The 2003/2004 Libby, Montana PM_2.5 source apportionment research study

Except for areas in California, Libby, Montana is the only designated EPA nonattainment area for fine particulate matter (PM_2.5) in the mid and western states. During the winter of 2003/2004, PM_2.5 speciated data (mass, elements, ions, organic/elemental carbon) were collected every six days from November 11, 2003 through February 27, 2004. Using a Chemical Mass Balance computer model (Version 8.0), these data were used to apportion the sources of PM_2.5 in the Libby valley. In support of the source apportionment program, a comprehensive evaluation of the particulate matter associated organic compounds (including polar organics, phenolics, polycyclic aromatic hydrocarbons, and ¹⁴C) present in the airshed was also conducted. CMB modeling results revealed that emissions from residential wood combustion was the major source of PM_2.5 throughout the winter months in Libby, contributing an average of 82% of the measured PM_2.5. Levoglucosan, a well-known chemical marker for wood smoke, had the highest measured concentrations of any of the 95 polar organic compounds quantified from the fine fraction, accounting for over 15.5% of the measured organic carbon fraction. Other semi-volatile organic compounds with high measured concentrations during the program were four phenolic compounds commonly found in wood smoke, including phenol, 2-methylphenol (o-cresol), 4-methylphenol (p-cresol), and 2,4-dimethylphenol. Results from ¹⁴C analysis indicate that as much as 82% of the measured ¹⁴C results from a wood smoke source. These indicators support modeling results that residential wood combustion was the major source of PM_2.5 in Libby, Montana throughout the winter months.