In this study, 24-hour average of PM10 were conducted at 2 locations (primary and high schools) of Lak Muang Connection (see also Figure 1) to confirm the levels of PM and to investigate traffic related PM contribution. Results are shown in Figure 3 and revealed that
concentrations of 24-hour average PM10 were 47 μg/m3 (32-61μg/m3) and 52 μg/m3 (35-
67μg/m3) at the primary school and high school, respectively during semester break while that during semester the concentrations were 74 μg/m3 (26-94 μg/m3) and 70 μg/m3 (37-90
μg/m3), respectively. Although the 24-hour average PM10 were not exceeded the NAAQS
of Thailand (120 μg/m3), most of them were exceeded the guideline values recommend by
WHO (50 μg/m3). In addition, concentrations of 24-hour average PM10 compared between
the two periods were considerably differences around 27 μg/m3 (57%) and 18 μg/m3 (35%),
respectively at the primary and high schools. Note that low PM10 concentrations on March 21,
2013 during the semester mainly affected by unexpected rain in that sampling day and hence
these PM values were excluded for the average concentration estimate.