Apportionment of ambient primary and secondary PM2.5 during a 2001 summer intensive study at the NETL Pittsburgh site using PMF2 and EPA UNMIX

Apportionment of primary and secondary pollutants during a July 2001 intensive study at the National Energy Technology Laboratory is reported. PM2.5 was apportioned into primary and secondary contributions using PMF2, and results were compared with apportionment based on UNMIX 2.3. Input to PMF2 included PM2.5 mass data from four per 24 hour PC-BOSS filters and TEOM, NOx, NO2, O-3, non-volatile, semi-volatile, and volatile organic material, elemental carbon, sulfate, and PIXE determined trace metals. Nine factors were identified in the PMF analysis. Six factors were associated with primary particles from crustal, mobile (gasoline and diesel), and three local sources high in trace metals. Three factors were associated with secondary sources. Two were associated with local emissions dominated by organic material, one was dominated by transported ammonium sulfate. UNMIX was able to identify the two major mobile sources, major local secondary source and transported secondary source. The three major sources of PM2.5 were identified as secondary transported material (dominated by ammonium sulfate) from west and southwest (46%), secondary material formed during mid-day photochemical processes (21%), and primary emissions from diesel (10%) and gasoline (8%) mobile sources. The other five sources accounted for the remaining 15% of the PM2.5. These findings are consistent with the majority of secondary ammonium sulfate in the Pittsburgh area resulting from distant transport, and so decoupled from local activity involving organic pollutants in the metropolitan area. In contrast, the major local secondary sources were dominated by organic material.