Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 18, 1879-1894, 2018
https://doi.org/10.5194/acp-18-1879-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
08 Feb 2018
Investigating biomass burning aerosol morphology using a laser imaging nephelometer
Katherine M. Manfred1,2, Rebecca A. Washenfelder2, Nicholas L. Wagner1,2, Gabriela Adler1,2, Frank Erdesz1,2, Caroline C. Womack1,2, Kara D. Lamb1,2, Joshua P. Schwarz2, Alessandro Franchin1,2, Vanessa Selimovic3, Robert J. Yokelson3, and Daniel M. Murphy2 1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA
2Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA
3Department of Chemistry, University of Montana, Missoula, MT 59812, USA
Abstract. Particle morphology is an important parameter affecting aerosol optical properties that are relevant to climate and air quality, yet it is poorly constrained due to sparse in situ measurements. Biomass burning is a large source of aerosol that generates particles with different morphologies. Quantifying the optical contributions of non-spherical aerosol populations is critical for accurate radiative transfer models, and for correctly interpreting remote sensing data. We deployed a laser imaging nephelometer at the Missoula Fire Sciences Laboratory to sample biomass burning aerosol from controlled fires during the FIREX intensive laboratory study. The laser imaging nephelometer measures the unpolarized scattering phase function of an aerosol ensemble using diode lasers at 375 and 405 nm. Scattered light from the bulk aerosol in the instrument is imaged onto a charge-coupled device (CCD) using a wide-angle field-of-view lens, which allows for measurements at 4–175° scattering angle with  ∼  0.5° angular resolution. Along with a suite of other instruments, the laser imaging nephelometer sampled fresh smoke emissions both directly and after removal of volatile components with a thermodenuder at 250 °C. The total integrated aerosol scattering signal agreed with both a cavity ring-down photoacoustic spectrometer system and a traditional integrating nephelometer within instrumental uncertainties. We compare the measured scattering phase functions at 405 nm to theoretical models for spherical (Mie) and fractal (Rayleigh–Debye–Gans) particle morphologies based on the size distribution reported by an optical particle counter. Results from representative fires demonstrate that particle morphology can vary dramatically for different fuel types. In some cases, the measured phase function cannot be described using Mie theory. This study demonstrates the capabilities of the laser imaging nephelometer instrument to provide realtime, in situ information about dominant particle morphology, which is vital for understanding remote sensing data and accurately describing the aerosol population in radiative transfer calculations.

Citation: Manfred, K. M., Washenfelder, R. A., Wagner, N. L., Adler, G., Erdesz, F., Womack, C. C., Lamb, K. D., Schwarz, J. P., Franchin, A., Selimovic, V., Yokelson, R. J., and Murphy, D. M.: Investigating biomass burning aerosol morphology using a laser imaging nephelometer, Atmos. Chem. Phys., 18, 1879-1894, https://doi.org/10.5194/acp-18-1879-2018, 2018.
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Short summary
In this study, we use a new laser imaging nephelometer to measure the bulk aerosol scattering phase function for biomass burning aerosol from controlled fires. By comparing measurements to models for spherical and fractal particles, we demonstrate that the dominant morphology varies by fuel type. This instrument has unique capabilities to directly measure how morphology affects optical properties, and can be used in the future for important validations of remote sensing retrievals.
In this study, we use a new laser imaging nephelometer to measure the bulk aerosol scattering...
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