Mapping organic coatings on atmospheric particles

To date there is no direct evidence of the distribution or characteristics of organic compounds in individual particles because techniques for chemically identifying organic compounds are not sufficiently sensitive to detect molecules or functional groups with masses below 10^-15 g [Husar and Shu, 1975]. Here we present detailed maps of organic groups (aromatic, alkyl, ketonic carbonyl and carboxylic carbonyl groups) and inorganic ions (potassium, carbonate, calcium) in individual dry particles with diameters ranging from 0.2 to 10 μ using a new technique for aerosol characterization by soft X-ray spectromicroscopy at atmospheric pressure. The maps show both the compounds present in individual particles and regions of different compositions within particles. The particle compositions on surfaces are enhanced in shorter chain or more oxygenated groups, providing the first observations of surface active carboxylic acids in organic coatings in atmospheric particles.