Particles were collected in dichotomous samplers at three sites in the Philadelphia area during summer, 1982, and analyzed by x-ray fluorescence, instrumental neutron activation, pyrolysis, and ion chromatography. An intermethod comparison showed that fine fraction results agreed within measurement error for S, Ca, Mn, Fe, Zn and Sb. A composite of chemical mass balance, multiple linear regression, and stratification by wind direction was used to apportion mass into ten categories. Primary emissions from residual oil combustion, catalytic crackers, an antimony roaster, and municipal incinerators contributed less than 10% of PM-10. The portions of average PM-10 attributed to crustal matter and vehicle exhaust were 17 + or - 2 and 6 + or - 2, respectively. That attributed to sulfate plus related water and ions was 50 to 55%. Wind stratified data indicated that 80 + or - 20% of the sulfate was from a regional background. Multiple linear regression of S vs tracers Se and either V or Ni indicated that 72 + or - 8 and 16 + or - 5% could be attributed to coal- and residual oil-fired power plants, respectively. (Copyright (c) 1987, American Chemical Society.)