2

 3 Dr. Shao-Hang Chu's paper entitled "Critical Design Value and Its Applications" explains the CDV approach and is

included in its entirety in Attachment A. This paper has been accepted for publication and presentation at the 94th Air and

Waste Management Association (A&WMA) Annual Conference in June 2001 in Orlando, Florida.

we were prepared to make case-by-case determinations that would make the 1987 PM10 NAAQS

no longer applicable in any area meeting the standards. In taking actions to remove the

applicability of the 1987 NAAQS, we would have removed, as well, the nonattainment

designation and Clean Air Act (CAA) part D requirements from qualifying areas. As a result of

the D.C. Circuit’s decision, for areas subject to the 1987 NAAQS, the only route to recognized

attainment of the NAAQS and removal of nonattainment status and requirements is formal

redesignation to attainment, including submittal of a maintenance plan. Since many areas have

been meeting the PM10 NAAQS for 5 years or more and have a low risk of future exceedances,

we believe a policy that would allow both the States and EPA to redesignate speedily areas that

are at little risk of PM10 violations would be useful. 

III. How did EPA develop the approach used in the LMP option?

The EPA has studied PM10 air quality data information for the entire country over the

past eleven years (1989-1999) and has determined that some moderate PM10 nonattainment areas

have had a history of low PM10 design values with very little inter-annual variation. When we

looked at all the monitoring sites reporting data for those years, the data indicate that most of the

average design values fall below 2 levels, 98 :g/m3 for the 24-hr PM10 NAAQS and 40 :g/m3

for the annual PM10 NAAQS. For most monitoring sites these levels are also below their

individual site-specific critical design values (CDV). The CDV is an indicator of the likelihood

of future violations of the NAAQS given the current average design value and its variability. 

The CDV is the highest average design value an area could have before it may experience a

future exceedance of the NAAQS with a certain probability. A detailed explanation of the CDV

is found in Attachment A3 to this policy which, because of its length, is a separate document

accompanying this memorandum. 

We believe that the very small amount of variation between the peaks and means in most

of the data indicates a very stable relationship that can be reasonably expected to continue in the

future absent any significant changes in emissions. The period we assessed provides a fairly

long historical record and the data could therefore be expected to have been affected by a full

range of meteorological conditions over the period. Therefore, the amount of emissions should

be the only variable that could affect the stability in the air quality data. We believe we can

reliably make estimates about the future variability of PM10 concentrations across the country

based on our statistical analysis of this data record, especially in areas where the amount of

emissions is not expected to change. 

IV. How do I qualify for the LMP option ?

To qualify for the limited maintenance plan option, an area should meet the following 

applicability criteria. The area should be attaining the NAAQS and the average PM10 design
3

 4The methods for calculating design values for PM10 are presented in a document entitled the “PM10 SIP Development

Guideline”, EPA-450/2-86-001, June 1987. The State should determine the most appropriate method to use from this Guideline

in consultation with the appropriate EPA Regional office staff.

 5If the EPA determines that the meteorology was not representative during the most recent five-year period, we may

reject the State’s request to use the LMP option and request, instead, submission of a full maintenance demonstration.

value4 for the area, based upon the most recent 5 years of air quality data at all monitors in the

area, should be at or below 40 :g/m3 for the annual and 98 :g/m3 for the 24-hr PM10 NAAQS

with no violations at any monitor in the nonattainment area5. If an area cannot meet this test it

may still be able to qualify for the LMP option if the average design values of the site are less

than their respective site-specific CDV. 

We believe it is appropriate to offer this second method of qualifying for the LMP

because, based on the air quality data we have studied, we believe there are some monitoring

sites with average design values above 40 :g/m3 or 98 :g/m3, depending on the NAAQS in

question, that have experienced little variability in the data over the years. When the CDV

calculation was performed for these sites we discovered that their average design values are less

than their CDVs, indicating that the areas have a very low probability (1 in 10) of exceeding the

NAAQS in the future. We believe it is appropriate to provide these areas the opportunity to

qualify for the LMP in this circumstance since the 40 :g/m3

 or 98 :g/m3 criteria are based on a

national analysis and don’t take into account each local situation.

The final criterion is related to mobile source emissions. The area should expect only

limited growth in on-road motor vehicle PM10 emissions (including fugitive dust) and should

have passed a motor vehicle regional emissions analysis test. It is important to consider the

impact of future transportation growth in the LMP, since the level of PM-10 emissions

(especially from fugitive dust) is related to the level of growth in vehicle miles traveled (VMT).

Attachment B (below) should be used for making the motor vehicle regional emissions analysis

demonstration. 

If the State determines that the area in question meets the above criteria, it may select the

LMP option for the first 10 year maintenance period. Any area that does not meet these criteria

should plan to submit a full maintenance plan that is consistent with our guidance in the Calcagni

Memo in order to be redesignated to attainment. If the LMP option is selected, the State should

continue to meet the qualifying criteria until EPA has redesignated the area to attainment. If an

area no longer qualifies for the LMP option because a change in air quality affects the average

design values before the redesignation takes effect, the area will be expected to submit a full

maintenance plan. 

Once an area selects the LMP option and it is in effect, the State will be expected to

recalculate the average design value for the area annually and determine if the criteria used to

qualify for the LMP will still be met. If, after performing the annual recalculation of the area’s

average design value in a given year, the State determines that the area no longer qualifies for the

LMP, the State should take action to attempt to reduce PM10 concentrations enough to requalify

for the LMP. One possible approach the State could take is to implement a contingency measure
4

or measures found in its SIP. If, in the next annual recalculation the State is able to re-qualify

for the LMP, then the LMP will go back into effect. If the attempt to reduce PM10 concentrations

fails, or if it succeeds but in future years it becomes necessary again to address increasing PM10

concentrations in the area, that area no longer qualifies for the LMP. We believe that repeated

increases in PM10 concentrations indicate that the initial conditions that govern air quality and

that were relied on to determine the area’s qualification for the LMP have changed, and that

maintenance of the NAAQS can no longer be assumed. Therefore, the LMP cannot be reinstated

by further recalculations of the design values at this point. Once the LMP is determined to no

longer be in effect, a full maintenance plan should be developed and submitted within 18 months

of the determination. 

Treatment of data used to calculate the design values.

Flagged Particulate Matter Data:

Three policies allow PM-10 data to be flagged for special consideration:

 

• Exceptional Events Policy (1986) for data affected by infrequent

events such as industrial accidents or structural fires near a

monitoring site;

• Natural Events Policy (1996) for data affected by wildfires, high

winds, and volcanic and seismic activities, and;

• Interim Air Quality Policy on Wildland and Prescribed Fires for

data affected by wildland fires that are managed to achieve

resource benefits.

We will treat data affected by these events consistently with these

previously-issued policies. We expect States to consider all data

(unflagged and flagged) when determining the design value. The EPA

Regional offices will work with the State to determine the validity of

flagged data. Flagged data may be excluded on a case-by-case basis

depending on State documentation of the circumstances justifying flags. 

Data flagged as affected by exceptional or natural events will generally

not be used when determining the design value. However, in order for

data affected by a natural event to be excluded, an adequate Natural

Events Action Plan is required as described in the Natural Events policy.

Data flagged as affected by wildland and prescribed fires will be used in

determining the design value. If the State is addressing wildland and

prescribed fire use with the application of smoke management programs,

the State may submit an LMP if the design value is too high only as a

result of the fire-affected data.

We are in the process of developing a policy to address agricultural

burning. When it is finalized we will amend the LMP option to account
5

for the new policy. 

V. What should an LMP consist of?

Under the LMP, we will continue to satisfy the requirements of Section 107(d)(3)(E) of

the Act which provides that a nonattainment area can be redesignated to attainment only if the

following criteria are met:

1. The EPA has determined that the NAAQS for the applicable pollutant has been 

attained.

2. The EPA has fully approved the applicable implementation plan under section

110(k).

3. The EPA has determined that the improvement in air quality is due to permanent 

and enforceable reductions in emissions.

4. The State has met all applicable requirements for the area under section 110 and 

part D.

5. The EPA has fully approved a maintenance plan, including a contingency plan, 

for the area under section 175A.

However, there are some differences between what our previous guidance (the Calcagni

memo) recommends that States include in a maintenance plan submission and what we are

recommending under this policy for areas that qualify for the LMP. The most important

difference is that under the LMP the demonstration of maintenance is presumed to be satisfied. 

The following is a list of core provisions which should be included in an LMP submission. Note

that any final EPA determination regarding the adequacy of an LMP will be made following

review of the plan submitted in light of the particular circumstances facing the area proposed for

redesignation and based upon all available information.

a. Attainment Plan

The State’s approved attainment plan should include an emissions inventory (attainment

inventory) which can be used to demonstrate attainment of the NAAQS. The inventory should

represent emissions during the same five-year period associated with the air quality data used to

determine whether the area meets the applicability requirements of this policy (i.e., the most

recent five years of air quality data). If the attainment inventory year is not one of the most

recent five years, but the State can show that the attainment inventory did not change

significantly during that five-year period, it may still be used to satisfy the policy. If the

attainment inventory is determined to not be representative of the most recent 5 years, a new

inventory must be developed. The State should review its inventory every three years to ensure

emissions growth is incorporated in the attainment inventory if necessary. 

b. Maintenance Demonstration 

The maintenance demonstration requirement of the Act will be considered to be satisfied

for the moderate PM10 nonattainment areas meeting the air quality criteria discussed above. If
6

the tests described in Section IV are met, we will treat that as a demonstration that the area will

maintain the NAAQS. Consequently, there is no need to project emissions over the maintenance

period. 

c. Important elements that should be contained within the redesignation request

1. Monitoring Network Verification of Continued Attainment

To verify the attainment status of the area over the maintenance period,

the maintenance plan should contain a provision to assure continued

operation of an appropriate, EPA-approved air quality monitoring

network, in accordance with 40 CFR part 58. This is particularly

important for areas using an LMP because there will be no cap on

emissions.

2. Contingency Plan

Section 175A of the Act states that a maintenance plan must include

contingency provisions, as necessary, to promptly correct any violation of

the NAAQS which may occur after redesignation of the area to

attainment. These contingency measures do not have to be fully adopted

at the time of redesignation. However, the contingency plan is considered

to be an enforceable part of the SIP and the State should ensure that the

contingency measures are adopted as soon as possible once they are

triggered by a specific event. The contingency plan should identify the

measures to be adopted, and provide a schedule and procedure for

adoption and implementation of the measures if they are required. 

Normally, the implementation of contingency measures is triggered by a

violation of the NAAQS but the State may wish to establish other triggers 

to prevent a violation of the NAAQS, such as an exceedance of the

NAAQS.
7

3. Approved attainment plan and section 110 and part D CAA requirements:

In accordance with the CAA, areas seeking to be redesignated to

attainment under the LMP policy must have an attainment plan that has

been approved by EPA, pursuant to section 107(d)(3)(E). The plan must

include all control measures that were relied on by the State to

demonstrate attainment of the NAAQS. The State must also ensure that

the CAA requirements for PM10 pursuant to section 110 and part D of the

Act have been satisfied. To comply with the statute, the LMP should

clearly indicate that all controls that were relied on to demonstrate

attainment will remain in place. If a State wishes to roll back or eliminate

controls, the area can no longer qualify for the LMP and the area will

become subject to full maintenance plan requirements within 18 months of

the determination that the LMP is no longer in effect.

V. How is Conformity treated under the LMP option?

The transportation conformity rule (40 CFR parts 51 and 93) and the general conformity

rule (58 FR 63214; November 30, 1993) apply to nonattainment areas and maintenance areas

operating under maintenance plans. Under either conformity rule one means of demonstrating

conformity of Federal actions is to indicate that expected emissions from planned actions are

consistent with the emissions budget for the area. Emissions budgets in LMP areas may be

treated as essentially not constraining for the length of the maintenance period because it is

unreasonable to expect that an area satisfying the LMP criteria will experience so much growth

during that period of time such that a violation of the PM10 NAAQS would result. While this

policy does not exempt an area from the need to affirm conformity, it does allow the area to

demonstrate conformity without undertaking certain requirements of these rules. For

transportation conformity purposes, EPA would be concluding that emissions in these areas need

not be capped for the maintenance period, and, therefore, a regional emissions analysis would

not be required. Similarly, Federal actions subject to the general conformity rule could be

considered to satisfy the “budget test” specified in section 93.158 (a)(5)(i)(A) of the rule, for the

same reasons that the budgets are essentially considered to be unlimited.

EPA approval of an LMP will provide that if the LMP criteria are no longer satisfied and 

a full maintenance plan must be developed to meet CAA requirements (see Calcagni Memo

referenced in footnote #2 for full maintenance plan guidance), the approval of the LMP would

remain applicable for conformity purposes only until the full maintenance plan is submitted and

EPA has found its motor vehicle emissions budgets adequate for conformity purposes under 40

CFR parts 51 and 93. EPA will condition its approval of all LMPs in this fashion because in the

case where the LMP criteria are not met and a full maintenance plan is required EPA believes

that LMPs would no longer be an appropriate mechanism for assuring maintenance of the

standards.

For further information concerning the LMP option for moderate PM10 areas please
8

contact Gary Blais at (919) 541-3223, or for questions about the CDV approach contact Dr.

Shao-Hang Chu at (919) 541-5382. For information concerning transportation conformity

requirements, please contact Meg Patulski of the Office of Transportation and Air Quality at

(734) 214-4842. 
9

OAQPS/AQSSD/IPSG:GBlais:NPerry,x5628

G:\user\share\nrpfiles\wpfiles\beal\LMP.wpd
ATTACHMENT B: 

MOTOR VEHICLE REGIONAL ANALYSIS METHODOLOGY

The following methodology is used to determine whether increased emissions from on-road

mobile sources could, in the next 10 years, increase concentrations in the area and threaten the

assumption of maintenance that underlies the LMP policy. This analysis must be submitted and

approved in order to be eligible for the LMP option.

The following equation should be used:

DV + (VMTpi x DVmv) # MOS

Where:

DV = the area’s design value based on the most recent 5 years of quality

assured data in :g/m3

 VMTpi= the projected % increase in vehicle miles traveled (VMT) over the

next 10 years

DVmv = motor vehicle design value based on on-road mobile portion of the

attainment year inventory in :g/m3

MOS = margin of safety for the relevant PM-10 standard for a given area: 

40 :g/m3

 for the annual standard or 98 :g/m3 for the 24-hour

standard 

Please note that DVmv is derived by multiplying DV by the percentage of the attainment year

inventory represented by on-road mobile sources. This variable should be based on both primary

and secondary PM10 emissions of the on-road mobile portion of the attainment year inventory,

including re-entrained road dust.

States should consult with EPA regarding the three inputs used in the above calculation, and all

EPA comments and concerns regarding inputs and results should be addressed prior to

submitting a limited maintenance plan and redesignation request. 

The VMT growth rate (VMTpi) should be calculated through the following methods:

1) an extrapolation of the most recent 10 years of Highway Performance Monitoring System

(HPMS) data over the 10-year period to be addressed by the limited maintenance plan; and 

2) a projection of VMT over the 10-year period that would be covered by the limited

maintenance plan, using whatever method is in practice in the area (if different than #1). 

Areas where method #1 is the current practice for calculating VMT do not also have to do

calculation #2, although this is encouraged. All other areas should use methods #1 and #2, and

VMTpi is whichever growth rate produced by methods #1 and #2 is highest. Areas will be

expected to use transportation models for method #2, if transportation models are available. 
2

Areas without transportation models should use reasonable professional practice. 

Examples

1. DV = 80 :g/m3

VMTpi = 36%

DVmv = 30 :g/m3

MOS = 98 :g/m3

 for 24-hour PM-10 standard

80 + (.36 * 30) = 91 

Less than 98 – Area passes regional analysis criterion.

2. DV = 35 :g/m3

VMTpi

= 25%

DVmv = 6 :g/m3

MOS = 40 :g/m3

 for annual PM-10 standard

35 + (.25 * 6) = 37 

Less than 40 – Area passes regional analysis criterion.

3. DV = 115 :g/m3

VMTpi

= 25%

DVmv = 60 :g/m3

MOS = 98 :g/m3

 for 24-hour PM-10 standard

115 + (.25 * 60) = 130

More than 98 – Area does not pass criterion. Full section 175A maintenance plan

required.