Acetone measurements in the upper troposphere and lower stratosphere—implications for hydroxyl radical abundances

Abstract

Atmospheric acetone serves as a precursor of PAN (peroxyacetyl nitrate) which represents a temporary reservoir for reactive nitrogen and has a potential to form aerosols. Acetone has recently been detected in the atmosphere by Penkett², using ground-level flask sampling and gas chromatography/mass spectrometry (GC/MS) analysis in the laboratory finding an average volume mixing ratio of 470 p.p.t.v. (parts per 10¹² by volume) in Atlantic air. Very recently, acetone was for the first time detected in the free atmosphere, at heights around the tropopause, by Arnold and his colleagues^3,4 using aircraft-borne chemical ionization mass spectrometry (CIMS). We report here on the first measurements of atmospheric acetone abundances over an extended altitude range (5,900–11,300 m) covering the lowermost part of the stratosphere and the upper troposphere. The measured upper tropospheric abundances (average 120 p.p.t.v.) are substantially lower than the average values (470 p.p.t.v.) measured at ground level. Above the tropopause, a marked decrease of the acetone mixing ratio was observed. Our present data have interesting implications for the chemistry of non-methane hydrocarbons and possibly also hydroxyl radical abundances.