Isotopic constraints on the oxidation and aerosol formation processes in urban polar environments

Sarah Albertin (2020-2022)

Directors : Slimane Bekki (LATMOS) et Joël Savarino
Funding : ministerial grant

Summary :
This thesis is part of the international ALPACA-CASPA project, the purpose of which is to study urban pollution in polar environments. ALPACA-CASPA addresses key issues on the processes governing the formation, composition and distribution of aerosols in the Arctic (from local and remote sources) in order to reduce uncertainties in predictions regarding the oxidation of aerosol precursors, formation and impact of aerosols on the particulate composition of the Arctic and its climate. The focus is on winter and early spring when anthropogenic emissions, including local arctic sources, contribute to arctic haze. New field data (in situ, remote sensing), laboratory isotopic analyzes, analyzes of existing observations and atmospheric modeling will be used to better characterize, understand and simulate the sources and cycles of arctic aerosols as well as the dynamics of the boundary layer. Assessments of the current and future impacts of anthropogenic aerosol sources on the Arctic climate will be improved. CASPA brings together 7 complementary French groups working on the chemistry, dynamics and geochemistry of the atmosphere. ALPACA brings together all the international teams involved in the project.
The object of this thesis work will consist in constraining the mechanisms of oxidation of chemical species, in particular nitrogen oxides, and of formation of nitrate and sulfate aerosols by using the tools resulting from the chemistry of stable isotopes and in particular the oxygen isotopic abnormalities. The first step will be to set up a system for collecting nitrogen oxides in order to be able to analyze their isotopic compositions. Secondly, tests reproducing atmospheric conditions will be carried out in an atmospheric simulation chamber. Finally, natural sample collections will be conducted in Fairbanks (Alaska), an experimental site chosen to study urban pollution in the Arctic. The data obtained will be interpreted in the light of studies in the simulation chamber, in situ measurements produced by other teams and photochemical box modeling (including a scheme of the isotopes of nitrogenous species).
The project is in part supported by the ALPACA program which is already funded by IPEV and LEFE giving access to the polar regions. The isotope chemistry component of the program is the result of a very close collaboration between LATMOS and IGE. This work is an integral part of the "reactive chemistry by isotopic approach" task of the ALPACA-CASPA project.

Keywords : atmospheric chemistry, polar regions, isotopic analyzes, field, laboratory, simulation chamber