Articles | Volume 10, issue 12
https://doi.org/10.5194/amt-10-4805-2017
https://doi.org/10.5194/amt-10-4805-2017
Research article
 | 
11 Dec 2017
Research article |  | 11 Dec 2017

Continuous light absorption photometer for long-term studies

John A. Ogren, Jim Wendell, Elisabeth Andrews, and Patrick J. Sheridan

Abstract. A new photometer is described for continuous determination of the aerosol light absorption coefficient, optimized for long-term studies of the climate-forcing properties of aerosols. Measurements of the light attenuation coefficient are made at blue, green, and red wavelengths, with a detection limit of 0.02 Mm−1 and a precision of 4 % for hourly averages. The uncertainty of the light absorption coefficient is primarily determined by the uncertainty of the correction scheme commonly used to convert the measured light attenuation to light absorption coefficient and ranges from about 20 % at sites with high loadings of strongly absorbing aerosols up to 100 % or more at sites with low loadings of weakly absorbing aerosols. Much lower uncertainties (ca. 40 %) for the latter case can be achieved with an advanced correction scheme.

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Short summary
A new photometer for continuous measurements of aerosol light absorption coefficient is described, optimized for long-term studies of the climate-forcing properties of aerosols. The device is small, sensitive, precise, and simple to operate. It is suitable for long-term measurements at remote locations and is currently in operation at about two dozen sites worldwide.