Time variation of aerosol in Bangkok

Abstract

The study of time variation of aerosol in Bangkok was conducted by using the aerosol optical thickness (AOT), Angstrom exponent and aerosol volume size distribution data, which were obtained from a measurement through the Aerosol Robotic Network (AERONET) during February 2003 – September 2004 at Chaulalongkorn site, comparing with other AERONET sites in Thailand, such as Omkoi, Mukdahan, Pimai and Huahin. In addition, the meteorological data in the same period and the particulate matter smaller than 10 um (PM10) data at Nonsi Vitthaya school in Bangkok during 1997-2004 were also used in this study. In summary, it was found that the seasonal variation of aerosol in term of AOT values was mostly high in summer and winter seasons with a relatively low in rainy season. By the comparison between the AOT values and daytime average air temperature in all seasons, found that in summer season while the air temperature was greater than 33 degrees celsius then most of AOT values were greater than 0.4. In winter season, the AOT values increased after the air temperature was decreased greater than 2 degrees celsius due to the influence of high pressure area from the Republic of China covered the upper part of Thailand. For rainy season, AOT values were relatively lower due to a rainfall has removed aerosols from the atmosphere, especially, whenever the 3 hours accumulated rainfall or continuous rainfall amount was greater than 10 mm. In addition, it was found that the variation period of AOT values showed as a cycle mostly within every 4-7 days, which corresponded to the variation of daytime average air temperature. The AOT increased within 1-2 days after air temperature increased. Conversely, When the air temperature decreased and then the AOT would decreased within 1-2 days later. Angstrom exponent values showed that the fine mode particles had been loading dominant in summer and winter seasons. For volume size distribution, it was founded that there were two modals and dominant by fine mode particles (radius less than 0.6 um). For the analysis of the PM10 time series, it was found that the cyclical variation of PM10 data had corresponded with climatic seasonal variation that PM10 had low concentration in rainy season and relatively high concentration in summer and winter seasons.