Atmospheric aerosol light absorption in the solar spectral region is dominated by black carbon (BC) and brown carbon (BRC) aerosol emitted primarily from natural combustion processes, such as…

This $494,738 federal grant was awarded by the National Aeronautics and Space Administration (NASA) to The Washington University, a private university in St. Louis, Missouri. The grant supports research to address challenges in modeling the spectral optical properties of brown carbon (BrC) aerosol and its influence on satellite retrieval algorithms.

The goal is to consolidate observationally-constrained data on BrC aerosol properties, such as complex refractive indices and single scattering albedo, into an optimized database. This database will be used to assess how changes in aerosol absorption and scattering due to atmospheric processing and vertical distribution impact the Ozone Monitoring Instrument's UV Aerosol Index (UVAI) and retrievals of aerosol optical depth and single scattering albedo. The research aims to improve the representation of BrC aerosol in chemical transport and climate models to better assess its radiative forcing and air quality impacts. This grant does not have a set-aside designation.

Atmospheric aerosol light absorption in the solar spectral region is dominated by black carbon (BC) and brown carbon (BRC) aerosol emitted primarily from natural combustion processes, such as wildfires. BRC is a class of light-absorbing organic aerosol (OA) with a brownish or yellowish visual appearance that strongly absorbs solar radiation in the blue and near ultraviolet (UV) wavelengths. There is growing observational evidence of these aerosols being emitted in significant amounts (up to 80% by number and mass) from biomass burning which could affect the top-of-atmosphere direct radiative forcing, especially in the upper troposphere. Additionally, these aerosols exhibit light absorption spectra similar to colored dissolved organic matter (cdom), which causes variations in ocean color. Thus, the strong near-UV light absorption by BRC aerosol poses a major challenge for UV-a radiance inversion algorithms when inverting scenes, especially over ocean surface, to constrain aerosol single scattering albedo (SSA), aerosol optical depth (AOD), and its vertical distribution for atmospheric correction. Our recent findings conducted as part of a 2015 NASA atmospheric composition: laboratory research study has shown that the complex refractive indices of BRC aerosol is highly variable and dynamically changes as a function of atmospheric processing, thereby adding further complexities to satellite retrievals and radiative forcing calculations. The goal of this proposal is to address the challenges associated with (i) prevailing ambiguity when IT comes to modeling the spectral optical properties of BRC aerosol as a function of diel cycle, and (II) poorly parameterized near-UV aerosol models in aerosol retrieval algorithms, e.g. ozone monitoring instrument s (OMI) omaeruv. First, we will perform closure analysis of aerosol refractive indices, optical and physico-chemical properties from measurements made by the PI s group as part of the fire influence on regional and global environments experiment (firex-AQ) field campaign during 2019. Next, the observationally-constrained, multi-space parameters spectral optical properties and size distribution of BRC aerosol as function of altitude and atmospheric processing will be consolidated into an optimized database for use in remote-sensing algorithms and models. This database will be utilized to perform forward radiative transfer modeling for systematically assessing how changes in aerosol absorption and scattering as a function of atmospheric processing and aerosol layer height (ALH) could influence the uvai, which is the method used for detecting aerosol absorption by OMI from measured radiances. Finally, the database will be utilized for omaeruv retrieval of AOD and SSA for select wildfire events intersected by OMI during firex-AQ and compared for improvements over past predictions and with aeronet dataset. The database, which will include new knowledge of aerosol complex refractive indices and SSA as function of wavelength, and other parameters including ALH, atmospheric processing, fire combustion conditions, fuel and fuel moisture content, composition is expected to benefit the atmospheric aerosol community at large by improving the representation of BRC aerosol in chemical transport and climate models toward accurate assessment of their impact on radiative forcing and air quality.