Abstract
Abstract. A reaction rate associated with the nighttime formation of an important diurnally varying species, N2O5, is determined from MIPAS-ENVISAT. During the day, photolysis of N2O5 in the stratosphere contributes to nitrogen-catalysed ozone destruction. However, at night concentrations of N2O5 increase, temporarily sequestering reactive NOx NO and NO2 in a natural cycle which regulates the majority of stratospheric ozone. In this paper, the reaction rate controlling the formation of N2O5 is determined from this instrument for the first time. The observed reaction rate is compared to the currently accepted rate determined from laboratory measurements. Good agreement is obtained between the observed and accepted experimental reaction rates within the error bars.
Highlights
The importance of N2O5 arises mainly from its role as a temporary reservoir for reactive NOx (NO and NO2) which catalyse the main ozone-destroying cycles in the stratosphere (Crutzen, 1970)
The main aim of this study is to determine the reaction rate controlling the nighttime formation of N2O5 in Reaction (R2) using measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the Environmental Satellite (ENVISAT)
The reaction rate controlling the conversion of NO and NO2 into N2O5 at night, which regulates the majority of ozone destruction at extra-polar latitudes, was determined from MIPAS-ENVISAT measurements
Summary
The importance of N2O5 arises mainly from its role as a temporary reservoir for reactive NOx (NO and NO2) which catalyse the main ozone-destroying cycles in the stratosphere (Crutzen, 1970). Concentrations of N2O5 increase at night and decrease during the day thereby exerting a regulating influence on the rate of ozone destruction throughout the extra-polar stratosphere. The formation of N2O5 proceeds at night via the following reactions. A study by Nevison et al (1996) assessed the effect of reactions involving ClONO2 and HNO3 on diurnal variations in NOx. At night, the reaction. Is important in the lower stratosphere and tends to increase the sunset/sunrise NOx ratio. Is important in the lower stratosphere where the aerosol loading is highest. They state that reactions involving ClONO2 and HNO3 have little influence on the diurnal NOx cycle above 35 km. Dudhia: Measurement of a diurnal NOx reaction rate from sun-synchronous orbit
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