Grantee Research Project Results
BC and Other Light-Absorbing Impurities in North American Great Plains Snow: Sources, Impacts, and a Comparison with North China Snow
EPA Grant Number: R835038Title: BC and Other Light-Absorbing Impurities in North American Great Plains Snow: Sources, Impacts, and a Comparison with North China Snow
Investigators: Doherty, Sarah , Hegg, Dean A. , Fu, Qiang , Warren, Stephen
Institution: University of Washington
EPA Project Officer: Chung, Serena
Project Period: July 1, 2011 through June 30, 2014 (Extended to June 30, 2015)
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: Climate Change , Air
Objective:
Model studies indicate that black carbon (BC) in snow may be responsible for a significant fraction of northern hemisphere warming, due to its ability to lower snow’s very high albedo and because of the feedback processes that follow which further reduce surface albedo. The highest concentrations of BC in snow are expected at the northern mid-latitudes, but the climate impacts of snow BC at these latitudes are relatively under-studied. Areas where the surface snow is not masked by tree cover are especially susceptible to the reduction of planetary albedo. Further, model-observation comparisons indicate that model deposition rates are the largest source of uncertainty in atmospheric BC distributions. Finally, measurements show that light-absorbing aerosol (LAA) other than BC, such as mineral dust, soil, and organic carbon co-emitted with BC, may also play a significant role in snow albedo reductions.
Approach:
We propose a study with five overall objectives: 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 N. 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 U.S. to the North Pole to make a first-order estimate of the contribution by N. American sources to BC in Arctic snow. This suite of objectives will be accomplished through two wintertime field expeditions in N. America, and a parallel expedition in China by colleagues at Lanzhou University and by using snow samples already in-hand. The BC and non-BC LAA in snow will be measured with a spectrophotometer, and trace species in snow will be determined via chemical analysis. Positive Matrix Factorization (PMF) and Potential Source Contribution Function (PSCF) analyses will then be used to determine LAA source types (e.g. forest, agricultural, or fossil fuel burning) and source regions. A regional model, WRF-Chem, will be used to determine climate impacts. This suite of work will help inform whether BC mitigation would reduce warming and snowpack reduction in the N. American Great Plains. More generally, it will improve understanding of the characteristics of snow LAA, BC deposition rates, and the climate efficacy of BC in snow.