EVOLUTION OF ALKYL NITRATES WITH AIR-MASS AGE

Alkyl nitrates (RONO(2)) and alkanes (RH) were measured at Scotia, Pennsylvania, in 1988 and at the Kinterbish Wildlife Area, Alabama, in 1992. A simple kinetic analysis was developed to relate the two species' concentrations based on the analytical solution of two sequential first-order reactions using OH chemistry, RONO(2) photolysis, and assuming peroxy radicals (ROO) + NO as the source of RONO(2). The analysis predicts an increase in RONO(2)/RH ratio with time. The C-4 and C-5 secondary alkyl nitrate/alkane ratios vary in a manner consistent with ROO + NO chemistry as their only source and photolysis and OK reaction as their only sinks. Comparison of ambient measurements of these compounds with predictions indicate that measured air masses experienced photochemical processing times consistent with alkyl nitrate evolution times between 0.1 and 5 days. The relationships of ethyl nitrate, n-propyl nitrate and 2-propyl nitrate ratios to their parent alkanes all indicate additional sources of RONO(2), probably of a photochemical nature. Decomposition of larger alkoxy radicals are discussed as one possible source of smaller ROO radicals.