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Climate Variability & Change

The GLORY Aerosol Polarimetry Sensor (APS) will be the first satellite sensor to retrieve information on atmospheric aerosol light absorption, which will be given in the form of aerosol single scattering albedo (SSA; the ratio of aerosol scattering and extinction coefficients with extinction being the sum of scattering and absorption) at several wavelengths. This product will be extremely important for reducing the prevailing large uncertainties in aerosol radiative forcing. Simplistically, aerosols cause cooling if their SSA is higher than the albedo of the underlying scene (increasing the planetary albedo) and cause warming if it is less (decreasing the planetary albedo). In addition, light-absorbing aerosols can continue to cause warming after deposition on high albedo snow and ice surfaces by increasing their albedo and subsequently increasing snow and ice melting. Aerosol light absorption in the solar spectral region in the atmosphere is dominated by black carbon (BC) emitted from anthropogenic and natural combustion processes. Combustion processes also emit organic carbon (OC), which may contain light absorbing brown carbon (BrC). It is currently unclear how much BrC is emitted and how strongly it absorbs shortwave radiation. Therefore, the radiative forcing of BrC is unknown. In addition, mineral dust (MD) aerosols also cause wavelength dependent light absorption. BrC occurring in combustion aerosols and MD aerosols are of specific interest for the APS SSA retrieval because of the strong wavelength dependence of the imaginary part of their refractive index and consequently of their absorption coefficient and SSA. In addition, while the 1/ë wavelength dependence of BC is well known, our recent work has shown that it can be modified by non-absorbing coatings, thereby adding further complexities to GLORY APS retrievals. We propose two objectives to (i) aid the development, tuning, and verification of APS algorithms for SSA retrieval, (ii) better characterize aerosol properties, sources, climate forcing towards improving their representation in chemical transport and climate models, and (iii) improve understanding of the impact of aerosol on air quality and climate change: 1. Characterize the SSA of laboratory-generated combustion aerosols as function of combustion conditions (flaming, smoldering, etc.), fuels, and wavelength; 2. Characterize the SSA of re-entrained mineral dust aerosols as function of chemical and mineralogical composition and wavelength for a size fraction relevant for long-range transport (i.e., PM2.5; particulate matter with an aerodynamic diameter smaller than 2.5 ìm). Aerosol characterization will use photoacoustic instruments developed by our group for the in situ, real time, first principle measurement of aerosol light absorption coefficients. These instruments are capable of operation at multiple wavelengths near the wavelengths of the GLORY APS and also have integrated nephelometers for the measurement of integrated scattering coefficients, thereby yielding a direct measurement of multi-wavelength SSA. In addition to the optical characterization, the aerosol mass density will be measured in real time and aerosols will be collected on filters for laboratory analysis. Laboratory analysis will yield aerosol chemical and mineralogical composition and aerosol morphology, which will all help to connect aerosol optical properties as measured by APS to their underlying physical, chemical, and mineralogical properties. This proposed laboratory research will be conducted in the initial 1.5 years project duration. A potential, additional 1.5 years of funding would be used to utilize the same instrumentation for field measurements of SSA and additional aerosol properties as function of aerosol and aerosol production parameters.

Project PI: Hans Moosmuller/Desert Research Institute, Nevada System of Higher Education

Phone: (775)674-7063

Email: Hans.Moosmuller@dri.edu

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Started: Sep 27, 2010

Last Activity: Jan 04, 2011

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