Abstract
In this study, the formula for evalusting the changes of Y-value of external sufaces due to the dirt was investigated. The changes of Y-value of external material surfaces were expressed by three parameters, mc which indicates the maximum value of soiling, tc which indicates the peak period of the degree of soiking, and R which indicates the washing effect. The results of the outdoor exposure tests were well simulated by the calculation by using the three parameters based on the areal occupation theory.
