Effects of physical and chemical nonlinearities on evolution of optical properties of biomass burning aerosol
Authors: Golovushkin Nikolai , Konovalov Igor , Beekmann Matthias 
Published: March 2020

&lt;p&gt;Aerosol from open biomass burning (BB) is known to strongly impact the Earth radiation budget. Therefore, a good knowledge of its optical properties and their evolution is an important prerequisite for accurate assessments of contributions of various factors to climate change by means of chemistry-transport and climate models. As a major component of typical BB aerosol is organic matter, the atmospheric evolution of BB aerosol can be strongly affected by the physical and chemical processes governing the gas-particle partitioning of organic compounds. Recently, it has been shown [1] that these processes can give rise to strongly nonlinear behavior of mass concentration of organic fraction of BB aerosol during its atmospheric lifetime. It has been also argued that chemical and physical nonlinearities can explain part of the observed diversity of the effects of BB aerosol atmospheric aging. The present study has extended the previous analysis of the nonlinear behavior of BB aerosol, focusing on the evolution of BB aerosol optical properties, such as, specifically, mass absorption and scattering efficiencies (MAE and MSE) in the near-UV and optical wavelength ranges. The evolution of aerosol in BB plumes was simulated with the MDMOA [1] microphysical box model that involves a schematic parameterization of the dilution process and represents the oxidation and gas-particle partitioning processes within the volatility basis set (VBS) framework. The Mie-theory-based simulations of the optical properties of aging BB aerosol were performed with the OPTSIM module [2] coupled with MDMOA. The simulations show that both MAE and MSE can exhibit strong and diverse changes during BB aerosol evolution mostly due to significant changes in the aerosol particle size distribution. Furthermore, similar to the mass concentration, both MAE and MSC of the aged BB aerosol depend in a nonlinear manner on the initial BB aerosol concentration and the initial size of a smoke plume and are sensitive to the choice of a concrete VBS scheme. The results of this study may have important implications for modeling of radiative effects of BB aerosol with chemistry-transport and climate models and for interpretation of remote observations of BB aerosol.&lt;/p&gt;&lt;p&gt;The study was supported by the Russian Foundation for Basic Research (grant No. 18-05-00911).&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;ol&gt;&lt;li&gt;Konovalov, I. B., Beekmann, M., Golovushkin, N. A., and Andreae, M. O.: Nonlinear behavior of organic aerosol in biomass burning plumes: a microphysical model analysis, Atmos. Chem. Phys., 19, 12091&amp;#8211;12119, https://doi.org/10.5194/acp-19-12091-2019, 2019.&lt;/li&gt;
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