Emission Factors Analysis

Technology No. 20160061

Midcontinent Independent System Operator Emission Study

A comprehensive study presents a unique analysis of marginal emission factors for three pollutants from electricity generation in the eleven-state Midcontinent Independent System Operator (MISO) region. Researchers estimate both average emission factors and marginal emission factors for carbon dioxide (CO2), sulfur dioxide (SO2), and nitrogen oxides (NOx) from fossil-fired generators in MISO, and the complete study provides data for multiple spatial scales: all of MISO, each sub-region (East, West, Central), each of the eleven  states, major utilities bidding in MISO and each generator bidding into MISO. Regional and temporal data were analyzed as well. Currently, no other detailed marginal emissions studies exist for any U.S. Regional Transmission Organization (RTO).

Marginal Emission Factors Analysis is More Accurate

Emission benefit estimates from energy efficiency interventions are typically based on average emission factors. However, these easy-to-calculate factors are based on a system average and tend to overestimate the benefits of such interventions. In fact, this study confirmed that MISO-wide emissions factors were generally higher for average emission factors than for marginal emissions factors. Marginal emission factors, which require greater data requirements and are more difficult to calculate, result in more accurate emission benefits.

Better Estimates for Best System of Emission Reduction Practices

Marginal emissions analysis can better estimate emissions displacement from Best System of Emission Reduction (BSER) practices proposed under EPA’s Clean Power Plan, whose goals are currently based on average emission factors. And while CO2 emission rate goals for 2030 are also based on average emissions factors, these goals could be calculated instead using more accurate marginal emissions factors and then estimating the difference. The study data may also serve to support technical, policy and investment decisions in MISO based on marginal vs. average emission factors. In addition, incremental emission factors for MISO generators can be used with environmental modeling software, such as PROMOD IV, in building scenarios for MISO energy efficiency interventions in line with EPA’s Section 111(d).


  • Provides marginal emissions analysis of several levels: regional, sub-regional, state and individual units
  • Offers a consistent metric for calculating displaced emissions in MISO
  • Notes significant regional and temporal differences as well as differences in average vs marginal emission factors
  • Could support effective technical, policy and investment decisions in MISO

Phase of Development - Product Available

Researchers estimate both average emission factors and marginal emission factors for carbon dioxide (CO2, sulfur dioxide (SO2), and mono-nitrogen oxides (NOx) from fossil-fired generators.

    Elizabeth J. Wilson
    Associate Professor, Humphrey School of Public Affairs
    Julian D. Marshall, PhD
    Adjunct Professor, Civil, Environmental, and Geo-Engineering
    External Link (www.cege.umn.edu)
    Maninder Pal Singh Thind
    Research Assistant, Environmental Engineering, Department of Civil, Environmental, and Geo-Engineering

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