HR: 16:45h
AN: A24A-03    [Abstracts]
TI: Measurement and Interpretation of Boundary Layer OH and HO2 in Coastal Antarctica
AU: * Bloss, W
EM: w.j.bloss@leeds.ac.uk
AF: School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT United Kingdom
AU: Lee, J
EM: jdl3@york.ac.uk
AF: School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT United Kingdom
AU: Heard, D
EM: d.e.heard@leeds.ac.uk
AF: School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT United Kingdom
AU: Salmon, R
EM: rasa@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road , Cambridge, CB3 0ET United Kingdom
AU: Bauguitte, S
EM: sbau@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road , Cambridge, CB3 0ET United Kingdom
AU: Roscoe, H
EM: hkro@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road , Cambridge, CB3 0ET United Kingdom
AU: Jones, A
EM: aejo@bas.ac.uk
AF: British Antarctic Survey, High Cross, Madingley Road , Cambridge, CB3 0ET United Kingdom
AB: Measurements of boundary layer OH and HO2 radical concentrations at Halley Base, Antarctica were conducted over an 8-week period during January and February 2005 (austral summer), as part of the CHABLIS (Chemistry of the Antarctic Boundary Layer and the Influence of Snow) project involving the British Antarctic Survey and the Universities of Leeds, York, East Anglia, Bristol and Imperial College. The HOx measurements were performed by laser-induced fluorescence, using the FAGE technique, with HO2 detected as OH following its chemical conversion by reaction with NO. The system was calibrated using the water photolysis / ozone actinometry approach. During the CHABLIS campaign, simultaneous measurements including NOx, VOCs, peroxy radicals, peroxides, HONO and HCHO, halogens and meteorological / radiation data were also performed, permitting a detailed comparison of measured and simulated radical activity, and estimation of the influence of snowpack emissions upon oxidant levels. OH and HO2 data were acquired on 37 days, including a near-complete 5-week time-series. The campaign average OH and HO2 levels were 3.9e5 cm-3 and 0.76 pptv respectively, with hourly mean levels over local solar noon of 7.9e5 cm-3 and 1.9 pptv respectively. These levels are significantly higher than those which would be expected for a pristine environment such as Halley in the absence of local snowpack (e.g. NOx) sources. Simple photochemical model calculations, constrained by measured photolysis rates, O3, NOx, CO and VOCs are presented: The simulated OH agrees reasonably well with the measurements, however discrepancies are observed, especially at high solar zenith angles, indicating the presence of additional radical sources; the roles of HONO and HCHO are discussed. The implications of these results for the oxidising capacity of the Antarctic boundary layer are discussed, and their contribution to our understanding of snowpack emissions of HOx and NOx precursors considered.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere: composition and chemistry
DE: 0738 Ice (1863)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005