Airborne ion trap CIMS using SF5- reagent ions: Atmospheric trace gas detection in the tropopause region and in aircraft exhaust plumes

Abstract

This work aims at the investigation of sulfur containing plumes in the tropopause region. For the first time an ion trap chemical ionization mass spectrometer (ITCIMS) was equipped with an SF5- ion source for the detection of SO2, HCl, HNO3 and HONO. This novel combination was tested in the laboratory and deployed on the research aircraft Falcon during the CONCERT (CONtrail and Cirrus ExpeRimenT) campaign. In October 2008 an SO2 layer in the lower stratosphere with mole fractions up to 510 pptv was detected, originating from the Mt. Kasatochi (Aleutian island) eruption in August 2008. Correlation analysis show an enhancement of the molar abundance ratios HCl/O3 and HNO3/NOy of 19 % and HNO3/O3 of 50 % inside the SO2 plume. The data were used to derive an upper limit of the e-folding lifetime of SO2 in the lower stratosphere at northern latitudes of 60 days. Besides natural sources, anthropogenic emissions of sulfur and nitrogen oxides from aircraft are discussed. SO2 and first laboratory-calibrated HONO measurements in young aircraft exhaust plumes of ten commercial airliners were conducted. Employing the measured HONO/NO molar abundance ratio of 0.042 +-0.010, the effective conversion efficiency of fuel sulfur to sulfuric acid was indirectly inferred. It compares well to former measurements.