Design of a Low-cost Differential Optical Absorption Spectroscopy Set-up for Simultaneous Monitoring of Atmospheric NO2 Concentration and Aerosol Optical Thickness

Miguel Y. Bacaoco, Vince Paul Juguilon, Arven I. Cafe, Catherine A. Tugado, Maria Angela B. Faustino, Gerry Bagtasa, Elmer S. Estacio


Air quality monitoring in urban areas is indispensable in understanding the environment and how anthropogenic factors contribute to the increasing volume of pollutants in the atmosphere. Differential optical absorption spectroscopy (DOAS) is a useful technique in identifying and quantifying trace amounts of air pollutants over a wide region. In this paper, a low-cost DOAS set-up was developed and was used to measure nitrogen dioxide (NO2) concentration and aerosol optical thickness (AOT) in the University of the Philippines Diliman campus. The temporal variation of NO2 concentration from the DOAS measurement was found to agree with the relative NO2 integrated absorbance from 430-450 nm. A calibration curve was then constructed with calculated sensitivity of 4.467 per mg•mm-3 (8.540 per ppm). The concentration range of the low-cost set-up is also able to detect unhealthy NO2 levels in the Philippines. Aerosol optical thickness was then retrieved and showed similar temporal variation with NO2 throughout the duration of the experiment. The correlation was attributed to the photochemical reaction of NO2 to NO3-, which then forms into aerosol. Average daily AOT at different wavelengths was then determined and was compared to AERONET’s data. The results were in agreement with each other and both displayed decreasing AOT at increasing wavelength, which is an expected behavior for a Mie-scattered light due to aerosol. More importantly, proof-of concept demonstration of low-cost DOAS set-up, capable of measuring trace amounts of NO2 and AOT, was successfully performed. Results show that the low-cost design can provide an alternative, cheaper and portable atmospheric NO2 and aerosol measurement technique with reliable sensitivity for environmental monitoring applications.


nitrogen dioxide (NO2), aerosol, differential optical absorption spectroscopy (DOAS), urban air pollution

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