1.10 Relationship with Meteorological Parameters
Weather variables play a major role in dispersing air
pollutants and thus the determination of the level of their
concentration. Bangkok has three seasons: the “cold season”
(December to January), “ dry season” (February to May) and
“rainy season” (June to October). Normally, high pollution can
be observed during the cold season at the beginning and at the
end, due to a high pressure system creating a more stable
atmosphere brought about by inversion layer phenomenon, thus,
more accumulation of pollutants in the air. Generally, during the
dry season, pollution is low due to high atmospheric dispersion
attributed to the existence of a less stable atmospheric system.
However, the graphs (Figure 4) indicate that almost the same
ambient air pollutant concentrations were recorded during rainy
and dry seasons. The findings revealed that seasonal variation
coupled with school term breaks and national holidays
contributed toward a lower air pollutant concentration during
both seasons. However, seasonal variation of sulphur dioxide
and ozone concentrations was not observed at each of the four
locations. This is probably due to the low sulphur content in the
gasoline. Present sulphur content in Thai gasoline is 0.01 %wt.
Sulphur dioxide emission was usually varied with sulphur
content in gasoline. Likewise, ozone emission is dependable
entirely on sunlight.