P22 On the interplay between upper and ground levels dynamics and chemistry in determining the surface aerosol budget

Curci, Gabriele, University L'Aquila, Luca Ferrero, University Milano Bicocca, Paolo Tuccella, University L'Aquila, Federico Angelini, ENEA, Francesca Barnaba, ISAC-CNR, Ezio Bolzacchini, University Milano Bicocca, Maria Cristina Facchini, Gian Paolo Gobbi, Tony Christian Landi, ISAC-CNR, Maria Grazia Perrone, Giorgia Sangiorgi, University Milano Bicocca, and Paolo Stocchi, ISAC-CNR, Italy

Several studies on the budget of aerosol species at ground level highlighted contributions of comparable magnitude from boundary layer processes, such as photochemical production, vertical mixing, deposition, and entrainment with free tropospheric air. However, quantitative assessments with comprehensive three-dimensional aerosol models are still rare. Here we use the WRF/Chem model to interpret observations of the aerosol concentration and its chemical composition both at surface level and along vertical profiles (tethered balloon and lidar) performed during an intensive campaign in July 2007 in Milan urban area. The model is added with a new diagnostic for aerosol budget analysis, building on that available for gas species.

The analysis illustrates a quite variegated evolution of budget terms, which we found to depend strongly on the hour of the day, the vertical level, the aerosol compound, and the aerosol size. Primary components are generally emitted near the ground and rapidly transported by turbulent motions to the upper levels, where they gradually disperse and age. For some secondary components, such as nitrate, we calculate a net chemical destruction in the bottom layers, as opposed to a net chemical production higher in the boundary layer, which supply new material to ground level aerosol through turbulent mixing.