Dynamic of semi-volatile compounds : transfer at air - soil interface
Organic and inorganic semi-volatile compounds, are found in the different compartments of the environment. While most of these pollutants are of anthropogenic origin, one part is produced naturally (some PAHs and metals). Because of their persistence and low degradability, these compounds are transported in the atmosphere, by a long range transport far from their emission sources. They deposit in various media (vegetation, water, soil), where they are stored temporarily or definititaly. Through geochemical cycles (succession of deposit-emission), they contaminate all the environment, including remote areas. The aim of this research is to study the speciation and the fate of pollutants at the soil-air interface, in sub-urban and mountain areas. A specific approach was carried out to define the role of soil in the trapping or remobilization of pollutants. The first part of the work is done in microcosm in order to identify key parameters that control the emissions of PAHs from mountain soils. Four parameters have been studied : temperature, humidity of air, organic matter content and soil moisture. From measurements, a thermodynamic approach predicted the mechanism involve in close relationship with the physicochemical properties of the compounds and soils. In parallel, field experiments : (i) clarified the nature of the pollutants found in the air and soil of each site, (ii) determined the mode of contamination ; (iii) estimated the seasonal variability of exchanges at the soil-air interface. Based on a litterature survey, a new sampler has been developed to estimate emissions from soils on particulate matter and in gaseous phases. Mass balances allowed to specify the role of the soil. A final modeling approach finalized the work. From experimental measurements got on site and in laboratory, two models available online, have been used : (i) to predict the distribution of a compound in the overall environment or specifically in the soil fractions, (ii) and to estimate the loss pathways and exchanges between soil and atmosphere. Data from simulations were compared with experimental results to valid both models towards soils studied.