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Objectives and mission – issues of the project

The project outlines the need for measurements at all scales (from microscale to mesoscale and from seconds to days) and the necessity to integrate satellite observations in models in order to better understand the whole aerosol system for contributing to climate and particulate pollution studies.

Whatever their source (natural or anthropogenic), airborne particles are transported over large distances (especially for the fine and ultrafine fraction) in the troposphere and cross different air masses. Many heterogeneous processes such as particle coagulation, gas condensation, surface reactivity, lead to changes in chemical composition but also in size and morphology of the particles. The aging of atmospheric particles affects their optical properties, so that light scattering is difficult to estimate leading to significant uncertainties in predicting changes in atmospheric radiative forcing.
–> The Labex CaPPA will contribute to link the properties needed for direct and indirect effect estimates to the physical and chemical processes involved along the whole aerosol cycle, nucleation-condensation-coagulation-reactivity-in cloud processes.

Aircrafts at high altitudes contribute to anthropogenic climate change by producing a cirrus-like trail of condensed vapor called a condensation trail or contrail that represents the most visible and perhaps the most important effect of aircraft engine emissions on the atmosphere. The release of aerosols in the aircraft exhaust is strongly suspected to provide nuclei on which ice crystals form. If the relative humidity of the surrounding air is high, contrails may persist for many hours and can evolve towards persistent cirrus-like clouds. In addition to the aerosol indirect effect estimate, as explained in the previous section.
–> The Labex CaPPA will assess the contribution of contrail cirrus to global radiative forcing; a specific study will be devoted to the impacts of aviation on climate.

Detailed knowledge of microphysical and chemical characteristics of atmospheric particles are also of critical importance to assess potentially adverse effects. Emissions from steelworks and smelters are known to largely contribute to aerosol mass concentrations, notably in their immediate vicinities, but few works report a detailed assessment of the microphysical and micro-chemical properties of these airborne particulates.
–> In the framework of the labex CaPPA, specific studies will be focused on the physico-chemical characterization and formation of fine particles in industrial plumes.

Most of the air quality-monitoring stations are located close to major urban areas leaving large areas without operational observations (handled in France by the Ministry of Ecology and LCSQA (Laboratoire Central de Surveillance de la Qualité de l’Air). Satellite remote sensing is well suited for a daily monitoring of the aerosol load but primary aerosol quantity derived from space borne remote sensors is the integrated aerosol optical thickness and ground measurements may be disconnected from columnar aerosols. In urban areas, aerosol concentration is strongly dependent on the daily evolution of the boundary layer and turbulent processes play a crucial role on vertical aerosol mixing. In the lower layers of the troposphere, the distribution of aerosols needs to be spatially resolved in order to understand the impact on pollution of local sources (urban and industrial) and long-range transport. Ground-based and in-situ measurements, models, and satellite observations should be viewed as a system, each component of which is necessary to better understand air quality:
–> The Labex CaPPA will develop integration tools, new products and methodologies through the joined efforts of the research teams.

In case of severe accident occurring to a nuclear power plant, release of radionuclides is a major issue to the environment.
–> The Labex CaPPA includes specific studies (experimental techniques and theoretical chemistry tools) dedicated to radionuclides atmospheric pollutants.