Soil-atmosphere exchange of radiatively and chemically active gases

Exchanges between the soils and the atmosphere may control or significantly affect the global budgets of many environmentally important trace gases, b oth natural and man-made. Flux measurements, taken in several ecosystems, s how that soils are a substantial source of chloroform (8 +/- 4 mu g/m(2)/d) and a sink for methyl chloride (-10(-3)(+6) mu g/m(2)/d). The known source s and sinks of these gases are insufficient to explain the observed concent rations. Our findings will help to balance the global budget of chloroform but may put the budget of methyl chloride further out of balance. We also f ound, consistent with previous research, that soils are a substantial sourc e of nitrous oxide and carbon monoxide and take up hydrogen and methane. Th e uptake of man-made chlorocarbons was observed, but the rates are small. O bserved fluxes of non-methane hydrocarbons showed few patterns except that soils may be a source of ethane and butane.