Importance of the representation of aerosol wet scavenging for aviation aerosol transport

Aircraft engines emit aerosols and aerosol precursor gases, mostly black carbon (soot) and sulfur dioxide, which remain longer in the atmosphere than aerosols emitted at the surface. Long-range transport during that long residence time means that aviation aerosols may interact with clouds far from the main flight corridors. The radiative forcing of interactions between aviation aerosols and clouds is so uncertain that even its uncertain range is unknown. Its quantification relies on climate models, where aerosol concentrations and long-range vertical and horizontal transport are strongly affected by wet scavenging, which can be parameterized in different ways with several tunable parameters. One could assume that the representation of wet scavenging is of secondary importance for the simulated residence time of aviation aerosols, because they are emitted high above precipitating clouds. In this work, we use the LMDZ-OR-INCA climate model to investigate the impact of three different scavenging parameterizations on total and aviation aerosol distributions, using regional and seasonal vertical profiles measured during the ATom and HIPPO airborne campaigns to evaluate the performances of the different parameterizations. Results confirm that the residence time and the mass budgets of black-carbon, sulfates and nitrates from all sources are significantly influenced by the scavenging scheme. Moreover, the skill of a scavenging parameterization to simulate vertical aerosol concentration profiles depends on geographical location, altitude and season, although no parametrizations are consistently better than the others. Unexpectedly, the scavenging parameterizations also affect aviation aerosol concentrations at flight cruise levels: although scavenging rates are small, residence time are long so differences accumulate. Near-surface aerosol concentrations, which are mainly due to Landing and Take-off Operations (LTO), are also affected by the choice of a wet scavenging parameterization. Results suggest it may be possible to design a new scavenging routine for LMDZ-OR-INCA model to better represent the long-range transport of aviation aerosols and reduce uncertainties in aviation aerosol-cloud interaction radiative forcing.