2012 Progress Report: BC and Other Light-Absorbing Impurities in North American Great Plains Snow: Sources, Impacts, and a Comparison with North China Snow

EPA Grant Number: R835038
Title: BC and Other Light-Absorbing Impurities in North American Great Plains Snow: Sources, Impacts, and a Comparison with North China Snow
Investigators: Doherty, Sarah , Fu, Qiang , Hegg, Dean A. , Warren, Stephen
Institution: University of Washington
EPA Project Officer: Wilson, Wil
Project Period: July 1, 2011 through June 30, 2014 (Extended to June 30, 2015)
Project Period Covered by this Report: July 1, 2011 through June 30,2012
Project Amount: $825,483
RFA: Black Carbon's Role In Global To Local Scale Climate And Air Quality (2010) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Climate Change , Air

Objective:

  1. Investigate the concentrations, sources and regional climate impacts of BC and other light-absorbing aerosol in snow in the North American Great Plains.
  2. Compare the concentrations, sources and regional climate impacts of LAA in snow for the North American Great Plains vs. the steppes of North Asia.
  3. Improve our understanding of (a) the deposition rates of BC to snow, which affects both atmospheric and snowpack BC concentrations; and (b) consolidation of BC and other LAA at the snowpack surface during melting, a potentially strong positive feedback mechanism.
  4. Test and improve our ability to measure BC and other LAA in snow by conducting a comparison of three methods for measuring BC: our ISSW Spectrophotometer, the Single Particle Soot Photometer and the thermo-optical method.
  5. Use snow BC concentrations extending from the northern United States to the North Pole to make a first-order estimate of the contribution by North American sources to BC in Arctic snow.

Progress Summary:

  1. Our main effort in year 1 was collaboration with colleagues at Lanzhou University (China) on analysis of snow samples from winter 2010 across north-central and north-east. Snow cover was thin and patchy across most of the sample sites across western and north-central China. These regions are also either in or downwind of desert areas. As a result, desert dust and local soil plays a strong role in light absorption by particulate matter in the snow. This reduces the impact of black carbon in snow on snow albedo. In northeast China, snow cover was deeper and more uniform, and black carbon dominates snow particulate light absorption. There is a strong north-south gradient in snow BC concentrations in eastern China. A preliminary comparison of snow BC concentrations with that estimated in one climate model show large differences at any given sampling site, but concentrations are generally consistent in terms of latitudinal and meridional gradients and in their overall range across north China.
  2. Analysis of the North China samples provided valuable lessons that are being incorporated into our planning for the January-March 2013 field campaign in North America. For example, gathering soil samples in regions with incomplete snow cover allows us to use similarities in the spectral absorption properties of soil and snow particulates to estimate the contribution of local soil to snow particulate light absorption. Lessons were also learned about optimizing sampling protocol, such as using glass jars rather than Whirlpak bags.
  3. Samples were analyzed from two field campaigns designed to study how black carbon and other light-absorbing particles are redistributed in the snowpack with melt. Previous anecdotal observations indicate that black carbon and other particles tend to remain at the snow surface once the snow starts to melt, because they are scavenged with <100% efficiency with melt water. Modeling studies indicate this may be an important positive feedback to the positive radiative forcing resulting from BC in snow. Our study shows that about 10-30% of black carbon and other light-absorbing particles are washed down with snow melt water, consistent with values used in one model study. Black carbon and other light-absorbing particulates appear to have equal scavenging efficiencies, so the positive feedback also applies to other light-absorbing particles. The snow studied did not have significant amounts of coarse soil/dust. However, we expect coarse particles to have a lower scavenging efficiency than the smaller combustion particles that dominated absorption in our snow samples.
  4. The ISSW spectrophotmeter we use to measure light-absorbing particles in snow is a unique instrument. Thus, we have undertaken a comparison of the ISSW with more commonly used methods in order to put our data set into context. This year, we completed a first comparison with an SP2 in collaboration with colleagues at NOAA. We used solutions of a pure BC standard (Fullerene), a pure dust standard, non-absorbing polystyrene latex spheres (PSLs), or a mixture of the BC and dust or BC and PSLs. The ISSW and SP2 measurements both agreed well with gravimetrically determined concentrations of BC, but the ISSW estimates were biased high when the BC was mixed with the dust standard. The implication is that for field samples where BC is mixed with other constituents, our estimates of BC are in the upper bounds on the true BC concentrations.

Future Activities:

Year 2 of this project will be primarily focused on preparation and execution of the January-March 2013 North American field campaign and analysis of the samples from this campaign. We will also be collaborating closely with our colleagues at PNNL, as proposed in the grant, to do regional modeling studies both in support of field campaign planning and to compare our measured snow BC concentrations against those in their model after the campaign. No delays to the project schedule are foreseen.


Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 10 publications 10 publications in selected types All 10 journal articles
Type Citation Project Document Sources
Journal Article Doherty SJ, Grenfell TC, Forsstrom S, Hegg DL, Brandt RE, Warren SG. Observed vertical redistribution of black carbon and other insoluble light-absorbing particles in melting snow. Journal of Geophysical Research–Atmospheres 2013;118(11):5553-5569. R835038 (2012)
R835038 (2013)
R835038 (Final)
  • Full-text: AGU-Full Text PDF
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  • Abstract: AGU-Abstract
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  • Journal Article Schwarz JP, Doherty SJ, Li F, Ruggiero ST, Tanner CE, Perring AE, Gao RS, Fahey DW. Assessing single particle soot photometer and integrating sphere/integrating sandwich spectrophotometer measurement techniques for quantifying black carbon concentration in snow. Atmospheric Measurement Techniques 2012;5(11):2581-2592. R835038 (2012)
    R835038 (2013)
    R835038 (Final)
  • Full-text: AMT-Full Text PDF
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  • Abstract: AMT-Abstract
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  • Journal Article Wang X, Doherty SJ, Huang J. Black carbon and other light-absorbing impurities in snow across Northern China. Journal of Geophysical Research–Atmospheres 2013;118(3):1471-1492. R835038 (2012)
    R835038 (2013)
    R835038 (Final)
  • Full-text: Wiley-Full Text PDF
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  • Abstract: Wiley-Abstract
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  • Supplemental Keywords:

    black carbon, climate, cryosphere, radiative forcing;

    Relevant Websites:

    http://www.atmos.washington.edu/sootinsnow/ Exit
    http://www.atmos.washington.edu/~sarahd/ Exit

    Progress and Final Reports:

    Original Abstract
    2013 Progress Report
    2014 Progress Report
    Final Report