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2008 LEAD (Pb) NAAQS IMPLEMENTATION 

Questions and Answers

INFRASTRUCTURE STATE IMPLEMENTATION PLANS (SIPs)

1 Q. Are states required to submit “infrastructure SIPs” for the revised Lead national ambient 

air quality standards (NAAQS)?

A. Yes. Under section 110 of the Clean Air Act (CAA), all states (including those without any 

nonattainment areas) are required to submit infrastructure SIPs within three years of the 

promulgation of a new or revised NAAQS. Since the Lead NAAQS was signed and widely 

disseminated on October 15, 2008, the infrastructure SIPs are due by October 15, 2011. Among 

the requirements for an infrastructure SIP is a permit program implementing prevention of 

significant deterioration (PSD).

PREVENTION OF SIGNIFICANT DETERIORATION (PSD) AND NONATTAINMENT NEW SOURCE 

REVIEW (NSR)

2 Q. What are the requirements under the Prevention of Significant Deterioration (PSD) and 

nonattainment New Source Review (NSR) permitting programs for Lead?

A. The PSD program and nonattainment NSR programs are often referred to as the major NSR 

program because these programs regulate only major stationary sources. The PSD program 

applies when a major stationary source of any pollutant, located in an area designated as 

attainment or unclassifiable for any criteria pollutant, is constructed, or undergoes a major 

modification. The nonattainment NSR program applies when a major source of a criteria 

pollutant that is located in an area that is designated as nonattainment for that pollutant is 

constructed or undergoes a major modification. The major source threshold under the PSD 

program is generally either 100 or 250 tons per year (tpy) of any regulated NSR pollutant, 

depending upon whether the source is included within one of the categories of sources listed in 

the applicable PSD regulations (40 CFR 51.166(b)(1)(i)(a) or 52.21(b)(1)(i)(a)). The major source

threshold for Lead under the nonattainment NSR program is 100 tpy for all source categories. 

Accordingly, the nonattainment NSR program for Lead applies when any major source of Lead

located in an area designated nonattainment for Lead is constructed, or undergoes a major 

modification. Under both programs, a major modification is a project at a major stationary 

source that results in a significant emissions increase and a significant net emissions increase, 

where “significant” for Lead emissions is defined as 0.6 tpy. 

The PSD requirements include but are not limited to the following:
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• Installation of Best Available Control Technology (BACT);

• Air quality monitoring and modeling analyses to ensure that a project’s emissions will not 

cause or contribute to a violation of any NAAQS;

• Notification of Federal Land Manager of nearby Class I areas; and

• Public comment on a permit.

Nonattainment NSR requirements include but are not limited to:

• Installation of Lowest Achievable Emissions Rate (LAER) control technology;

• Offsetting new emissions with creditable emissions reductions;

• A certification that all major sources owned and operated in the state by the same owner are 

in compliance with all applicable requirements under the CAA;

• An alternatives analysis demonstrating that the benefits of the proposed source significantly 

outweigh the environmental and social costs imposed as a result of its location, construction, or 

modification; and

• Public comment on a permit.

SIP DEVELOPMENT 

3 Q. When are Lead attainment demonstration SIPs due?

A. Attainment demonstration SIPs are due eighteen months after the effective date of an 

area’s designation. For the first round of designations the attainment SIPs are due June 30, 

2012. For the second round of designations, the attainment SIPs are expected to be due 

June 30, 2013. 

4 Q. When is the attainment date?

A. Areas are required to attain the revised Lead standard as expeditiously as practicable, but no 

later than 5 years from the date the nonattainment designation became effective. The 

attainment date for the first round is December 31, 2015, and the attainment date for the 

second round is expected to be December 31, 2016. 

5 Q. How do you measure reasonable further progress (RFP) for Lead?

A. Demonstrating reasonable further progress requires adherence to an ambitious compliance 

schedule. The schedule is expected to provide for periodic yields in significant emissions 

reductions or linear progress when appropriate. The U. S. Environmental Protection Agency 

(EPA) recommends that SIPs for Lead nonattainment areas provide a detailed schedule for 

compliance of reasonably available control measures (RACM), including reasonably available 

control technology (RACT), and accurately indicate the corresponding annual emission 

reductions to be achieved. Expeditious implementation of RACM and RACT by the sources in 

the nonattainment areas helps to ensure attainment of the standard by the attainment date. 
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6 Q. How do you calculate the amount of emissions reduction necessary for contingency 

measures?

A. EPA thinks a reasonable guide to the amount of emissions reduction that a single measure 

or group of measures should achieve for contingency purposes would be equal to the amount 

represented by annual average RFP in the attainment plan. For example, if the attainment plan 

provides for 1 tpy of Lead reductions over a 5-year attainment horizon, the recommended 

target for contingency measures would be at least 0.2 tpy. Contingency measures should 

generally go into effect, when necessary, without significant action on the part of the state or 

EPA.

EPA recommends using the year of designation (either 2010 or 2011) as the base year for the 

contingency measure calculation. States may use another year if they show another year is 

more appropriate. For example, if complete emissions data for 2010 are not available, a state 

may wish to use emissions data from the 2008 periodic inventory. The basic formula is:

Annual average RFP = (Attainment level emissions – base year emissions (2010 or 2011)) ÷ 5,

where 5 is the number of years between the base year and attainment year (2015 or 2016).

Traditionally the amount of reductions required for contingency measures has been measured 

in terms of tpy reductions at a source. However, where a single source is responsible for 

nonattainment, it may be possible to identify the amount of reductions required by reference 

to reductions in ambient air concentrations (e.g., measures sufficient to reduce ambient air 

concentrations by 0.02 μg/m3

). EPA would need to evaluate the approvability of such an 

approach on a case-by-case basis based on the sources within the nonattainment area, the 

modeling used, and available control measures.

7 Q. Will the EPA approve a Lead SIP that contains triggers for early implementation of 

contingency measures?

A. Yes. If an attainment SIP relies on a specific set of control measures to demonstrate timely 

attainment of the NAAQS, then those control measures are considered necessary for 

attainment and are not contingency measures. A SIP must also contain additional control 

measures that must be implemented if an area fails to attain or fails to demonstrate RFP. (See 

General Preamble for the Implementation of Title I of the Clean Air Act Amendment of 1990, 

57 FR 13498, April 16, 1992). If a state elects to implement contingency measures earlier than 

would be triggered by such a failure, EPA does not believe that the state needs to adopt 

additional contingency measures to backfill for the early activation of those contingency 

measures. Of course, if an area fails to attain or fails to demonstrate RFP then additional

contingency measures are needed and must be adopted in accordance with previous guidance. 

(See ”Early Implementation of Contingency Measures for Ozone and Carbon Monoxide (CO) 

Nonattainment Areas,” G.T. Helms, August 13, 1993, available at

http://www.epa.gov/ttn/oarpg/t1pgm.html.
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8 Q. Are Lead nonattainment areas eligible for one-year attainment date extensions?

A. No. CAA, Subpart 1, Section 172(a)(2)(D) precludes the Administrator from granting 

attainment date extensions where the statute separately establishes a specific attainment date, 

such as the 5-year deadline established in section 192(a).

9 Q. In order to demonstrate attainment, when do control measures need to be operational?

A. Control measures for the 2008 NAAQS need to be in place as expeditiously as practicable. In 

order for control measures to result in three years of monitored clean data by the attainment 

date, areas designated in the first round of designations (effective December 31, 2010, and 

requiring attainment demonstrations that show that the area will attain the standard as 

expeditiously as practicable, but no later than December 31, 2015) would need to have all 

necessary controls in place no later than November 1, 2012, and the corresponding date for 

areas designated in the second round of designations is expected to be November 1, 2013. 

EPA will consider on a case-by-case basis the approvability of attainment demonstration SIPs 

where control measures are scheduled to be operational after November 1, 2012 / 

November 1, 2013. An attainment SIP may be approvable even if the state does not anticipate 

having 3 full years of clean data by the attainment date. See EDF v. EPA, 369 F.3d 193 (2d Cir. 

2004); Sierra Club v. EPA, 356 F3d 296 (D.C. Cir. 2004) amended 2004 WL 877850 (D.C. Cir. 

2004); available at:

2d Circuit case--

http://www.ca2.uscourts.gov

DC Circuit case-- 

http://www.cadc.uscourts.gov

EMISSIONS INVENTORY

10 Q. For reporting emissions to the National Emissions Inventory (NEI), what are EPA’s plans 

for the reporting threshold for Lead?

A. EPA recognizes the discrepancy between the 0.5 tpy Lead threshold for the Lead Monitoring 

Rule and the NEI reporting threshold of 5 tpy. To resolve this inconsistency, EPA is considering 

proposing changes to align the thresholds by changing the Air Emissions Reporting Rule (AERR)

that governs the reporting requirements for the NEI. Given the long rule making timeline, which

can last more from 1 to 2 years, EPA does not expect that any revision to the rule (if made) 

would occur in time to require the new threshold for the 2011 NEI (reporting for 2011 NEI is

required by the end of 2012). However, given the discrepancy in the rules that currently exists, 

states are encouraged to voluntarily collect data on smaller Lead sources and report the data to 
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EPA for the 2011 NEI. Note 40 CFR 51.117(e) states: “The point source inventory on which the 

summary of the baseline for Lead emission inventory is based must contain all sources that 

emit 0.5 or more tons of Lead per year.”

MODELING

11 Q. What is the appropriate emissions rate (peak seasonal, monthly, or annual rate) to 

use for the three-month rolling average?

A. Modeling analyses should conform with EPA’s guidelines on air quality models contained in 

Appendix W to 40 CFR part 51. http://www.epa.gov/ttn/scram/guidance/guide/appw_05.pdf.

Modeling input data, including emission rates, are addressed in Section 8.0 of Appendix W. The 

averaging period for the 2008 Lead NAAQS is a rolling 3-month average evaluated over a 3-year 

period. Accordingly, emissions limits should be based on concentration estimates for this same 

period (3-month average) as described in Section 10.2.3 of Appendix W. The emissions rate to 

input into AERMOD for attainment demonstrations is based on the maximum allowable or 

permit limit emissions, often 1-hour limits. Table 8-1 of Appendix W (see below) gives the 

calculation methodology to use to calculate the emissions rate to input into AERMOD. The 

input emissions rate for a source subject to SIP limits is a product of the maximum allowable or 

permit limit emissions, operating level (actual or design capacity, whichever is greater, or 

federally enforceable permit condition) and operating factor. This same calculation is also used 

for nearby sources. For “other” sources, the operating level is the annual level when actually 

operating averaged over the most recent two years. For definitions of nearby and other 

sources, see Section 8.2.3 of Appendix W.
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For the purpose of deriving permit limits for Lead based on modeling, we interpret the above 

procedures as follows. In general, the maximum hourly emission rate (PTE) should be used as 

the basis for establishing emission limits and for model input. This approach is appropriately 

conservative for emissions units that: 1) could be operated at a relatively high capacity factor 

(% of available capacity) over the applicable averaging period, 2) are associated with noncontinuous compliance monitoring methods (e.g., periodic source testing), and 3) have 

emissions that are not well correlated with production or other measureable surrogate 

monitoring parameters. Additionally, where significant uncertainty exists with respect to 

estimated emissions, modeling peak hourly rates may be necessary to account for this 

uncertainty. 

In certain cases, longer term average emission rates or emissions representative of actual 

operating schedules may be approved for use in modeling demonstrations and corresponding 

permit limitations. Consistent with Appendix W, where a source is willing to accept an 

enforceable limitation on operating schedule, emissions need only be modeled during 

allowable periods of operation. Longer-term average emission limits (e.g., monthly average, 

3-month average, or 3-month total) may be approved for qualifying emissions units. To be 
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approvable, such limitations must be enforceable as a practical matter. We emphasize that 

approval of model input data and proposed emissions limits must be granted by the reviewing 

authority on a case-by-case basis, taking into account source and emissions unit-specific 

factors. Modeled emission rates, including any proposed limitations on emissions or source 

operation, should be documented in the modeling protocol, and any associated permit 

application materials submitted to the reviewing agency for approval. 

12 Q. What is the required for modeling for attainment demonstrations? When should 

allowable emissions be used and when should permits be used?

A. Modeling for attainment demonstrations is used to show that a nonattainment area will be 

in attainment by the attainment date. The modeling is used to show the effectiveness of control 

measures on the sources. For attainment modeling, maximum allowable or federally 

enforceable permit limits should be the basis of the model input emissions, as described in 

Section 8.1 and Table 8-1 of Appendix W and the Guideline for Air Quality Models.

http://www.epa.gov/scram001/guidance/guide/appw_05.pdf

13 Q. What is EPA’s policy on conducting model evaluations to avoid under or over 

predictions compared to monitoring results?

A. As part of the model promulgation process, AERMOD has been evaluated in several studies 

and showed excellent performance. For details about the AERMOD evaluation results see the 

AERMOD Evaluation Paper at 

http://www.epa.gov/ttn/scram/7thconf/aermod/aermod_mep.pdf.

Any potential bias in modeled results versus monitored concentrations would most likely be 

introduced by the user (inaccurate characterization of emissions or use of non-representative 

meteorological data in the modeling) and if found should be explained by the user.

Depending on the level of emissions used (allowable versus actual) and the number of monitors 

being used in the evaluation, it may be possible to conduct a model evaluation for the specific 

case being modeled. In terms of the number of monitors, comparison to a single monitor is not 

considered sufficient to indicate a model bias. If maximum allowable emissions or permitted 

emissions are used as the model input emissions (either for the SIP modeling or use in 

designations modeling), it would be expected that modeled concentrations would not be 

comparable to monitored concentrations because of the nature of the emissions level. 

For designations modeling using actual emissions, if emissions have been characterized 

accurately and input meteorological data is representative of the area being modeled, one way 

to measure the performance of the modeled results against monitored values is to use 

quantile-quantile plots (QQ plots) by plotting the observed and modeled values in ranked order, 

i.e. highest monitored value paired with highest modeled value at monitor receptor locations. 

This creates concentration pairs of monitored and modeled concentrations that are no longer 

paired in time space and is considered a pragmatic procedure to evaluate model performance 

as noted in the AERMOD Evaluation Paper.
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14 Q. What is EPA’s policy on modeling for contingency measures?

A. It is not necessary to model the effect of implementing contingency measures. However, 

modeling is one way to help gauge the potential effectiveness of backstop measures and may 

demonstrate that any contingency measures that are adopted in the SIP are sufficient to be 

approved by EPA. Modeling of contingency measures should follow the guidelines in Appendix 

W.

15 Q. When will the new AERMOD, AERMET, and AERMINUTE updates be released?

A. The latest updates to AERMET, and AERMINUTE, version 11059, were released on March 8, 

2011. The latest updates to AERMOD and AERMAP were released on April 14, 2011 (version 

11103).

16 Q. Will AERMOD calculate the Lead NAAQS design value?

A. AERMOD does not calculate the Lead NAAQS design value. A post-processor called 

LEADPOST will calculate the Lead NAAQS design values from monthly modeled output.

LEADPOST is available on EPA’s SCRAM website at: 

http://www.epa.gov/ttn/scram/models/aermod/leadpost.zip

17 Q. If the modeling uses 5 years of National Weather Service data do all years have to be 

modeled in one run or can individual years be modeled?

A. The modeled design value is calculated as the rolling 3-month average concentration at each 

receptor across the five years. AERMOD does not calculate the design value, so post-processing 

is required. The EPA post-processor, LEADPOST, can be used to calculate the design values. The 

five years of model output do not have to be in one AERMOD run. Each individual year can be 

run separately and the output for each year can be input into LEADPOST. LEADPOST will read 

the individual files and calculate the design values across the five years provided that each

year’s runs have the same receptors and source group contributions.