A33D-0190
Improved simulation of black carbon optical properties using a new aerosol mixing-state resolved model, MOSAIC-mix

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Ping Pui (Joseph) Ching1, Rahul A Zaveri2, Richard C Easter3, Nicole Riemer4 and Jerome D Fast1, (1)Pacific Northwest National Laboratory, Richland, WA, United States, (2)Pacific Northwest Natl Lab, Richland, WA, United States, (3)Battelle PNNL, Richland, WA, United States, (4)University of Illinois, Atmospheric Sciences, Urbana, IL, United States
Abstract:
The optical properties of black carbon (BC) particles depend not only on their sizes, but also on their mixing state. It is essential to simulate both the constantly-evolving size and mixing state of BC aerosols for more accurate computations of BC optical properties that also reduce the uncertainties associated with BC impacts on climate.

A novel and computationally efficient size (Ddry) and mixing state (dry BC mass fraction, wBC) resolved version of the Model for Simulating Aerosol Interactions and Chemistry, called MOSAIC-mix, is introduced within a box-model framework. While high-wBC-resolution MOSAIC-mix is verified and presents good performance with reference to an explicit particle-resolved aerosol model, PartMC-MOSAIC, this study aims to systematically develop a low-wBC-resolution MOSAIC-mix that resolves aerosol dry size and BC mass fraction and is computationally efficient. Based on more than 20000 various bin configurations tested for 10 different atmospherically relevant environmental scenarios using low-wBC-resolution MOSAIC-mix, we demonstrate that (1) average errors in absorption coefficient significantly decrease from 21.4% in Ddry resolved-only simulations that use an internal mixing approximation to 4.3% (24 Ddry bins x 2 wBC bins) to 2.8% (24 Ddry bins x 3 wBC bins); (2) the error reduction extent shrinks as wBC bin number increases.

Low-wBC-resolution MOSAIC-mix contributes to more accurate simulations of optical properties of absorbing aerosol like BC than the internal mixing approximation used by the version of MOSAIC implemented in several three-dimensional atmospheric models. With a relatively small number of Ddry and wBC bins, the novel MOSAIC-mix successfully captures the time-evolving size and mixing state of BC aerosols, provides computationally affordable resolution in size and mixing state, and is suited to regional climate modeling to examine the impacts of absorbing aerosol on aerosol-radiation-cloud feedbacks.

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