Aircraft-based operation of an aerosol mass spectrometer: Measurements of tropospheric aerosol composition

The Aerodyne quadrupole aerosol mass spectrometer was deployed on the Falcon twin jet research aircraft operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR). This was the first deployment of an AMS in a jet aircraft. Aerosol mass concentration measurements in the troposphere up to altitudes of about 11 km were performed within two measurement flights on 12 and 14 May 2003 over southern Germany. Background aerosol data were gained up to 6 km, while aircraft exhaust aerosol was be sampled at higher altitudes on 14 May, indicating the presence of sulfuric acid and unburned hydrocarbons in the exhaust particles. The boundary layer aerosol on 12 May was found to be composed of 49% organics, 12% sulfate, 15% ammonium, and 24% nitrate by mass. The upper edge of the boundary layer was marked by a sharp decrease of nitrate and ammonium at an altitude of 3 km, while sulfate and organics decreased to a much lesser degree. On 14 May, the boundary layer aerosol was composed of 23% organics, 20% sulfate, 24% ammonium, and 33% nitrate by mass, and the boundary layer reached up to about 5000 m and had no sharp upper edge. The size distributions indicated internal mixtures of ammonium sulfate and –nitrate in the boundary layer, while the organics were externally mixed. Additionally, a smaller mode consisting only of ammonium sulfate, was detected. This bimodal structure of ammonium sulfate was also detected above the boundary layer in 6 km altitude on 14 May.