The effect of sampling duration on the ability to resolve source types using factor analysis

The effects of sampling duration on source identification using factor analysis method were examined in this paper. Principal factor analyses were performed on the data collected as part of the Philadelphia Regional and Local Sulfur Aerosol Concentrations Study conducted from July to October 1982. The data were mass concentrations of 22 trace elements analyzed by proton induced x-ray emission (PIXE) analysis and their associated analytical uncertainties that are a measure of the precision of the measurements. A weighting scheme is applied to the concentrations of the elements to emphasize the precisely measured elements for factor analysis. Furthermore, a new method was used to eliminate the problem of Heywood cases in the factor analyses. Results show the influence of sampling duration on the number of resolvable factors as well as the amount of variance explained by the factors. The analyses show that reducing the sampling duration can increase the number of sources identified by the model. Idiosyncrasies not found in the total data are shown on the separate analyses on daylight and non-daylight data.