One– and Three–Hour PM_2.5 Characterization, Speciation, and Source Apportionment Using Continuous and Integrated Samplers

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 PM_2.5 mass), an Aethalometer (elemental carbon), a TSI CPC (particle count), and a Nephelometer (light scattering by particles, b_sp). Fine particle composition and mass were determined on a three–hour basis using the PC–BOSS diffusion denuder sampler. Total PM_2.5 mass–determined with the RAMS agreed with constructed mass determined 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 NO_x emissions from mobile sources and wood smoke combustion.

Acknowledgments

The US Environmental Protection Agency funded and collaborated in the research described in this article under cooperative agreement CR827364 and STAR grant R827993 with Brigham Young University. The views expressed in this article are those of the authors and do not necessarily reflect the views or policies of the EPA or NPS. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. The technical assistance in this research of Rupprecht and Patashnick, Schleicher and Schuell, and ARS is gratefully acknowledged. Cooperation by Art King and Neal Olson of the State of Utah Division of Air Quality in providing the gas–phase data is also gratefully acknowledged.

Notes

^a Slopes are given for (1) calculated intercept and (2) zero intercept.

^c NA, σcould not be calculated because the sample bias was greater than α.

^a NA, α_i could not be determined due to low concentrations. Literature value used to correct b_sp.

^b Eatough et al., 2002.