Sulfur dioxide measurements in the lower, middle and upper troposphere: Deployment of an aircraft-based chemical ionization mass spectrometer with permanent in-flight calibration

Measurements of atmospheric SO 2 have been made at altitudes between ground level and 12 km in the lower, middle and upper troposphere. The measurements were carried out within the framework of the ITOP (Intercontinental Transport of Ozone and Precursors) campaign in summer 2004 above Europe and the Eastern Atlantic. They were made using a novel very sensitive and fast-response aircraft-based ion trap CIMS instrument (ITCIMS; CIMS=chemical ionization mass spectrometry), which was continuously calibrated using isotopically labelled SO 2. During a total of eight flights of the research aircraft FALCON (DLR) air masses of different origin and different degree of pollution, indicated by measured elevated atmospheric SO 2 mole fractions, were intercepted. Often elevated concentrations of SO 2, which stemmed from North America were observed over Europe and the eastern Atlantic.