Final Report: Particle-Resolved Simulations for Quantifying Black Carbon Climate Impact and Model Uncertainty

EPA Grant Number: R835042
Title: Particle-Resolved Simulations for Quantifying Black Carbon Climate Impact and Model Uncertainty
Investigators: Riemer, Nicole , West, Matthew
Institution: University of Illinois at Urbana-Champaign
EPA Project Officer: Wilson, Wil
Project Period: June 1, 2011 through May 31, 2014 (Extended to May 31, 2015)
Project Amount: $449,902
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:

The central research question of this project was to assess the importance of black carbon (BC) mixing state for predicting black carbon climate impacts. We set out to answer this question by meeting the following objectives: (1) calculate key quantities for modeling black carbon eff ects in global and regional climate simulations (including the aging time-scale, optical properties, and cloud condensation nuclei [CCN] number); (2) quantify the uncertainty in these quantities in climate predictions resulting from inadequate representation of black carbon aerosol mixing state in existing models; and (3) provide a testbed for the evaluation of proposed new approximate aerosol modeling algorithms. Our main tool to achieve these objectives was the particle-resolved model PartMC-MOSAIC (Riemer, et al., 2009; Zaveri, et al., 2008). 

Summary/Accomplishments (Outputs/Outcomes):

The project led to several breakthroughs in terms of the development of new theory and new methods, as well as in terms of new science results regarding our understanding of the role that black carbon mixing state plays in determining black carbon climate impacts. These are summarized as follows: 
  1. New theory and new method development:
    1. Theoretical framework for mixing state quanti cation: The introduction of the mixing state index enabled the first rigorous quanti cation of the degree of "mixedness" of an aerosol population. This mixing state index represents a useful metric by which to compare and contrast ambient particle mixing state for diff erent locations or for diff erent model scenarios, and to compare and contrast model results and observations. This enabled us to attribute forcing errors to mixing state, because we now can precisely characterize the extent to which any given scenario in our scenario library features a highly mixed or unmixed aerosol population. 
    2. Multi-scale modeling framework: To formulate numerical parameter estimates and usage recommendations for global and regional models, it was essential to develop a suitable coarse-graining method that destills the results from detailed particle-resolved simulations down to a small number of parameters that can be tracked by larger-scale models. We have developed and applied such an approach for calculating black carbon aging timescales, which characterize the transition of black carbon from hydrophobic to hydrophilic, and for calculating black carbon absorption enhancement. 
    3. Algorithmic improvements in the underlying PartMC model: Improving the numerical algorithms was key to enabling larger scenario libraries to be generated, with each scenario using more computational particles to improve accuracy of the key output quantities (e.g., aging timescales). We developed a fast binning method for particle sorting that enables more efficient simulation of particle events, especially coagulation, and an acceleration coagulation sampling for rare particles, to speed up the simulations of environments containing low-concentration but high-mass particles (for example, coarse mode road dust).
  2. Science results: 
    1. Black carbon aging time-scale analyses: Our de nition of the black carbon aging time-scale based on CCN activity constitutes a critical step forward as it represents a criterion based on relevant physics. Our method to calculate aging time-scales directly is unique and only possible because we are able to track per-particle composition including both condensation and coagulation as important aging mechamisms. As part of this project, we used results for the scenario library to investigate what factors control the variability of aging time scales. 
    2. Mixing state impacts on black carbon absorption: While black carbon is the most strongly absorbing
      component of the atmospheric aerosol, a discrepancy exists between absorption observed in the atmosphere and absorption predicted by models. We show that approximations in model representations of aerosol composition, which are commonly used in global models, lead to overestimation in predicted absorption enhancement by coated black carbon. We not only offer an explanation for the discrepancy between modeled and observed absorption enhancement, but also demonstrate how detailed simulations at the particle scale can be used to infer relevant information for global-scale models. 
    3. Development of real-world scenarios: The comparison of PartMC model simulations and ship track data was the first of its kind. Over the course of this project, we expanded this work by developing scenarios based on data from the MEGAPOLI campaign and based on the CARES campaign, tightening the connection between particle-resolved modeling and particle-resolved observations such as ATOFMS, SP2, and spectro-microscopy methods. 
  3. Outputs and outcomes 
    1. Scenario Library: The scenario library of a wide range of idealized urban plume scenarios is a valuable resource to systematically investigate black carbon aging processes and their impact on climate relevant properties. The usefulness of these data is not only limited to our project, but extends to the community. For example, our collaborators at PNNL use output from the scenario library to benchmark their new multi-dimensional externally mixed sectional aerosol model (MOSAIC-Mix). We will make the scenario library output available on IDEALS (the Illinois Digital Environment for Access to Learning and Scholarship), which is a persistent and reliable repository hosted by the University of Illinois at Urbana-Champaign. 
    2. PartMC is publicly available at http://lagrange.mechse.illinois.edu/partmc/. The current version (2.3.0) has processing code added to calculate particle composition entropy and uses the accelerated stochastic particle loss algorithm for dry deposition. 


Journal Articles on this Report : 9 Displayed | Download in RIS Format

Other project views: All 24 publications 9 publications in selected types All 9 journal articles
Type Citation Project Document Sources
Journal Article Ching J, Fast J, West M, Riemer N. Metrics to quantify the importance of mixing state for CCN activity. Atmospheric Chemistry and Physics 2017;17(12):7445-7458. R835042 (Final)
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  • Journal Article Curtis JH, Michelotti MD, Riemer N, Heath MT, West M. Accelerated simulation of stochastic particle removal processes in particle-resolved aerosol models. Journal of Computational Physics 2016;322:21-32. R835042 (Final)
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  • Journal Article Fierce L, Riemer N, Bond TC. Explaining variance in black carbon's aging timescale. Atmospheric Chemistry and Physics 2015;15(6):3173-3191. R835042 (Final)
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  • Journal Article Fierce L, Bond TC, Bauer SE, Mena F, Riemer N. Black carbon absorption at the global scale is affected by particle-scale diversity in composition. Nature Communications 2016;7:12361 (8 pp.). R835042 (Final)
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  • Journal Article Fierce L, Riemer N, Bond TC. Toward reduced representation of mixing state for simulating aerosol effects on climate. Bulletin of the American Meteorological Society 2017;98(5):971-980. R835042 (Final)
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  • Journal Article Healy RM, Riemer N, Wenger JC, Murphy M, West M, Poulain L, Wiedensohler A, O'Connor IP, McGillicuddy E, Sodeau JR, Evans GJ. Single particle diversity and mixing state measurements. Atmospheric Chemistry and Physics 2014;14(12):6289-6299. R835042 (2013)
    R835042 (Final)
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  • Journal Article Michelotti MD, Heath MT, West M. Binning for efficient stochastic multiscale particle simulations. Multiscale Modeling & Simulation 2013;11(4):1071-1096. R835042 (2012)
    R835042 (2013)
    R835042 (Final)
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  • Journal Article Riemer N, West M. Quantifying aerosol mixing state with entropy and diversity measures. Atmospheric Chemistry and Physics 2013;13(22):11423-11439. R835042 (2012)
    R835042 (2013)
    R835042 (Final)
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  • Journal Article Tian J, Riemer N, West M, Pfaffenberger L, Schlager H, Petzold A. Modeling the evolution of aerosol particles in a ship plume using PartMC-MOSAIC. Atmospheric Chemistry and Physics 2014;14(11):5327-5347. R835042 (2012)
    R835042 (2013)
    R835042 (Final)
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  • Supplemental Keywords:

    black carbon aging, particle-resolved model, mixing state 

    Progress and Final Reports:

    Original Abstract
    2011 Progress Report
    2012 Progress Report
    2013 Progress Report