On the relationship between acetone and carbon monoxide in different air masses

[摘要] Carbon monoxide and acetone measurements are presented for five aircraftmeasurement campaigns at mid-latitudes, polar and tropical regions in the northern hemisphere. Throughout all campaigns, free tropospheric airmasses, which were influenced by anthropogenic emissions, showed a similarlinear relation between acetone and CO, with a slope of 21-25 ppt_vacetone/ppb_v CO. Measurements in the anthropogenically influenced marineboundary layer revealed a slope of 13-16 ppt_v acetone/ppb_v CO. The differentslopes observed in the marine boundary layer and the free troposphere indicate that acetone is emitted by the ocean in relatively clean air massesand taken up by the ocean in polluted air masses. In the lowermost stratosphere, a good correlation between acetone and CO was observed aswell, however, with a much smaller slope (~5 ppt_v acetone/ppb_v CO)compared to the troposphere. This is caused by the longer photochemical lifetime of CO compared to acetone in the lower stratosphere, due to theincreasing photolytic loss of acetone and the decreasing OH concentration with altitude. No significant correlation between acetone and CO wasobserved over the tropical rain forest due to the large direct and indirectbiogenic emissions of acetone.

The common slopes of the linear acetone-CO relation in various layers of theatmosphere, during five field experiments, makes them useful for model calculations. Often a single observation of the acetone-CO correlation,determined from stratospheric measurements, has been used in box model applications. This study shows that different slopes have to be considered formarine boundary layer, free tropospheric and stratospheric air masses, andthat the acetone-CO relation cannot be used for air masses which are stronglyinfluenced by biogenic emissions.

[学科分类] 大气科学