Since the air quality monitoring network in Thailand was distributed unevenly and
incompletely, levels of air quality in some areas remained unclear. In 2012, levels of PM in
Nakhon Si Thammarat, the biggest city in the south of Thailand in term of population, were
preliminarily assessed at three main traffic connections: Tha Wang, Ku Khwang and Lak
Muang. The levels of PM were considerably high comparing to NAAQS of Thailand and the
air quality guidelines of World Health Organization (WHO) [11]. Particularly at Lak Muang
Connection where there are two old and famed schools: primary and high schools located, PM air quality could pose a serious problem on adverse health impacts for student exposures.
Traffic emissions were identified as the key source of PM in the city [11,12].