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CHAPTER 15. EMISSIONS ANALYSIS

TABLE OF CONTENTS

15.1 INTRODUCTION ......................................................................................................... 15-1

15.2 AIR EMISSIONS DESCRIPTIONS AND REGULATION......................................... 15-1

15.2.1 Carbon Dioxide.............................................................................................................. 15-2

15.2.2 Sulfur Dioxide................................................................................................................ 15-2

15.2.3 Nitrogen Oxides............................................................................................................. 15-2

15.2.4 Mercury.......................................................................................................................... 15-3

15.2.5 Particulate Matter........................................................................................................... 15-3
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CHAPTER 15. EMISSIONS ANALYSIS

15.1 INTRODUCTION

The U.S. Department of Energy (DOE) will conduct an emissions analysis as part of the 

notice of proposed rulemaking for electric motors. To assess the impacts of proposed energy 

conservation standards on certain environmental indicators, DOE will use a variant of the Energy 

Information Administration (EIA)’s National Energy Modeling System (NEMS).aEIA uses 

NEMS to produce the Annual Energy Outlook (AEO).

1 DOE will use a variant known as NEMSBT to provide key inputs to the analysis, based on the latest version of the Annual Energy 

Outlook. 

In the emissions analysis, DOE uses NEMS-BT to estimate the reduction in power sector 

emissions of carbon dioxide (CO2), nitrogen oxides (NOX), and mercury (Hg) that may result 

from new energy conservation standards for electric motors. NEMS-BT is run similarly to the 

AEO NEMS, except that electric motors energy use is reduced by the amount of energy saved 

(by fuel type) due to each considered efficiency standard level. The inputs of national energy 

savings come from the NIA spreadsheet model, while the output is the forecasted physical 

emissions. The net benefit of each considered standard level is the difference between the 

forecasted emissions estimated by NEMS-BT at that level and the AEO Reference Case. DOE 

conducts the emissions analysis as a policy deviation from the most recent AEO, which is likely 

to be AEO 2012. The results of the emissions analysis include changes in NOX, mercury, and 

CO2 emissions in 5-year forecasted increments for each trial standard level.

In addition to estimating impacts of standards on power sector emissions, DOE will 

estimate emissions impacts in production activities that provide the energy inputs to power 

plants. (These are referred to as “upstream” emissions.) This full-fuel-cycle analysis includes 

impacts on emissions of methane and nitrous oxide, both of which are recognized as greenhouse 

gases.

15.2 AIR EMISSIONS DESCRIPTIONS AND REGULATION

Below are descriptions of the air emissions that DOE will consider in the emissions 

analysis, and the regulations that affect these emissions. Each version of NEMS-BT reflects the 

estimated impacts of all regulations that had been promulgated by a specific date.

 

a

For more information on NEMS, refer to the U.S. Department of Energy, Energy Information Administration 

documentation. A useful summary is National Energy Modeling System: An Overview 2003, DOE/EIA-0581(2003). 

March 2003. EIA approves use of the name NEMS only to describe an official version of the model without any 

modification to code or data. Because this analysis entails some minor code modifications, and the model is run 

under policy scenarios that are variations on EIA assumptions, DOE refers to the model as NEMS-BT (BT is DOE’s 

Building Technologies Program). NEMS-BT was previously called NEMS-BRS.
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15.2.1 Carbon Dioxide

In the absence of any Federal emissions control regulation of power plant emissions of 

CO2, a DOE standard is likely to result in reductions of these emissions. The CO2 emission 

reductions likely to result from a standard will be estimated using NEMS-BT and national energy 

savings estimates drawn from the NIA spreadsheet model. The net benefit of the standard is the 

difference between emissions estimated by NEMS-BT at each standard level considered and the 

AEO Reference Case. NEMS-BT tracks CO2 emissions using a detailed module that provides 

results with broad coverage of all sectors and inclusion of interactive effects.

15.2.2 Sulfur Dioxide

SO2 emissions from affected electric generating units (EGUs) are subject to nationwide 

and regional emissions cap and trading programs, and DOE has preliminarily determined that 

these programs create uncertainty about the potential standards’ impact on SO2 emissions. Title 

IV of the Clean Air Act sets an annual emissions cap on SO2 for affected EGUs in the 48 

contiguous states and the District of Columbia (D.C.). SO2 emissions from 28 eastern states and 

D.C. were also limited under the Clean Air Interstate Rule (CAIR), at 70 FR 25162 (May 12, 

2005), which created an allowance-based trading program. Although CAIR has been remanded 

to EPA by the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit), see 

North Carolina v. EPA, 550 F.3d 1176 (D.C. Cir. 2008), it remains in effect temporarily, 

consistent with the D.C. Circuit’s earlier opinion in North Carolina v. EPA, 531 F.3d 896 (D.C. 

Cir. 2008). On July 6, 2011, EPA promulgated a replacement for CAIR, entitled “Federal 

Implementation Plans: Interstate Transport of Fine Particulate Matter and Ozone and Correction 

of SIP Approvals,” but commonly referred to as the Cross-State Air Pollution Rule or the 

Transport Rule. 76 FR 48208 (August 8, 2011). On December 30, 2011, however, the D.C. 

Circuit stayed the new rules while a panel of judges reviews them, and told EPA to continue 

enforcing CAIR (see EME Homer City Generation v. EPA, No. 11-1302, Order at *2 (D.C. Cir. 

Dec. 30, 2011)).

The attainment of emissions caps is typically flexible among EGUs and is enforced 

through the use of emissions allowances and tradable permits. Under existing EPA regulations, 

any excess SO2 emissions allowances resulting from the lower electricity demand caused by the 

imposition of an efficiency standard could be used to permit offsetting increases in SO2

emissions by any regulated EGU. However, if the standard resulted in a permanent increase in 

the quantity of unused emissions allowances, there would be an overall reduction in SO2

emissions from the standards. While there remains some uncertainty about the ultimate effects of 

efficiency standards on SO2 emissions covered by the existing cap and trade system, the NEMSBT modeling system that DOE uses to forecast emissions reductions currently indicates that no 

physical reductions in power sector emissions would occur for SO2. 

15.2.3 Nitrogen Oxides

Under CAIR, there is a cap on NOX emissions in 28 eastern states and the District of 

Columbia. All these States and D.C. have elected to reduce their NOX emissions by participating 

in cap-and-trade programs for EGUs. Therefore, energy conservation standards for electric 
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motors may have little or no physical effect on these emissions in the 28 eastern states and the 

D.C. for the same reasons that they may have little or no physical effect on NOX emissions. DOE 

is using the NEMS-BT to estimate NOX emissions reductions from possible standards in the 

States where emissions are not capped.

15.2.4 Mercury

In the absence of caps, a DOE energy conservation standard could reduce Hg emissions 

and DOE plans to use NEMS-BT to estimate these emission reductions. On December 21, 2011, 

EPA announced national emissions standards for hazardous air pollutants (NESHAPs) for 

mercury and certain other pollutants emitted from coal and oil-fired EGUs. 76 FR 24976. The 

NESHAPs do not include a trading program and, as such, DOE’s energy conservation standards 

would likely reduce Hg emissions. For the emissions analysis for this rulemaking, DOE plans to 

estimate mercury emissions reductions using NEMS-BT based on AEO2011, which does not 

incorporate the NESHAPs. DOE expects that future versions of the NEMS-BT model will reflect 

the implementation of the NESHAPs.

15.2.5 Particulate Matter

DOE acknowledges that particulate matter (PM) exposure can impact human health. 

Power plant emissions can have either direct or indirect impacts on PM. A portion of the 

pollutants emitted by a power plant are in the form of particulates as they leave the smoke stack. 

These are direct, or primary, PM emissions. However, the great majority of PM emissions 

associated with power plants are in the form of secondary sulfates, which are produced at a 

significant distance from power plants by complex atmospheric chemical reactions that often 

involve the gaseous (non-particulate) emissions of power plants, mainly SO2 and NOX. The 

quantity of the secondary sulfates produced is determined by a very complex set of factors 

including the atmospheric quantities of SO2 and NOX, and other atmospheric constituents and 

conditions. Because these highly complex chemical reactions produce PM comprised of different 

constituents from different sources, EPA does not distinguish direct PM emissions from power 

plants from the secondary sulfate particulates in its ambient air quality requirements, PM 

monitoring of ambient air quality, or PM emissions inventories. For these reasons, it is not 

currently possible to determine how the amended standard impacts either direct or indirect PM 

emissions. Therefore, DOE is not planning to assess the impact of these standards on PM 

emissions. Further, as described previously, it is uncertain whether efficiency standards will 

result in a net decrease in power plant emissions of SO2, which are now largely regulated by cap 

and trade systems. 
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REFERENCES 

 

1 Energy Information Administration (April 2011), Annual Energy Outlook 2011 with 

Projections to 2035, Washington, DC. Report No. DOE/EIA-0383(2011). 

http://www.eia.gov/forecasts/aeo/