Implications of the New NAAQSImplications of the New NAAQS

All4 Inc. Air Quality Training Seminar

Montgomery, AL

December 7, 2010

Colin T. McCallAll4 Inc.

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Agenda NAAQS Background Current NAAQS Revisions NAAQS Implications and PSD

Considerations NAAQS Implementation Process Example AERMOD Modeling Planning Ahead Conclusions

NAAQS Background

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CAA-§109 National Ambient Air Quality Standards

109(b) – the NAAQS• Primary standards: attainment and

maintenance protect public health with adequate margin of safety

• Secondary standards: protect public welfare

109(d)(1) – timing• Every 5 years, “thorough” review of NAAQS• Revise as necessary• May also be done more frequently

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CAA-§109 National Ambient Air Quality Standards

109(d)(2) – Clean Air Scientist Advisory Committee (CASAC)• Appointed by U.S. EPA• 7 members: at least one physician, one

member of the National Academy of Sciences, one representative of state air pollution control agencies

• Review and recommend new NAAQS to EPA

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NAAQS Background “Backdrop” of the Clean Air Act. States design their SIPs and enforce

and implement their regulations to meet the NAAQS.

Air quality construction permit programs are designed around NAAQS compliance:• PSD: Maintaining NAAQS attainment• NNSR: Getting into NAAQS attainment

Current NAAQS Revisions

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Current NAAQS Revisions Lead PM2.5

CO Ozone NO2 (Primary and Secondary) SO2 (Primary and Secondary)

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NAAQS SummaryPollutant Averaging Period

Historic NAAQS (µg/m3)

Revised NAAQS (µg/m3)

CO1-Hour 10,000 10,000

8-Hour 40,000 40,000

Ozone 8-Hour 75 ppb60 – 70 ppb (proposed)

Pb 3-Month Rolling 1.5 0.15

PM10 24-Hour 150 150

PM2.5

24-Hour 65 35

Annual 15 15

NO2

1-Hour N/A 188

Annual 100 100

SO2

1-Hour N/A 196

3-Hour 1,300 1,300

24-hour 365 N/A

Annual 80 N/A

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PollutantNAAQS

Promulgation Date

Designations

Effective(approximate date)

110(a) SIPs Due

(3 yrs after NAAQS promulgation)

Attainment Demonstration

Due

Attainment Date

PM2.5 (2006) Sept 2006 Dec 2009 Sept 2009 Nov 2012Nov

2014/2019

Pb Oct 2008Nov 2010/2011

(extra time for new monitors)

Oct 2011June

2012/2013Nov

2015/2016

NO2 (primary)

Jan 2010 Feb 2012 Jan 2013 Aug 2013 Feb 2017

SO2 (primary)

June 2010 July 2012 June 2013 Jan 2014 July 2017

Ozone Aug 2010 Aug 2011(based on 2008-10 data)

Aug 2013 Dec 2013(to be proposed)

Dec 2017 (Moderate)

CO May 2011 June 2013 May 2014 Dec 2014 May 2018

PM2.5 (2011)

Oct 2011 Dec 2013 Oct 2014 Dec 2016Dec

2018/2023

NO2/SO2 Secondary

March 2012 April 2014 March 2015 Oct 2015 N/A

Anticipated NAAQS Implementation Milestones

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New NAAQS Considerations Historic NAAQS levels often not viewed

as impacting day-to-day permitting. New 1-Hour NAAQS levels are very

stringent (example for SO2):• SO2 3-Hour to Annual Ratio: 16.25

• SO2 1-Hour to Annual Ratio: 2.45

It may be difficult to directly demonstrate compliance with the NAAQS.

NAAQS Implications and PSD

Considerations

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NAAQS Implications NAAQS attainment status dictates air

quality permitting requirements (PSD and BACT versus NNSR and LAER).

Traditionally, a direct NAAQS compliance demonstration has only been required as part of a PSD permitting project.

PSD NAAQS modeling is a two step process: (1) SIL Evaluation; (2) full NAAQS assessment.

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PSD Permitting Considerations Step 1 of a PSD NAAQS assessment is a

significant impact level (SIL) analysis. U.S. EPA has established interim SILs:

• 24-Hour PM2.5 SIL: 0.3 µg/m3

• 1-Hour NO2 SIL: 7.5 µg/m3

• 1-Hour SO2 SIL: 7.9 µg/m3

Exceedance of the SILs will trigger a facility-wide NAAQS evaluation.

Consider short-term emissions increases.

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Interacting with the NAAQS Situations that call for facility-specific

NAAQS evaluations:• Attainment/Nonattainment Designations

(under the current U.S. EPA administration).• Major air permitting projects (PSD vs. NNSR).• Discretionary requests by a state agency.

More stringent NAAQS levels will result in more stringent state developed emission limits, monitoring, etc.

NAAQS Implementation

Process

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Attainment/Nonattainment Designations

U.S. EPA philosophy on the SO2 NAAQS implementation process:• Proposed NAAQS rule - designations

based on ambient monitoring data• Final NAAQS rule - designations based

primarily on air quality modeling data Shift to reliance on air quality

modeling will become a critical issue for individual facilities.

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SO2 NAAQS Monitoring Data

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SO2 NAAQS Implementation

NAAQS Implementation Schedule: • June 2011: Initial state nonattainment

recommendations to U.S. EPA (most counties will be “unclassifiable”)

• June 2013: State SIP submittals to achieve compliance with the NAAQS (including air quality modeling for individual facilities)

• 2017: Full NAAQS compliance in all areas

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SO2 NAAQS SIP Submittals

U.S. EPA: Revising PSD/NNSR programs to include new NAAQS is not sufficient. Five components are required:• “Attainment Emissions Inventory”• Maintenance Demonstration• Control Strategy• Contingency Plan• Verification of Continued Attainment

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SO2 NAAQS Implementation

State SIPS will be based on AERMOD dispersion modeling for the following individual facilities (by order of priority):• SO2 Actual Emissions > 100 tpy

• SO2 PTE > 100 tpy

• Smaller facilities “with a potential to cause or contribute” to a NAAQS violation

Minor facilities may still have trouble.

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Facility Specific NAAQS Evaluation

Modeling is based on potential-to-emit emission rates (not actual emissions).

Modeling must account for operating scenarios/loads that result in worst-case plume dispersion.

Must use representative meteorological data.

Ambient background data must be added to modeled concentrations.

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Stringency of the NAAQS Many facilities with any combination of

the following may have difficulty modeling NAAQS compliance:• Elevated emission rates (fuel oil

combustion, process SO2, etc.)

• Low stack heights• Building downwash to any extent• Complex terrain

Example AERMOD Modeling

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NAAQS Modeling Strategy

Start with an evaluation of each individual emission source.

Each source will have different factors that drive resulting ambient concentrations.

The cumulative ambient concentration from all sources (plus background) will be evaluated against the NAAQS.

Evaluate each source against the NAAQS as a first step.

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NAAQS Modeling Strategy

Big picture factors that will drive ambient concentrations for individual sources:•Elevated emission rates•Stack velocity (orientation of release

and flowrate)•Stack temperature (plume buoyancy)•Stack height versus surrounding terrain•Surrounding buildings and structures

(i.e., building downwash)

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Hypothetical Modeling Example

Modeling of a hypothetical facility with the following SO2 emission sources:

•Process SO2 source

•Fuel oil combustion SO2 source

•Backup engine source NAAQS modeling evaluation is based

on SO2 potential to emit.

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“Process” SO2 Source

SO2 Emission Rate: 240 lb/hr (CEMs) Stack Height: 290 feet Stack Diameter: 16.5 feet Exhaust Temp: 350 °F Exhaust Flow: 230,000 acfm Elevated emission rate, buoyant

source, tall stack (taller than the tallest buildings at the facility)

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Process SO2 Source Impacts

Highest impacts are in complex terrain far from the facility.

Wind speed doesn’t match location of elevated concentrations.

Impacts occur during periods of atmospheric stability and low mixing heights. Typically early morning, low wind speed conditions.

High concentrations due partially to the limitations of the AERMOD dispersion model.

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Combustion SO2 Source

SO2 Emission Rate: 20 lb/hr (AP-42) Stack Height: 60 feet Stack Diameter: 2 feet Exhaust Temp: 225 °F Exhaust Flow: 16,000 acfm Buoyant source, short stack (shorter

than the tallest buildings at the facility)

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Combustion SO2 Source Impacts

Elevated concentrations are closer to the facility.

Building downwash effects have a noticeable impact on ambient concentrations.

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Engine SO2 Source

SO2 Emission Rate: 3 lb/hr (Vendor) Stack Height: 10 feet Stack Diameter: 1.3 feet Exhaust Temp: 935 °F Exhaust Flow: Horizontal Discharge Horizontal discharge, short stack

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Engine SO2 Source Impacts

Elevated ambient concentrations at the facility fenceline for two reasons:•Low stack height (10 feet)•No plume buoyancy due to

horizontal discharge. Ambient air considerations become

very important (i.e., public access).

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Modeling Refinements

“Process” SO2 Emission Source:

• Stack height increase is technically and economically infeasible.

• Raw materials are fixed due to product and consumer demand.

• Upgrades to the scrubber could achieve control of ~30% of the current uncontrolled emission rate (240 lb/hr to approximately 160 lb/hr).

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Modeling Refinements

Combustion SO2 Emission Source:

• Stack height increase is technically and economically infeasible.

• Fuel oil firing is desirable due to cost savings considerations.

• Raw materials to the source bring inherent scrubbing capacity: 50 to 65% based on previous studies.

• 50% inherent scrubbing brings emission rate to 10 lb/hr (justify through testing).

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Modeling Refinements

Engine SO2 Emission Source:

•Simplest fix is to “turn up” the horizontal stack discharge.

•No changes to the vendor guaranteed emission rate of the engine.

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Cumulative Concentrations The facility must cumulatively comply

with the NAAQS level. Addressing each individual source helps

as a first cut. This scenario still exceeds the 1-hour

NAAQS level for SO2 when the sources are taken cumulatively.

Haven’t even considered ambient background…..

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Ambient Background Concentrations

NAAQS evaluation requires background concentrations to be added to modeled concentrations.

Example 1-hour attainment ambient concentrations:• NO2: 30 - 80 µg/m3 (NAAQS: 188)

• SO2: 50 - 100 µg/m3 (NAAQS: 196)

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Ambient Background Challenges

Availability of representative ambient monitoring data.

Monitor must be representative of the background concentrations at the facility.

Pre-construction monitoring may be required in the absence of representative ambient monitoring data.

Rural versus urban setting is important for availability and good data.

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Ambient SO2 Monitors

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Ambient NO2 Monitors

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Ambient PM2.5 Monitors

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Ambient Background Challenges

Less room available for your facility to contribute to the NAAQS levels.

U.S. EPA “Tier 1” approach for combining modeled and monitored concentrations:• Combine 99th percentile cumulative

modeling concentration with peak hourly monitored concentration

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Ambient Background Considerations

188

NO

2 1-h

our C

once

ntra

tion

(g/

m3 )

80

NAAQS Level

Monitored Background Value

108 g/m3 available for modeling

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Temporal Pairing

New option for combining air quality modeling and ambient monitoring data.

Eliminates conservativeness of combining concentrations that occurred at different times.

U.S. EPA generally approves of the approach in recent guidance.

Specific evaluations need approval on a case-by-case basis (work with the state).

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Temporal Pairing Example

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Temporal Pairing Example

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Temporal Pairing Example

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Temporal Pairing Example

Planning Ahead

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Planning Ahead Emissions Strategies:

•Evaluate adequacy of emission limits

•Evaluate emissions control options•Evaluate alternate fuels and fuel

specifications Facility Fence Line Strategies

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Planning Ahead Stack/Exhaust Strategies:

•Combined source exhausts•Co-located exhaust points to

increase buoyancy•“Turn up” horizontal stacks•Increase stack heights

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Planning Ahead Air Quality Modeling Strategies:

•Temporal pairing approach•Plume transport time•Surrounding surface characteristics•Wind speed monitor thresholds•Mechanical mixing height

considerations•Alternative models (CALPUFF, etc.)

•Atmospheric chemistry options for NO2

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Conclusions The new 1-hour NAAQS levels are so

stringent that they will drive project feasibility and project design.

NAAQS will replace BACT as the most critical PSD permitting issue.

NAAQS modeling will be required even in the absence of new projects.

Plan early for new projects and for the SO2 NAAQS implementation process.