The organic fraction of fine particulate matter (PM_2.5) in ambient environments is composed of non-polar and polar compounds. While many studies have examined the non-polar component, on average it accounts for only 10-25% of the organic mass. Polar organic compounds can come from gas-to-particle conversion of oxidation products of natural and anthropogenic hydrocarbons and from wood combustion. Only a limited number of studies have been conducted to examine this component of ambient PM2.5.

A study of the ambient aerosol was undertaken in Philadelphia, PA, USA during the summer of 2001 as part of NEOPS. The goal was to measure the overall polarity of PM2.5 and to identify classes of particle-bound polar oxygenates, and where possible individual compounds, containing carbonyl and hydroxyl functional groups. PM_2.5 samples were collected and analyzed for gravimetric mass, inorganic composition by ion chromatography, polar oxygenated compounds by gas chromatography-mass spectroscopy, and the total organic and elemental carbon by a thermal-optical method. The chemical analyses also included determining the polarity of the PM_2.5 by measuring the organic carbon concentrations in a series of extraction solvents of increasing polarity. Detailed analysis of the organic carbon was undertaken using a double derivatization technique with PFBHA for the derivatization of carbonyl groups and BSTFA for hydroxyl groups. Organic and elemental carbon were measured from aerosol collections onto quartz filters.

The study was carried out for a five day period from 22-27 July 2001. Integrated filter samples were taken for two 24-hour and one 48-hour sampling periods. Gravimetric results indicated total mass loadings from 14 to 21 µg m^-3 for the sampling periods during that time frame. The organic mass was found to comprise 34% of the total gravimetric mass. Organic carbon analysis of the hexane extract indicated that 25% of the organic carbon was nonpolar. The mass spectra data were consistent with the presence of the following classes of oxygenates: oxo mono carboxylic acids, trihydroxy monocarboxylic acids, normal dicarboxylic acids, oxo dicarboxylic acids, hydroxy dicarboxylic acids, methoxy dicarboxylic acids, dihydroxy dicarboxylic acids, tricarboxylic acids, and photooxidation products of a-pinene and toluene in the PM_2.5. The detailed analysis of the organic fraction at the site suggested the presence of chemical markers related to photooxidation products of aromatic hydrocarbons.

Disclaimer: This work has been funded fully, or in part, by the United States Environmental Protection Agency, under Contract Number 68-D5-0049 to ManTech Environmental Technology, Inc. It has been subjected to Agency review and approved for publication.