Improved estimation of PM_(2.5) brown carbon contributions to filter light attenuation  

作　　者：Judith C.Chow L.-W.Antony Chen Xiaoliang Wang Mark C.Green John G.Watson 

机构地区：[1]Division of Atmospheric Sciences,Desert Research Institute,Reno,NV,USA [2]State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi’an,China [3]Graduate Faculty,Department of Atmospheric Sciences,University of Nevada,Reno Nevada,USA [4]Department of Environmental and Occupational Health,School of Public Health,University of Nevada,Las Vegas,NV,USA

出　　处：《Particuology》2021年第3期1-9,共9页颗粒学报（英文版）

基　　金：partially supported by the National Park Service IMPROVE Carbon Analysis Contract P16PC00229.

摘　　要：Multiwavelength light attenuation measurements have been acquired as part of thermal/optical carbon analysis in the U.S.Chemical Speciation Network(CSN)and the Interagency Monitoring of PROtected Visual Environments(IMPROVE)network beginning in 2016.These are used to estimate PM_(2.5)brown carbon(BrC)contributions to light absorption at various wavelengths,a useful method for separating biomass burning contributions from other sources.Attenuation of light transmitted through the filter deviates from Beers Law as the mass of light absorbing materials increase.This study estimates the effects of these deviations with empirical adjustment factors applied to samples for CSN from 2016 to 2017 and for IMPROVE from 2016 to 2019.Accounting for the filter loading effect results in an annual average increase of∼6-7%BrC contribution to light attenuation:from 3.6%to 10.7%for the urban,more heavily loaded CSN samples;and from 23.7%to 29.5%for the non-urban IMPROVE samples.An alternative method is examined for BrC and black carbon(BC)adjustments by calculating the AbsorptionÅngström Exponent(AAE)for BC(i.e.,AAE_(BC))based on the ratios of 635 nm/780 nm light attenuation rather than assuming AAE_(BC)of unity.These paired-wavelength calculations result in a median AAE_(BC)of 0.76 for CSN and 0.8 for IMPROVE,with the majority of samples(i.e.,91%of CSN and 70%of IMPROVE)showing AAE_(BC)<1.By assuming negligible contributions from BrC to AAE at longer wavelengths,the amount of light attenuation at shorter wavelengths(e.g.,405 nm)where BrC is dominant can be calculated.The paired-wavelength method applied to the filter loading adjusted data has a greater effect on urban(fresh)than on non-urban(aged)aerosols,resulting in a factor of two increase in annual averaged BrC light attenuation(from 10.7%to 21.6%)for CSN and by a factor of 1.11(from 29.5%to 32.7%)for IMPROVE samples.This result demonstrates the importance of particle loading and AAE correction on quantifying BrC light attenuation from multi-wavelength thermal/optical anal

关 键 词：Organic carbon Brown carbon Elemental carbon Black carbon AbsorptionÅngström Exponent 

分 类 号：X513[环境科学与工程—环境工程]