3.2 Particulate matters in the study area
As mentioned earlier, Nakhon Si Thammarat province is a big city in the south of Thailand
with high traffic volume that was recognized as potential source of PM for the area. One of
the particular sites from previous study by Kanabkaew et al. (2013) [11] showed that levels of estimated 24-hour average PM10 concentrations (32-72 μg/m3) at Lak Muang Connection
were rather high in comparison to the 24-hour average PM10 of NAAQS (120 μg/m3) and
WHO guidelines (50 μg/m3).
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.
Increasing traffic volume during the semester starts was regarded as a main factor for
traffic congestions in Bangkok and big cities in Thailand [17], particularly during rush
hour periods: 6:30-8:30 and 15:00-17:00 [18]. Low speed of vehicles during congestion
could contribute higher PM emitted to the atmosphere. Gillies et al. (2001) [4] found that
vehicle speed of 42.6 km/h can increase PM10 concentrations around 1.7 times higher than
at speed of 72.6 km/h. Dropping off/picking up the school children by their parents may
lead to the idled vehicles that consequently would be another reason of higher PM
emissions.
A number of epidemiological studies had been conducted worldwide [5-10] and in Thailand[6-9] to investigate effects of PM on human health, particularly for risk people, i.e. schoolchildren. A 10 μg/m3 increase in PM10 may lead to excess health risk by around 1% of
mortality [6,7]. From our study, school children at Lak Muang Connection, Nakhon Si
Thammarat faced more than 1% of excess risk for mortality. To minimize the potential health
impacts, we recommended that appropriate policies and measures should be provided in
place to tackle the potential PM air quality problems. Including proper traffic management, particularly during dropping off/picking up students at the schools (morning/evening hours) may cut off the significant PM levels and hence reduce health burdens. Permanent air quality monitoring stations would be also considered to install at urban area of Nakhon Si Thammarat for air pollutants surveillance.
ภาพ Figure 3. Temporal variation of 24-hour average PM10: (a) During semester break and (b) During semester