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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

w RESEARCH TRIANGLE PARK, NC 27711 

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PROG

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SEP 2 5 2009 

OFFICE OF 

MEMORANDUM AIR QUALITY PLANNING 

AND STANDARDS 

SUBJECT: Guidance on SIP Elements Required Under Sections 110(a)(1) and (2) 

for the 2006 24-Hour Fine Particle (PM2,5) National Ambient Air Quality 

Standards (NAAQS) 

FROM: William T. Harnett, Director ~j6wl !+ kA~ 

Air Quality Policy Division (C539-01) 

TO: Regional Air Division Directors, Regions I-X 

. The purpose of this memorandum is to provide guidance on addressing the 

"infrastructure" elements for State Implementation Plans (S1Ps) required under sections 

110(a)(1) and 110(a)(2) of the Clean Air Act (CAA) for the 2006 24-hour PM2.5 NAAQS (71 FR 

61144). On December 18, 2006, EPA revised the 24-hour average PM2,5 primary and secondary 

NAAQS from 65 micrograms per cubic meter (μg/m 3 ) to 35 μg/m3 . Under sections 110(a)(1) 

and 110(a)(2) of the CAA, after promulgation of a new or revised NAAQS, each state is required 

to submit a plan to provide for the implementation, inaintenance, and enforcement of that 

NAAQS. 

States are required to address basic SIP requirements (see Attachment A), to assure 

attainment and inaintenance of the standards. By law, SIPs to address sections 110(a) (1) and 

110(a)(2) are to be submitted by states within 3 years after promulgation of a new or revised 

standard. lIn many cases the section 110(a)(2) SIPs for the 1997 PM2,5 NAAQS may already be 

adequate to implement the 2006 24-hour PM2.5 NAAQS. Many of the required section 110(a)(1) 

and 1 I 0(a)(2) SIP elements relate to the general information and authorities that constitute the 

"infrastructure" of a state's air quality management program, and these have been in place since 

the initial SIPs were submitted in response to the - 1970 Clean Air Act. However, it is still the 

responsibility of each state to make this determination for each new or revised NAAQS. 

Determinin;" Completeness of State Submittals 

As required by section 110(a)(1), states will have to review and revise, as appropriate, 

their existing particulate matter SIPs to ensure that they are adequate to address the 2006 24-hour 

PM2,5 NAAQS. States should, in consultation with EPA Regional Offices, refer to applicable 

EPA regulations governing SIP subznittals in 40 CFR Part 51 — e.g., Subpart H("Prevention of 

' Although the rule for the revised PM2. 5standard has an effective date of Deceinber 18, 2006, the rule was signed 

by the Administi•ator and publically disseininated on Septeniber 21, 2006. Tlierefore, the deadline for submittal of 

110(a) SIPs for the 2006 24-hour PM2. 5NAAQS is Septeinber 21, 2009 based on the signature date. 

Intemet Address (URL) • http://www.epa.gov 

Recycled/Recyclable . Printed wfth Vegetable Oil Based Inks on Recycled Paper (Minimum 25% Postconsumer) 
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Air Pollution Emergency Episodes"), Subpart I("Review of New Sources and Modifcations"), 

Subpart J(Ainbient Air Quality Surveillance), Subpart K(Source Surveillance), Subpart L. 

(Legal Authority), Subpart M("Intergovernmental Consultation"), Subpart O(Miscellaneous 

Plan Content Requirements), Subpart P("Protection of Visibility"), and Subpart Q("Reports"). 

If a state determines that its existing SIP is adequate, then the state needs to certify through a SIP 

subinittal (e.g., a letter to the Agency fi -om the Governor orhis/her designee) that demonstrates 

the existing SIP contains provisions addressing all requirements of the seetion 110(a)(2) 

infrastructure elements as applicable for the 2006 24-hour PM2.5 NAAQS. For purposes of the 

2006 24-hour PM2.5 NAAQS, in cases where a state believes that it meets the requirements of 

sections I 10(a)(1) anci 110(a)(2) without further revision of its SIP, EPA believes it is 

appropriate for the statc to submit a certification letter without holding an additional public 

hearing. Because prior submissions for infrastructurc requirements will have met the statutory 

requirements for notice and public hearing, EPA believes that such process is not required now. 

The public will have an oppoitunity to review the ceitifcation when EPA takes action on the 

submittal through the notice-and-eomment rulemaking process. 

In order for EPA to determine that a submittal for a SIP is complete, the submittal must 

affirmatively address all required eleinents/sub-elements, and should include docuinentation 

deinonstr•ating a correspondence betweez each infrastrueture element and an equivalent state 

statutoiy or regulatoiy authority in the existing or subnlitted SIP. At a minimum, a complete 

submission is a letter from an appropriate state official (i.e., Governor or designee) certifying 

compliance with each element and with a specific description of how compliance with each 

element is achieved. Submissions lacking a detailed explanation for how the state's SIP ineets 

each applicable requirement of section I 10(a)(2) should be deemed incomplete. Subinissions 

that address some but not all elements/sub-elements should not be deemed complete for the 

unaddressed elements/sub-elements, but will result in findings of failure to submit for only the 

unaddressed elements/sub-elements. After EPA makes a finding of failure to submit, the state 

would only be requu•ed to submit those elements that were found not to have been subinitted in 

order for EPA to make a determination that the SIP is fully complete. Letters stating that the 

state will submit a SIP revision some tiine in the i'uture are not complete. 

A finding that the submittal is complete does not niean that the submittal is approvable 

because the cotnpleteness review only addresses whether the state has provided information 

suffieient to warrant formal EPA review for approvability. Once EPA determines a SIP 

submission to be cornplete , or after six inonths when that submission is deemed conlplete by 

operation of law, EPA has up to 1 year to take action on (,i.e., to approve or disapprove) the 

submission. EPA must proinulgate a Federal Implementation Plan (FIP) for the state if EPA 

takes any ofthe following final actions associated with the required SIP: (1) determines that a 

state has failed to make a SIP submission, (2) deterinines that a state has made an ineomplete 

submission, or (3) disapproves a SIP submission. Any ofthese actions starts a two year FIP 

clock. In order to stop or rescind a FIP, the state must subinit, and EPA must approve, a SIP 

submission that mects the applicable requirements. 
Guidance for Satisfying the Section 110(a)(2)(D) Reguirement 

Cotnpliance with CAA section 110(a)(2)(D) requires that states address 4 separate 

elements. 

1. SIP Submi'ssions from States pertaining to the "significant contribution" 

requirenient of section 110(a)(2)(D)(i). 

Section I 10(a)(2)(D)(i)(I) specifically provides that each state's SIP must contain 

adequate provisions to prohibit ain• pollutant emissions from within the state that signifieantly 

contribute to nonattainment ofthe NAAQS in any other state. Tlierefore, the state's subinission 

must explain wliether or not emissions from the state have this impact and, if so, address the 

impact. 

The state's conclusion must be suppotted by an adequate technical analysis. Information to 

support the state's determination with respect to significant contribution to nonattainment inight 

include, but is not limited to, information eoncerning etnissions in the state, tneteorological 

conditions in the state and the potentially irnpacted states, monitored ambient concentrations in 

the state and the potentially impacted states, the distance to the nearest area that is not attainiug 

the NAAQS in another state, and air quality inodeling. The EPA believes that it would be 

appropriate for states to tnake this assessment by considering the impact of current or futurc 

emissions on nearby nonattainment areas, and evaluating the air quality impact and potential 

initigation strategies. 2 Using these kinds of evaluations, it is EPA's intention to complete a rule 

to address interstate pollution transpott in the eastern half of the continental United States. 

PPA is currently working on a new rule to replace the CAIR rule that will address issues 

raised by the court in North Carolina v. EPA, 531 P.3d 896 (D.C. Cir. 2008). That new rule will 

assist states with obligations to address interstate transport that significantly contributes to 

nonattainment in another state. However, all states inust submit cotnplete I] 0 SIPs at this time 

that address the requiretnents of section 110(a)(2)(D) fbr the 2006 24-hour PM2.s NAAQS, and 

states eannot wait for the CAIR replacement rule without getting a finding of failure to submit at 

this time. In addition, even if the CAIR rule were not remanded by the court, states cannot rely 

on the current CAIR rule for this submission for the 2006 24-hour PM2.5 NAAQS because the 

CAIR rule does not address this NAAQS. 

2. SIP Submissions from States pertaining to the "interfere with inaintenance" 

requirement of section 110(a)(2)(D)(i). 

Section 110(a)(2)(D)(i)(I) specifically provides that eaclt state's SIP must contain 

adequate provisions to prohibit air pollutant emissions fTom within the state that intertere with 

inaintenance of the NAAQS in any other state. States' submissions tnust address this 

indepeudent requircment of the statute. This provision requires evaluation of impacts on areas of 

other states that are meeting the 2006 24-hour PM2.S NAAQS, not merely areas formerly 

2If assessing ftrture emissions the state should attempt to represent a fiiture year d at is no furtlier in the future t'han 

thc year in which attainnrent of the NAAQS is required in the downwind state. In most cases we expect the 

attainment date to be no later than 5 years front tbc date of nonattaimnent designations. Since designations are 

expected to be issued in 2009, the maxiniwn attaimnent date would be 2014. 
designated nonattainment that are subject to a maintenanoe SIP. Therefore, the state's 

submission must explain whether or not emissions fi ~ om the state have tliis impact and, if so, 

address the iinpact. 

A state's subinission for this requirement sliould provide the technical information which the 

state deems appropriate to support its conclusions. Suitable infonnation might include, but is not 

limited to, information concerning emissions in the state, iineteorological conditions in the state 

and the potentially impacted states, monitored ambient concentrations in the state and the 

potentially impacted states, and air quality modeling. 

Using these kinds of evaluations, it is EPA's intention to coinplete a rule to address interstate 

pollution transpoil in the eastern half ofthe continental United States. However, all states must 

submit complete 110 SIPs at this time that address the requirements of section 110(a)(2)(D) for 

the 2006 24-hour PMz,s NAAQS and states camiot wait for the CAIR replacement rule without 

getting a finding of failure to submit at this tiine. 

3. SII' submissions pertaining to the "prevention of significant deterim•ation" 

requirement of section I10(a)(2)(D)(i). 

Section 110(a)(2)(D)(i)(II) contains a requirement tor all states to submit S1Ps that 

contain adequate provisions prohibiting ".... any source or other type of emission activity within 

the state fToin emitting any air pollutant in amounts whicli will interfere with measures required 

to be included in the applicable implementation plan for any other state ....to prevent signifcant 

deterioration of air quality ..." 

EPA believes this requirement is satisfied for PM2.5 if a state's SIP includes 

preconstruction review prograins for major sources that satisfy the requirements of 40 CPR 

51.165(b)(1) and 40 CPR 51.166 (i.e., New Source 12eview for major stationary sources locating 

in attainment areas when the source w'rll cause or contribute to a violation of the NAAQS, and 

Prevention of Significant Deterioration (PSD), respectively). tJnless the area lias known 

outstanding permit prograin deficiencies, it is not necessary, at this time, for states to make a SIF 

subinission containing rule changes specifically to addre,ss section I 10(a)(2)(D)(i)(II) for the 

2006 24-hour PM2s NAAQS. Ifthis is the case, thc state_cari submit an appiropriate cerCification 

as described previously in this guidance. 

All areas are currently required to have some form of preconstruction permitting program 

for PMz.s.- This program may include a transitional program or a program that conforms with the 

minimuin requirements of EPA's May 2008 final rule on implementation of the NSR program 

for PM2.5• 73 P'ed. Reg. 28321. In this action, EPA issued new final rules for certain 

components of PMz.s preconstruction permitting prograins for attannnent and iionattaininent 

areas. States are currently require,d to revise their preconstruction review permit programs to 

incorporate these new rcquirements into an approved SIP by May 2011. However, this provision 

under the May 2008 rules has been challenged and is now under a petition for reconsideration 

whereby EPA has agreed to reconsider the schedule for revising state PSD programs for PM2.5. 

Accordingly, E'PA may revise the schedule for submitting tlle revised PSD SIPs for EPA 

approval. For the present time, however, the deadline for adopting anci submitting PM2.5 SIPs for 

NSR/PSD is May 2011. Thus, states are not required to adopt the May 2008 rules for the 
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purposes of satisfying the section I 10(a) SIP requirement by September 2009 and may rely 

instead on iinpleinenting a transitional prograin for PM2.5. For example, the state's PSD program 

would satisfy the requuements of 40 CFR 51.166 at this time if the applicable rule defines the 

pollutants subject to regulation, e.g., "regulated NSR pollutant," in such way as to automatically 

include any new NAAQS, e.g., 24-hour PM2. sNAAQS, that EPA inay proinulgate. 

States witli PSD FIPs in place generally are required under a delegation agreeinent witli 

EPA to implement PSD in accordance with the federal PSD program, which provides for the 

automatic protection of any new NAAQS that EPA may promulgate. "Fhese states must ensure 

that their delegation agreement clearly authorizes them to implemezt the federal PSD prograin 

requirements as ainended in May 2008. If a delegation agreement is deficient in this regard, the 

state should work with EPA to modify the agreement to enable implementation of PMz. s 

requirements. 

In addition to the PSD permitting prograin, a state's SIP may inelude additional measures 

as necessary to prevent air pollution in excess of the PSD inerenient that defines significant 

deterioration for each area. 40 CFR 51.166(a). However, EPA has not yet established PSD 

increments for PM2,5. Without these components of a PSD program, it is difficult for states to 

detei•mine if additional measures are needed to prevent significant deterioration within the state. 

Likewise, a neighboring state cannot detennine whether its SIP would interfere with such 

additional measures in another state's SIP. However, notwithstanding the absence ofPSD 

increments for PM2.s> EPA believes that at this time states may continue to rely on their existing 

PSD and NNSR permitting programs to prevent significant deterioration of air quality within 

their own boundaries and in adjacent states until such inerements are established. 

4. SIP Submissions from States pertaining to the "protect visibility" requireinent of 

section 110(a)(2)(D)(i). 

Section 110(a)(2)(D)(i)(II) also contains a requirement for all states to submit SIPs that 

contain adequate provisions prohibiting "... any source or other type of emission activity within 

the state fi•om emitting any air pollutant in amounts whieh will interfere with measures required 

to be included in the applicable impleinentation plan for any other state ....to protect visibility." 

EPA believes this requiremcnt can be satisfied by an approvcd SIP addressiiig reasonably 

attributable visibility iinpairment (RAVI), if required, aiid an approved SIP addressing regional 

haze. EPA promulgated regulations in 1980 to address RAVI in Class I areas that is caused by 

the emissions of air pollutants fi•om one source, or a small number of sourees. See 45 FR 80084 

(December 2, 1980) and current 40 CFR 51.300 — 51.307. A state must take specified steps to 

address RAVI after a Federal Land Manager at any tiine certifies that I2AVI exists at a specific 

C1ass 1 Area. 40 CFR 51.302(c)(1). 

Under the 1980 regulations, 35 states and the U.S. Virgin Islands were required to subinit 

SIPs to address RAVI. EPA issued FIPs to address the requirements of RAVI for those states 

that had failed to submit SIPs. See 50 FR 28544 (July 12, 1985) and 52 FR 45132 (November 

24, 1987). EPA is not aware of any certification by a Federal Land Manager of existing RAVI 

that remains unaddressed by a currently approved SIP or FIP. Accordingly, we believe that 

states for which EPA has approved into the state's current SIP soine or all RAVI eleinents, 
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should be able to make a relatively simple SII' submission verifying that no source within the 

state emits pollutants that interfere with RAVI measures included in the applicable 

implementation plan (SIP or FIP) of any other state. As noted above for PSD, those states 

having full or partial FIPs in place will not satisfy the indtpendent section 110(a)(2)(D)(i)(II) 

requirement unless they submit, and EPA apptroves into the SIP, all required RAVI eleuients. 

In 1999, EPA issued regulations requiring states to address regional liaze impacting 

visibility in Class I areas. See 64 FR 35714 (July 1, 1999) and eurrent 40 CFR 51.308 - 51.309. 

Regional haze is visibility impairment that is produced by a multitude of sources and activities 

which emit visibility-impairing pollutants and their precuisors and which are loeated across a 

broad geographic area. States are currently under an obligation to subinit SIPs that cwntain 

measures to address regional haze, including a long-term strategy to address visibility 

impairment for eacli Class I area which may be affected by emissions from a state. These SIP 

submissions were due on December 17, 2007. In January 2009, EPA found that 37 states, the 

District of Columbia, and the U.S. Virgin Islands had failed to inake all or pati ofthe required 

SIP submissions to address regional haze. See 74 FR 2392 (January 15, 2009). These findings 

require EPA to issue FIPs within 2 years, by January, 2011, unless the states subtnit SIPs and 

EPA approves them before that date. States that intend to rely on the required regional haze SIPs 

to satisfy this element of their section 110(a) SIP but have not formally indicated this intention in 

a SIP submission, or have not yet submitted the regional haze SIP, may receive an additional 

finding of failure to submit this element of thein• section I 10(a) SIP. EPA will be able to fully 

approve the submittal as satisfying section I I 0(a)(2)(D)(i)(II) only after we have taken fmal 

action approving tlie regional hazc SIP. 

Guidance for Satisfying the Section 110(a)(2)(G) Reguirement 

To address the section I I0(a)(2)(G) element, states with air quality control regions 

identified as either Priority I, Priority IA, or Priority II by the "Prevention of Air Pollution 

Emergency Episodes" rules at 40 CFR 51.150, inust develop emergency episode contingency 

plans. Currently, those regulations do not specifically address PM2,5. 

Until the Agency t7nalizes chauges to the emergency episode regulations to establish for 

PMz,sspecific levels for classifying areas as Priority I, IA, and 11 for PMz, s, and to establish a 

significant harin level (SHL), EPA recommends that states through their publ'rc processes set 

Priority levels and emergency action levels for PM2.5 necessary to develop emergency episode 

plans consistent witli the requireinents in 40 CFR 51.150 through 51.153. We furfher 

recoinmend that states consider the levels discussed in the February 12, 2007 EPA issue paper 

titled "Revising the Air Quality Index and Settuig a Significant Harm Level for PMz,s" and to 

Attaclnnent B to this guidanee in establishing Priority levels and etnergency action levels, 

including a SHL. 3Using the recommendations in Attachinent B, for the purposes of satisfying 

the requirements of section 110(a)(2)(G), states would develop emergency episode ~}~ lans fot-any 

area that has monitored and recorded 24-hour PMz, slevels greater than 140.4 μg/rn since 2006. 

If this level was never exceeded in any area of the state, flle state can certify that it has 

appropriate general emergency powers to address PM2.s-related episodes, and that no specific 

3 "llie issue paper can be fouud at http://www.epa.gov/ttn/caaa/gen/agi issue paper 020707.pdf 
emergeney episodc plans are necessary at this time, given the existing inonitored levels." States 

should develop submissions to meet this requirement througli appropriate public processes. 

In submittals addressing the 1997 PM2_5 NAAQS, several states committed to make SIP 

submittals addressing section 110(a)(2)(G) only afl er EI'A completed a rulemaking to establish a 

SHL for PM2.5. We understand the motivation for taking this approach, and EPA is working to 

complete this rulemaking. Nevetiheless, under section 110(k)(1)(B), EPA cannot find such 

subtnittals to be complete. It is for this reason that EPA is providing the recommendations in this 

memorandum as guidance for states to tnake submittals to address section I 10(a)(2)(G). The 

SHL, Priority levels, and emergency action levels recotnmended in Attachment B are relevant 

for both the 1997 PMz,s NAAQS and the 2006 PM2s NAAQS. If a state elects not to make a 

submittal that addresses section 110(a)(2)(G) for the 2006 24-hour PM2.5 NAAQS in accordance 

with the Agency's recoimnendations or otherwise meeting the statutory requirements, EPA will 

have reason to inake a finding of failure to submit for this NAAQS. 

For Further Information 

If you have any questions concerning thisguidance, please contact David Sanderg at 

(919) 541-3356. Please ensure that the appropriate air agency officials for states in your Region 

are made aware ofthis guidance. 

Attachments 

cc: Br•ian McLean, OAP 

Kevin McLean, OGC 

Margo Oge, OTAQ 

Steve Page, OAQPS 

Peter Tsirigotis, OAQPS 

Richard Wayland, OAQPS 

Lydia Wegman, OAQPS 

° Under these conditions the contingency plan portion of section 110(a)(2)(G) for the 1997 PMz. sNAAQS, for 

which wc issued a Gntiing for failttre to subnait in Oetober 2008, may also be resolved (73 PR 62902). 
Attachment A: Required Section 110 "Infrastructure" SIP Elements s 

Section 110(a)(2)(A) - Emission limits and other control measures: requires SIPs to include 

enforceable etnission lirnits and other control measures, rneans, or techniques, and sclieclules for 

compliance. 

Section 110(a)(2)($) - Atnbient air quality monitoring/data system: requires SIPs to provide 

for establishment and operation of ambient air quality inonitors, collection and analysis of 

ambient air quality data, and to make these data available to EPA upon request. 

Sectiott 110(a)(2)(C) - Program for enforcement of control meastn•es: requu•es SIPs to 

inelude a progratn providing for enforcement of all SIP measures and the regulation of 

construction of new and modified stationary sources as necessary to assure that the NAAQS are 

achieved, including a permit program as required in parts C and D. 

Section 110(a)(2)(D) — Interstate transport provisions: requires SIPs to contain adequate 

provisions prohibiting emissions generated within the state fi•om contributing significantly to 

nonattainment in, or interfering with maititenance by, any other state with respect to the 

NAAQS, or from interfering with measures requu•ed to be included in the SIP of any other state 

to prevent significant deterioration or to protect visibility: 

Section 110(a)(2)(E) - Adequate resources: requires SIPs to providc necessary assurances for 

adequate personnel, funding, and authority under state law to earry out its SIP, to contain 

requirements addressing potential conflicts of interest, and to provide necessary assurances that 

the state retains responsibility Ibr ensuring adequate implementation of the SIP whcre the state 

relies on a local or regional government for implementation of any SIP provision. 

Seetion 110(a)(2)(F) - Stat'ronary source monitoring system: requires SIPs to establish a 

system to monitor emissions from stationary sources, to submit periodic etnissions repotls, to 

correlate the emissions reports with the corresponding SIP emission litnits and statidards, aud to 

make emissions reports available to the public. 

Section 110(a)(2)(G) - Emergency episodes: requires SIPs to provide for authority to address 

activities causing imminent and substantial endangerment to public health and to provide for 

adequate contingency plans to itnplement such authority. 

Section 110(a)(2)(I3) - Future SIP revisions: requires SIPs to provide for SIP revisions in 

response to changes in the NAAQS, or availability of improved metliods for attaining the 

NAAQS, and in response to an EPA finding that the SIP is substantially inadequate. 

Section 110(a)(2)(J) - Consultation with govertmtent officials, public notitication, PSD and 

visibility protection: requires states to provide a process for consultation with local 

governments and Federal Land Managers carrying out NAAQS implementation requiremcnts; 

sThe specific nonttainment area plan requirements of sections 110(a)(2)(C) and 110(a)(2)(I) are subject to the 

timing requirenient of section 172, not the timing requireinent of section I 10(a)(1), and therefore not considered 

required elements of the "infrastructure SIP." 
requires SIPs to notify the public if NAAQS are exceeded in an area and to enhance public 

awareness of ineasures that can be taken to prevent exceedances; and requires SIPs to meet 

applicable requirements ofpart C related to prevention of significant deterioration and visibility 

protection. 

Section 110(a)(2)(K) - Air quality modeling/data: requires S1Ps to provide for the performance 

of air quality modeling for predicting effects on air quality of emissions of any NAAQS pollutant 

and the submission of sucll data to EPA upon request. 

Seetion I10(a)(2)(L) - Permitting fees: requires SIPs to require eacli major stationary source to 

pay permitting fees to cover the cost ofreviewing, acting upon, implementing and enforcing a 

permit until such fee requiretnent is superseded by EI'A approval of a fee prograin under title V 

of the Clean Air Act. 

Section 110(a)(2)(M) - Consultation/participation by affected local entities: r -equn-es SIPs to 

provide for consultation and participation in SIP development by local political subdivisions 

affeeted by the SIP. 
Attachment B: Recommended htterim Significant Tlarm Level, Priority Levels, and Action 

Levels for PM2,5 Emergency Episode Plans (EEPs) 

Current AQI - PMzs AQI Under Recommended Recommended Consideration - 

24-hour 

EEP Priority 

Region EEP Action 

Index 24-hour Average Classification Level k ~ Category Values Avera e (μg~ma)t ~ ( μ~m) 

Good 0-50 0.0-15.4 0.0-15.4 

Moderate 51-100 15.5-40.4 15.5-35.4 

tJnhealthy for 

Sensitive Groups 101-150 40.5-65.4 35.5-55.4 

Unhealthy 151-200 65.5-150.4 55.5-140.4 

Very Unhealthy 201-300 150.5-250.4 140.5-210.4 Priority Level ll Alert 

I3azardous 1 301-400 250.5-350.4 210.5-280.4 Priority Level Warning I and IA 

Hazarcious 2 401-500 350.5-500 280.5-350.4 Emergency 

Significant Harm Level (SHL) 350.5 

j' For a discussion of possible revisions to the AQI and SHL, see the EPA issue paper found 

athttp;i/www.eha._gpy/ttn/caai/g n/adi nsuc_oa?cr,02Q707Rdf 

* Based on historical incidence of 24-hour average concentrations using the most recent 3 

calendar years ofdata. 

** See 40 CFR.Part 51 Appendix L"Exarnple Regulations for Prevention ofAir Pollution 

Einergency Episodes" for an example of the application of enlergency action levels.