GAS-PHASE ULTRAVIOLET-ABSORPTION CROSS-SECTIONS AND ATMOSPHERIC LIFETIMES OF SEVERAL C-2-C-5 ALKYL NITRATES

Gas-phase ultraviolet absorption cross-sections of ethyl nitrate, 1-pr opyl nitrate, 2-propyl nitrate, 2-methyl, 1-propyl nitrate, 1-butyl ni trate and 1-pentyl nitrate have been measured over the wavelength rang e 220-340 nm using a dual-beam, diode array spectrometer. Each alkyl n itrate spectrum appears to be the sum of at least two Gaussian-shaped absorptions with an intense pi-pi band extending from 190-240 nm havi ng a shoulder between 250-340 nm due to a n-pi system. The absorption cross-sections recorded for ethyl nitrate, 1-propyl nitrate, 2-propyl nitrate and 1-butyl nitrate are within 10% of previous data: those of 2-methyl, 1-propyl nitrate and 1-pentyl nitrate have been measured fo r the first time. For ethyl nitrate, absorption cross-sections between 280-340 nm in the tail of the near-ultraviolet band declined with dec reasing temperature from 298-233 K. A two-dimensional numerical model of tropospheric chemistry was used to calculate atmospheric lifetimes with respect to photodissociation and OH radical reaction that are mar kedly dependent on season, latitude and altitude. Relatively long, sur face level atmospheric lifetimes of several days to weeks confirm that the C-2-C-5 alkyl nitrates may act as temporary reservoirs for NOx an d suggest that they may also constitute a significant fraction of tota l reactive odd-nitrogen, NOy, particularly during winter at northern h emisphere high latitudes.