A large terrestrial source of methyl iodide

We have identified terrestrial sources of methyl iodide (CH3I) and assessed their importance in its atmospheric budget using a synthesis of field observations. Measurements include those from NASA DC- 8 research flights over the United States and the North Atlantic, the AIRMAP long- term ground- observing network in New England, and a field campaign at Duke Forest, North Carolina. We found an average CH3I flux of similar to 2,700 ng m(-2) d(-1) to the atmosphere from midlatitude vegetation and soils, a value similar in magnitude to previous estimates of the oceanic source strength. The large- scale aircraft measurements of vertical profiles over the continental U. S. showed CH3I-mixing ratios comparable to and greater than those observed over the North Atlantic. Overall, midlatitude terrestrial biomes appear to contribute 33 Gg yr(-1) to the CH3I global budget.