NUMERICAL EVALUATION OF CONTRIBUTIONS OF POLLUTANT SOURCES EXTRACTED BY CONSTRAINED OBLIQUE ROTATIONAL FACTOR-ANALYSIS FOR PRECIPITATION DATA - EXTRACTION OF FEATURES OF PRECIPITATIONS AT HYOGO AND AKITA AREAS

A statistical method developed by our group, ''the constrained oblique rotational factor analysis'' enables feature reduction and grouping o f the pollutant sources in precipitations from their chemical composit ions. A study applied to the precipitations has indicated the necessit y of the numerical evaluation of contributions of the extracted source s. In this paper, a procedure for the numerical evaluation is demonstr ated; and, as one application, the precipitations collected in Hyogo p refecture are compared with those in Akita prefecture. The analysis ha s proposed that an ion-balance check of the extracted pollutant source gives a simple criterion about how many pollutant sources should be e xtracted. As a result, the causes of lowering of the pH of the precipi tation of these two areas are explained by two sources: 1) an acidic s ource with sulfuric acid predominant brought over the Sea of Japan fro m China by winter monsoons; and 2) another acidic source with sulfuric acid and nitric acid predominant emitted domestically. The seasonal c hanges of acidity of the precipitation of Japan depend upon the amount s of these two contributions.