KINETICS OF THE REACTIONS OF PROPIONYLPEROXY RADICALS WITH NO AND NO2- PEROXYPROPIONYL NITRATE FORMATION UNDER LABORATORY CONDITIONS RELATED TO THE TROPOSPHERE

Peroxyacyl nitrates [RC(O)OONO2] are formed in the atmosphere in the o xidative degradation of many organic compounds of both anthropogenic a nd biogenic origin. They are important oxidant components of photochem ical smog and can cause eye irritation and plant damage. Moreover, per oxyacyl nitrates act as temporary reservoirs for reactive intermediate s involved in photochemical smog formation, and they play an important role in the transport of NO, in the troposphere. It is therefore esse ntial to establish reliable data on the kinetics and mechanisms of the ir formation and removal for inclusion in models of atmospheric chemis try. The kinetic data base for the most atmospherically abundant of th e series, acetylperoxy nitrate [CH3C(O)OONO2, PAN], is quite well esta blished, but data are lacking for the higher homologues, e.g., peroxyp ropionyl nitrate [CH3CH2C(O)O2NO2, PPN], which has also been detected in the troposphere. Here we report data on a relative rate study of th e reactions CH3CH2C(O)O-2 . + NO2 + M --> CH3CH2C(O)O2NO2 + M (1) and CH3CH2C(O)O-2 . + NO --> CH3CH2 . + CO2 + NO2 (2) carried out in an at mospheric flow system in which the relative yields of CH3CH2C(O)O2NO2 (PPN) have been measured as a function of the ratio of reactants [NO]/ [NO2]. Over the temperature range 249-302 K, at a total pressure of si milar to 1 atm, the ratio was independent of temperature with a mean v alue of k(1)/k(2) = 0.43 +/- 0.07, where the error limits are 2 sigma. This ratio is 1.05 times higher than the corresponding ratio for PAN. In a second type of experiment involving the relative rates of format ion of PPN and PAN in the flow system, as a function of [NO]/[NO2], th e value (k(1)/k(2))PPN/(k(1)/k(2))PAN = 0.89 +/- 0.13 was determined. The results are discussed with reference to literature data of k(1)/k( 2) for PPN and PAN.