Source Apportionment Studies

Quantitatively identifying the relative contributions of different source types to ambient air pollutant concentrations is referred to as source apportionment. When an area experiences high concentrations of PM or ozone, particularly when the concentrations are in exceedance of an air quality standard, analysts seek to identify the contributing emissions sources to assist policy makers in developing control strategies. STI analysts use several source apportionment methods including investigation of the spatial and temporal characteristics of data; cluster, factor, and other multivariate statistical techniques; positive matrix factorization (PMF); UNMIX; the chemical mass balance (CMB) model; and trajectory analysis tools such as PORCSH (Probability of Regional Source Contribution to Haze).