Distributions of PM10 concentrations The simulated results show that the PM10 distribution patterns of the 6 winter cases are similar and the PM10 dispersion patterns of the 5 rainy season episodes are also similar. Therefore, some representative simulated cases were used to study typical PM10 distributions in each season. Pollutants are dispersed by atmospheric motions. During winter, Saraburi is influenced by the northeast monsoon and prevailing wind is northeasterly wind. Whereas, prevailing winds are southwesterly and southerly winds in rainy season under the influence of the southwest monsoon. Wind speed and wind direction during the PM10 episodes can be observed from wind roses as shown in Figure 4.
Figure 5. Horizontal distributions of daily average PM10 concentrations (μg/m3) at surface layer and wind vector on (a) 24 December 2005 (in winter) (b) 3 August 2005 (in rainy season)
Figure 4. Wind rose at Nah Phra Laan monitoring station during (a) winter episodes, (b) rainy season episodes
In winter, the wind blows the particulate matters from emission sources toward the southwest. Figure 5(a) shows the PM10 distribution in winter episode on 24 November 2005. The highest daily average PM10 concentration appears about 5 km southwest from the monitoring station. The peak concentration is about 300 μg/m3 that is nearly three times of the 24-hr NAAQS. Figure 5(b) shows the PM10 distributions in rainy season episode on 3 August 2005. The southwesterly wind transport particulate matters from emission sources toward the hill. The highest daily average PM10 concentration is about 250 μg/m3 at Nah Phra Laan center. The highest concentration is about two times of the 24-hr NAAQS.