As an example, based on the language in the Clean Air Act and the ozone and PM2.5

rules, areas with an attainment date of no later than June 15th 2010 (for moderate ozone

nonattainment areas) or April 5th, 2010 (for PM2.5 nonattainment areas)26, need to have emission

reductions implemented no later than the beginning of 2009 (for PM2.5) or the beginning of the

2009 ozone season (for 8-hour ozone). Therefore, modeling the year before the attainment

deadline (2009 in this case) is generally appropriate for both ozone and PM2.5 attainment

demonstrations. However, attainment dates are expressed as “no later than” three, five, six, or

nine years after designation and nonattainment areas are required to attain as expeditiously as

practicable. Therefore, additional considerations are necessary before a modeling year can be


Using moderate ozone nonattainment areas as an example, these areas have an attainment

date of no later than June 15, 2010, or as expeditiously as practicable. States/Tribes are required

to conduct a Reasonably Available Control Measures (RACM) analysis to determine if they can

26One key difference between ozone and PM2.5 planning is that all PM2.5 nonattainment areas

have a single classification and a single set of attainment deadlines. The PM2.5 nonattainment areas are

required to attain the standard within 5 years of designation or as expeditiously as practicable. They can

also request up to a 5 year extension of the attainment deadline. The procedures for justifying an

extension of the attainment date are contained in the PM implementation rule (40 CFR 50.1004). In this

guidance document, we will assume that areas will model a future year based on attaining within the first

5 year period. Areas that request and are granted attainment date extensions should consult with their

Regional Office regarding future year modeling analyses and requirements


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