Genelita B. Tubal¹, Mariano Estoque² and John Holdsworth²

¹University of the Philippines – NISMED, Diliman, Quezon City, Philippines
²Ateneo de Manila University, Loyola Heights, Quezon City, Philippines

The development of the daytime boundary layer (BL) over Metro Manila, Philippines in May 1999 was observed using a monostatic, biaxial, vertically-pointing Mie Scattering 532 nm Nd:YAG lidar. Together with meteorological and satellite cloud cover data, it was observed that the BL development and much of its detailed structure were greatly affected by the cloud cover and prolonged sea breeze. Fair-weather active clouds inhibited the growth of the BL. The base of the fair-weather cloud field was much lower and hence of the mean BL height when the relative humidity was high, which was the usual condition then. Sudden shift in wind direction and the consequent change in BL depth were seen to be closely associated with the position of big convective cell clouds. The BL at the downdraft side of the convective cell was much lower than at its updraft side. The enormous convective clouds that usually developed from midmorning also produced vast intrusion of clean FA air, about half the depth of the BL in depth and in width thereby making the BL cleaner. Prolonged sea breeze created a much lower BL than when there was no sea breeze. Pollution concentration episodes were very much dependent on the BL growth and cloud cover development. Low pollution concentrations where observed when the BL was high and when intrusion of FA air was significant.