Environmental Risk Assessment: Comparison of Receptor and Air Quality Models for Source Apportionment

ABSTRACT

Source apportionment of particulate matter has been commonly performed using receptor models, but studies suggest that the assumptions in receptor models limit the accuracy of results. An alternative approach is the use of three-dimensional source-oriented air quality models. Here, a comparison is conducted between the PM_2.5 apportioned from the Chemical Mass Balance (CMB) receptor model using organic tracers as molecular markers with those from the source-based Community Multiscale Air Quality (CMAQ) model. Source apportionment was conducted at sites in the southeastern United States for July 2001 and January 2002. PM_2.5 source apportionment results had moderate discrepancies, which originate from different spatial scales, fundamental limitations, and uncertainties of the two models. Results from CMB fluctuated temporally more than real variation due to measurement and source profile errors and uncertainties, whereas those from CMAQ could not capture daily variation well. In addition, results from CMB are mass contributions for the monitoring location, whereas those from CMAQ represent the average mass contributions of the model's grid. It is difficult to assess which approach is “better.” Indeed, both models have strengths and limitations, and each model's strengths can be utilized to help overcome the other model's limitations.

Key Words:

• source apportionment
• particulate matter
• CMB
• CMAQ

ACKNOWLEDGMENTS

This research was supported by the U.S. Environmental Protection Agency under Agreements RD82897602, RD83107601, RD83096001, and RD83479901. We thank John Jansen of the Southern Company, Eric Edgerton in the Atmospheric Research & Analysis, Inc., and researchers involved in ASACA, USEPA-STN, IMPROVE, and SEARCH projects for their assistance and hard work developing the data used. We also appreciate comments from Sergey Napelenok.