The annual cycle of peroxides and ozone in marine air at Cape Grim, Tasmania |
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| Authors: | G P Ayers S A Penkett R W Gillett B Bandy I E Galbally C P Meyer C M Elsworth S T Bentley B W Forgan |
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| Institution: | (1) Division of Atmospheric Research, CSIRO, Private Bag 1, 3195 Mordialloc, Vic, Australia;(2) School of Environmental Sciences, University of East Anglia, NR4 7TJ Norwich, England;(3) Bureau of Meteorology, Box 1289K, 3001 Melbourne, Australia |
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| Abstract: | The concentration of gas-phase peroxides has been measured almost continuously at the Cape Grim baseline station (41° S) over a period of 393 days (7702 h of on-line measurements) between February 1991 and March 1992. In unpolluted marine air a distinct seasonal cycle in concentration was evident, from a monthly mean value of>1.4 ppbv in summer (December) to <0.2 ppbv in winter (July). In the summer months a distinct diurnal cycle in peroxides was also observed in clean marine air, with a daytime build-up in concentration and decay overnight. Both the seasonal and diurnal cycles of peroxides concentration were anticorrelated with ozone concentration, and were largely explicable using a simple photochemical box model of the marine boundary layer in which the central processes were daytime photolytic destruction of ozone, transfer of reactive oxygen into the peroxides under the low-NOx ambient conditions that favour self-reaction between peroxy radicals, and continuous heterogeneous removal of peroxides at the ocean surface. Additional factors affecting peroxides concentrations at intermediate timescales (days to a week) were a dependence on air mass origin, with air masses arriving at Cape Grim from higher latitudes having lower peroxides concentrations, a dependence on local wind speed, with higher peroxides concentrations at lower wind speeds, and a systematic decrease in peroxides concentration during periods of rainfall. Possible physical mechanisms for these synoptic scale dependencies are discussed. |
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| Keywords: | photochemistry hydrogen peroxide ozone Cape Grim Tasmania |
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