OBSERVATION OF UPPER-TROPOSPHERIC SULFUR-DIOXIDE-POLLUTION AND ACETONE-POLLUTION - POTENTIAL IMPLICATIONS FOR HYDROXYL RADICAL AND AEROSOL FORMATION

Aircraft-based measurements of sulfur dioxide, acetone, carbon dioxide , and condensation nuclei (CN) were made over the north-eastern Atlant ic at upper tropospheric altitudes, around 9000 m. On October 14, 1993 , strong SO2- and acetone-pollution (both up to 3 ppbv) were observed, which were accompanied by a CO2-enhancement of up to 6 ppmv, and larg e CN-concentrations of up to about 1500 cm(-3) (for radii greater than or equal to 6 nm). CN, excess CO2, and to a lesser degree also aceton e, were positively correlated with SO2. Air mass trajectory analyses i ndicate, that most of the air masses encountered by our aircraft origi nated from the polluted planetary boundary layer of the North-Eastern U. S. approximately 4-5 days prior to our measurements, and that pollu ted boundary layer air experienced fast vertical transport to the uppe r troposphere as well as horizontal transport across the Atlantic. Fro m our data we conclude, that in the polluted air mass around 9000 m al titude HOx-formation, photochemical SO2-conversion to gaseous H2SO4, a nd eventually also CN-formation by homogeneous bimolecular (H2SO4-H2O) nucleation may have taken place with enhanced efficiency.