Two-Dimensional NMR Studies of Water-Soluble Organic Matter in Atmospheric Aerosols

The potential and the limitations of combining two-dimensional nuclear magnetic resonance (2D NMR) techniques to deliver new qualitative information on the substructures present in water-soluble organic compounds (WSOC) from fine atmospheric aerosols collected during Winter and Spring/Summer seasons are highlighted in this study. The WSOC fractions were extracted from quartz filter samples and further separated into hydrophobic acids and hydrophilic acids fractions by using a XAD-8/XAD-4 isolation procedure. Despite different spectral resolution, it was found that the aliphatic material of both samples includes mostly long-chain (carbons greater than 3 or 4) and branched mono- and dicarboxylic acids, carbonyl, and ester structural types. The presence of such structural fragments could be associated to secondary organic aerosol formation. It has been further demonstrated that spectral signatures typical of anhydrosugars from cellulose and methoxyphenols from lignin can be identified among the carbohydrate and aromatic moieties of the Winter sample. Their presence highlights the major influence of biomass burning on atmospheric particulate matter collected during colder periods. The data reported here demonstrate the success of 2D NMR techniques to investigate aerosol WSOC composition, as well as to evaluate aerosol source fingerprints.