Pollution transport and cloud effects

During the preparation phase for the recent ICARTT (International Consortium for Research on Atmospheric Transport and Transformation) campaign in 2004, we combined model predictions of the export of pollution from the USA with high-resolution imagery fro m geostationary satellites. Very often, we found that pollution plumes were aligned with the cloud features. In the case of shallow clouds just off-shore the coast line, it was often quite obvious that clouds were "burned away" by pollution downwind of ma jor cities (e.g., Boston, New York) in the morning, presumably due to the absorption of solar radiation (and, thus, the generation of heat) by black carbon aerosols. However, we also observed the opposite case of enhanced reflectivity of the clouds, li kely due to the indirect effects caused by sulfate aerosols. In this study, we want to use model calculations based on meteorological analyses and validated with aircraft measurements during the ICARTT campaign to first determine the fraction of pollution exported from the USA underneath and within clouds. Then, the properties of clouds in polluted and unpolluted (but otherwise similar) airstreams shall be compared in a statistical analysis. This will allow to identify cases where clouds are "burned away" and where the reflectivity of clouds is increased by the pollution export. Hopefully, a quantitative analysis of the effect of pollution on clouds during ICARTT will also be possible. Furthermore, the FLEXPART model system (maintained and further develop ed at NILU) will be prepared for forecasting pollution transport during an upcoming major field campaign in Texas in the summer of 2006. This project will mainly look into the effects of the petrochemical industry on the atmospheric composition. The visi t of Owen Cooper at NILU will strengthen the existing co-operation between NILU and NOAA.