Reducing uncertainties in aerosol optical properties with cavity ring-down spectroscopy
Toole, Justin Richard
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The initial success of the Aerosol-Cavity Ring-Down Spectroscopy (A-CRDS) technique has led to recent investigations in particle morphology, aerosol mixtures, relative humidity effects, and even field studies. Uncertainties in aerosol extinction measurements are typically quoted as 1-10%; however, reported uncertainties assume the employed commercial instruments are absolutely accurate. Obtaining meaningful and precise measurements will require a complete understanding of the sources of error as instruments begin to reach their limits. An A-CRDS system was developed to improve precision and accuracy in aerosol optical property measurements with a novel calibration procedure. Scattering and absorption components of the complex refractive index are retrieved with the highest confidence level reported to date. This technique addresses systematic errors in commercial instruments and the inability to precisely characterize aerosol flows through the optical cavity. Further, this calibration method is shown to reduce absolute errors in the extinction measurements to less than 1%.