Articles | Volume 18, issue 8
Research article
23 Apr 2018
Research article |  | 23 Apr 2018

Using spectral methods to obtain particle size information from optical data: applications to measurements from CARES 2010

Dean B. Atkinson, Mikhail Pekour, Duli Chand, James G. Radney, Katheryn R. Kolesar, Qi Zhang, Ari Setyan, Norman T. O'Neill, and Christopher D. Cappa

Abstract. Multi-wavelength in situ aerosol extinction, absorption and scattering measurements made at two ground sites during the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES) are analyzed using a spectral deconvolution method that allows extraction of particle-size-related information, including the fraction of extinction produced by the fine-mode particles and the effective radius of the fine mode. The spectral deconvolution method is typically applied to analysis of remote sensing measurements. Here, its application to in situ measurements allows for comparison with more direct measurement methods and validation of the retrieval approach. Overall, the retrieved fine-mode fraction and effective radius compare well with other in situ measurements, including size distribution measurements and scattering and absorption measurements made separately for PM1 and PM10, although there were some periods during which the different methods yielded different results. One key contributor to differences between the results obtained is the alternative, spectrally based definitions of fine and coarse modes from the optical methods, relative to instruments that use a physically defined cut point. These results indicate that for campaigns where size, composition and multi-wavelength optical property measurements are made, comparison of the results can result in closure or can identify unusual circumstances. The comparison here also demonstrates that in situ multi-wavelength optical property measurements can be used to determine information about particle size distributions in situations where direct size distribution measurements are not available.

Short summary
We use in situ measurements of particle light extinction to assess the performance of a typical aerosol remote retrieval method. The retrieved fine-mode fraction of extinction, a property commonly used to characterize the anthropogenic influence on the aerosol optical depth, compares well with the in situ measurements as does the retrieved effective fine-mode radius, which characterizes the average size of the particles that contribute most to scattering.
Final-revised paper