Marginal emissions factors for the U.S. electricity system.

Area of Science:

• Environmental Science
• Energy Systems Analysis
• Atmospheric Chemistry

Background:

• Growing interest in reducing U.S. electricity generation emissions through renewable energy, energy efficiency, and conservation.
• Supply- and demand-side interventions can displace energy and emissions from conventional power plants.
• Marginal Emissions Factors (MEFs) provide a consistent metric for assessing avoided emissions.

Purpose of the Study:

• To present the first systematic calculation of MEFs for the U.S. electricity system.
• To estimate regional MEFs for CO2, NOx, and SO2.
• To explore trends in MEFs based on system load, time of day, and month.

Main Methods:

• Utilized hourly generation and emissions data from 2006-2011.
• Employed regression analysis to estimate regional MEFs.
• Determined the share of marginal generation from coal-, gas-, and oil-fired power plants.

Main Results:

• Estimated regional MEFs for CO2, NOx, and SO2 across the U.S. electricity system.
• Found significant regional variations in emissions benefits; Midwest efficiency measures avoid substantially more CO2, SO2, and NOx compared to the West.
• Demonstrated that Average Emissions Factors (AEFs) can significantly misestimate avoided emissions.

Conclusions:

• MEFs are crucial for accurately assessing the environmental impact of energy interventions.
• Regional differences in generation mix lead to varying emissions reductions from energy efficiency.
• Policy and interventions should consider regional MEFs for maximizing emission reduction benefits.