Corrections for the Effects of Particle Trajectory and Beam Intensity Profile on the Size Spectra of Atmospheric Aerosols Measured with a Forward Scattering Spectrometer Probe

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  • 1 Air Quality Group, Environmental Research Laboratories/N0AA, Boulder, Colorado
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Abstract

Distortion of the size spectra measured with a forward mattering spectrometer probe (FSSP) under different transit time modes—“inhibit”, “normal”, and “delayed”—was evaluated using the theoretical analyses by Baumgardner and Spowart and the results of the response time and beam intensity profile measurements of the NOAA FSSP. The Baumgardner and Spowart work is extended to correct the FSSP atmospheric aerosol data collected under the “inhibit” or “delayed” mode. A correction algorithm is developed using the non-negative least squares (NNLS) method to reconstruct the original size distribution from a distorted one measured with an FSSP under the inhibit or delayed mode. A lognormal fit to the corrected size spectra was able to successfully recover from the original size distributions from the distorted artificial ones obtained from the theoretical simulation of the FSSP performance. When the actual test flight data for atmospheric aerosols measured with the NOAA FSSP under the inhibit and delayed modes were corrected using the NNLS correction scheme, the two corrected size spectra converged, implying the measurement of the same sample of particles.

Abstract

Distortion of the size spectra measured with a forward mattering spectrometer probe (FSSP) under different transit time modes—“inhibit”, “normal”, and “delayed”—was evaluated using the theoretical analyses by Baumgardner and Spowart and the results of the response time and beam intensity profile measurements of the NOAA FSSP. The Baumgardner and Spowart work is extended to correct the FSSP atmospheric aerosol data collected under the “inhibit” or “delayed” mode. A correction algorithm is developed using the non-negative least squares (NNLS) method to reconstruct the original size distribution from a distorted one measured with an FSSP under the inhibit or delayed mode. A lognormal fit to the corrected size spectra was able to successfully recover from the original size distributions from the distorted artificial ones obtained from the theoretical simulation of the FSSP performance. When the actual test flight data for atmospheric aerosols measured with the NOAA FSSP under the inhibit and delayed modes were corrected using the NNLS correction scheme, the two corrected size spectra converged, implying the measurement of the same sample of particles.

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