Halogen atom concentrations in the Arctic troposphere derived from hydrocarbon measurements: Impact on the budget of formaldehyde

As part of the Polar Sunrise Experiment in 1998 measurements of hydrocarbon s were made at the Canadian Arctic station Alert. Halogen atom concentratio ns play a key role in determining formaldehyde mixing ratios. Formaldehyde mixing ratios observed during ozone depletion episodes agree with those cal culated from time integrated halogen atom concentrations. Formaldehyde is t he most important lass mechanism for active bromine and at the same time an important source for HOx radicals. Via these reactions formaldehyde will i ndirectly influence chlorine chemistry and thus feedback mechanisms involvi ng halogen atom concentrations and formaldehyde are likely to play a major role in the development of tropospheric ozone depletion episodes during pol ar sunrise.