AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Two Wrongs Do Make a Right: The Interplay Between Assumed Morphology and the Direct Radiative Effect of Light-absorbing Organic Aerosol
RAWAD SALEH, Allen Robinson, Neil Donahue, Peter Adams, Carnegie Mellon University
Abstract Number: 190 Working Group: Aerosols, Clouds, and Climate
Abstract Mie theory is widely employed in aerosol direct radiative effect (DRE) calculations and to retrieve the absorptivity (imaginary part of the refractive index) of light-absorbing organic aerosol (OA) from measurements. However, OA is often internally mixed with black carbon and may exhibit complex morphologies whose optical behavior cannot be predicted using Mie theory, introducing errors in the retrieved absorptivities. In this study, we performed numerical experiments and global radiative transfer modeling (RTM) to investigate the propagation of these errors to the calculated global DRE of light-absorbing OA emitted by biomass-burning. The numerical experiments involved retrieving OA absorptivities from pseudo measurements that simulated common light-absorption measurements performed in the laboratory and the field. We performed the retrievals using either the true complex morphology or simplified spherical core-shell morphology, where Mie theory could be applied. We then used the resulting absorptivities as inputs to an RTM to calculate the global DRE of biomass-burning carbonaceous aerosols.
We show that using the true OA absorptivity, retrieved with the true complex morphology, can lead to significant errors in DRE when the RTM employs Mie theory. On the other hand, when Mie theory is consistently applied in both OA absorptivity retrieval and the RTM, the errors cancel out, yielding accurate DRE. RTMs employing Mie theory should thus use parametrizations of light-absorbing OA derived from retrievals based on Mie theory.