Evaluation of the potential source contribution function using the 2002 Quebec forest fire episode

Particle data consisting of PM2.5 (particulate matter <2.5 μm aerodynamic diameter), light scattering coefficient (bscat), organic carbon (OC), elemental carbon (EC), and sulfate were measured for 2-h intervals from 1 July to 3 August 2002 in Philadelphia using semicontinuous monitors. The potential source contribution function (PSCF) combines the particle data with air parcel back trajectories to identify potential source areas and the preferred pathways that give rise to the observed high particle concentrations in Philadelphia. Five day back trajectories arriving 12 times a day at 500 m above ground level were calculated using NOAA HYSPLIT with the vertical mixing model. PSCF analyses were performed based on the average values as criterion values for the measured particle parameters. During this period, there was a major forest fire in central Quebec that penetrated the eastern United States to well south of Philadelphia, Pennsylvania. This event permits the testing of the ability of the PSCF analysis to identify the known source location of this fire, which is observed clearly in the maps for PM2.5, OC and EC. The other maps can also be interpreted in terms of the likely sources of the observed concentrations.