Development and application of a methodology to identify and rank the important factors affecting in-vehicle particulate matter

► Two-step approach has been developed to rank the variables affecting IAQ in a bus. ► Regression trees and ANOVA have been used in the methodology. ► Indoor PM levels are analyzed and quantified as function of independent variables. ► Vehicular SO2 significantly influenced sub-micron particles (secondary PM2.5). ► This is a new approach as compared to earlier IAQ studies.