Effects of day-of-week trends and vehicle types on PM_2.5-bounded carbonaceous compositions

Carbonaceous compositions of PM_2.5 were measured in the heart of Bangkok from 17th November 2010 to 19th January 2012, and a data set of 94 samples was constructed. Effects of day-of-week trends and vehicle types on PM_2.5-bound TC, OC, and EC were carefully investigated. In this study, OC was the most important contributor to the total PM_2.5 mass concentration. The average PM_2.5-bound OC content measured at CHAOS (18.8±9.18μgm^-3) was approximately 11 times higher than at Chaumont, Switzerland (1.7μgm^-3), but approximately five times lower than at Xi'an, China (93.0μgm^-3). The application of diagnostic binary ratios of OC/EC and estimations of secondary organic carbon (SOC) coupled with autocorrelation plots (Box and Jenkins) highlight the enhanced impacts of traffic emissions, especially from diesel vehicles, on PM_2.5-bound carbonaceous compositions on weekdays relative to weekends. Hierarchical cluster analysis (HCA) coupled with principal component analysis (PCA) underline the importance of diesel emissions as the primary contributors of carbonaceous aerosols, particularly during weekdays.