Study of the relationship between physico-chemical and optical properties

During their transport in the atmosphere, mineral aerosols undergo size segregation related to the sedimentation of the coarse particles. This segregation also implies a change of the composition and the shape of the aerosol. It is important to quantify the influence of various factors on the optical properties to assess the degree of precision with which they must be described to correctly estimate the direct radiative effect.

This assessment is based on the analysis of the results of experiments of optical, consisting of closure to calculate the optical properties of scattering and absorption from the measured physicochemical properties, and then compare the result of the calculation the measured optical properties. On the basis of these results, it is sought to establish empirical correlations between physicochemical and optical properties robust and simple enough to be integrated in chemistry-transport models.

 

Figure 1: Vertical profile of dissemination at 3 wavelengths of aerosols sampled on board of the ATR-42 in West Africa during AMMA in the case of Sahel and Saharan aerosols, marine aerosols and aerosols resulting from the combustion of biomass. The different types of aerosols are discriminated by variations in their properties of diffusion based on the wavelength. The spectral dependence is low for aerosols of bigger size (desert type) and very strong for the fine aerosols (such as carbonaceous aerosols from biomass fires) (Formenti et al., 2011).