Improved Mobile Application for Measuring Aerosol Optical Thickness in the Ultraviolet-A Wavelength

This paper illustrates an advanced development for mobile measurement of aerosol optical thickness (AOT) in the ultraviolet-A region, with the improvements of 1) a new solar positioning bubble operating in the smartphone that assists accurate pointing of smartphone's camera to the sun and 2) a robust calibration method using Ångström exponent that is applicable to the AOTs at different wavelengths. This paper develops a new calibration method at 340-nm AOT. In addition, a very high adjusted R-square of 96.9% was observed when compared with a Microtops II sunphotometer on five different days. In addition, a mean percentage difference of 7.8% compared with Microtops II sunphotometer was achieved. This new mobile application and new sensing device work well in different atmospheric conditions, and provide effective hand-held, in-situ measurement of AOT that is comparable with a professional-grade instrument.