Field experimental investigations on the Fe(II)- and Fe(III)-content in cloudwater samples

The Fe(II)/Fe(III)-partition in cloudwater samples collected during two fie ld campaigns is evaluated. It turned out that the simultaneous occurrence o f complexing and reducing substances in the atmosphere and the cloud proces sing increase the solubility of iron compounds present in aerosol particles . A correlation between the concentration of iron(II) in the liquid phase a nd the intensity of the solar irradiation was observed for most of the clou dwater samples. This could be due to the fact that both the photochemical r eduction of the iron(III) complexes and the photochemical reductive dissolu tion of iron(III)(hydr)oxides are depending on the pH-value. Iron(II) seems to be oxidised back to iron(III) preferably by hydrogen peroxide during th e night. Positive correlations were received e.g. between the concentration of dissolved iron and the concentration of oxalate and between the percent age of iron(III) and the concentration of hydrogen peroxide. A negative cor relation was found e.g. between the concentration of dissolved iron and the pH-value. The uncertainty of the whole process of sampling and analysis wa s investigated and the conformity of the results was satisfying considering the sometimes difficult conditions during a field campaign.