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sur le développement des zones arides et semi-arides

Titre : Laboratory Study of Semi-Arid Biomass Smoke Hygroscopicity : Role of Phenology, Chemistry and Combustion Conditions

Auteur : Gomez, Samantha

Université de soutenance : New Mexico Institute of Mining and Technology

Grade : Master of Science in Environmental Engineering 2018

Résumé
Biomass burning emissions have substantially increased with continued warming and drying in the southwestern U.S., impacting air quality and atmospheric processes. To better quantify impacts of biomass burning aerosols, an extensive laboratory study of fresh smoke emissions was conducted at Los Alamos National Laboratory (LANL). Laboratory burn experiments with selected native and invasive southwestern U.S. fuels were used to elucidate the role of fuel type, chemical composition, and combustion conditions on the hygroscopicity of smoke. This thesis focus on a custom controlled relative humidity nephelometry system using the direct measurement of aerosol light scattering with two nephelometers—one at dry conditions and one at a controlled high relative humidity (RH 85%). Aerosol hygroscopicity was highly variable with the enhancement in light scattering coefficient ranging from 1.02 < ƒ(RH=85%) < 2.1 and corresponding to the kappa parameter (Kneph) ranging from 0 to 0.18. Hygroscopicity is determined primarily by the fuel’s inorganic ion content. For example, invasive halophytes with high inorganic salt content exhibit much greater water uptake than native coniferous species with low inorganic content. Combustion temperature and phase, flaming or smoldering, play a secondary role in the water uptake of smoke. High temperature ignition methods create flaming conditions that enhance hygroscopicity while lower temperature smoldering conditions diminish hygroscopicity. Our results construct an empirical relation between Kneph and the inorganic content of the fuel and smoke to predict water uptake. These interactions determine the radiative forcing and atmospheric lifetime of biomass burning emissions. Several ambient biomass burning events were observed throughout the course of the biomass burning experiments. These events provided an opportunity for validation and comparisons with laboratory results

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