Diurnal Characteristics of Angstrom Turbidity Parameters Over Manila, Philippines

Abstract

The diurnal variation of the aerosol optical depth (AOD) at 500nm wavelength and the Angstrom turbidity coefficients (α and β) were derived from direct beam measurements. Results of the measurements showed that the AOD, α, and β variations at different time intervals were mainly influenced by human activities and industrial operations as the day progressed. Hourly variability of AOD (in terms of percent departure from the daily mean) showed that it increases from morning and then reaches its maximum diversion from the mean (25%) at noontime (around 11 AM local time) and then slowly decreases in the afternoon. The wavelength exponent showed an almost similar pattern of diurnal variability as AOD. Its variation ranges at about 6 % above and below the average value of α. However β has a different pattern as compared to AOD and α. It consistently departs above the mean at around 20% in the morning and close to 30% below the mean in the afternoon. Daily values of AOD range from 0.545 to 2.174 with values frequently in the range of 0.5 to 1.5. Daily α was frequently around 1.75 but its values ranged from 0.502 to 3.236. This denoted that fine particles were dominating over coarse particles.