2.5
Naydene N. Maykut
Puget Sound Clean Air Agency, 110 Union St., Seattle, WA 98101
Joellen Lewtas
US EPA, National Exposure Research Lab., 1200-6 th
Ave, Seattle, WA 98101
Timothy V. Larson
Department of Civil and Environmental Engineering, Box 352700, University of
Washington, Seattle, WA 98195
Three years of PM
2.5
speciated data were collected and chemically analyzed using the IMPROVE protocol at the Beacon Hill site in Seattle. The data were analyzed by the Chemical Mass Balance Version 8 (CMB8) and Positive Matrix Factorization
(PMF) source apportionment models. These models were both used to identify the major sources of PM
2.5 mass, whereas only the PMF model was used to apportion the sources of organic and elemental carbon. The major sources of PM
2.5
identified by the PMF model are vegetative burning and diesel vehicles. This is generally consistent with the CMB8 analysis which also identified motor vehicles (combined diesel and gasoline) and vegetative burning as major sources. Both models identified secondary sulfate and nitrate as contributing 20-30% of the PM
2.5
. Using individual organic carbon (OC) and elemental carbon fractions (EC) in the PMF analysis allowed this model to allocate the PM
2.5
, OC and EC to vegetative burning, diesel vehicles, gasoline vehicles, fuel oil and secondary sources associated with sulfates.
A major difference in the results from the two models was the split between vegetative burning and motor vehicles. In the PMF analysis vegetative burning accounted for 35% of the mass, 57% of the OC and 47% of the EC. The CMB8 model attributed 17% of the PM
2.5
mass to vegetative burning. Using CMB, motor vehicles accounted for the largest source of PM
2.5
(44%). Using the PMF model, two motor vehicle source profiles were identified. One profile clearly corresponded to diesel vehicles (16% PM
2.5
) and accounted for 36% of the total EC and 19% of the total OC in the aerosol. The second motor vehicle source profile was less dominated by EC and likely represents the gasoline and other non-diesel mobile sources. This motor vehicle source accounted for 6% of PM
2.5
, 4.5% of the total OC, and 1% of the
EC. The present study was undertaken to refine the results from previous analyses and to determine the usefulness of applying the PMF model to the Seattle ambient aerosol data. Results from the PMF model add insight to the source apportionment results. We found that using both models produces more robust results than using either model alone. This work has been funded by the U S Environmental Protection
Agency. It has been subjected to Agency review and approved for publication.

For more information:
Joellen Lewtas, Senior Research Scientist
U.S. EPA, NERL, Human Exposure and Atmospheric Sciences Division
1200-6th Ave., OEA-095
Seattle, WA 98101 phone 206-553-1605 FAX –0119 lab phone 360-871-8872, (FAX –8747) lewtas.joellen@epa.gov