Aerosol optical depth (AOT) was measured at Xavier University of Louisiana (29.96ᵒ N, 90.11ᵒ W and about 3m above sea level) using a hand-held sun photometer. AOT was measured at two different wavelengths (green at 505nm and red at 625nm) during the period from Sept-2017 to Feb-2018. In this study, we investigate the relationship between AOT and temperature, precipitation, barometric pressure and relative humidity. The maximum monthly average value for green AOT was 0.176 (measured in September) and the minimum monthly value is 0.040 (measured in January). For the red AOT the maximum monthly average value was 0.123 (measured in September) and the minimum is 0.034 (measured in December). The AOT–temperature relationship was predominantly positive, meaning that high AOT values correspond to high temperatures and low AOT values correspond to low temperatures. Relationship between AOT and rainfall is negative, meaning high rainfall averages are associated with low AOT values. AOT and atmospheric pressure have a predominantly negative relationship. The relationship between relative humidity and AOT is a complicated one and is hard to qualify as relative humidity varies very little during the study period.
Aerosol optical depth (AOT) was measured at Xavier University of Louisiana (XULA, 29.96° N, 90.11° W and 3m above sea level) using a GLOBE handheld sun photometer. The measurements were done at two different wavelengths, 505nm and 625nm. The measured values were used to extrapolate the AOT values for wavelengths 667nm, 551nm, 532nm and 490nm at the XULA site. The measured and calculated AOT values were then compared with values from the nearest AERONET station at Wave CIS site 6 (AERONET, 28.87° N, 90.48° W and 33m above sea level), which is 60 miles south of XULA. In this study we tracked the annual and daily variations of AOT for a 12-month period from September 2017 to August 2018. These data show good qualitative agreement between the two stations in the 12-month period. Both sets of data show distinct peaks in February and May. Both sets of data show low AOT values in the winter months and high AOT values in the summer months. The hourly AOT variations averaged over the 12-month period was also investigated for the XULA site. The data show two peaks, one at 9:00 am and another at 3:00pm. We also compared AOT data from two independently calibrated GLOBE sun photometers at the XULA site. The data show that the two instruments are in excellent agreement. The R-squared value for the 505nm channel is 0.92 and the R-squared value for the 625nm channel is 0.95.
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