Grantee Research Project Results
Final Report: Interplay Between Black and Brown Carbon from Biomass Burning and Climate
EPA Grant Number: R835883Title: Interplay Between Black and Brown Carbon from Biomass Burning and Climate
Investigators: Murphy, Shane Michael
Institution: University of Wyoming
EPA Project Officer: Chung, Serena
Project Period: January 1, 2016 through December 31, 2018 (Extended to September 30, 2020)
Project Amount: $349,847
RFA: Particulate Matter and Related Pollutants in a Changing World (2014) RFA Text | Recipients Lists
Research Category: Air , Climate Change , Early Career Awards
Objective:
The original objective of this research grant were to
1.) Observe the wavelength-resolved single scattering albedo (SSA) of aerosol biomass burning emissions in the Western United States
2.) Determine the contribution of black versus brown carbon to observed aerosol absorption
3.) Quantify the enhancement of black carbon absorption caused by organic coatings
4.) Update the refractive indices of organic and black carbon aerosol from biomass burning in the NCAR Community Atmosphere Model (CAM5) with data obtained from in-situ measurements
5.) Assess the regional and global climate impacts of improved optical properties under a range of future biomass burning scenarios
6.) Investigate the current and future radiative forcing and climatic effect from brown carbon absorption utilizing CAM5
As detailed in Section II of this summary, these objectives were accomplished along with additional objectives related to identifying individual chemical components responsible for brown carbon absorption.
Summary/Accomplishments (Outputs/Outcomes):
Deployments of the mobile lab were made in the early fall of both 2017 and 2018. In both years, the University of Wyoming mobile lab was equipped with our custom 2-wavelength, four channel photoacoustic absorption spectrometer (PAS) coupled with a thermal denuder, two cavity attenuated phase shift-single scattering albedo (CAPS-SSA) instruments, and an aerosol mass spectrometer (AMS). Particle size distributions were measured differently in 2017 vs. 2018. In 2017, two scanning mobility particle sizers (SMPS) were deployed. After this deployment it was noted that there was considerably variability in the aerosol flow rate of the SMPS’s. While the data was of acceptable quality (less than 20% variability) this observation lead PI Murphy to have a summer intern from France design and integrate an automated flow regulation system consisting of a PID controller and a solenoid valve. This system is now standard on our SMPS systems and has dramatically improved the accuracy of particle concentration measurements. In 2018 we measured particle size distributions with the Ultra High Sensitivity Aerosol Spectrometer which improved sensitivity but occasionally had saturation problems in heavy smoke. Two channels of the PAS, at wavelengths of 405 nm and 660 nm continuously measured the absorption due to dry ambient air (dry channels) while the other two channels measured absorption at the same wavelengths, but from particles that had been thermally denuded at 300oC (denuded channels). The CAPS-SSA operates at wavelengths of 450 and 660 nm, measuring extinction and scattering coefficients of ambient air. Particle size distributions of dried ambient and thermally denuded aerosols were measured by the two SMPS and the chemical composition of the ambient aerosol was continuously measured by the AMS. In addition, to study the effect of the volatility of the organic aerosol on brown carbon, the thermal denuder was set at different temperatures and the resulting impact on absorption and particle size distribution was assessed.
Two deployments occurred in Fall 2017. The first deployment was during the Rice Ridge fire near Seeley lake, MT. Fresh smoke was measured near the evacuation lines as well as aged smoke at different downwind distances (measurements taken at Holter lake, MT and Story, WY, one to four hundred miles downwind). These measurements gave a clearer picture of the dependence of aerosol optical properties on aging/dilution. Furthermore, the effect of aging on brown carbon absorption was assessed from these measurements and the change in volatility of organic aerosol during aging in ambient conditions was assessed. Our second deployment was in October, 2017 and measured two different fires (Tubbs fire of Santa Rosa, CA, and Lion Fire near Kernville, CA) in California. During our second deployment, we focused on measuring fresh smoke emissions. The observations from the 2017 deployment demonstrated that the observed aerosol optical properties in Montana and California were in-line with parameterizations of SSA and brown carbon with the EC (elemental carbon) to OC (organic carbon) ratio developed by our group from data obtained at the Missoula Firelab (Pokhrel et al., 2016 and 2017). This observed agreement between field measurements and the fire lab parameterization was a primary motivator for our recently published Nature Communications paper first-authored by Wyoming Ph.D. Hunter Brown titled, “Biomass burning aerosols in most climate models are too absorbing.” Hunter’s work looked at data from campaigns throughout the world and compared the observed optical properties to those of the Pokhrel parameterization from the Firelab. It was found that data from these campaigns from South America, Africa, Southern Asia and the Boreal forests also lined up with the parameterization from the firelab. However, a wide array of CMIP global climate models (GCM’s) showed results that were much more absorbing than the field observations. Hunter’s paper demonstrates that this has significant climate implications and also suggests several ways in which models can be modified to improve agreement with field observations. One of these is to increase the mean particle size of particles emitted by biomass burning. Another idea is to employ optical parameterizations that cause less enhancement of black carbon by organic carbon.
In 2018 the mobile lab was deployed to several fires in Wyoming in the late summer/early fall after the PAS and CAPS-SSA instruments were deployed on the NCAR C-130 for the WE-CAN campaign. The success of the Wyoming PAS system during the WE-CAN campaign was a direct result of the field testing and measurements done in 2017 on the mobile lab in Montana and California. Indeed, in addition to the direct scientific results of this project, development of the Wyoming PAS instrument into an easily deployable field instrument has been a key result. Two deployments occurred in Fall 2018. The first deployment was during the Ryan Fire near Saratoga, Wyoming. Fresh smoke was measured near the source and aged smoke from this fire was measured from Laramie, Wyoming. Laramie is approximately 80 miles downwind of the fire source giving several hours (~6) of aging. This fire provides another good case study on the impact of aging on optical properties. The second deployment was to the Roosevelt and Martin Fires near Pinedale and Bondurant, Wyoming. Measurements during these fires were made near source, but at dramatically different concentrations to evaluate the impact of dilution on the optical properties of the aerosol.
In 2018 Hunter Brown was the lead author of a paper titled, “Radiative Effect and Climate Impacts of Brown Carbon with the Community Atmosphere Model (CAM5).” This paper was motivated by the large impact of brown carbon found in the field deployments and Flame-IV laboratory studies. The paper underwent significant revisions to include the effect of bleaching on brown carbon. Our observations from Montana and other field campaigns suggested that brown carbon bleaches with a lifetime of about 1 day at typical tropospheric OH levels. When bleaching was not included in CAM5, the global direct radiative forcing of brown carbon was found to be approximately 0.12 W/m2. Implementing a lifetime of brown carbon of approximately 1 day at typical tropospheric OH levels in the model significantly reduced the global radiative impact of brown carbon to a direct radiative forcing of 0.055 W/m2. These results emphasize the importance of having an accurate parameterization for aging of brown carbon.
Katherine Foster, a Wyoming graduate student, published a paper in early 2019 to establish our calibration technique for the photoacoustic absorption spectrometer (PAS). The technique we developed to calibrate the PAS is the first particle-based technique that does not require a particle with a known refractive index and does not require monodisperse particles. The ability to calibrate with particles with an unknown refractive index is particularly important because a calibration standard of particles with known refractive index does not exist. Other groups utilize calibrations that employ reactive gases, ozone and nitrogen dioxide in particular. These calibrations present significant issues including the potential for reactive losses and dependence of the calibration result on the bath gas.
Our group was approved to utilize some of the funding from this grant to participate in the the Moonlight chamber experiments for four weeks during June/July of 2019 at NCAR. Other participating universities included the University of Washington and Colorado State University. The Wyoming team measured brown carbon absorption with our custom 2-wavelength four channel photoacoustic absorption spectrometer (PAS) coupled with the thermal denuder, and scattering and extinction with two cavity attenuated phase shift-single scattering albedo (CAPS-SSA) monitors. The goal for these chamber experiments was to make measurements of aerosol absorption with speciated mass spectrometer measurements of both gas and aerosol-phase composition to quantify the impact of specific chemical species observed in ambient wildfire smoke on brown carbon. The chamber experiments were highly successful with absorption measurements made by both the PAS and by a particle into liquid sampler (PILS) coupled to a UV-Vis spectrometer. The measurements made by these two very different methodologies agreed well to within known instrument accuracies giving higher confidence to the measurements made. The absorption measurements also correlated well with aerosol organic mass (measured by an aerosol mass spectrometer (AMS)) and to individual species measured in the aerosol phase (measured by a chemical ionization mass spectrometer). It was found that significant absorption could be attributed to nitrogen containing reaction products of phenols. Given this “calibration” of how much absorption is derived from specific chemical products, the data have now been used to attribute the fraction of brown carbon absorption derived from phenol reaction products in ambient smoke. These results have been published by Palm et al. (paper details in Table 1) with co-authors Ph.D. student Yingjie Shen and postdoc Rudra Pokhrel from the Wyoming group. The data from the Moonlight experiments relating PAS absorption to PILS absorption will also be critical in two papers that will be submitted this spring detailing absorption measurements from the WE-CAN field project.
Many of the technical findings from this project are detailed in the four publications that resulted from this grant. These publications are listed in Section III of this report. The following few paragraphs give brief summaries of the technical findings.
Brown et al. (2018) demonstrated that including brown carbon in the CAM global climate model (GCM) caused a net positive radiative effect. This effect was similar in magnitude to that found by previously by chemical transport models, but this was the first time brown carbon was integrated into a GCM. Inclusion of a bleaching parameter that removes absorption from brown carbon via OH reaction with a lifetime of a day roughly halved the positive radiative effect.
Foster et al. (2019) demonstrated a novel calibration technique for the PAS that was critical to obtaining accurate absorption results during the field deployments for this grant and for airborne deployments that were funded after this grant (the WE-CAN campaign). The technique presented in this paper has significant advantages over previous approaches in that it utilizes particles for the calibration and does not rely upon reactive gases.
Palm et al. (2020) utilized the results from the Moonlight chamber experiments to attribute a significant fraction of the absorption measured during WE-CAN airborne measurements to specific nitro-phenols especially reaction products of Catechol. This paper represents a significant advance in that specific chemical compounds were identified that cause a sizeable fraction of the brown carbon absorption in ambient smoke plumes. The results were consistent across numerous plumes that were measured in many different states across the Western U.S.
Brown et al. (2021) is the pinnacle result of this grant. It does what we set out to do in the project, namely compare field observed single scattering albedo (SSA) to that generated by a number of GCM’s. The key to enabling this comparison was to plot SSA vs. the black carbon to organic carbon ratio (BC:OC) for both model an observations. Plotting SSA vs. BC:OC ratio allows comparison of model vs. field results for similar aerosol instead of looking at a result for aerosol with all different types of coating thickness for the BC. It also allows for comparison of intensive properties, eliminating effects from inaccurate emission inventories. The results clearly showed that the majority of GCM’s including the CAM model are generating aerosol that is too absorbing (too low an SSA). Causes of this were identified in the CAM model to be primary biomass burning aerosol that is too large and approaches to calculating absorption, namely the mass mixing rule fro refractive index, that cause too much absorption enhancement of black carbon absorption. This significant paper should result in the improvement of many GCM parameterizations of absorbing aerosol from biomass burning.
All of the field data collected for this project has been quality assured to meet the standards set forth in the original quality assurance plan for this grant. All data is stored on University of Wyoming Dept. of Atmospheric Science servers and is available to the public upon request. The data is backed up and secure, this is the same data location where the Department stores NSF King Air data from projects. Data availability of model runs is detailed in Brown et al., (2018, 2020).
Overall, this project produced a lot of impactful science. It also lead to the development of new calibration methods and to important field testing of the Wyoming PAS. We have recently submitted a proposal to commercially develop the Wyoming PAS, something that would not have been possible before the research summarized here was carried out.
References:
Pokhrel, R.P.; Beamesderfer, E.R.; Wagner, N. L.; Langridge, J. M.; Lack, D. A.; Jayarathne, T.; Stone, E.A.; Stockwell, C. E.; Yokelson, R. and S. M. Murphy*, “Relative Importance of Black Carbon, Brown Carbon and Absorption Enhancement from Clear Coatings in Biomass Burning Emissions” Atmospheric Chemistry and Physics, 17(8), 5063-5078, 2017
Pokhrel, R.P.; Wagner, N. L.; Langridge, J. M.; Lack, D. A.; Jayarathne, T.; Stone, E.A.; Stockwell, C. E.; Yokelson, R. and S. M. Murphy*, “Parameterization of Single Scattering Albedo (SSA) and Absorption Angstrom Exponent (AAE) with EC/OC for Aerosol Emissions from Biomass Burning” Atmospheric Chemistry and Physics, 16, 9549-9561, 2016.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 6 publications | 2 publications in selected types | All 2 journal articles |
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Brown H, Liu X, Feng Y, Jiang Y, Wu M, Lu Z, Wu C, Murphy S, Pokhrel R. Radiative effect and climate impacts of brown carbon with the community atmosphere model (CAM5). Atmospheric Chemistry and Physics 2018;18:17745-17768. |
R835883 (2018) R835883 (2019) R835883 (Final) |
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Foster K, Pokhrel RP, Burkhart MD, Murphy SM. A novel approach to calibrating a photo-acoustic absorption spectrometer using polydisperse absorbing aerosol. Atmospheric Measurement Techniques 2019;12(6): 3351-3363. |
R835883 (2018) R835883 (2019) R835883 (Final) |
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Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
- 2019 Progress Report
- 2018 Progress Report
- 2017 Progress Report
- 2016 Progress Report
- Original Abstract
2 journal articles for this project