Titre : Tracking volcanic sulphate : modelling tropospheric volcanic sulphate formation
and its oxygen isotopic signatures 

17 Septembre 2018, à 14h00 à
l'Amphithéâtre Durand - Bâtiment Esclangon - Campus Jussieu.

Volcanic emissions are a major source of pollutants, notably sulphur. Volcanic sulphur is oxidized in the atmosphere, forming sulphate aerosols that influence climate via absorption and dispersion of incoming solar radiation. While tropospheric volcanic sulphur emissions can influence climate only at local and regional scales, they are important for acid deposition and hazardous effects on human health. Besides, large uncertainties are still pertaining to the tropospheric cycle of volcanic sulphur, notably on its oxidation and conversion into sulphate aerosols within volcanic plumes. Recent observations show that volcanic plumes can also contain large amounts of reactive halogens that destroy ozone and affect the budget of atmospheric oxidants. However, halogens influence on volcanic sulphur oxidation is still unclear.

The purpose of this work is to investigate sulphur oxidation in a wide range of volcanic plumes, and volcanic halogens influence on in-plume chemistry. Volcanic sulphur processing is investigated with the aid of a photochemical box-model (CiTTyCAT), which contains a detailed description of sulphur and halogens heterogeneous chemistry on liquid water-rich phases and sulphate aerosols. The chemical scheme is also coupled to an oxygen isotope transfer scheme, monitoring the evolution of volcanic sulphate 
17O. The isotopic oxygen composition of volcanic sulphate, namely the excess of 17O (D17O), is being explored, providing unexpected constraints on sulphur oxidation pathways within plumes, and on halogens role during volcanic sulphate formation.