DRAFT

For WRAP Market Trading Forum Review

Stationary Source NOx and PM Emissions

in the WRAP Region:

An Initial Assessment of Emissions, Controls,

and Air Quality Impacts

May 30, 2003

Western Governors’ Association

1515 Cleveland Place, Suite 200

Denver, CO 80202

Comments should be provided by June 13 to:

Lee Alter

715 North Park Avenue, 2nd Floor

Tucson, AZ 85721

lalter@westgov.org
PREFACE

Regulatory Framework for Tribal Visibility Implementation Plans

The regional haze rule explicitly recognizes the authority of tribes to implement the provisions of

the rule, in accordance with principles of federal Indian law, and as provided by the Clean Air

Act §301(d) and the tribal authority rule (TAR) (40 CFR §§49.1– .11). Those provisions create

the following framework:

1. Absent special circumstances, reservation lands are not subject to state jurisdiction.

2. Federally recognized tribes may apply for and receive delegation1 of federal authority to

implement CAA programs, including visibility regulation, or "reasonably severable"

elements of such programs (40 CFR §§49.3, 49.7). The mechanism for this delegation is a

tribal implementation plan (TIP). A reasonably severable element is one that is not integrally

related to program elements that are not included in the plan submittal, and is consistent with

applicable statutory and regulatory requirements.

3. The regional haze rule expressly provides that tribal visibility programs are “not dependent

on the strategies selected by the state or states in which the tribe is located” (64. Fed. Reg.

35756), and that the authority to implement §309 TIPs extends to all tribes within the

GCVTC region (40 CFR §51.309(d)(12)).

4. The EPA has indicated that under the TAR tribes are not required to submit §309 TIPs by the

end of 2003. Rather, they may choose to opt-in to §309 programs at a later date (67 Fed.

Reg. 30439).

5. Where a tribe does not seek delegation through a TIP, EPA, as necessary and appropriate,

will promulgate a federal implementation plan (FIP) within reasonable timeframes to protect

air quality in Indian country (40 CFR §49.11). EPA is committed to consulting with tribes

on a government-to-government basis in developing tribe-specific or generally applicable

TIPs where necessary (See, e.g., 63 Fed. Reg. 7263-64).

The amount of modification, if any, needed for this report to fulfill tribal needs may vary

considerably from tribe to tribe. The authors have striven to ensure that all references to tribes in

the document are consistent with principles of tribal sovereignty and autonomy as reflected in the

above framework. Any inconsistency with this framework is strictly inadvertent and not an

attempt to impose requirements on tribes which are not present under existing law.

Tribal Participation in the WRAP

Tribes, along with states and federal agencies, are full partners in the WRAP, having equal

representation on the WRAP Board as states. Whether Board members or not, it must be

remembered that all tribes are governments, as distinguished from the “stakeholders” (private

interest) which participate on Forums and Committees but are not eligible for the Board.

 

1 Tribes also possess a more fundamental source of authority to regulate their environments, based on their inherent

authority as sovereign nations, which predates the formation of the United States. However, in the context of air

pollution regulation and visibility planning in particular, tribal authority will more likely be based on delegation of

federal authority.
Despite this equality of representation on the Board, tribes are very differently situated than

states. There are over four hundred federally-recognized tribes in the WRAP region, including

Alaska. The sheer number of tribes makes full participation impossible. Moreover, many tribes

are faced with pressing environmental, economic, and social issues, and do not have the

resources to participate in an effort such as the WRAP, however important its goals may be.

These factors necessarily limit the level of tribal input into and endorsement of WRAP products.

The tribal participants in the WRAP, including Board members Forum and Committee members

and co-chairs, make their best effort to ensure that WRAP products are in the best interest of the

tribes, the environment, and the public. One interest is to ensure that WRAP policies, as

implemented by states and tribes, will not constrain the future options of tribes who are not

involved in the WRAP. With these considerations and limitations in mind, the tribal participants

have joined the state, federal, and private stakeholder interests in approving this report as a

consensus document.
TABLE OF CONTENTS

Section I: Executive Summary

Prepared by WRAP Staff

Section II: NOx and PM Emissions from Stationary Sources

Prepared by WRAP Staff

Section III: Nitrate and PM Ambient Concentrations

Prepared by WRAP Staff

Section IV: A Conceptual Model of Regional Haze in the West

and the Role of Stationary Source NOx and PM Emissions

Prepared by Armistead Russell, Georgia Institute of Technology

Section V: Summary of Air Quality Modeling Results

Prepared by WRAP Staff, the University of California at Riverside, and

ENVIRON Corporation

Section VI: Summary of Emission Controls Available for Large Stationary Sources of

NOx and PM

Prepared by Reaction Engineering Incorporated and Energy &

Environmental Strategies
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SECTION I:

EXECUTIVE SUMMARY

Background and Purpose

The primary purpose of this report is to provide the information necessary for western states and

tribes to fulfill the requirements of Section 309(d)(4)(v) of the U.S. Environmental Protection

Agency’s (EPA) regional haze rule (40 CFR 51.309). Specifically, the rule states:

Provisions for stationary source NOx and PM. The plan submission must include a

report which assesses emissions control strategies for stationary source NOx and PM,

and the degree of visibility improvement that would result from such strategies. In the

report, the State must evaluate and discuss the need to establish emission milestones for

NOx and PM to avoid any net increase in these pollutants from stationary sources within

the transport region, and to support potential future development and implementation of

a multipollutant and possibly multisource market-based program. The plan submission

must provide for an implementation plan revision, containing any necessary long-term

strategies and BART requirements for stationary source PM and NOx (including

enforceable limitations, compliance schedules, and other measures) by no later than

December 31, 2008.

The regional haze rule provides the nine western states within the Grand Canyon Visibility

Transport Region (GCVTR) an opportunity to submit state implementation plans (SIPs)

containing policies and programs recommended in the final report of the Grand Canyon

Visibility Transport Commission (June 1996). Such plans must be submitted by December 31,

2003. GCVTR states electing not to submit SIPs under Section 309 must submit SIPs under

Section 308 of the regional haze rule in the 2005-07 time frame. Indian tribes have the option to

submit tribal implementation plans (TIPs) under either section at any time. Moreover, the TIPs

may include reasonably severable elements of the rule. A map of the WRAP region, mandatory

federal Class I areas addressed by the regional haze rule, and WRAP state and tribal members is

provided in Figure I-1.

A major provision of Section 309 is the control of stationary source sulfur dioxide (SO2)

emissions. The provision quoted above – for a report on stationary sources of NOx and PM – is

to ensure that states begin the process of evaluating other pollutants from stationary sources.

Hence, this report is meant as a starting point for a potentially multi-year process of evaluating

stationary sources and designing further control strategies where appropriate. At a minimum,

this process must include the determination of best available retrofit technology (BART) for

certain sources1

 and the resulting visibility improvements and may include an alternative (e.g.,

emissions trading) program achieving greater reasonable progress towards the national visibility

goal of no man-made impairment.

 

1

 BART-eligible sources are those which belong to one of 26 industrial categories, have the potential to emit at least

250 tons per year of a visibility-impairing pollutant, and were put into place between 1962 and 1977.
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Organization of Report

This report is required for the GCVTR states choosing to submit SIPs under Section 309 of the

region haze rule, but since all states must ultimately address stationary source NOx and PM

emissions from BART-eligible and potentially other stationary sources, the scope of this report

goes somewhat beyond the nine states in the GCVTR and the limited number of BART-eligible

sources in the WRAP region. For example, the air quality modeling evaluates the impact of

emission changes within the GCVTR, but at all Class I areas within the contiguous WRAP

region. Also, emission control technologies evaluated in Section VI were chosen on the basis of

source types throughout the WRAP region, which do not differ substantially from those types

within the GCVTR. They were also chosen on the basis of all existing source types, not just

BART-eligible source types, partly because sources eligible for BART as a result of pollutants

other than SO2 have not yet been identified2

 and partly because an alternative program to BART

could apply to a much broader universe of sources. By extending the scope of this report beyond

the nine GCVTR states and beyond the BART-eligible stationary sources, it not only becomes

applicable to a wider range of WRAP members and potential control strategies but serves to

coordinate regional development of such strategies. It is also a most cost-effective approach than

dealing with the nine GCVTR states separately.

As noted above, this report contains analyses and information to initiate a process for evaluating

stationary sources of NOx and PM – a process required of all states and open to Indian tribes as

well. The Executive Summary contains highlights of the report, but it is also where specific

issues raised in Section 309(d)(4)(v), such as interpollutant trading, are directly and succinctly

discussed. This is intended to help Section 309 states and tribes address the literal requirements

of the rule.

Table I-1 shows how analyses within this report were designed to address the specific

requirements of the rule. Emissions data can be used to assess emission control strategies and to

evaluate the need for milestones by illustrating the relative significance of different source

categories to total NOx and PM emissions, both now and in the future. Ambient monitoring data

can be used to assess emission control strategies by illustrating where and how much nitrate and

primary PM may contribute to actual visibility impairment. The conceptual model is intended to

support this entire assessment and to provide a common, scientifically-founded understanding of

western haze and the role of stationary sources in anticipation of a multi-year assessment of their

importance and control options. The conceptual model is intended to provide a more complete

framework than what can be provided alone by the air quality modeling and other assessments.

Air quality modeling is used in a “sensitivity capacity” to assess emission control strategies, their

degree of visibility improvement, and the need for milestones to prevent any future increase in

emissions. A summary of current NOx and PM control technologies and their costs, trends, and

secondary and multi-pollutant impacts can be used to assess emission control technologies and

the need for milestones to support multisource and multipollutant programs. This summary is

also a useful starting point for addressing the BART requirements in Section 308 SIPs and

Section 309 SIP revisions. All these analyses are expected to be updated and improved by the

WRAP before such SIPs are adopted.

 

2

 The full universe of BART-eligible sources does not need to be identified until SIPs and SIP revisions are due in

2005-08, although this identification process is expected to begin in 2003.
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Table I-1. Analyses Contained in this Report and Their Relation to the Requirements in

Section 309(d)(4)(v) of the Regional Haze Rule.

Requirements of 309(d)(4)(v)

EmissionsDataAmbientDataConceptualModelAir QualityModelControlTechnologies

Assess emission control strategies X X X X X

Assess degree of visibility improvement

that would result from such strategies X X

Evaluate and discuss the need to establish

milestones to avoid any net increase X XX

Evaluate and discuss the need for

milestones to support potential future

development of multipollutant and

multisource market-based programs

X X

Implementation plan revision by

December 31, 2008

Finally, emissions in Alaska are not presented because resources did not permit examination of a

second emissions inventory database, nor are air quality modeling results presented for Alaska

because the visibility modeling system for Alaska is currently under development. However,

ambient monitoring data for Alaska are presented, and the conceptual model and control

technology information are applicable as well.

Summary of Findings

Analysis of current and future emissions, ambient monitoring data, and very limited modeling

results does not show stationary source NOx and PM emissions to be a major contributor to

regional haze (typically about 2 percent on average) in the vast majority of western Class I areas.

These findings may change as emission projections are updated and as ambient monitoring data

from new sites is collected and analyzed, and especially as modeling capabilities are improved

and as modeled and monitored data become available for the best and worst visibility days

instead of seasonal and annual averages.

Regardless of this or future regional technical analyses, the remedy embodied in reasonably

attributable visibility impairment requirements under the regional haze rule is still available

where BART-eligible sources of NOx and PM are found to have direct impact on specific

mandatory federal Class I areas. Furthermore, when considering NOx and PM milestones,

attention should be given to the reasonable progress goals in the regional haze rule, which
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generally entail steady and continuing emission reductions and no degradation on the best

visibility days. Where stationary source NOx emission reductions are appropriate, substantial

reduction may be feasible with commercially-available technologies for about $300 to $1,200

per ton.

Assessment of Emission Control Strategies for Stationary Sources of NOx and PM

Since this report is primarily a starting point for addressing stationary source NOx and PM

emissions, the control of which would not be determined until the 2005-08 timeframe, specific

emission control strategies including such elements as level of control, applicability, and

emissions trading are not discussed. Rather, this report identifies significant issues in assessing

and designing such control strategies and provides some preliminary emissions, monitoring, and

modeling results.

Stationary source NOx emissions are currently about 25 percent of the WRAP NOx emission

inventory. Nitrate aerosols, however, are currently responsible (on average) for only 10 percent

of the light extinction budget, with relatively few sites measuring a contribution of more than

20 percent. Assuming the contribution of stationary sources to nitrate is roughly equal to their

proportion of the emission inventory, then stationary source NOx emissions might be expected to

contribute to about 2-3 percent of the region’s light extinction. Stationary sources, however,

have unique emission characteristics that may disproportionately impact visibility (e.g., stack

heights, transport distances, and proximity to Class I areas), and NOx is known to influence the

formation of other aerosol species. Moreover, the significance of NOx emissions may change as

sulfur and ammonia emissions change and as NOx emissions from stationary sources increase to

about 33 percent of the WRAP inventory in the year 2018.

To determine the effectiveness of stationary source NOx controls, it is therefore important to

have an air quality model that can account for the processes above. The WRAP’s current

modeling system, while sufficient for analyzing the regional impact of some emission changes, is

not predicting nitrate concentrations well enough to support a decision on whether or not

stationary source NOx controls are an effective way at achieving reasonable progress. Several

improvements to the modeling system are underway, including implementation of a source

apportionment tool, but until the model produces better nitrate results, other means of assessment

will be necessary to determine the appropriate level of NOx control in future SIPs.

Given the model’s current performance, its use in this report is limited to the summer months

(July through September), when it is performing best for nitrate, but also when nitrate

concentrations are lowest. Furthermore, its use is limited to two “sensitivity analyses” – a

50 percent stationary source NOx reduction and a 50 percent stationary source PM10 reduction.

The purpose of the sensitivity analyses is to gauge how nitrate and other atmospheric

constituents might respond to significant changes in emissions. Results are summarized in the

next part of this Executive Summary and discussed in more detail in Section V of the report.

As advancements are made towards understanding the air quality impacts of stationary source

NOx emissions, it is appropriate to investigate the potential level of control that can be achieved,

and at what cost. Section VI of this report identifies 34 NOx control technologies. Most of these
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are commercially available, while others are near-available. Those for coal-fired boilers (by far

the largest category of stationary source NOx emissions) typically achieve 30 to 50 percent NOx

control at a cost of about $300 to $1,200 per ton.3 Actual costs and emission reductions are

highly dependent on boiler type, vintage, and configuration, fuel burned, and existing controls.

For these reasons, it is important to have recent, extensive, and reliable data on the emission

source population, some of which is lacking in the WRAP inventory, such as current control

information, utility boiler heat rates, information on the process producing the emissions (e.g.,

from natural gas compressor stations), and utilization rates (e.g., from industrial internal

combustion engines). Future WRAP emission inventories should include such information.

Visibility impairment sometimes occurs when a high portion of the NOx emissions are in the

form of (or converted to) nitrogen dioxide gas (NO2). However, this is not common to most

stationary sources and is typically considered a plume blight or local issue, not a regional haze

issue that would be addressed by the regional haze rule.

Stationary source PM10 emissions are currently 6 percent of the WRAP PM10 inventory and may

grow slightly to 7 percent by 2018, not including wind-blown fugitive dust emissions, for which

an inventory is under development. PM10 (versus NO2 and particles large than 10 microns)

accounts for nearly all the man-made light extinction, but the amount attributable to primary

stationary source emissions is difficult to determine.4 Since most of the coarse fraction (between

2.5 and 10 microns) is believed to be primary and only some of the fine fraction is believed to be

primary, a rough estimate of the contribution of primary PM10 emissions to light extinction can

be gleaned by examining the percent attributable to coarse material. As shown in Section III,

this is approximately 10 to 15 percent (on average) across most of the WRAP region, with

generally lower percentages in the Pacific Northwest and higher percentages in the southeast part

of the region. Assuming the contribution of stationary sources to primary PM10 is roughly equal

to their proportion of the emission inventory, then stationary source PM10 emissions might be

expected to contribute to about 1 percent of the region’s light extinction. Coupled with the fact

that stationary source PM10 emissions are relatively well controlled in the West, there does not

appear to be much potential in a stationary source PM control strategy for purposes of regional

haze. PM10 emissions, however, appear to have a greater visibility impact per ton than NOx

emissions, as shown in Section V. Also, some PM10 emission co-benefits may result from multipollutant technologies described in Section VI, so reductions in stationary source PM10 emissions

could conceivably be part of a broader air quality management strategy and/or part of a broader

strategy to achieve reasonable progress under the visibility regulations – e.g., to prevent

degradation on the cleanest days.

Finally, the appropriate level of stationary source NOx and PM control, if any, should be

informed by a comprehensive assessment of costs and benefits, not just those associated with

facility compliance and visibility improvements. To this end, the WRAP is completing work on

an economic analysis framework to conduct such analyses in a consistent and technically sound

manner.

 

3

 One exception is selective catalytic reduction (SCR), which is capable of achieving 70 to 90+ percent control at

costs of approximately $1,200 to $2,000 per ton.

4

 As explained in Section II of this report, the term “PM” used in Section 309(d)(4)(v) of the regional haze rule is

construed as primary PM10 emissions.
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Degree of Visibility Improvement Resulting from Emission Control Strategies for

Stationary Sources of NOx and PM

As discussed above, based on the most recent ambient monitoring and emissions data, stationary

source NOx and PM emissions do not appear to be a large contributor to regional haze at most

Class I areas in the West. But due to the complexity of atmospheric processes and possible

trends in the emissions of other pollutants affecting nitrate formation, a regional-scale modeling

effort is underway to more carefully assess the visibility improvement from potential control

strategies. Given the model’s current performance, its application in this report is limited to the

June-September timeframe – when nitrate performance is best, but also when nitrate

concentrations are lowest – and it is only used in a sensitivity analysis “mode”, meaning two

scenarios were modeled to gauge how nitrate and other atmospheric constituents might respond

to significant changes in emissions: one in which emissions of NOx are reduced by 50 percent

(412,000 tpy) from stationary sources in the GCVTR with emissions of NOx greater than

100 tpy, and an identical scenario for PM10 (98,000 tpy).

Current modeling results indicate that the stationary source NOx and PM10 emission reductions

described above would reduce regional haze (in Mm-1) by 0.5 percent and 0.4 percent,

respectively, when averaged across all sites in the GCVTR over the June-September time period,

although some areas would see an improvement of 2 to 5 percent on some days. On a purely

ton-per-ton basis, reductions in stationary source PM10 emissions appear to yield greater regional

haze benefits than reductions in NOx emissions, since they produced almost the same visibility

benefit at one-fourth the emission change.

The NOx emission reductions had the greatest impact in southern CA, where ammonium nitrate

concentrations in Class I areas are predicted to decrease by 0.15 to 0.25 ug/m3. A second area of

reductions is predicted in the central-east Rocky Mountains, especially in north-central CO.

Although the reductions are not as large as in southern CA (0.04 to 0.11 ug/m3), they are larger

than average across the domain and exhibit the largest percentage reduction (10 to 20 percent).

It is interesting to compare these results with those simulating the effects of the SO2 backstop

emissions trading program, or Annex. In the case of the Annex, an SO2 emission reduction of

15 percent (132,000 tons) in the GCVTR produced a sulfate reduction of 4 percent averaged

across all Class I areas in the GCVTR on the 20% worst modeled days. In the case of the NOx

sensitivity run, a NOx emission reduction of 15 percent (412,000 tons) in the GCVTR produced

a nitrate reduction of 5 percent averaged across all Class I areas in the GCVTR on the JulySeptember modeled days. The nitrate reduction does not produce as much visibility benefit at

most Class I areas because its concentrations are much smaller, but the response of nitrate to

NOx reductions is similar in proportion to the response of sulfate to SO2 reductions.

NOx changes appear to have very little effect on aerosol concentrations beyond changes in

nitrate. Other species that could be indirectly affected – e.g., ozone concentrations and

subsequent oxidation of SO2 and organic gases into the particulate phase – do not appear

influenced by the levels of NOx reductions (16 percent of the total inventory) assumed in this

analysis.
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The PM10 emission reductions had a maximum impact of about 0.1 to 0.5 ug/m3, or about 4 to

8 percent. Compared to the NOx reduction scenario, reductions in ambient PM10 are more

dispersed, with a greater number of local maximums. This may reflect the fact that there are a

fewer number of large PM10 sources than large NOx sources and that much of the PM10

emissions are coarse particles, with shorter transport distances.

All modeling results in this report are subject to change after the modeling improvements

described in Section V are implemented. Results may also change when compiled for the best

and worst visibility and nitrate days throughout the year, as opposed to a three-month summer

average. For reasons described in Section V, the three-month summer average probably tends to

reduce the apparent impact of emission changes.

The Need to Establish Milestones to Avoid Any Net Increase in NOx and PM Emissions

from Stationary Sources

Sensitivity modeling was also done to evaluate the impacts of a 25 percent simultaneous increase

in stationary source NOx and PM10 emissions. The increase in nitrate formation was

approximately half the magnitude of the decrease resulting from the NOx reduction scenario.

However, the increase in PM10 (nitrates and primary particulates) and visibility impairment were

about the same in the 25 percent increase scenario as in the two 50 percent decrease scenarios

because both pollutants were increased simultaneously.

The need to establish milestones to avoid any net increase in NOx and PM emissions from

stationary sources should be determined when more complete and accurate modeling results (and

ambient data analyses) are available, prior to submittal of the Section 309 SIP revisions in

2007-08. In addition to the modeling results per se, consideration should be given to meeting the

reasonable progress goals of the regional haze rule, which generally imply a steady and

continuous reduction in emissions and a prevention of degradation on the best visibility days.

The Need for Milestones to Support Potential Future Development of Multipollutant and

Multisource Market-Based Program

Milestones are not absolutely necessary to support potential multipollutant and multisource

market-based programs. For example, a group of sources could theoretically comply with an

SO2 milestone by reducing emissions of other pollutants, and/or in other sectors, for which no

milestones exist. Regardless, the key issues raised by such programs do not involve the

milestones as much as the uncertainties associated with such emissions trading.

As discussed in Section IV, there are a number issues that must be addressed. Most of these

relate to the visibility-improvement value of eliminating a ton of emissions. Different pollutants

have different impacts on visibility on a per ton basis. Establishing an “equivalency ratio” to

allow X tons of one pollutant to be reduced in lieu of Y tons of another would require significant

analysis, and the certainty of such values may be suspect (especially for NOx) or insufficient to

ensure a specific level of visibility improvement. Moreover, the equivalency ratio between two

pollutants may vary across the region, between seasons, and possibly over time as the
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composition of the atmosphere changes. These same uncertainties (involving trades among

pollutants) also pertain to trades among a single pollutant, most notably NOx, as nitrate

concentrations are highly variable by season and location.

Trading across emission source categories poses a couple of additional issues. First, all

categories would have to have sufficient emissions monitoring to validate emission credits, and

monitoring of non-stationary sources is generally less accurate and verifiable than monitoring of

stationary sources. Second, concentrated emissions from stacks may have different impacts than

diffuse emissions at ground-level.

The uncertainties identified above could be reduced through further research, and the remaining

uncertainties could be further addressed by limiting the emission trading markets to certain

subregions, pollutants, or seasons where the equivalency ratios are fairly certain and stable.

However, such market restrictions could limit the economic benefits the market is intended to

provide. In short, some level of multipollutant and/or multisource market based program could

be a feasible way of meeting the long-term national visibility goal, and several of the

technologies described in Section VI of this report are capable of multipollutant reductions, but

substantially more research should be performed before committing to such programs, especially

in the 2007-08 timeframe.
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Figure I-1. Map of the WRAP Region, Members, and Mandatory Federal Class I Areas.