15-i 

CHAPTER 15. EMISSION ANALYSIS 

TABLE OF CONTENTS

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

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

15.3 GLOBAL CLIMATE CHANGE ................................................................................... 15-4

15.4 ANALYTICAL METHODS FOR AIR EMISSIONS ................................................... 15-6

15.5 EFFECTS ON POWER PLANT EMISSIONS ............................................................. 15-8

15.6 EFFECTS ON UPSTREAM FUEL-CYCLE EMISSIONS .......................................... 15-8

REFERENCES ........................................................................................................................ 15-10

LIST OF TABLES

Table 15.5.1 Power Sector Emissions from AEO2011 Reference Case, 2010-2035 ................. 15-8

Table 15.6.1 Estimated Upstream Emissions of Air Pollutants as a Percentage of Direct 

Power Plant Combustion Emissions .................................................................. 15-9
15-1 

CHAPTER 15. EMISSION ANALYSIS

15.1 INTRODUCTION

This chapter describes potential changes to emissions of carbon dioxide (CO2) and three 

air pollutants that may result from new and amended energy conservation standards for 

automatic commercial ice makers. The impacts on air emissions are largely driven by changes in 

power plant types and quantities of electricity generated under each of the considered standard 

levels. Changes in electricity generation are described in the utility impact analysis in chapter 13 

of this preliminary technical support document. 

15.2 AIR EMISSIONS DESCRIPTIONS AND REGULATION

This analysis will consider three pollutants: sulfur dioxide (SO2), nitrogen oxides (NOX), 

and mercury (Hg). An air pollutant is any substance in the air that can cause harm to humans or 

the environment. Pollutants may be natural or man-made (i.e., anthropogenic) and may take the 

form of solid particles (i.e., particulates or particulate matter (PM)), liquid droplets, or gases.a

The U.S. Department of Energy’s (DOE’s) analysis also considers CO2. 

 Sulfur Dioxide. Sulfur dioxide, or SO2, belongs to the family of sulfur oxide gases (SOx). 

These gases dissolve easily in water. Sulfur is prevalent in all raw materials, including crude oil, 

coal, and ore that contains common metals like aluminum, copper, zinc, lead, and iron. SOx

gases are formed when fuel containing sulfur, such as coal and oil, is burned, and when gasoline 

is extracted from oil, or metals are extracted from ore. SO2 dissolves in water vapor to form acid, 

and interacts with other gases and particles in the air to form sulfates and other products that can 

be harmful to people and their environment.1

 Nitrogen Oxides. Nitrogen oxides, or NOX, is the generic term for a group of highly 

reactive gases, all of which contain nitrogen and oxygen in varying amounts. Many of the 

nitrogen oxides are colorless and odorless. However, one common pollutant, nitrogen dioxide 

(NO2), along with particles in the air can often be seen as a reddish-brown layer over many urban 

areas. NO2 is the specific form of NOX reported in this document. NOX is one of the main 

ingredients involved in the formation of ground-level ozone, which can trigger serious 

respiratory problems. It can contribute to the formation of acid rain, and can impair visibility in 

areas such as national parks. NOX also contributes to the formation of fine particles that can 

impair human health.1

 Nitrogen oxides form when fossil fuel is burned at high temperatures, as in a combustion 

process. The primary man-made sources of NOX are motor vehicles, electric utilities, and other 

industrial, commercial, and residential sources that burn fossil fuels. NOX can also be formed 

naturally. Electric utilities account for about 22 percent of NOX emissions in the United States.2

 

a More information on air pollution characteristics and regulations is available on the U.S. Environment Protection 

Agent (EPA)’s website at www.epa.gov. 
15-2 

Mercury. Coal-fired power plants emit mercury, or Hg, found in coal during the burning 

process. While coal-fired power plants are the largest remaining source of human-generated Hg 

emissions in the United States, they contribute very little to the global Hg pool or to 

contamination of U.S. waters.1

 U.S. coal-fired power plants emit Hg in three different forms: 

oxidized Hg (likely to deposit within the United States); elemental Hg, which can travel 

thousands of miles before depositing to land and water; and Hg that is in particulate form. 

Atmospheric Hg is then deposited on land, lakes, rivers, and estuaries through rain, snow, and 

dry deposition. Once there, it can transform into methylmercury and accumulate in fish tissue 

through bioaccumulation. 

 

Americans are exposed to methylmercury primarily by eating contaminated fish. Because 

the developing fetus is the most sensitive to the toxic effects of methylmercury, women of 

childbearing age are regarded as the population of greatest concern. Children exposed to 

methylmercury before birth may be at increased risk of poor performance on neurobehavioral 

tasks, such as those measuring attention, fine motor function, language skills, visual-spatial 

abilities, and verbal memory.3

 

 Carbon Dioxide. Carbon dioxide, or CO2, is not a criteria pollutant (see below), but it is 

of interest because of its classification as a greenhouse gas (GHG). GHGs trap the sun’s radiation 

inside the Earth’s atmosphere and either occur naturally in the atmosphere or result from human 

activities. Naturally occurring GHGs include water vapor, CO2, methane (CH4), nitrous oxide 

(N2O), and ozone (O3). Human activities, however, add to the levels of most of these naturally 

occurring gases. For example, CO2 is emitted to the atmosphere when solid waste, fossil fuels 

(oil, natural gas, and coal), wood, and wood products are burned. In 2007, over 90 percent of 

anthropogenic (i.e., human-made) CO2 emissions resulted from burning fossil fuels.4

 Concentrations of CO2 in the atmosphere are naturally regulated by numerous processes, 

collectively known as the “carbon cycle.” The movement of carbon between the atmosphere and 

the land and oceans is dominated by natural processes, such as plant photosynthesis. While these 

natural processes can absorb some of the anthropogenic CO2 emissions produced each year, 

billions of metric tons are added to the atmosphere annually. In 2007, the United States’ CO2

emissions from electricity generation accounted for 39 percent of total U.S. GHG emissions.4

Particulate Matter. Particulate matter, or PM, also known as particle pollution, is a 

complex mixture of extremely small particles and liquid droplets. Particle pollution is made up 

of a number of components, including acids (e.g., nitrates and sulfates), organic chemicals, 

metals, and soil or dust particles.

 PM impacts are of concern due to human exposures that can impact health. Particle 

pollution—especially fine particles—contains microscopic solids or liquid droplets that are so 

small that they can get deep into the lungs and cause serious health problems. Numerous 

scientific studies have linked particle pollution exposure to a variety of problems, including: 

increased respiratory symptoms, such as irritation of the airways, coughing, or difficulty 

breathing; decreased lung function; aggravated asthma; development of chronic bronchitis; 

irregular heartbeat; nonfatal heart attacks; and premature death in people with heart or lung 

disease.
15-3 

DOE acknowledges that 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, the U.S. 

Environmental Protection Agency (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 below, it is uncertain whether efficiency standards will result in 

a net decrease in power plant emissions of SO2, and of NOx in many states, because those 

pollutants are now largely regulated by cap-and-trade systems. 

Air Quality Regulation. The Clean Air Act Amendments of 1990 list 188 toxic air 

pollutants that EPA is required to control.6 EPA has set national air quality standards for six 

common pollutants (also referred to as “criteria” pollutants), two of which are SO2 and NOX. 

Also, the Clean Air Act Amendments of 1990 gave EPA the authority to control acidification 

and to require operators of electric power plants to reduce emissions of SO2 and NOX. Title IV of 

the 1990 amendments established a cap-and-trade program for SO2, in all 50 states and the 

District of Columbia, intended to help control acid rain. 6 This cap-and-trade program serves as a 

model for more recent programs with similar features.

 In 2005, EPA issued the Clean Air Interstate Rule (CAIR) under sections 110 and 111 of 

the Clean Air Act (40 CFR Parts 51, 96, and 97).b

 70 FR 25162–25405 (May 12, 2005). CAIR 

limited emissions from 28 eastern states and D.C. by capping emissions and creating an 

allowance-based trading program. Although, CAIR was 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 remained 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, 2010, EPA issued the Transport Rule proposal, a replacement for CAIR, 

75 FR 45210 (Aug. 2, 2010). On July 6, 2011, EPA promulgated the final Transport Rule, 

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 (Aug. 8, 2011). 

With respect to Hg emissions, in 2005, EPA issued the final rule entitled “Standards of 

Performance for New and Existing Stationary Sources: Electric Steam Generating Units,” under 

 

b See www.epa.gov/cleanairinterstaterule/. 
15-4 

sections 110 and 111 of the Clean Air Act (40 CFR Parts 60, 63, 72, and 75).8 This rule, called 

the Clean Air Mercury Rule (CAMR), was closely related to the CAIR and established standards 

of performance for Hg emissions from new and existing coal-fired electric utility steam 

generating units. The CAMR regulated Hg emissions from coal-fired power plants. On 

February 8, 2008, the U.S. Court of Appeals for the D.C. Circuit issued its decision in State of 

New Jersey, et al. v. Environmental Protection Agency,

c

 in which the Court, among other 

actions, vacated the CAMR. 

15.3 GLOBAL CLIMATE CHANGE

Climate change has evolved into a matter of global concern because it is expected to have 

widespread, adverse effects on natural resources and systems. A growing body of evidence 

points to anthropogenic sources of GHGs (e.g., CO2), as major contributors to climate change. 

Because this rule, if finalized, will likely decrease CO2 emission rates from the fossil fuel sector 

in the United States, DOE here examines the impacts and causes of climate change and then the 

potential impact of the rule on CO2 emissions and global warming. 

 Impacts of Climate Change on the Environment. Climate is usually defined as the 

average weather, over a period ranging from months to many years. Climate change refers to a 

change in the state of the climate, which is identifiable through changes in the mean and/or the 

variability of its properties (e.g., temperature or precipitation) over an extended period, typically 

decades or longer. 

 The World Meteorological Organization and United Nations Environment Programme 

(UNEP) established the Intergovernmental Panel on Climate Change (IPCC) to provide an 

objective source of information about climate change. According to the IPCC Fourth Assessment 

Report (IPCC Report), published in 2007, climate change is consistent with observed changes to 

the world’s natural systems; the IPCC expects these changes to continue.9

 Changes that are consistent with warming include warming of the world’s oceans to a 

depth of 3,000 meters; global average sea level rise at an average rate of 1.8 mm per year from 

1961 to 2003; loss of annual average Arctic sea ice at a rate of 2.7 percent per decade, changes in 

wind patterns that affect extra-tropical storm tracks and temperature patterns, increases in intense 

precipitation in some parts of the world, as well as increased drought and more frequent heat 

waves in many locations worldwide, and numerous ecological changes.9

 Looking forward, the IPCC describes continued global warming of about 0.2 °C per 

decade for the next two decades under a wide range of emission scenarios for CO2, other GHGs, 

and aerosols. After that period, the rate of increase is less certain. The IPCC Report describes 

increases in average global temperatures of about 1.1 °C to 6.4 °C at the end of the century 

relative to today. These increases vary depending on the model and emissions scenarios.9

The IPCC Report describes incremental impacts associated with the rise in temperature. 

At ranges of incremental increases to the global average temperature, IPCC reports, with either 

high or very high confidence, that there is likely to be an increasing degree of impacts such as 

 

c 517 F.3d 574, 583 (D.C. Cir. 2008).
15-5 

coral reef bleaching, loss of wildlife habitat, loss to specific ecosystems, and negative yield 

impacts for major cereal crops in the tropics, but also projects that there likely will be some 

beneficial impacts on crop yields in temperate regions. 

 Causes of Climate Change. The IPCC Report states that the world has warmed by about 

0.74 °C in the last 100 years. The IPCC Report finds that most of the temperature increase since 

the mid-20th century is very likely due to the increase in anthropogenic concentrations of CO2

and other long-lived GHGs, such as methane and NOx in the atmosphere, rather than from 

natural causes. 

Increasing the CO2 concentration partially blocks the earth’s re-radiation of captured 

solar energy in the infrared band, inhibits the radiant cooling of the earth, and thereby alters the 

energy balance of the planet, which gradually increases its average temperature. The IPCC 

Report estimates that currently, CO2 makes up about 77 percent of the total CO2-equivalentd

global warming potential in GHGs emitted from human activities, with the vast majority 

(74 percent) of the CO2 attributable to fossil fuel use.10 For the future, the IPCC Report describes 

a wide range of GHG emissions scenarios, but under each scenario CO2 would continue to 

comprise above 70 percent of the total global warming potential.10

Stabilization of CO2 Concentrations. Unlike many traditional air pollutants, CO2 mixes 

thoroughly in the entire atmosphere and is long-lived. The residence time of CO2 in the 

atmosphere is long compared to the emission processes. Therefore, the global cumulative 

emissions of CO2 over long periods determine CO2 concentrations because it takes hundreds of 

years for natural processes to remove the CO2. Globally, 49 billion metric tons of CO2 –

equivalent of anthropogenic (man-made) GHGs are emitted every year.e

 Of this annual total, 

fossil fuels contribute about 29 billion metric tons of CO2.

11 

 

Researchers have focused on considering atmospheric CO2 concentrations that likely will 

result in some level of global climate stabilization, and the emission rates associated with 

achieving the “stabilizing” concentrations by particular dates. They associate these stabilized 

CO2 concentrations with temperature increases that plateau in a defined range. For example, at 

the low end, the IPCC Report scenarios target CO2 stabilized concentrations range between 

350 ppm and 400 ppm (essentially today’s value)—because of climate inertia, concentrations in 

this low-end range would still result in temperatures projected to increase 2.0 °C to 2.4 °C above 

pre-industrial levelsf

 (about 1.3 °C to 1.7 °C above today’s levels). To achieve concentrations 

between 350 ppm to 400 ppm, the IPCC scenarios present that there would have to be a rapid 

downward trend in total annual global emissions of GHGs to levels that are 50 to 85 percent 

below today’s annual emission rates by no later than 2050. Since it is assumed that there would 

 

d GHGs differ in their warming influence (radiative forcing) on a global climate system due to their different 

radiative properties and lifetimes in the atmosphere. These warming influences may be expressed through a common 

metric based on the radiative forcing of CO2 (i.e., CO2-equivalent). CO2 equivalent emission is the amount of CO2

emission that would cause the same- time integrated radiative forcing, over a given time horizon, as an emitted 

amount of other long- lived GHG or mixture of GHGs. e Other non-fossil fuel contributors include CO2 emissions from deforestation and decay from agriculture biomass; 

agricultural and industrial emissions of methane; and emissions of nitrous oxide and fluorocarbons.

f IPCC Working Group 3 Table TS 2.
15-6 

continue to be growth in global population and substantial increases in economic production, the 

scenarios identify required reductions in GHGs emissions intensity (emissions per unit of output) 

of more than 90 percent. However, even at these rates, the scenarios describe some warming and 

some climate change is projected due to already accumulated CO2 and GHGs in the 

atmosphere.

12

The Beneficial Impact of the Rule on CO2 Emissions. It is anticipated that the Rule will 

reduce energy-related CO2 emissions, particularly those associated with energy consumption in 

buildings. The U.S. Energy Information Administration (EIA) reports in its 2011 Annual Energy 

Outlook (AEO2011)

13 that U.S. annual energy-related emissions of CO2 in 2008 were about 

5.8 billion metric tons, of which 1.1 billion tons were attributed to the commercial buildings 

sector (including energy–using products such as automatic commercial ice makers). Most of the 

GHG emissions attributed to commercial buildings are emitted from fossil fuel-fired power 

plants that generate electricity used in this sector. In the AEO2011 Reference Case, EIA 

projected that annual energy-related CO2 emissions would grow from 5.7 billion metric tons in 

2015 to 6.3 billion metric tons in 2035, an increase of 11 percent, while commercial emissions 

would grow to from 1.0 billion metric tons to 1.3 billion metric tons, an increase of 28 percent. 

The Incremental Impact of the Rule on Climate Change. It is difficult to correlate 

specific emission rates with atmospheric concentrations of CO2 and specific atmospheric 

concentrations with future temperatures because the IPCC Report describes a clear lag in the 

climate system between any given concentration of CO2 (even if maintained for long periods) 

and the subsequent average worldwide and regional temperature, precipitation, and extreme 

weather regimes. For example, a major determinant of climate response is “equilibrium climate 

sensitivity,” a measure of the climate system response to sustained radioactive forcing. It is 

defined as the global average surface warming following a doubling of CO2 concentrations. The 

IPCC Report describes its estimated, numeric value as about 3 °C, but the likely range of that 

value is 2 °C to 4.5 °C, with cloud feedbacks the largest source of uncertainty. Further, as 

illustrated above, the IPCC Report scenarios for stabilization rates are presented in terms of a 

range of concentrations, which then correlates to a range of temperature changes. Thus, climate 

sensitivity is a key uncertainty for CO2 mitigation scenarios that aim to meet specific temperature 

levels. Because of how complex global climate systems are, it is difficult to know to what extent 

and when particular CO2 emissions reductions will impact global warming. 

15.4 ANALYTICAL METHODS FOR AIR EMISSIONS 

For each of the considered TSLs, DOE will calculate total power-sector emissions based 

on output from the National Energy Modeling System (NEMS-BT) model (see chapter 13 for 

description of the model). 

Coal-fired electric generation is the single largest source of electricity in the United 

States. Because the mix of coals used significantly affects the emissions produced, the model 

includes a detailed representation of coal supply. The NEMS-BT model considers the rank of the 

coal as well as the sulfur contents of the fuel used when determining optimal dispatch.14
15-7 

Within the NEMS-BT model, planning options for achieving emissions restrictions in the 

Clean Air Act Amendments include installing pollution control equipment on existing power 

plants and building new power plants with low emission rates. These methods for reducing 

emission are compared to dispatching options such as fuel switching and allowance trading. 

Environmental regulations also affect capacity expansion decisions. For instance, new plants are 

not allocated SO2 emissions allowances according to the Clean Air Act Amendments. 

Consequently, the decision to build a particular capacity type must consider the cost (if any) of 

obtaining sufficient allowances. This could involve purchasing allowances or over complying at 

an existing unit.

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 standards’ impact on SO2 emissions. 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 NEMS-BT modeling system that 

DOE uses to forecast emissions reductions currently indicates that no physical reductions in 

power sector emissions would occur for SO2.

g

 

The CAIR established 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 automatic 

commercial ice makers 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 SO2

emissions. 

 With respect to Hg, in the absence of CAMR or another trading program, a DOE standard 

would likely change Hg emissions and DOE will use NEMS-BT to estimate these emission 

reductions. However, DOE continues to review the impact of rules that reduce energy 

consumption on Hg emissions, and may revise its assessment of Hg emission reductions in future 

rulemakings. 

 As noted in chapter 13, NEMS-BT model forecasts end in year 2035. Rather than 

extrapolate beyond this year, DOE assumes that emissions impacts beyond 2035 are equal to the 

impacts in 2035. 

 

g In contrast to the modeling forecasts of NEMS-BT that SO2 emissions will remain at the cap, during the years 2007 

and 2008, SO2 emissions were below the trading cap. This raises the possibility that standards could cause some 

reduction in SO2 emissions. However, because DOE does not have a method to predict when emissions will be 

below the trading cap, it continues to reply on NEMS-BT and thus does not estimate SO2 emissions reductions at 

this time.
15-8 

15.5 EFFECTS ON POWER PLANT EMISSIONS

Table 15.5.1 shows AEO2011 Reference Case power plant emissions in selected years. 

The Reference Case emissions are the emissions shown by the NEMS-BT model to result if none 

of the TSLs are promulgated (the base case). 

Table 15.5.1 Power Sector Emissions from AEO2011 Reference Case, 2010-2035 

NEMS-BT Results 2010 2015 2020 2025 2030 2035

CO2 (million metric tons) 2,303 2,138 2,225 2,360 2,444 2,526

NOX (million tons) 2.57 1.99 1.98 2.00 2.03 2.05

Hg (tons) 40.51 26.88 26.82 28.21 29.08 29.91

15.6 EFFECTS ON UPSTREAM FUEL-CYCLE EMISSIONS

Upstream fuel-cycle emissions refer to the emissions associated with the amount of 

energy used in the upstream production and downstream consumption of electricity, including 

energy used at the power plant.17 Upstream processes include the mining of coal or extraction of 

natural gas, physical preparatory and cleaning processes, and transportation to the power plant. 

The NEMS-BT does a thorough accounting of emissions at the power plant due to downstream 

energy consumption, but does not account for upstream emissions (i.e., emissions from energy 

losses during coal and natural gas production). Thus, this analysis will report only power plant 

emissions.

 However, previous DOE environmental assessment documents have developed 

approximate estimates of effects on upstream fuel-cycle emissions. These emissions factors 

provide the reader with a sense of the possible magnitude of upstream effects. These upstream 

emissions would be in addition to emissions from direct combustion. 

 Relative to the entire fuel cycle, estimates based on the work of Dr. Mark DeLuchi, and 

reported in earlier DOE environmental assessment documents, find that an amount 

approximately equal to eight percent, by mass, of emissions (including SO2) from coal 

production are due to mining, preparation that includes cleaning the coal, and transportation from 

the mine to the power plant.18 Transportation emissions include emissions from the fuel used by 

the mode of transportation that moves the coal from the mine to the power plant. In addition, 

based on Dr. DeLuchi’s work, DOE estimated that an amount equal to approximately 14 percent 

of emissions from natural gas production result from upstream processes. 

Emission factor estimates and corresponding percentages of contributions of upstream 

emissions from coal and natural gas production, relative to power plant emissions, are shown in 

Table 15.6.1 for CO2 and NOX. The percentages provide a means to estimate upstream emission 

savings based on changes in emissions from power plants. This approach does not address Hg 

emissions.
15-9 

Table 15.6.1 Estimated Upstream Emissions of Air Pollutants as a Percentage of Direct 

Power Plant Combustion Emissions

Pollutant

Percent of Coal

Combustion Emissions

Percent of Natural Gas

Combustion Emissions

CO2 2.7 11.9

NOX 5.8 40
15-10

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15-11

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