Ammonium nitrate and semivolatile organic compounds (SVOC) are significant components of fine particles in many urban atmospheres. These components, however, are not properly measured by current EPA accepted methods, such as the R&P TEOM monitor, due to loss of semivolatile material (SVM) from particles in the heated environment of the filter during sampling. The accurate determination of semivolatile material is important due to the possible effects of these species on human health, visibility, and global climate change. The concentration and composition of fine particulate material were determined using a combination of continuous and integrated samplers at the Brigham Young University-EPA Environmental Monitoring for Public Access and Community Tracking (BYU-EPA EMPACT) monitoring site in Salt Lake City, Utah over a six-day sampling period (30 January to 4 February) during the winter of 2001. Continuous samples were collected using a RAMS (total PM 2.5 mass), a TEOM monitor (nonvolatile PM2.5 mass), an Aethalometer (elemental carbon), a TSI CPC (particle count), and a Nephelometer (light scattering by particles, bsp). Fine particle composition and mass were determined on a three-hour basis using the PC-BOSS diffusion denuder sampler. Total PM2.5 massdetermined with the RAMS agreed with constructed mass de- Address correspondence to Delbert J. Eatough, Department of Chemistry and Biochemistry, Brigham Young University, c100 Benson Science Building, Provo, Utah 84602-5700. E-mail: delbert eatough@byu.edu termined from the chemical composition measured in collocated PC-BOSS-integrated samples. Results from this study indicate that semivolatile material (ammonium nitrate and semivolatile organic compounds) is a significant component of fine particle mass. Semivolatile organic compounds were the major contributor to light scattering during the six-day sampling period. Semivolatile nitrate, but not organic material, was suggested to be hygroscopic by the nephelometric data. The majority of the SVM observed appeared to be secondary material formed from photochemical reactions of the organic and NOx emissions from mobile sources and wood smoke combustion.

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