The impact of aerosols upon the climate may be very important at local or regional scales, specifically in areas with elevated levels of anthropogenic or natural atmospheric particles. The aerosols can either disperse or absorb the radiation, having a direct effect on the planetary albedo and the climatic system. Additionally, the influence of aerosols in the formation and development of cloud condensation nuclei indirectly affects the radiative balance because of the albedo intensifying due to clouds. The quantification of the effect of aerosols on the radiative balance is still inaccurate; the associated relative error can reach 100% (IPCC, 2001). In order to reduce these uncertainties precise measurements of the chemical composition of aerosols and their complex refraction index are required over long periods of time.

In situ and columnar (integrated and vertical profile) measurements will be carried out in order to establish a correlation between optical and chemical properties of the atmospheric aerosol, for diverse synoptic scenarios and origins of the air masses. The interactions between the atmospheric components and the particulate matter (sulphation or nitrification of the mineral material and marine aerosols, Alastuey et al., 2005) will be characterized paying special attention to episodes of North African dust and regional recirculation. Data on levels of potentially toxic metals will be also provided to evaluate the air fluxes for these atmospheric pollutants. This implies that the project can work with an important database where day to day changes in vegetation and how meteorology acts on them are indirectly registered.

New aerosol parameters of high interest for climate and air quality such as number of submicron aerosols, real time measurements of black carbon and organic compounds will complement the already complex measurements of aerosols being carried out in Montseny. Radiative transfer computation will be performed using the optical and physical properties retrieved under the influence of different types of aerosols to derive the radiative forcing of the atmospheric aerosol and its contribution to the climate change. Special attention will be paid to the influence of vertical distribution of atmospheric aerosol on this radiative forcing.