HYDROCARBON MEASUREMENTS IN THE SPRING ARCTIC TROPOSPHERE DURING THE ARCTOC-95 CAMPAIGN

The hydrocarbon measurements made during the ARCTOC 95 field campaign (16 April-10 June 1995) at Ny Alesund Spitsbergen (78 degrees 55'N, 11 degrees 56'E) allow the estimation of Cl and Br atom concentrations d uring periods of low ozone concentrations in the lower troposphere. In -situ analyses for nonmethane hydrocarbons and selected halocarbons we re carried out with two GC-FID/ECD systems allowing a time resolution of about 2 hours and detection limits in the lower ppt range. A third GC was used to monitor the CO mixing ratio with a 5 min time resolutio n, Additionally, about 70 whole air samples were collected in stainles s steel canisters and analysed for hydrocarbons (C-2-C-8), some haloca rbons, methane, CO, and CO2 at the laboratory in Julich. 15 of those s amples were taken at the measurement site, the others were collected o n top of Zeppelin Mountain (474 m a.s.l., distance from measurement si te 1000 m). In-situ measurements as well as canister samples shorted t hat all nonmethane hydrocarbans were present at low mixing ratios. CO levels were found to be between 100 and 140 ppb showing a nearly const ant decrease from April to June. During an ozone depletion event (18-2 4 April) the hydrocarbon pattern changed drastically. The mixing ratio s of alkanes and ethyne decreased together with ozone, whereas benzene , chloromethane, and CO mixing ratios remained nearly constant. From t he ratio of NMHC background mixing ratios and those during low ozone p eriods the time integrated Cl and Br atom concentrations were calculat ed to some 10(10) molecules.s.cm(-3) and 5.10(12) molecules.s.cm(-3), respectively.