Tropospheric heterogeneous chemistry of haloacetyl and carbonyl halides

Abstract

A series of uptake studies have been completed for the gas phase carbonyl halides CCl 2 O and CF 2 O and the haloacetyl halides CCl 3 CClO, CF 3 CFO and CF 3 CClO which are oxidation intermediates of volatile fluorocarbon, chlorocarbon and hydrofluorocarbon (HCFC) species in the atmosphere. The experimental apparatus in these studies employs a fast moving monodispersed train of droplets (50 to 200 μm in diameter) passed through a low pressure flow reactor. Experiments were done as a function of droplet pH and gas/droplet interaction time. The measured uptake coefficients (γ) for all these molecules are less than our experimental detection limit of 5 × 10 −4 for pH 7 droplets at 300 K. From the results of the measurements and other available data, the uptake coefficients for these species are estimated to be 10 −6 < γ < 10 −4 . The lower limit is sufficiently large so that the tropospheric removal rate of the species is not expected to affect the ozone depletion potential values of the HCFC parent species for CF 2 O, CF 3 CFO and CF 3 CClO. However with such uncertainty it is not possible to determine the partitioning of the ocean/land deposition of the species.