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 h ave been made in the exhaust plume of a commercial jet aircraft (Airbu s A310) in flight at altitudes around 10.4 km and at two plume ages ar ound 3.0 and 3.6 s. Negative ions observed inside the exhaust plume ar e mostly NO3-(HNO3)(m) and HSO4-(HNO3)(m) with m less than or equal to 2. Outside the plume in the ''background'' atmosphere the same negati ve ion species with the same R = (HSO4-(HNO3)(m))/(NO3-(HNO3)(m)) were observed. This indicates that the ions observed in the plume were ent rained ambient atmospheric ions. By contrast no indications for negati ve chemiions (with masses less than or equal to 1100 amu) produced by the airbus engines were found in the plume. Furthermore our measuremen ts 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 t o aerosol-particles and/or ion-recombination with positive chemiions. We propose that the observed entrained ions can serve as probes for im portant plume components including gaseous sulfuric acid, aerosol part icles and chemiions. Making use of this analytical potential we infer upper limits for the gaseous sulfuric acid concentration, total aeroso l surface area density, and positive chemiion concentration. We conclu de that initially formed gaseous sulfuric acid must have experienced r apid gas-to-particle conversion already in the very early plume at plu me ages < 1.6 s.