AIRCRAFT-BORNE MEASUREMENTS OF PEROXY-RADICALS IN THE MIDDLE TROPOSPHERE

We have performed aircraft-borne measurements of peroxy radicals in th e free troposphere over southern Germany (48 degrees N). The measureme nts were carried out on board a Dornier 228 research aircraft. At alti tudes between 3.7 and 7.8 km measured peroxy radical concentrations we re between 2 x 10(8) and 7 x 10(8) cm(-3). Peroxy radicals were measur ed using amplifying chemical conversion of peroxy radicals to sulfuric acid via reactions with NO and SO2 and detection of sulfuric acid by ion molecule reaction-mass spectrometry (IMR-MS). The instrument was c alibrated at the ground and thoroughly characterized by laboratory and in-flight diagnostic measurements. The accuracy of the present aircra ft-borne measurements is estimated to be about +/-45%. Regular backgro und measurements have been performed during the flights to determine t he extent of spurious radical or H2SO4 production, which may occur thr ough ion source produced radicals or thermal decomposition of PAN or H NO4 in the sampling system.