FORMATION AND THERMAL-DECOMPOSITION OF BUTYL-SUBSTITUTED PEROXYACYL NITRATES - N-C4H9C(O)OONO2 AND I-C4H9C(O)OONO2

The butyl-substituted peroxyacyl nitrates n-C4H9C(O)-OONO2 and i-C4H9C(O)OONO2 have been synthesized in the liquid phase, prepared in-situ in the gas phase by sunlight irradiation of aldehyde-NO mixtures, measured by electron capture gaschromatography, and characterized in a number of gas-phase and liquid-phase tests. Gas-phase yields as a fraction of initial NO were 0.39 for the n-butyl isomer and 0.20 for the isobutyl isomer. The corresponding gas-phase aldehyde oxidation mechanisms are outlined. Thermal decomposition in the presence of excess NO yielded n-butanal and isobutanal as the major carbonyl products. Thermal decomposition rates at ambient temperature and atmospheric pressure are comparable to that of PAN [CH3C(O)OONO2], with k298 = 1.8 X 10(-4) s-1 for n-C4H9C(O)OONO2 and 2.4 X 10(-4) s-1 for i-C4H9C(O)OONO2. Emission data for precursor hydrocarbons indicate C4H9C(O)OONO2/PAN ambient concentration ratios of <0.19 in urban air. Atmospheric implications for the formation and removal Of C4H9C-(O)OONO2 are briefly discussed.