THE CLOUDWATER CHEMISTRY OF IRON AND COPPER AT GREAT DUN FELL, UK

The role of iron and copper in the transformation of photooxidants (HO 2/O-2(-)) and pollutants in clouds was examined at a rural site (Great Dun Fell, U.K.). The observed concentrations of dissolved iron (60-16 00 nM) and copper (4.2-31 nM) were lower than those previously reporte d at other locations. Measurement of the oxidation state of dissolved iron provided insight into the rates and mechanisms of cloudwater tran sformation reactions. Whenever the iron-containing aerosols were nucle ated for more than several minutes prior to collection, measured iron oxidation states agreed with predictions based upon known rate constan ts for iron redox reactions. During daytime, the reduction of dissolve d Fe(III) by HO2/O-2(-) and Cu(I) or the photoreduction of Fe(III)-oxa lato complexes resulted in the establishment of a steady state, with r espect to iron oxidation states, in which more than 50% of the dissolv ed iron was present as Fe(II). At night, Fe(II) was slowly oxidized by H(2)O2 and O-3. (C) 1997 Elsevier Science Ltd.