Improved estimation of PM2.5 brown carbon contributions to filter light attenuation (Open Access)
Judith C. Chow*, L.-W. Antony Chen, Xiaoliang Wang, Mark C. Green, John G. Watson
Keywords: Organic carbon, Brown carbon, Elemental carbon, Black carbon, Absorption Ångström Exponent
DOI: 10.1016/j.partic.2021.01.001
美国沙漠研究所Judith C. Chow 教授团队开发的多波段有机碳/元素碳分析方法自2016年起被美国颗粒物化学组分观测网（CSN network）以及能见度观测网（IMPROVE network）采用。该方法可推算PM2.5中棕碳在不同波长下对光吸收系数的贡献，进而有效地将生物质燃烧产生的碳与其它碳源相区分。然而，基于滤膜的光衰减测量会由于颗粒物的遮蔽效应而使光吸收系数定量产生偏差。
近期，Judith C. Chow 教授团队在PARTICUOLOGY上发表了题为“Improved estimation of PM2.5 brown carbon contributions to filter light attenuation”的研究论文，对上述方法进行了改进。该文章详细分析了美国城市和自然保护区近十万个滤膜样品的数据，总结了滤膜光衰减和吸光颗粒物载荷的关系，对载荷效应进行了修正；同时通过对每个样品在635–780 nm波长的吸收来测量黑碳Ångström指数（AAE）避免了不准确的黑碳AAE=1的假设，从而更准确地推算了棕碳的吸光效应。
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亮点导读
# Multiwavelength thermal/optical carbon analysis permits brown carbon estimates.
# Light attenuation deviates from Beer's Law at loadings greater than 3 μg/cm2.
# Filter loading correction factor increase as wavelength decreases for a given elemental carbon filter loading.
# The conventional assumption that the black carbon Absorption Ångström Exponent equals one is not confirmed by multiwavelength measurements.
研究背景
碳气溶胶是大气气溶胶的重要组分，它通常根据化学成分可以分为有机碳（OC）和元素碳（EC）或者根据光学性质分为黑碳 （BC），棕碳 (BrC)，和不吸光碳。棕碳是对紫外和可见光波段有吸收效应的有机碳，因为其广泛的排放和对辐射强迫、大气能见度和光化学反应的重要影响而被关注。然而，目前对于棕碳的基础研究刚刚起步，对于它的来源、排放、组成、演变及光学化学性质的认识还十分有限。
美国沙漠研究所的Judith C. Chow 教授团队开发了多波段有机碳/元素碳分析仪，该仪器在用热光法进行常规的有机碳和元素碳分析的基础上增加了从近紫外到红外（405–980 nm）的多波段光衰减测量，从而推算棕碳和黑碳对光吸收系数的贡献。然而，基于滤膜的光衰减测量会由于颗粒物的遮蔽效应而使光吸收系数定量产生偏差。
内容简介
本文详细分析了美国位于城市地区的颗粒物化学组分观测网（CSN network；2016–2017）和位于国家自然保护区的能见度观测网（IMPROVE network；2016–2019）近十万个滤膜样品的数据，总结了光衰减和吸光颗粒物载荷的关系，从而对载荷效应进行了修正。本文还指出通常假设的黑碳吸收Ångström指数（AAE）为1不准确并可能因此低估棕碳对光吸收系数的贡献。从635–780 nm波长分析的数据显示CSN 和IMPROVE 黑碳的AAE中位值分别为0.76和0.80。本文强调在元素碳浓度超过1.5 µg/m3时有必要对载荷效应进行修正并使用实际测量得到的黑碳AAE，从而推算棕碳及黑碳对光吸收系数的准确贡献。
作者介绍
研究方向：空气质量、大气观测、碳气溶胶、颗粒物分析、健康效应等
Dr. Judith C. Chow is a Research Professor in the Division of Atmospheric Sciences at the Desert Research Institute (DRI), Nevada System of Higher Education. She is the founder and director of DRI's Environmental Analysis Facility and led the development of three generations of thermal/optical carbon analyzers. Dr. Chow has served on many monitoring and research advisory committees for air quality, including the National Academy of Sciences/National Research Council Committee on "Research Priorities for Airborne Particulate Matter". She was a chartered member of the U.S. EPA's Clean Air Scientific Advisory Committee (CASAC) and a member of U.S. EPA's Ambient Air Monitoring and Methods Subcommittee (now the Air Monitoring and Methods Subcommittee). She authored more than 400 journal articles with a h-index of 79. Dr. Chow obtained her Sc.D. in Environmental Science and Physiology from Harvard University.
研究方向：空气污染，源解析及风险评估
Dr. Antony Chen (陳隆文) is an associate professor in the Department of Environmental and Occupational Health at the School of Public Health, University of Nevada, Las Vegas. Dr. Chen researches atmospheric aerosols and co-pollutants from natural and anthropogenic sources, focusing on development of monitoring and modeling methods for assessing public exposure and health risks. He has ~100 peer-reviewed publications with an h index of 36. Dr. Chen leads the UNLV Urban Air Quality Laboratory and teaches Air Pollution, Atmospheric Measurement and Modeling, and Environmental Health courses at both graduate and undergraduate levels. Dr. Chen obtained his Ph.D. in Chemical Physics-Atmospheric Chemistry from the University of Maryland and worked at Desert Research Institute for 10 years prior to joining UNLV.
研究方向：气溶胶物理化学性质表征、测量仪器开发、污染源排放测量等
Dr. Xiaoliang Wang (王小亮) is a Research Professor in DRI's Division of Atmospheric Sciences. He has been involved in the development of an array of instruments for characterizing aerosol properties, including nanoparticle aerodynamic lenses, the TSI DustTrak DRX Aerosol Monitor, the DRI portable dilution sampling system, and the DRI Model 2015 Multiwavelength Thermal/Optical Carbon Analyzer. He is the recipient of the 2020 Benjamin Y.H. Liu Award from the American Association for Aerosol Research (AAAR), for his outstanding contributions to aerosol instrumentation and experimental techniques. Dr. Wang obtained his Ph.D. in Mechanical Engineering from University of Minnesota and is a graduate of the Thermal and Environmental Engineering Departments at Tsinghua University. He worked for 4 years at TSI Inc. before joining DRI.
研究方向：空气污染、雾霾和能见度观测、气象观测和分析等
Dr. Mark C. Green is a Research Professor in DRI's Division of Atmospheric Sciences. He has over 30 years' experience in the fields of air pollution and meteorology with research focuses on determining the causes of haze in both remote and urban areas and the attribution of suspended particles to emission sources. Dr. Green obtained his Ph.D. in Atmospheric Science from University of California at Davis.
研究方向：颗粒物源解析、空气质量和能见度观测、污染源表征、低成本传感器等
Dr. John G. Watson is a Research Professor in DRI's Division of Atmospheric Sciences. He developed the U.S. EPA's Chemical Mass Balance receptor modeling software and has prepared guidance documents for network design, continuous particulate monitoring, and pollutant chemical speciation. He has designed and led dozens of major aerosol and visibility characterization studies. Dr. Watson has authored more than 400 peer-reviewed journal publications with a h-index of 74, including the Air & Waste Management Association (A&WMA) 2002 critical review on "Visibility: Science and Regulation" and the 2017 critical review on "Air quality measurements—From rubber bands to tapping the rainbow". Dr. Watson obtained his Ph.D. in Environmental Sciences from Oregon Graduate Institute, now the Oregon Health and Science University.
编辑、翻译：《颗粒学报》编辑部