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

该项目的目标是开发一种新型的光声气溶胶光吸收和反照率光谱仪(PALAAS)，用于实时、原位、第一原理测量气溶胶的光吸收、散射和单次散射反照率光谱。PALAAS的应用将包括对以下物质的光学性质的研究：(1)生物质燃烧阴燃时大量排放的棕色碳，其光学性质基本上未知；(2)矿物粉尘，按质量计算是环境中的主要气溶胶，具有复杂的吸收光谱；(3)气溶胶吸收光谱与由于气溶胶沉积引起的雪和冰表面反照率光谱变化之间的联系。由于表面反照率的改变，气溶胶沉积在冰雪表面后，会造成额外的不确定因素。气溶胶光吸收系数的普通滤光片测量存在大量系统误差；气溶胶光吸收系数的单波长光声测量不足以描述具有强烈和未知吸收波长依赖性的气溶胶(例如，棕色碳和矿物粉尘气溶胶)的辐射影响，这可能对大气气溶胶吸收和降低气溶胶单次散射反照率作出非常重要的贡献，气溶胶单次散射反照率是气溶胶辐射强迫的一个关键量。此外，由于环境气溶胶浓度和光学特性在空间和时间上具有很大的不均一性，因此需要利用光学卫星遥感对全球、空间和时间分辨的气溶胶辐射强迫进行覆盖。然而，卫星监测需要详细的气溶胶吸收光谱知识。PALAAS将利用覆盖400至2000纳米太阳光谱范围的新型宽带超连续激光，同时测量32个可定制光谱波段的气溶胶光吸收和散射系数以及气溶胶单次散射反照率，从而使波段数量比最先进的三波长光声仪器增加约一个数量级。这32个波段的同时吸收和散射测量将使用棱镜脉冲压缩器来实现，以(1)在空间上分离超连续光谱，(2)用定制的光学斩波器以单独的声频调制每个光谱波段，(3)将光谱重新组合成激光光束，以及(4)通过光声谐振器发送激光光束。通过快速傅里叶变换(FFT)分析对调制频率进行解码，可以同时测量所有32个波长段的散射系数和吸收系数。该仪器将为气溶胶光学、辐射强迫和卫星遥感领域带来潜在的变革，它将提供第一个实时、现场的气溶胶光吸收、散射和反照率光谱的第一原理测量。广泛影响：由于气溶胶造成的辐射强迫和气候变化建模的不确定性以及它们鲜为人知的光学性质，在面对这些不确定性时，预测全球和区域气候变化、制定和实施缓解战略并说服社会相信科学预测的准确性是更具挑战性的。因此，在气候变化影响人类的背景下，上述讨论的知识价值将产生重要的、更广泛的社会影响。教育部分将涉及高中生、本科生、研究生和博士后，特别针对代表性不足的群体。特别是，该项目将为：(1)通过与瓦肖县学区资优计划的现有合作伙伴关系，为不同的高中生群体提供研究经验；(2)通过将本科生和研究生纳入内华达大学雷诺分校的正式课程，为他们提供研究经验；(3)雇用一名参与仪器开发的博士后研究助理。博士后将在仪器开发、气溶胶光谱学和跨学科环境研究方面得到PIS项目的指导。仪器分类：将开发光声气溶胶光吸收和阿尔贝德光谱仪，以扩大气溶胶短波辐射传输领域的研究能力，将其应用于气候变化和卫星遥感研究。

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.