Observation of Upper Tropospheric Sulfur Dioxide- 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 Atlantic at upper tropospheric altitudes, around 9000 m. On October 14, 1993, strong SO 2- and acetone-pollution (both up to 3 ppbv) were observed, which were accompanied by a CO 2-enhancement of up to 6 ppmv, and large CN-concentrations of up to about 1500 cm -3 (for radii ≥ 6 nm). CN, excess CO 2, and to a lesser degree also acetone, were positively correlated with SO 2. Air mass trajectory analyses indicate, that most of the air masses encountered by our aircraft originated from the polluted planetary boundary layer of the North-Eastern U. S. approximately 4-5 days prior to our measurements, and that polluted boundary layer air experienced fast vertical transport to the upper troposphere as well as horizontal transport across the Atlantic. From our data we conclude, that in the polluted air mass around 9000 m altitude HO x-formation, photochemical SO 2-conversion to gaseous H 2SO 4, and eventually also CN-formation by homogeneous bimolecular (H 2SO 4-H 2O) nucleation may have taken place with enhanced efficiency

First Gaseous Ion Composition Measurements in the Exhaust Plume of a Jet Aircraft in Flight: Implications for Gaseous Sulfuric Acid, Aerosols, and Chemiions

Mass spectrometric composition measurements of gaseous negative ions have been made in the exhaust plume of a commercial jet aircraft (Airbus A310) in flight at altitudes around 10.4 km and at two plume ages around 3.0 and 3.6 s. Negative ions observed inside the exhaust plume are mostly NO3-(HNO3)m and HSO4-(HNO3)m with m ≤ 2. Outside the plume in the "background" atmosphere the same negative ion species with the same R = (HSO4-(HNO3)m)/(NO3-(HNO3)m) were observed. This indicates that the ions observed in the plume were entrained ambient atmospheric ions. By contrast no indications for negative chemiions (with masses ≤ 1100 amu) produced by the airbus engines were found in the plume. Furthermore our measurements indicate a modest decrease of the total concentration of entrained negative ions in the plume compared to the ambient atmosphere outside the plume. This decrease may be due to ion-removal by ion-attachment to aerosol-particles and/or ion-recombination with positive chemiions. We propose that the observed entrained ions can serve as probes for important plume components including gaseous sulfuric acid, aerosol particles and chemiions. Making use of this analytical potential we infer upper limits for the gaseous sulfuric acid concentration, total aerosol surface area density, and positive chemiion concentration. We conclude that initially formed gaseous sulfuric acid must have experienced rapid gas-to-particle conversion already in the very early plume at plume ages ‹ 1.6 s