Composition of PM2.5 during the summer of 2003 in Research Triangle Park, North Carolina

A field study was carried out during the summer of 2003 to examine the overall composition of fine particulate matter (PM2.5) in Research Triangle Park, North Carolina, USA, with particular emphasis on polar compounds from secondary organic aerosol (SOA). Collected samples were examined for gravimetric mass, organic and elemental carbon concentrations, inorganic ion concentrations, and detailed organic composition. On average, the ambient PM2.5 was found to consist of 41% organic matter, 2% elemental carbon, 12% ammonium, 37% sulfate, and less than 1% nitrate and oxalate. Mass concentrations ranged from 6.4 to 31.4 μg m−3. The acidity of the aerosol was also estimated, and higher PM2.5 and organic mass concentrations were generally observed under acidic conditions. A suite of chemical derivatization methods was used in conjunction with gas chromatography–mass spectrometry (GC–MS) to identify and quantify 29 polar organic compounds. Most of these compounds have been previously identified in laboratory photooxidation studies from hydrocarbon precursors, including isoprene, monoterpenes, β-caryophyllene, and toluene. From laboratory studies, several of these polar compounds have been proposed as tracers for SOA, and concentrations measured in this study indicate the contributions of the precursor hydrocarbons to ambient SOA could be important. Some of the organic tracers, particularly those associated with isoprene SOA, represented a greater fraction of the organic carbon when the aerosol was acidic.