Receptor modeling and aerosol transport

While receptor modeling techniques have been repeatedly shown to be useful in quantifying the sources of urban aerosols, the estimation of contributions from distant pollution transport has proved more difficult. In this paper, the applicability of usual receptor modeling assumptions to transported aerosol modeling is assessed, and past attempts at apportioning transported aerosols summarized. It is shown that Chemical Mass Balance (CMB) and multivariate receptor oriented models (e.g. Principal Component Analysis) each have their own strengths and shortcomings when addressing aerosols which have undergone significant transport. In particular, multivariate methods are preferable when doubt exists as to the identity and nature of sources influencing a monitoring site, while CMB models are most appropriate when all important sources and their downwind characteristics are known. As a result, it is concluded that these two approaches might best be used sequentially, with multivariate methods preceding CMB in transported aerosol assessments. In part because of this, available qualitative and quantitative receptor modeling literature indicate that multivariate model applications have been better able to discern and quantify these as yet ill-defined transported aerosol contributions, to date. In general, these results support the assessment that the Midwest sulfur dioxide source region is a major source of Eastern U.S. sulfates and fine particulate matter. Recommendations for future improvements in the treatment of transported aerosols by receptor models are also presented.