The U.S. Environmental Protection Agency (EPA) revised the ozone NAAQS on March 

12,2008 (73 FR 16436; March 27,2008). The new primary ozone standard was lowered from 

0.08 parts per million (ppm) to a level of 0.075 ppm based on numerous epidemiological studies 

conducted during the past decade in which many of the health effects associated with ozone 

exposure were identified. These studies showed health effects at and below the level of the 0.08 

ppm standard, which was promulgated in 1997. Prolonged (i.e., 8-hour) exposure to ozone is 

associated with increased mortality and a range of serious morbidity health effects, including 

aggravation of a variety of respiratory symptoms and lung impairment, asthma attacks, 

respiratory hospital admissions and emergency department visits, and cardiovascular problems. 

In March 2008, EPA also strengthened the secondary ozone standard to provide increased 

protection against adverse public welfare effects including impacts on vegetation and forested 

ecosystems. EPA made the secondary standard identical in all respects to the revised primary 

standard. 

Section 107(d) of the Clean Air Act (CAA) governs the process for area designations 

following the establishment of new or revised NAAQS. Under section 107(d), states are 

required to submit recommendations on designations for their areas to EPA not later than one 

year after the promulgation of a new or revised standard. If, after careful consideration of the 

recommendations, EPA intends to promulgate a designation that deviates from a state 

recommendation, EPA must notify the state at least 120 days prior to promulgating the final 

designation, and EPA must provide the state an opportunity to demonstrate why the potential 

Internel Address (URL) hltpJhw.epa.gov RecyckdlRecycbble 0 Printed with Vegetabie Oil Based lnkson 100% Pos!mnsumer, Process Chlorine Free Recycled Paper 
(FEM) monitors that are sited and operated in accordance with 40 CFR Part 58. Special Purpose 

Monitors (SPM) using an FRM or FEM which have operated for more than 24 months are 

eligible for comparison to the relevant NAAQS, subject to the requirements given in the 

October 17,2006 Revision to Ambient Air Monitoring Regulations (71 FR 61236). Procedures 

for using the air quality data to determine whether a violation has occurred are given in 40 CFR 

Part 50 Appendix P, as revised on March 27,2008 (73 FR 165 1 1). We expect to base the final 

designations in March 20 10 on the most recent quality-assured data which would be from 2006- 

2008 or 2007-2009. 

Air quality monitoring data affected by exceptional events may be excluded from use in 

identifying a violation if they meet the criteria for exclusion, as specified in the Final Rule on the 

Treatment of Data Influenced by Exceptional Events (72 FR 13560; March 22,2007). We 

recently issued a direct final rule to provide schedules for flagging exceptional event data and 

submitting documentation specifically for ozone data collected from 2005 through 2009 that are 

used in the designations process for the 2008 ozone NAAQS. (See 73 FR 58042; October 6, 

2008). These schedules reflect our interest in assuring that the exceptional events claims can be 

fully considered by EPA in the final designations. 

' This information is available on EPA's website at www.epa.gov/ttn/airs/airsaqs/. 
tribes base their boundary recommendations on an evaluation of the 9 factors listed in,attachment 

2. These factors are consistent with those used in the designations process for the 1997 ozone 

standard and are factors EPA plans to consider in evaluating and making decisions on the 

nonattainment area boundaries for the 2008 ozone standards. Additionally, states and tribes may 

The Office of Management and Budget (OMB) delineates CBSAs (metropolitan and 

micropolitan statistical areas) and CSAs. OMB adopted new standards for defining metropolitan 

and micropolitan statistical areas on December 27, 2000 (65 FR 82229). A micropolitan 

statistical area has a population of at least 10,000 but less than 50,000. A metropolitan statistical 

area has a population of at least 50,000. 

For lists of the CBSAs and CSAs and their geographic components see 

www.census.~ov/populatiod~~~/metroareas/metrodef.html. EPA recommends using the most 

recent available updated lists of the statistical areas. The lists are updated annually to reflect the 

most recent Census Bureau population estimates. 

Memorandum from John S. Seitz, Director of Office of Air Quality Planning and Standards to 

Air Directors, Regions I-X, "Boundary Guidance on Air Quality Designations for the 8-Hour 

Ozone National Ambient Air Quality Standards," March 23, 2000. 

In addition, CAA section 107(d)(4) established the consolidated metropolitan statistical area or 

metropolitan statistical area as the presumptive boundary for the most polluted areas that were 

designated nonattainment by operation of law in 199 1 for the 1-hour ozone NAAQS. 
Staff in EPA's Office of Air Quality Planning and Standards are available for assistance 

and consultation throughout the designation process. Questions on this guidance may be directed 

to Carla Oldham at 9 19-54 1-3347. 

Attachments (2) 

cc: Air Division Directors, Regions I-X 

Greg Green, OAQPS 

Bill Harnett, OAQPS 

Brian McLean, OAP 

Margo Oge, OTAQ 

Stephen D. Page, OAQPS 

Peter Tsirigotis, OAQPS 

Richard Wayland, OAQPS 

Lydia Wegman, OAQPS 
inappropriate. 

EPA promulgates final ozone designations. 

No later than March 12,20 10 

* This schedule assumes EPA has sufficient information to promulgate designations within 2 years. In 

the event EPA determines that insufficient information is available to do so, the designation process could 

be extended up to one year, but no later than March 12,20 1 1. 
areas, Reservations, metropolitan planning organizations (MPOs)) 

Level of control of emission sources 

Analysis of these factors may support nonattainment boundaries that are either larger or 

smaller than the presumptive boundary. EPA plans to consider these factors, along with any 

other relevant information, in determining whether to make modifications to the boundary 

recommendations from states and tribes. The factors listed above, while generally 

comprehensive, are not intended to be exhaustive. States and tribes may submit additional 

information they believe is relevant for EPA to consider. In general, a state's or tribe's 

demonstration supporting their boundary recommendation for an area should show that: 1) 

violations are not occurring in nearby portions that are excluded from the recommended area, 

and 2) the excluded nearby portions do not contain emission sources that contribute 

meaningfully to the observed violations. While states are not bound to use the approach outlined 

here, EPA plans to evaluate a state recommendation and determine whether to modify such 

recommendation based on the above factors and any other information the Agency determines is 

relevant. 

For lists of the CBSAs and CSAs and their geographic components see 

www.census.~ov/population/www/metroareas/metrodef.html.