Modelling of chemical and physical aerosol properties during the ADRIEX aerosol campaign

A global aerosol model with relatively high resolution is used to simulate the distribution and radiative effect of aerosols during the Aerosol Direct Radiative Impact Experiment (ADRIEX) campaign in August and September 2004. The global chemical transport model Oslo CTM2 includes detailed chemistry, which is coupled to aerosol partitioning of sulphate, nitrate and secondary organic aerosols. In accordance with aircraft observations the aerosol model simulates a dominance of secondary aerosols compared to primary aerosols in the ADRIEX study region. The model underestimates the aerosol optical depth (AOD) at 550 nm in the main region of the campaign around Venice. This underestimation mainly occurs during a 3–4 day period of highest AODs. At two AERONET (Aerosol Robotic Network) stations related to the ADRIEX campaign outside the Po valley area, the model compares very well with the observed AOD. Comparisons with observed chemical composition show that the model mainly underestimates organic carbon, with better agreement for other aerosol species. The model simulations indicate that the emission of aerosols and their precursors may be underestimated in the Po valley. Recent results show a large spread in radiative forcing due to the direct aerosol effect in global aerosol models, which is likely linked to large differences in the vertical profile of aerosols and aerosol absorption. The modelled vertical profile of aerosol compares reasonably well to the aircraft measurements as was the case in two earlier campaigns involving biomass burning and dust aerosols. The radiative effect of aerosols over the northern part of the Adriatic Sea agrees well with the mean of three satellite-derived estimates despite large differences between the satellite-derived data. The difference between the model and the mean of the satellite data is within 10% for the radiative effect. The radiative forcing due to anthropogenic aerosols is simulated to be negative in the ADRIEX region with values between −5 and −2 W m−2. Copyright c © 2008 Royal Meteorological Society and Crown Copyright