Since the purpose of this research is to test the association between aerosols and anthropogenic O3, this analysis diverged from typical source-apportionment PMF in two important ways.
First, the selection of a preferred PMF solution was guided by the need to isolate combustion aerosol sources, even when they Brefeldin A are part of a larger aerosol mass (for example, Asian combustion products are intimately mixed with Asian dust (VanCuren, 2003)). This resulted in a solution that is somewhat over-resolved, particularly for local-source mixtures.
Second, since the fractions of measured O3 associated with the PMF factors may not be related to their aerosol mass fractions, the analysis used normalized variables (each IMPROVE species value was divided by the mean for that species in the pooled data set), which emphasizes diagnostic trace elements, de-emphasizes mass, and causes all factors to have a mean value of 1.
The preferred solution produced 10 aerosol factors from the pooled LAVO and GRBA IMPROVE data. Plots of the normalized composition profiles and their time series scores are shown in Fig. 2, and their contributions to mean PM2.5 mass at LAVO and GRBA are shown in Table 1. The factors are grouped into two broad classifications, based largely on their temporal patterns.