Investigation of aerosol optical properties in Bangkok

Aerosol optical depth and Angstrom coefficients for three sites in Bangkok and suburbs are examined: Silpakorn University at Nakhon Pathom, NP (13.82°N, 100.04°E), the Asian Institute of Technology at Phatum Thani, AIT (14.08°N, 100.62°E) and the Thai Meteorological Department at Bangkok, BK (13.73°N, 100.57°E). Sunphotometers have been used to measure direct normal spectral irradiance at these sites for a period of 2 years (2004–2005). Cloudless conditions were selected and Bouguer’s law was employed to obtain aerosol optical depth. All three sites exhibit strong seasonal variations, with the highest values occurring at the height of the dry season in April, and the lowest occurring during the rainy season in July. April turbidity conditions are very high, as evidenced by maximum 500 nm optical depths of between 1.4 to 2.0 that were measured at all three locations. The Angstrom exponent á also showed a marked seasonal change, with highest values at the height of the dry season.