Inorganic salts in atmospheric particulate matter: Raman spectroscopy as an analytical tool.

Atmospheric particulate matter is composed of inorganic and organic components of natural and anthropogenic origin. Wind-transport is probably the most important process responsible for the emission of solid particulate matter into the troposphere, but there are also important contributions from chemical reactions due to the interaction of different atmospheric components in presence of water and solar radiation. Sulfate, nitrate and carbonate salts can be both reactants and products in this complex dynamic system, and there is no doubt about their important impact on the climate. Both simple and mixed salts can be produced in atmosphere by dissolution-crystallization processes. The Raman spectra of 45 representative salts of the atmospheric environment were recorded and the bands assigned. The chemometric analysis of the spectroscopic data of these 45 salts demonstrates the suitability of Raman spectroscopy to classify and identify sulfate, nitrate and carbonate salts of atmospheric importance. Salts were classified into three groups: "sulfates", "nitrates or carbonates" and "sulfate-nitrates or sulfate-carbonate". This kind of information is relevant in atmospheric studies because specific characteristics of the salts can provide valuable information about the origin of the salts, the atmospheric chemistry and climate forcing, thus contributing to the evaluation of environmental impacts.