Evaluation of Sources of Acidity in Rainwater Using a Constrained Oblique Rotational Factor Analysis

Abstract

Acidity (or basicity) of sources of rainwater pollutants, whether they work as acids, bases, or neutral substances, is not easily evaluated by using conventional multivariate analysis such asthe principal component analysis (PCA) or that with the Varimax rotation. We examined the application of an oblique rotational factor analysis in this work based on the nonnegative constraint as to the ion concentrations except hydrogen ion and to the contributions of pollutant sources in rainwater. The method is as follows : (1) the PCA, (2) the Varimax rotation, and (3) the oblique rotation with partially nonnegative constraint. The method and its validity are demonstrated by using analytical data for 391 rainwater samples collected at Hyogo prefecture in Japan during 1991-1992. As a result, four predominant pollutant sources were extracted ; they were a source with sea salt origin, a source acidifying rainwater, a source basifying rainwater, and a source specific to potassium ion. At most, six pollutant sources were extracted and were reasonably interpreted from the chemical, biological, geographical, and meteorological points of view.