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Thesis abstract:

Subject to numerous anthropogenic (gaseous and particulate atmospheric pollution burden) and natural (desert dust events ...) forcings, but also heavily populated on its shores, the Mediterranean is recognized as a region particularly sensitive to the evolution of atmospheric pollutants and climate change. Today, the assessment of the future composition of the atmosphere in the Mediterranean is a major environmental and health issue. In particular, the simulation of the secondary organic aerosol (SOA) in the western basin remains little discussed in the literature, particularly because of the complexity of the subject. The ChArMEx (Chemistry-Aerosol MEditerranean Experiment) intensive campaign, which aims to scientifically evaluate the current and future state of the Mediterranean atmospheric environment, has given us the opportunity to improve our understanding of the organic fraction as well as total aerosols over the Mediterranean, using a 3D modeling approach.

As a first step, different simulation schemes of organic aerosols (OA) taking into account the evolution of the semi-volatile organic compounds in the atmosphere (functionalization versus fragmentation), as well as the formation of the non-volatile SOA, have been implemented in the CHIMERE model. The comparison of these schemes with the measurements make it possible to highlight the main sources of OA formation in the western basin of the Mediterranean and to define the configuration of the most appropriate scheme for the simulation of this aerosol. We found that the scheme that takes into account the non-volatile SOA fragmentation and formation processes fits best to the mass cocnentration, oxidation state, and origin of the OA measured in the ChArMEx project, especially in Cap Corse and Mallorca.

Subsequently, we utilized the CHIMERE model in order to present a detailed look at the future conditions of the Mediterranean basin. Future scenarios proposing different intensities for climate change have been investigated. In particular, the isolated effects of different drivers (regional climate, anthropogenic emissions and long-distance transport) have been identified, and the share of each in the evolution of the composition of the atmosphere for the main components of particulate matter has been estimated. In order to quantify the effect of the change of the scheme used for the simulation of the OA on future scenarios, 15 years of historic simulations and 15 years of future simulations were performed with three different OA simulation schemes. The results show that the percentage change in biogenic SOA can be underestimated by a factor of 2 in a simple scheme for the simulation of the SOA, compared to a scheme taking into account the functionalization, fragmentation and formation of non-volatile SOA.

In order to bring a more regional perspective on the Mediterranean coasts, 5 years of simulations have been carried out on the PACA region on the south-eastern coasts of France, in order to study the exposure of the population to atmospheric pollutants, as well as the combined impact of demographic evolution (population change) and future atmospheric scenarios on this exposure in two case studies at the 2030 and 2050 horizons. The results show that the individual exposure as well as the cumulative exposure of the population decreases for most atmospheric compounds. On the other hand, the risk associated with the exposure of the entire population to ozone, biogenic SOA and desert dust could increase over large parts of the region, particularly in urban areas with high levels of population growth.