ACETONE IN THE ATMOSPHERE - DISTRIBUTION, SOURCES, AND SINKS

Acetone (CH3COCH3) was found to be the dominant nonmethane organic spe cies present in the atmosphere sampled primarily over eastern Canada 0 -6 km, 35 degrees-65 degrees N) during ABLE3B (July to August 1990). A concentration range of 357 to 2310 ppt (=10(-12) v/v) with a mean val ue of 1140 +/- 413 ppt was measured. Under extremely clean conditions, generally involving Arctic flows, lowest (background) mixing ratios o f 550 +/- 100 ppt were present in much of the troposphere studied. Cor relations between atmospheric mixing ratios of acetone and select spec ies such as C2H2, CO, C3H8, C2Cl4 and isoprene provided important clue s to its possible Sources and to the causes of its atmospheric variabi lity. Biomass burning as a source of acetone has been identified for t he first time. By using atmospheric data and three-dimensional photoch emical models, a global acetone source of 40-60 Tg (=10(12) g)/yr is g )/yr is estimated to be present. Secondary formation from the atmosphe ric oxidation of precursor hydrocarbons (principally propane, isobutan e, and isobutene) provides the single largest source (51%). The remain der is attributable to biomass burning (26%), direct biogenic emission s (21%), and primary anthropogenic emissions (3%). Atmospheric removal of acetone is estimated to be due to photolysis (64%), reaction with OH radicals (24%), and deposition (12%). Model calculations also sugge st that acetone photolysis contributed significantly to PAN formation (100-200 ppt) in the middle and upper troposphere of the sampled regio n and may be important globally. While the source-sink equation appear s to be roughly balanced, much more atmospheric and source data, espec ially from the southern hemisphere, are needed to reliably quantify th e atmospheric budget of acetone.