Evolution of alkyl nitrates with air mass age

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Abstract
Alkyl nitrates (RONO2) 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, RONO2 photolysis, and assuming peroxy radicals (ROO) + NO as the source of RONO2. The analysis predicts an increase in RONO2/RH ratio with time. The C4 and C5 secondary alkyl nitrate/alkane ratios vary in a manner consistent with ROO + NO chemistry as their only source and photolysis and OH 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 RONO2, probably of a photochemical nature. Decomposition of larger alkoxy radicals are discussed as one possible source of smaller ROO radicals.