Determination of athmospheric turbidity parameters and aerosol size distribution using a feedback-controlled sun-tracking sunphotometer

Atmospheric turbidity parameters and aerosol size distribution over Manila were obtained using a feedback-controlled sun-tracking sunphotometer from 24 April 2006 26 September 2006. A total of 38 experiment days were conducted. A combination of mathematical and feedback system algorithms was used. The tracking system was incorporated by a data acquisition system that used a PCI-6023E DAQ card. The Sunphotometer Data Acquisition and Processing System (SunDAPS) was developed using LabVIEW 6.1 to acquire and analyze data, and control the sun-tracker automatically using a desktop computer. Calibration procedure was performed in La Salle College-Antipolo in 30 April 2006 using the Langley method. The procedure yielded high correlation coefficients (R \u3e 0.900). A look-up table (LUT) of wavelength exponents was generated from the extinction coefficient from different aerosol types (urban, continental average, continental clean or rural, maritime polluted and maritime clean), which was used to determine the log-normal size distribution of each data set. Size distribution of aerosol using the Junge model was also determined from the wavelength exponent. The daily variation of aerosol optical depth (AOD) for each wavelength, wavelength exponent (a) and Angstrom turbidity coefficient (b), were derived from the direct beam measurements. The values of AOD range from 0.159 (675 nm) to 0.800 (368 nm) while b and a varied from 0.113 to 0.325 and 0.04 to 1.185, respectively. The average value of b per weekday showed that weekdays (with Monday the greatest) exhibit relatively high values of beta than weekends (Saturday being the least). The monthly variation of b showed that the month of May contained the least amount of aerosols. The prevailing value of AOD is around 0.300 to 0.500 while b was predominantly valued from 0.150 to 0.250, with both distributions having the same shape. On the other hand, a reveal the slight dominance of continental aerosols (58%) over the maritime aerosols (42%). However, during the month of September maritime aerosols (79%) were more dominant than continental aerosols (21%). AOD and b gathered from 24 April 2006 to 8 September 2006 show high positive linear correlation (R = 0.818). When plotted against the AOD at 500 nm and b, as lie on the region of low to moderate AODs and bs. The average PM2.5 mass concentration determined in two locations (DLSU-Manila and LSC-Antipolo) were found to be 8.54 µg/m3 and 15.3 µg/m3. The results in LSC-Antipolo were within the range of values obtained in Good Shepherd Spiritual Center, Antipolo by the Manila Observatory (PM2.5 = 18.2 µg/m3). A positive correlation (R = 0.121) of PM2.5 mass concentration with a and negative correlation (R = -0.821) with b was also determined. Moreover, the b in Antipolo was significantly lesser than in Manila. Also the diurnal variation of AOD (500 nm) showed a low standard deviation (SD = 0.019) while the slope of the best-fit line was almost horizontal (slope = 0.006)