MRI: Development of a Photo-Acoustic Light Absorption and Albedo Spectrometer for the Characterization of Aerosol Radiative Transfer in the Solar Spectrum

点击翻译按钮获取中文摘要

The goal of this project is to develop a novel Photoacoustic Aerosol Light Absorption and Albedo Spectrometer (PALAAS) for real time, in situ, first principle measurement of aerosol light absorption, scattering, and single scattering albedo spectra. Applications of PALAAS will include research into the optical properties of (1) brown carbon, which is emitted in large quantities by smoldering biomass burning and has largely unknown optical properties; (2) mineral dust, which by mass is the dominant ambient aerosol, and has a complex absorption spectrum; and (3) the connection between aerosol absorption spectra and modification of snow and ice surface albedo spectra due to aerosol deposition.Intellectual merit: Atmospheric aerosols and their radiative forcing cause the largest uncertainties in understanding and modeling global and regional climate change. Additional uncertainties are caused after aerosol deposition on snow and ice surfaces due to surface albedo modification. Common filter measurements of aerosol light absorption coefficients suffer from a large number of systematic errors; single wavelength photoacoustic measurements of aerosol light absorption coefficients are insufficient to characterize the radiative impact of aerosols with a strong and unknown wavelength dependence of absorption (e.g., brown carbon and mineral dust aerosols), which may make a very significant contribution to atmospheric aerosol absorption and to the lowering of aerosol single scattering albedo, a key quantity in aerosol radiative forcing. In addition, optical satellite remote sensing is needed for global, spatially-, and time-resolved coverage of aerosol radiative forcing because of the large spatial and temporal inhomogeneities of ambient aerosol concentration and optics. However, detailed knowledge of aerosol absorption spectra is needed for satellite monitoring. PALAAS will utilize a novel broadband super continuum laser covering the solar spectral range from 400 to 2000 nm for simultaneous measurement of aerosol light absorption and scattering coefficients and aerosol single scattering albedo in 32 customizable spectral bands, thereby increasing the number of bands by about one order of magnitude over state-of-the-art three-wavelength photoacoustic instruments. Simultaneous absorption and scattering measurements in these 32 bands will be enabled using a prism pulse compressor to (1) spatially separate the super continuum spectrum, (2) modulate each spectral band at an individual acoustic frequency with a custom optical chopper, (3) recombine the spectrum into a laser beam, and (4) send the laser beam through a photoacoustic resonator. Measurements of the scattering coefficient with a scattering sensor in the photoacoustic instrument and the absorption coefficient with the photoacoustic instrument can be achieved for all 32 wavelength bands simultaneously by decoding modulation frequencies with fast Fourier transform (FFT) analysis. This instrument will be potentially transformative for the field of aerosol optics, radiative forcing, and satellite remote sensing by providing the first real time, in situ, first principle measurements of aerosol light absorption, scattering, and albedo spectra.Broader impacts: Due to the uncertainties in radiative forcing and climate change modeling caused by aerosols and their poorly known optical properties, it is more challenging to predict global and regional climate change, formulate and put into place mitigation strategies, and convince society of the accuracy of scientific predictions in the face of these uncertainties. Therefore, the intellectual merits discussed above will have important broader societal impacts in the context of climate change affecting humanity. An educational component will involve high school, undergraduate, graduate, and postdoctoral students, specifically targeting underrepresented groups. In particular, the project will provide research experiences for (1) a diverse group of high school students through an existing partnership with the Washoe County School District Gifted and Talented Program; (2) undergraduate and graduate students through inclusion in formal classes at the University of Nevada, Reno, student employment, senior thesis, and Ph.D. dissertations; and (3) employment of a postdoctoral research associate participating in the instrument development. The postdoc will be mentored by the project PIs in instrument development, aerosol spectroscopy, and interdisciplinary environmental research.Instrument categorization: The Photoacoustic Aerosol Light Absorption and AlbedoSpectrometer will be developed to expand research capabilities in the area of aerosol shortwave radiative transfer with applications to climate change and satellite remote sensing research.