Aerosol Absorption Measurement using Photoacoustic Spectroscopy: Sensitivity, Calibration, and Uncertainty Developments

Light absorption by aerosols is one of the most uncertain parameters associated with the direct and indirect aerosol effects on climate and is one of the most difficult quantities to measure. This article describes the development of a sensitive method of measuring aerosol absorption at 532 nm with excellent time response (detection limit: 0.08 Mm⁻¹, 60 second average) using photoacoustic absorption spectroscopy. An accurate calibration method (accuracy of 1–2%) at atmospherically relevant absorption levels and independent validation of the photoacoustic technique is presented. An upper limit to the instrument precision for aerosol absorption measurement is ∼6% (2σ, 30 sec) while instrument accuracy is calculated to be ∼5%. A standard for aerosol absorption measurement techniques using well characterized absorbing aerosol is also proposed.

Acknowledgments

This work was funded by NOAA's Climate program. The authors acknowledge Steven Ciciora, Bill Dubé, Richard McLaughlin, and Erik Richards for help in design, development, and construction. Thanks to Thomas Giddings at the University of Colorado for the TEM images.

Notes

¹Certain commercial equipment, instruments, or materials are identified in this article in order to adequately specify the experimental procedure. Such identification does not imply recognition or endorsement by the National Oceanic and Atmospheric Administration, nor does it imply that the material or equipment identified are necessarily the best available for the purpose.

²See footnote 1.