree with measured concentrations of NO, NO 2 , and ClO throughout the day, but fail to account for high concentrations of OH and HO 2 observed near sunrise and sunset. The morning burst of [OH] and [HO 2 ] coincides with the rise of [NO] from photolysis of NO 2 , suggesting a new source of HO x that photolyzes in the near UV (350 to 400 nm) spectral region. A model that allows for the heterogeneous production of HNO 2 results in an excellent simulation of the diurnal variations of [OH] and [HO 2 ]. Copyright 1994 by the American Geophysical Union.