The University of L’Aquila climate-chemistry model (ULAQ-CCM) is a global coupled model including troposphere and stratosphere and a rather comprehensive aerosol module. The validation of aerosol products from the ULAQ model has focused on surface aerosol mass density on remote sites, total optical depth on a regional basis, aerosol extinction profiles using SAGE-II and HALOE data and black carbon (BC) vertical profiles using recent aircraft campaign data. Three numerical experiments were performed with the ULAQ model using emission inventories from the collaborative European project EC-REACT4C: no aircraft emissions (EXP1), NOx and H2O emissions only (EXP2), and including all gas and particle emissions (EXP3). These experiments have the purpose to study the direct radiative forcing (RF) of sulphate and BC aerosols and to study the indirect impact on the NOx-HNO3 balance (and hence on O3) via heterogeneneous chemistry on the surface of sulphate particles. The ULAQ-CCM calculated changes of sulphuric acid aerosol surface area density reach maximum values of 1.5 μm2/cm3 at about 10 km altitude in the NH mid-latitudes. Aircraft emissions of BC particles may significantly affect the mass density of carbonaceous aerosols (0.3 ng/m3 at the same location). One conclusion is that the impact of aviation SO2 and freshly emitted ultrafine sulphuric acid aerosols is to reduce the net RF associated to aviation emissions of NOx (i.e. O3 and CH4), H2O and sulphur from 4.5 mW/m2 to 3.1 mW/m2, via changes of heterogeneous chemistry and cooling due to additional or larger sulphate particles.
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