Measurements of acetone, acetic acid, and formic acid in the northern midlatitude upper troposphere and lower stratosphere

We have measured acetone, acetic acid, and formic acid concentrations in th e upper troposphere and lower stratosphere over Germany. The measurements w ere performed by ion molecule reaction mass spectrometry using new kinetic data on ion molecule reactions of formic and acetic acids with negative ion s obtained at our laboratory. Mean volume mixing ratios between 384 and 832 parts per trillion (pptv) for acetone, 110 and 357 pptv for acetic acid, a nd 59 and 215 pptv for formic acid were obtained. The correlation between f ormic acid and acetic acid was very poor (r(2) = 0.14). A better correlatio n could be observed for acetone and acetic acid, with a correlation coeffic ient r(2) = 0.46 and a slope (acetic acid/acetone) of 0.31. For acetic acid a maximum around 9 km was observed. A significant fraction of the acetic a cid observed in the lower stratosphere may be due to in situ photochemical production by reactions of HO2 and CH3O2 With peroxy acetyl radicals produc ed by the photolysis of acetone. In the upper troposphere, vertical transpo rt is much more efficient, and significant acetic acid production is only p ossible if HOx concentrations are elevated, making the production of acetic acid fast enough to compete with vertical transport.