Chloroform Emissions from the Arctic Tundra

The global budget of atmospheric chloroform (CHCl3) has many uncertainties, especially regarding the magnitude of its natural and anthropogenic sources. CHCl3 has an atmospheric lifetime of ~0.5 years based on reaction with hydroxyl radical and a north to south interhemispheric gradient of 2-3. Thus, a majority of CHCl3 emissions comes from the Northern Hemisphere, with half or more of the emissions emanating from 30-90 °N. The production of CHCl3 has been observed in microalgae, termite mounds, forest soils, rice paddies and temperate peatlands, but direct flux measurements are very limited. Here we report CHCl3 emissions measured from the Arctic tundra during the 2005 and 2006 growing seasons near Barrow, Alaska (n=60) and Toolik Lake, Alaska (n=16). These sites encompassed a range of vegetation zones, from wet sedge coastal tundra to upland tussock tundra. Fluxes were highly variable, ranging from 0 to 260 nmol m-2 d-1 and showed no clear trends with microtopography or time of season, although many of the highest fluxes were found at the moist meadow sites. Chloroform fluxes did not correlate with methane or methyl halide fluxes. A rough extrapolation based on average observed fluxes suggests that the tundra globally can account for 1-2% of the total estimated source of atmospheric chloroform.