1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, 82234 Wessling, Germany
2Max Planck Institute for Nuclear Physics, (MPIK), Atmospheric Physics Division, P.O. Box 103980, 69029 Heidelberg, Germany
3Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland
4Department of Technology, Metropolia University of Applied Sciences, P.O. Box 4000, 00180 Helsinki, Finland
Abstract. We report on sulfur dioxide (SO2) induced formation of aerosols and cloud condensation nuclei in an SO2 rich aged (9 days) pollution plume of Chinese origin, which we have detected at 5–7 km altitude during a research aircraft mission over the East Atlantic off the West coast of Ireland. Building on our measurements of SO2 and other trace gases along with plume trajectory simulations, we have performed model simulations of SO2 induced formation of gaseous sulfuric acid (GSA, H2SO4) followed by GSA induced formation and growth of aerosol particles. We find that efficient photochemical SO2 conversion to GSA took place in the plume followed by efficient formation and growth of H2SO4-H2O aerosol particles. Most particles reached sufficiently large sizes to act as cloud condensation nuclei whenever water vapor supersaturation exceeded 0.1–0.2%. As a consequence, smaller but more numerous cloud droplets are formed, which tend to increase the cloud albedo and to decrease the rainout efficiency. The detected plume represents an interesting example of the environmental impact of long range transport of fossil fuel combustion generated SO2.