CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Unidad Ejecutora - UE
congresos y reuniones científicas
Photo-transformation of nitrate levitated particles and influence on their hygroscopic properties.
S. SENG; Y. TOBÓN; L. C. JUNCAL; M. MOREAU; S. SOBANSKA
Conferencia; European Aerosol Conference; 2015
European Aerosol Assembly (EAA), a body that now represents 12 national or regional aerosol societies, and the Italian Aerosol Society (IAS).
The effect of aerosol particles on climate change is still not very accurately estimated since many heterogeneous processes lead to changes in chemical composition but also in size and morphology of the particles. Studying the aging processes of aerosols at the single particle scale is an added value to better understand the physicalchemical mechanisms intervening in heterogeneous atmospheric processes since these processes are complex and still remain unresolved.Nitrate is mainly formed in the atmosphere by reaction of NOx with sea salt or ammonia. Several papers have been published on the thermodynamics, phase transition, and hygroscopicity of pure or mixed nitrates salts. In addition, nitrate photochemistry is well known and is recognized to generate NO2 and nitrite ions. Nonetheless, photochemical studies of nitrate salts insingle levitated particles as well as the influence of the photoproducts on the hygroscopic properties have not been conducted.Micro-Raman spectroscopy, coupled to an environmental levitation cell, is especially useful for studying, at micrometric scale, the in-situ modificationsof aerosol when exposed to reactive environments or humidity without the influence of a contacting surface. In this work, we have used micro-Raman spectroscopy coupled to an environmental acoustic levitation cell to study the physical and chemical processes occurring in pure or mixed sodium and ammonium nitrate single particles when exposed to UV-Vis light and their hygroscopic properties before and after irradiation.Aqueous nitrate levitated drops were irradiated with UV-Vis light and Raman spectra were recorded as a function of the irradiation time. After irradiation, NO2- and ONOO- ions were observed to arise in the droplets as shown in figure 1.Relative humidity cycles were performed after and before irradiation and modifications of the humidity cycle were observed before irradiation as shown infigure 2. Thus, a lower DRH value was evidenced as consequence of photochemical products.In this work, the photo-transformation of pure or mixed sodium and ammonium nitrate single levitated particles were investigated by μ-Raman spectroscopycoupled to an environmental levitation cell. NO2- and ONOO- ions were evidenced as the main photo-products in the process. An alteration in the hygroscopicproperties of the particles after irradiation was clearly evidenced