FEBUKO and MODMEP: Field measurements and modelling of aerosol and cloud multiphase processes

An overview of the two FEBUKO aerosol–cloud interaction field experiments in the Thüringer Wald (Germany) in October 2001 and 2002 and the corresponding modelling project MODMEP is given. Experimentally, a variety of measurement methods were deployed to probe the gas phase, particles and cloud droplets at three sites upwind, downwind and within an orographic cloud with special emphasis on the budgets and interconversions of organic gas and particle phase constituents. Out of a total of 14 sampling periods within 30 cloud events three events (EI, EII and EIII) are selected for detailed analysis. At various occasions an impact of the cloud process on particle chemical composition such as on the organic compounds content, sulphate and nitrate and also on particle size distributions and particle mass is observed. Moreover, direct phase transfer of polar organic compound from the gas phase is found to be very important for the understanding of cloudwater composition. For the modelling side, a main result of the MODMEP project is the development of a cloud model, which combines a complex multiphase chemistry with detailed microphysics. Both components are described in a fine-resolved particle/drop spectrum. New numerical methods are developed for an efficient solution of the entire complex model. A further development of the CAPRAM mechanism has lead to a more detailed description of tropospheric aqueous phase organic chemistry. In parallel, effective tools for the reduction of highly complex reaction schemes are provided. Techniques are provided and tested which allow the description of complex multiphase chemistry and of detailed microphysics in multidimensional chemistry-transport models

Long-Range Atmospheric Transport of Polycyclic Aromatic Hydrocarbons: A Global 3-D Model Analysis Including Evaluation of Arctic Sources

We use the global 3-D chemical transport model GEOS-Chem to simulate long-range atmospheric transport of polycyclic aromatic hydrocarbons (PAHs). To evaluate the model’s ability to simulate PAHs with different volatilities, we conduct analyses for phenanthrene (PHE), pyrene (PYR), and benzo[a]pyrene (BaP). GEOS-Chem captures observed seasonal trends with no statistically significant difference between simulated and measured mean annual concentrations. GEOS-Chem also captures variability in observed concentrations at nonurban sites (r = 0.64, 0.72, and 0.74, for PHE, PYR, and BaP). Sensitivity simulations suggest snow/ice scavenging is important for gas-phase PAHs, and on-particle oxidation and temperature-dependency of gas-particle partitioning have greater effects on transport than irreversible partitioning or increased particle concentrations. GEOS-Chem estimates mean atmospheric lifetimes of <1 day for all three PAHs. Though corresponding half-lives are lower than the 2-day screening criterion for international policy action, we simulate concentrations at the high-Arctic station of Spitsbergen within four times observed concentrations with strong correlation (r = 0.70, 0.68, and 0.70 for PHE, PYR, and BaP). European and Russian emissions combined account for 80% of episodic high-concentration events at Spitsbergen.Massachusetts Institute of Technology. James H. Ferry Fund for Innovation in Research EducationNational Science Foundation (U.S.) (Atmospheric Chemistry Grant 1053648)Massachusetts Institute of Technology. Leading Technology and Policy Initiativ