Identification of sources of atmospheric PM at the Pittsburgh Supersite—Part II: Quantitative comparisons of single particle, particle number, and particle mass measurements

Abstract

A single particle mass spectrometer, RSMS-3, and a MOUDI were deployed during the Pittsburgh Air Quality Study (PAQS), July 2001–September 2002, to obtain size resolved measurements of elemental composition for particulate matter (PM) within the Pittsburgh area. Elemental mass distributions from analysis of the MOUDI stages were directly compared to those constructed using the single particle data, in conjunction with coincident SMPS measurements, for specific days within the PAQS. Results from one episode on 27 October 2001 showed that approximately 80% of the metal containing particles detected on this day belonged to the Na/Si/K/Ca/Fe/Ga/Pb particle class. The density and shape factor of these particles were estimated to be 3.9±0.8 g/cc and 1.5±0.2, respectively, and the relative sensitivity factors for individual metals showed little variation with respect to particle diameter over the size range of 70–800 nm. Compared to the 27 October 2001 episode, there was a larger degree of variability in the metal containing particles detected during another episode on 14 March 2002. The Ca and Pb mass distributions from this day represent an ensemble of externally mixed particles. Estimates of particle density were provided for the dominant particle types, including EC/OC/Ca, Al/Si/Ca/Fe, EC/OC/Pb and Na/K/Zn/Pb, and estimates of particle shape factor were provided for the EC/OC/Ca and Na/K/Zn/Pb classes. Comparison with the 27 October 2001 Ca and Pb mass distributions revealed that the RSMS data reconstructed the MOUDI mass much better from the Ca/Pb containing particles detected on 14 March 2002 than those observed on 27 October 2001, suggesting that the single particle instrument sensitivity to both Ca and Pb depends on the particle matrix.