Gj. Frost et al., Organic peroxyl radical photolysis in the near-infrared: Effects on tropospheric chemistry, J PHYS CH A, 103(49), 1999, pp. 10169-10178
We investigate the effects of near-infrared photolysis of organic peroxyl r
adicals (RO2) on tropospheric chemistry. We propose that the excitation of
an RO2 to its lowest excited electronic state with near-infrared (near-IR)
light is followed by intramolecular reactions that produce hydroxyl (OH) or
hydroperoxyl (HO2) radicals. Spectra to this low-lying state have recently
-been obtained, but absorption cross sections for this electronic transitio
n and yields of the resulting photoproducts have not been directly measured
. We suggest a limiting range of cross sections from estimates for the same
transition in HO2 and by comparison to other allowed electronic transition
s. On the basis of a thermochemical assessment, we propose that OH and an a
ldehyde are the principal photoproducts of near-IR photolysis of RO2. These
photolysis reactions are included in a model of the troposphere with a sta
ndard photochemical mechanism and conditions appropriate to remote, rural,
and urban locations. Inclusion of RO2 photolysis has a small effect on any
of the major tropospheric chemical constituents if lower limit estimates of
the absorption cross sections are used. Midrange or upper limit cross sect
ion estimates result in significant departures from the currently accepted
photochemical scheme. These studies provide a clear need for further measur
ements of RO2 absorption cross sections and photoproduct yields, which are
the principal uncertainties.