• As of December 14, 2012, the EPA announced that the number of nonattainment areas are 46 ozone (8-hour 2008 standard), 41 ozone (8-hour 1997 standard), 9 sulfur dioxide, 46 PM-10, 35 PM-2.5 (1997 Standard), 32 PM-2.5 (2006 Standard), 2 lead (original standard), and 21 lead (2008 Standard) in the United States. There are no CO and NO2 nonattainment areas in the United States. Maps of the ozone, carbon monoxide, sulfur dioxide, lead (2008), PM-10, and PM-2.5 nonattainment areas are available for review and download.

• On December 14, 2012, the EPA announced that it was going to change the annual health National Ambient Air Quality Standard (NAAQS) for fine particles to 12.0 micrograms per cubic meter (ug/m3) and retain the 24-hour fine particle standard of 35 ug/m3. The agency also retained the existing standards for coarse particle pollution (PM10).

• On October 11, 2011, environmental and public health groups sued the Obama administration for rejecting stronger ozone standards. The environmental law group, Earthjustice, filed the lawsuit on behalf of the American Lung Association, Environmental Defense Fund, Natural Resources Defense Council, and Appalachian Mountain Club. The suite is associated with the President rejecting the EPA's recommendation for more restrictive Ozone National Ambient Air Quality Standards. In July, the Agency had recommended that the ozone human health standard be reduced to 0.070 ppm from 0.075 ppm and that a new vegetation standard be set at the 13 ppm-hour level. For more information about the Agency's proposed changes to the ozone standards, please go to http://www.epa.gov/airquality/ozonepollution/actions.html

• On September 2, 2011, President Obama requested that the EPA withdraw the Agency's draft Ozone National Ambient Air Quality Standards, which it had submitted for review to the President's Office of Management and Budget on July 11. The President cited the importance of reducing regulatory burdens and regulatory uncertainty, particularly as the Nation's economy continues to recover. The President stated "Work is already underway to update a 2006 review of the science that will result in the reconsideration of the ozone standard in 2013. Ultimately, I did not support asking state and local governments to begin implementing a new standard that will soon be reconsidered." The White House press release can be found by clicking here. The letter from the White House's OMB to EPA Administrator Lisa Jackson provided specific reasons for the President's decision. The letter can be read by clicking here.

On September 22, 2011, the EPA announced that it was moving forward to implement the 2008 ozone standard, starting with the recommendations the states made in 2009 and updating them with the most current, certified air quality data. The Agency anticipates issuing proposed changes to the states' recommendations later this fall. EPA indicates that it will quickly initiate and complete a rulemaking to establish nonattainment area classification thresholds so that it can finalize the designations. Based on initial review of the 2008-2010 ozone air quality data, 52 areas that monitor air quality exceed the 0.075 ppm standard. EPA expects to finalize the nonattainment designations for the 2008 ozone standard by mid-2012. However, EPA notes that it faces litigation with respect to the timing of the designations and expects that the resolution of the litigation may well affect the precise timing of the schedule for designations.

On January 7, 2010, the EPA announced its proposal to strengthen the national ambient air quality standards for ground-level ozone. The EPA's proposal decreased the 8-hour “primary” ozone standard level, designed to protect public health, to a level within the range of 0.060-0.070 parts per million (ppm). EPA proposed establishing a distinct cumulative, seasonal “secondary” standard, referred to as the W126 index, which is designed to protect sensitive vegetation and ecosystems, including forests, parks, wildlife refuges, and wilderness areas. Dr. Lefohn, A.S.L. & Associates' President, developed and proposed the W126 index almost 25 years ago as a metric that could be used to protect vegetation from ozone exposure. EPA proposed to set the level of the W126 secondary standard within the range of 7-15 ppm-hours. The proposed revisions resulted from a reconsideration of the identical primary and secondary ozone standards set at 0.075 ppm in March 2008. The Agency's decision was planned to be made in August 2010. However, on August 20, the Agency announced that it will delay its announcement to on or around the end of October. In early November, the EPA announced that it would reach a final decision on the ozone standards by December 31, 2010. On December 8, 2010, the EPA announced that it would delay its final decision on the ozone standards until July 2011. EPA announced on July 26 that it would not make a decision on the ozone standards by its previously announced deadline of July 29. On August 12, EPA indicated to the court that it is "fully committed" to the ozone standards and it would move forward once the White House review was complete. Based on several considerations, on September 2, 2011, the President requested that the EPA withdraw its proposal.

For those interested in reviewing the historical reasons for recommending the range of concentrations for the primary and secondary ozone standards, information is available. On August 25, 2006, the EPA's Clean Air Scientific Advisory Committee (CASAC) met in Research Triangle Park at a public meeting to discuss and recommend to the EPA the range of ozone concentrations that the Agency should consider for establishing the human health and vegetation ozone standards. The EPA taped and then transcribed the meeting's proceedings and provided an unofficial transcript to the public on CASAC's discussion. Please click here to download the transcript.

For identifying violating counties for the 2006-2008 period for the proposed human health and vegetation ozone standards, please visit our maps webpage. Please note that for the 8-h ozone standard, there will be more counties that violate the standard than the US EPA has estimated due to the selection methodology that the Agency utilizes in identifying monattainment areas. For more information, please join A.S.L. & Associates in the Discussion area on Facebook.

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As part of the proposed changes to the current 8-hour ozone human health standard, the EPA estimated that the percentage of violating counties with monitors for the 0.060, 0.065, and 0.070 ppm thresholds would be 96%, 90%, and 76%, respectively. For the 3-year average of the annual maximum 3-month cumulative 12-hour W126 secondary ozone standard, the EPA estimated that the percentage of violating counties with monitors for the 7 and 15 ppm-hour thresholds would be 91% and 31%, respectively.

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Some of the background concerning the events that led to the EPA's Administrator's decision on revising the 8-hour ozone standard helps in better understanding the process. On March 12, 2008, the EPA Administrator announced a decision on the human health and vegetation ozone standards. At that time, EPA revised the 8-hour "primary" ozone standard, designed to protect public health, to a level of 0.075 parts per million (ppm). The previous standard, set in 1997, was 0.08 ppm. EPA decided not to adopt the cumulative exposure index as the vegetation standard (i.e., secondary ozone standard). Although the EPA Administrator recommended the W126 index as the secondary ozone standard, based on advice from the White House (Washington Post, April 8, 2008; Page D02), the EPA Administrator made the secondary ozone standard the same as the primary 8-hour average standard (0.075 ppm). On May 27, 2008, health and environmental organizations filed a lawsuit arguing that the EPA failed to protect public health and the environment when it issued in March 2008 new ozone standards. On March 10, 2009, the US EPA requested that the Court vacate the existing briefing schedule and hold the consolidated cases in abeyance. EPA requested the extension to allow time for appropriate EPA officials that were appointed by the new Administration to review the Ozone NAAQS Rule to determine whether the standards established in the Ozone NAAQS Rule should be maintained, modified, or otherwise reconsidered. Based on the September 2, 2011 decision by the President, it appears that health and environmental organizations may be headed back to court.

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• The range of suggested values for the W126 standard is mainly based on the recommendations that were made at a Workshop that took place in Raleigh, North Carolina in 1996. To better understand what took place at this workshop, please click here. The EPA recommends an accumulation over a 12-hour (8 am – 8 pm) exposure period over a 3-month period giving greater weight to exposures at higher levels of ozone. Our analyses and peer-reviewed published papers indicate that such a secondary ozone standard, in the proposed form, would overestimate vegetation effects. For information about why the use of a 12-hour versus a 24-hour accumulation period would contribute to the inconsistency problem of the W126 index, please click here. You can learn more about the subject of vegetation effects by visiting our Table of Contents web page.

• As part of the current review of the ozone standarrds, for the EPA's Clean Air Scientific Advisory Committee (CASAC) meeting in Chapel Hill, NC that took place on May 19-20, 2011, we prepared a 55-page summary of what we believe the research status is of surface ozone policy-relevant background. There is much controversy on what the range of background ozone is in the United States. The EPA, using a model, believes that background ozone is in the range of 15-35 ppb. However, models tend to poorly estimate the contribution of natural processes, such as stratospheric intrusions into the lower troposphere. Our research is indicating that frequent occurrences greater than or equal to 50 ppb that occur at both high- and low-elevation monitoring sites across the US are influenced by transport from the stratosphere to the lower troposphere. The enhanced ozone concentrations that appear to be related to stratospheric transport occur during the springtime and sometimes during the summertime. In addition, long-range transport of Eurasian biomass burning, as well as wildfires in the US, contribute to background ozone concentrations. Estimating the range of background ozone properly is important because the range of background concentrations is used in the EPA's risk assessment for human health and vegetation, as well as assessing the amount of emission reductions required to attain a specific ozone level (i.e., standard). If the actual background level of ozone is higher than EPA estimates with models, then the Agency may overestimate human health as well as vegetation risks and present inaccurate information to the public and policymakers. If you would like to read the 55-page report by Allen S. Lefohn and Samuel J. Oltmans on the status of policy-relevant background (PRB) ozone, please click here.

• For several years, A.S.L. & Associates has had an on-going effort to better understand the range and frequency of occurrence of background ozone levels that may not be affected by emission reduction strategies. In a paper published in May 2001, the research team consisting of Allen Lefohn, Samuel Oltmans, Tom Dann, and Hanwant Singh discussed that background ozone levels were higher and that the natural short-term variability was more frequent and greater than previously believed. The authors are associated with the following institutions: A.S.L. & Associates, NOAA, Environment Canada, and NASA, respectively. In our 2001 paper, we concluded that hourly levels greater than or equal to 50 ppb occur more frequently as a result from natural sources than previously believed. In 2006, the US EPA defined Policy-Relevant Background (PRB) for ozone as those concentrations that would occur in the United States in the absence of anthropogenic emissions in continental North America (i.e., the United States, Canada, and Mexico). PRB concentrations include contributions from (1) natural sources everywhere in the world and (2) anthropogenic sources outside the United States, Canada, and Mexico. In 2008, we published results, using empirical data, confirming that at some locations in the US, PRB ozone concentrations are greater than or equal to 50 ppb. In late September 2009, the National Research Council released the report, Global Sources of Local Pollution. In the report, the Committee states that modeling and analysis supports the finding that Policy-Relevant Background (PRB) is 20-40 ppb for the United States. Unfortunately, the NRC conclusion does not agree with the peer-review literature using empirical data that hourly averaged PRB ozone concentrations are greater than or equal to 50 ppb. Although spatially low-resolution models have been exercised and indicated that conclusions reached by Lefohn et al. (2001) were incorrect, our current research and the results published by other research groups support the conclusions reached by Lefohn et al. (2001) that PRB ozone concentrations are greater than or equal to 50 ppb at both high- and low-elevation monitoring sites. Clearly, low-resolution models are unable to adequately capture the important processes that are important for characterizing PRB and therefore, underestimate policy relevant background concentrations. The latest results using GEOS-Chem models continue to underestimate PRB ozone concentrations. An Internet-based slide presentation is available for purposes of previewing our paper. Also please be sure to check out the answer to our quiz that identifies the month in which the highest 8-hour daily maximum concentration occurred for the 4 remote ozone monitoring sites. Additional information on background ozone concentrations can be found in the Air Quality Analyses section of our Table of Contents. In-depth discussions are provided on this very important topic.

• EPA released its design value findings on air quality on September 2, 2010 and concluded for the period 2007-2009:

	14 of the 126 areas originally designated nonattainment for the 8-hour O3 National Ambient Air Quality Standard (NAAQS) failed to meet the 1997 8-hour O3 NAAQS for the period 2007-2009 (see Table);
	2 of the areas originally designated nonattainment had incomplete data (see Table);
	No additional unclassifiable/attainment areas failed to meet the O3 NAAQS in 2007-2009 (see Table);
	As of September 2, 2010, 79 of the 126 areas originally designated nonattainment for the 8-hour O3 NAAQS are classified as maintenance areas, meaning they have been redesignated to attainment (see Table);
	Four of the original 39 areas designated nonattainment for the PM2.5 NAAQS in April, 2005 (using 2001-2003 data) failed to meet the annual PM2.5 NAAQS in 2007-2009. Twenty-nine of the original 39 nonattainment areas met the annual NAAQS in 2007-2009. Six areas have insufficient data to allow a determination of compliance with respect to the annual PM2.5 NAAQS in 2007-2009; in each of these six areas, one or more sites for which compliance cannot be determined for 2007-2009 clearly violated the NAAQS in a previous period (e.g., for 2006-2008) (see Table);
	Eighteen of the 31 areas originally designated nonattainment for the 24-hour PM2.5 NAAQS failed to meet the NAAQS with 2007-2009 data. Nine of the original 31 nonattainment areas met the 24-hour PM2.5 NAAQS in 2007-2009. The other four areas are shown to have incomplete data with respect to the 24-hour PM2.5 NAAQS; in each of these four areas, one or more sites for which compliance cannot be determined for 2007-2009 clearly violated the NAAQS in a previous period (e.g., for 2006-2008). (see Table);
	For 2007-2009, no counties, outside of existing nonattainment areas, did not meet the PM2.5 annual NAAQS (see Table). Five counties, outside of existing nonattainment areas, did not meet the PM2.5 24- hour NAAQS for 2007-2009. (see Table);
	There were 59 counties not meeting the new daily maximum 1-hour SO2 average NAAQS (see Table);
	There was one county, Cook county Illinois, that did not meet the new daily maximum 1-hour average NO2 NAAQS (see Table);

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• On EPA's web site (www.epa.gov/airtrends/ozone.html), the Agency summarized ozone trends for the periods 1980-2010 and 1990-2010. Figures 1 and 2 below have been reproduced from the Agency's current website. Lefohn, Shadwick, and Oltmans (2010) have statistically quantified in a paper published in the peer-reviewed journal, Atmospheric Environment, a site-by-site trending analysis for the period 1980-2008 and 1994-2008. Although the figures below illustrate a national average change, Lefohn et al. (2010) point out that many ozone monitoring sites show no statistical changes over time as well as a small number of sites show increases in trending. Please see the publications list for the citation. Table 1 below lists the changes over the past several years.

Figure 1. National 8-hour Ozone Air Quality Trend, 1980-2010. Based on annual fourth highest daily maximum 8-hour ozone concentration trended over the period of time.
(Source: www.epa.gov/airtrends/ozone.html)

Figure 2. National 8-hour Ozone Air Quality Trend, 1990-2010. Based on annual fourth highest daily maximum 8-hour ozone concentration trended over the period of time.
(Source: www.epa.gov/airtrends/ozone.html)

Table 1. Comparison of trending by US EPA for two exposure metrics for several time periods.

Exposure Metric	1980-2005	1980-2006	1980-2007	1980-2008	1990-2005	1990-2006	1990-2007	1990-2008
2nd Highest 1-Hour Average	-28%	-29%	-29%	-32%	-12%	-14%	-14%	-18%
4th Highest 8-Hour Average	-20%	-21%	-21%	-25%	-8%	-9%	-9%	-14%

As indicated above, Lefohn et al. (2010) published their trending findings for surface ozone monitoring sites across the United States. Using statistical trending on a site-by-site basis of the (1) health-based annual 2nd highest 1-hour average concentration and annual 4th highest daily maximum 8-hour average concentration and (2) vegetation-based annual seasonally corrected 24-hour W126 cumulative exposure index, they investigated temporal and spatial statistically significant changes that occurred in surface ozone in the United States for the periods 1980-2008 and 1994-2008. For more information about the Lefohn et al. (2010) and Lefohn et al. (2008) (for the period 1980-2005 and 1990-2005) findings, please click here.

Since 1997, we have been discussing the "piston" effect in the peer-reviewed literature (see publications listing). In 1997, we predicted that there would be a leveling off of improvements in O3 concentrations as O3 emission precursors were reduced at some monitoring sites Our prediction apparently has been verified by our most current analysis (Lefohn et al., 2010). The "piston" effect, as described in the peer-review literature and on this web site, affects the ability of the nation to attain the 8-hour ozone standard. As we discussed in our original paper, the peak hourly average concentrations (i.e., hourly average concentrations greater than or equal to 0.10 ppm) are reduced much faster than the mid-level concentrations (i.e., 0.06-0.099 ppm). In the most recent EPA Ozone Criteria Document (2006), the Agency notes "The highest O3 concentrations have tended to decrease over the past 15 years, while there has been little change in O3 concentrations near the center of the distribution." The document notes that this is consistent with results published in Europe. Interesting, the Agency notes in the document that there has been an increase in O3 concentrations at the lower levels throughout the monitoring period, which is consistent with data obtained in Europe, showing that O3 minima increased during the 1990s because of reduced titration of O3 by reaction with NO in response to reductions in NOx emissions. Based on our published findings, the EPA has attempted to take into consideration the "piston" effect by utilizing theoretical rollback models that allow the higher hourly average ozone concentrations to be reduced at a faster rate than the mid-level values. Clearly the "piston" effect heavily influences the Nation's ability to attain an 8-hour ozone standard. We discuss more about the "piston" effect and how it affects the attainability of the ozone standard in our concerns web area.

• On EPA's web site (http://www.epa.gov/airtrends/aqtrends.html), the Agency summarizes emission trends for the period 1980-2008. The tables below are the most current estimates provided by EPA on its web page as of October 2009.

National Emissions Estimates
(fires and dust excluded)
For Common Pollutants and their Precursors

	1980	1985	1990	1995	2000	2005	2008
Carbon Monoxide (CO)	178	170	144	120	102	93	78
Lead	0.074	0.023	0.005	0.004	0.003	0.002	0.002
Nitrogen Oxides (NOx)	27	26	25	25	22	19	16
Volatile Organic Compounds (VOC)	30	27	23	22	17	18	16
Particulate Matter (PM) PM10 PM2.5	6 NA	4 NA	3 2	3 2	2 2	2 1	2 1
Sulfur Dioxide (SO2)	26	23	23	19	16	15	11
Totals	267	250	220	191	161	148	124

Notes:
1. In 1985 and 1996 EPA refined its methods for estimating emissions. Between 1970 and 1975, EPA
revised its methods for estimating PM emissions.
2. The estimates for 2005 and beyond are from the final version 2 of the 2005 NEI.
3. For CO, NOx, SO2 and VOC emissions, fires are excluded because they are highly variable; for
direct PM emissions both fires and dust are excluded.
4. PM estimates do not include condensable PM.
5. EPA has not estimated PM2.5 emissions prior to 1990.
6. The 1999 estimate for lead is used for 2000, and the 2002 estimate for lead is used for 2005 and
2008.
7. PM2.5 emissions are not added when calculating the total because they are included in the PM10
estimate.

Source: http://www.epa.gov/airtrends/sixpoll.html

Percent Change in Air Quality

Pollutant	1980 versus 2008	1990 versus 2008
CO	-79	-68
Ozone (8-hour)	-25	-14
Lead	-92	-78
Nitrogen Dioxide	-46	-35
PM10 (24-hour)	--	-31
PM2.5 (Annual)	--	-19
PM2.5 (24-hour)	--	-20
Sulfur Dioxide	-71	-59

Notes:
1. --- Trend data not available
2. PM2.5 air quality based on data since 2000
3. Negative numbers indicate improvements in air quality

Source: http://www.epa.gov/airtrends/aqtrends.html

Percent Change in Emissions

Pollutant	1980 versus 2008	1990 versus 2008
CO	-56	-46
Lead	-99	-79
Nitrogen Oxides	-40	-35
VOC	-47	-31
Direct PM10	-68	-39
Direct PM2.5	--	-38
Sulfur Dioxide	-56	-51

Notes:
1. --- Trend data not available
2. Direct PM10 emissions for 1980 are based on data since 1985
3. Negative numbers indicate reductions in emissions

Source: http://www.epa.gov/airtrends/aqtrends.html

• On February 24, 2009, the U.S. Court of Appeals for the D.C. Circuit remanded the National Ambient Air Quality Standards (NAAQS) for fine particulate matter (PM2.5) to EPA for reconsideration of the annual level of the standard (which EPA left at 15 micrograms per cubic meter (µg/m3)) and reconsideration of the secondary PM2.5 NAAQS. With respect to the annual PM2.5 NAAQS, the court held that the agency “failed to explain adequately why an annual level of 15 µg/m3 is ‘requisite to protect the public health,’ including the health of vulnerable subpopulations, while providing ‘an adequate margin of safety.’ 42 U.S.C.§ 7409(b)(1).” For the secondary standards, the court held that EPA “unreasonably concluded that the NAAQS are adequate to protect the public welfare from adverse effects on visibility.” The court denied petitions for review of the primary daily standard for coarse PM and the petition for review of EPA’s revocation of the primary annual standard for coarse PM. The Court opinion can be read by clicking here.

On September 21, 2006, EPA announced with regard to primary standards for fine particles (generally referring to particles less than or equal to 2.5 micrometers (µm) in diameter, PM2.5) that it revised the level of the 24-hour PM2.5 standard to 35 micrograms per cubic meter (µg/m3) and retained the level of the annual PM2.5 standard at 15 µg/m3. With regard to primary standards for particles generally less than or equal to 10 µm in diameter (PM10), EPA retained the 24-hour PM10 and revoking the annual PM10 standard. With regard to secondary PM standards, EPA made them identical in all respects to the primary PM standards, as revised. The issue of reliability of the epidemiological time-series methodologies continued to be of concern to the Administrator. The Administrator noted in his decision that there were many sources of uncertainty and variability inherent in the inputs to the assessment and that there was a high degree of uncertainty in the resulting PM2.5 risk estimates. Such uncertainties generally related to a lack of clear understanding of a number of important factors, including, for example, the shape of concentration-response functions, particularly when, as here, effect thresholds can neither be discerned nor determined not to exist; issues related to selection of appropriate statistical models for the analysis of the epidemiologic data; and the role of potentially confounding and modifying factors in the concentration-response relationships. For those interested in the possible violation areas for the revised 24-hour PM-2.5 standard based on 2004-2005 data, please click here.

• On December 22, 2008, EPA designated areas throughout the United States as "nonattainment" and "unclassifiable/attainment" for the 24-hour national air quality standard (35 ug/m3) for fine particulate matter (PM2.5). The EPA designated 211 counties or parts of counties as nonattainment. These nonattainment areas include counties with monitors violating the standards and nearby areas that contribute to that violation. A map of the EPA's PM2.5 designations for nonattainment can be reviewed by clicking here. For a comparison of the violators for the PM2.5 annual standard (2005-2007) and the PM2.5 24-hour average standard (35 ug/m3), please click here.

• In December 2008, we presented at the AGU Fall Conference in San Francisco a summary of one of our several research efforts dealing with changes in tropospheric ozone levels. The talk was presented at the Tropospheric Gaseous Composition in the Regional and Global Perspective 1 - A11F-03 session. The title of our presentation was: "Tropospheric Ozone Changes from Surface and Ozonesonde Observations." The research was presented by the lead author, Samuel Oltmans, NOAA Earth System Research Laboratory Global Monitoring Division, Boulder, Colorado. The talk explored the following:
  • What are the implications from this record of observations?
  • Are the records consistent in regions with multiple records?
  • At what geographic scale can conclusions about trends be drawn (global, hemispheric, regional)? and
  • Are changes related to precursor emissions, transport variability, stratospheric input?

Based on our analyses, our conclusions are

• In the Northern Hemisphere, there is a different pattern of long-term changes between North America, Europe, and Japan;
• Over North America there does not appear to be a significant increase over the 30 years of measurements, although there have been shorter term fluctuations;
• Western Europe saw the largest increases prior to 1990 but a significant decrease in growth rates (and in some cases declines) over the past 15 years over continental Europe;
• In Japan, increases were primarily prior to the mid 1980s, but with recent increases in Okinawa;
• In the Southern Hemisphere mid latitudes, at Cape Point, Cape Grim, and Lauder, ozone has increased significantly with the increases coming primarily in the austral spring;
• In Hawaii (North Pacific tropics), increases appear to be associated with decadal transport shifts;
• The tropical south Pacific (Samoa) has not shown significant changes in tropospheric ozone; and
• At the South Pole, earlier declines have reversed so that overall there has been almost no change.

Some possible implications of recent (i.e., 30 year) observed changes are

• The relationship between emission changes and longer term hemispheric and global tropospheric ozone changes is not adequately understood;
• The climate forcing of tropospheric ozone changes over the recent past is still very uncertain; and
• It will be difficult to assess the climate forcing reductions that can be gained by reducing tropospheric ozone with the current network of observations.

Co-authors of the research study are A. Lefohn, J. Harris, H.-E. Scheel, E. Brunke, H. Claude, D. Tarasick, I. Galbally, G. Bodeker, J. Davies, T. Koide, B. Johnson, C. Meyer, F. Schmidlin, E. Cuevas, A. Redondas, P. Simmonds, and B. Buchman.

Over the past several years, there have been several articles quoting other sources indicating that surface ozone concentrations are increasing everywhere. Our most current research results do not support this claim. Our research continues to monitor the status of worldwide ozone levels by performing sophisticated analyses using surface ozone and ozonesonde data. Previous peer-reviewed papers on background ozone trends that we have published are

Oltmans S. J., Lefohn A. S., Scheel H. E., Harris J. M., Levy H. II, Galbally I. E. , Brunke E. G., Meyer C. P., Lathrop J. A., Johnson B. J., Shadwick D. S., Cuevas E., Schmidlin F. J., Tarasick D. W., Claude H., Kerr J. B., Uchino O., and Mohnen V. (1998) Trends of ozone in the troposphere. Geophysical Research Letters. 25:139-142.

Oltmans S. J., Lefohn A. S., Harris J. M., Galbally I., Scheel H. E., Bodeker G., Brunke E., Claude H., Tarasick D., Johnson B.J., Simmonds P., Shadwick D., Anlauf K., Hayden K., Schmidlin F., Fujimoto T., Akagi K., Meyer C., Nichol S., Davies J., Redondas A., and Cuevas E. (2006) Long-term changes in tropospheric ozone. Atmospheric Environment. 40:3156-3173.

• Canada has identified the ozone concentrations for the 4th highest 8-hour levels across the U.S. and Canada. Maps are available that compare the U.S. and Canada for your review.

• Sometimes policymakers do not pay careful attention to the technical details associated with important scientific topics. For example, EPA indicated in April 2004 in its report, The Ozone Report - Measuring Progress Through 2003, that for the period 1990 - 2003, six locations experienced statistically significant increases in ozone: Great Smoky Mountains (Tennessee) in the eastern United States and Mesa Verde (Colorado), Rocky Mountain (Colorado), Craters of the Moon (Idaho), Canyonlands (Utah), and Yellowstone (Wyoming) in the West.

Yellowstone National Park is a relatively remote site for ozone monitoring in the United States. The greatest frequency of ozone concentrations greater than or equal to 0.05 ppm occurs in the spring, which we believe implies a natural stratospheric contribution to the site. We have not observed trends in ozone in the park since the beginning of monitoring. Our ozone trending analysis includes data through 2005. Our review of the latest data for 2006 indicate that no statistically significant ozone trends would be identified for Yellowstone National Park if the additional year were included in our analysis. We pointed out several years ago that EPA's trending results were due to a change in the physical location of the actual ozone monitor. In 1996, the monitoring site was changed and this resulted in two distinct sets of data being generated. Based on our analysis, EPA should not have combined the two sets of data for trends analysis in its April 2004 report. EPA, in its latest estimates of trending at national parks, did not attempt to identify a trend for the Yellowstone National Park site for the period 1990 - 2004 because of the change in physical location (EPA, 2006 - see page AX3-113). The scientific information showing the changes in the monitoring site and the effects on trends from 1987 through 2001 is available for review.

In May 2006, the U.S. National Park Service provided on its web site (http://www2.nature.nps.gov/air/) the results of its 2005 Annual Performance and Progress Report: Air Quality in National Parks report. Based on air quality data covering the period 1995-2004, the National Park Service announced that both Yellowstone National Park and Glacier National Park are experiencing statistically significant increases in ozone concentrations. This finding contradicts our own peer-reviewed published analyses (Oltmans et al. 2006) and the information provided in EPA's Ozone Criteria Document published in 2006. Although EPA did not attempt to determine an ozone trending for Yellowstone National Park for the scientific reasons detailed above, the Agency did report that no statistically significant trend was observed at Glacier National Park for the period 1990-2004. Thus, our most recent trending analyses (Oltmans et al., 2006) and EPA's analysis agree that no trend appears to exist at Glacier National Park. In addition, our most recent analysis (Oltmans et al., 2006) also shows no trending at Yellowstone National Park. We believe there are clear reasons for the discrepancy between the results presented by the National Park Service and those by EPA and A.S.L. & Associates. Based on our review of the National Park Service analysis of ozone data, we believe that at this time, no trends in surface ozone are occurring at either Yellowstone National Park or Glacier National Park. For additional information, please review our technical comments.

Oltmans S. J., Lefohn A. S., Harris J. M., Galbally I., Scheel H. E., Bodeker G., Brunke E., Claude H., Tarasick D., Johnson B.J., Simmonds P., Shadwick D., Anlauf K., Hayden K., Schmidlin F., Fujimoto T., Akagi K., Meyer C., Nichol S., Davies J., Redondas A., and Cuevas E. (2006) Long-term changes in tropospheric ozone. Atmospheric Environment. 40:3156-3173.

U.S. Environmental Protection Agency (2006) Air Quality Criteria for Ozone and Related Photochemical Oxidants. Research Triangle Park, NC: Office of Research and Development; report no. EPA/600/R-05/004af.

• Our research team has used ordinary kriging to develop surface ozone models for the years 1982 to 2009. Our most recent work has included the kriging of the W126 integrated and the N100 exposure indices. To read more about our Team's use of kriging to spatially characterize surface ozone, please visit our kriging web page.

• Over the past years, A.S.L. & Associates and its consultants have commented on the strengths and weaknesses associated with the mathematical and statistical methodologies used in epidemiological studies to link exposure with human health effects. Many of the statistical caveats raised throughout the PM and Ozone Criteria Documents and the PM and Ozone Staff Papers indicate a pattern of inconsistent results that is troubling. Examples of the growing pattern of inconsistent and inconclusive findings include the following:
  

• Instability of PM mortality effect estimates resulting from different model specifications of weather effects and time trends.
• Instability of PM effect estimates resulting from different selections of monitoring sites within cities.
• Increased heterogeneity of PM effect estimates across cities.
• Greater diversity of findings among studies and across study areas.
• Contradictory results from mortality displacement studies.
• PM effect lags that are inconsistent across cities and across studies.
• Exposure-response relationships that are inconsistent across cities and across studies.
• Inconsistencies between short-term and long-term effect studies, such as respiratory effects of fine particles.
• Contradictory findings among long-term studies.

Additional details about the Team's epidemiological concerns are discussed on our epidemiological concerns web page. The Team's comments on the first draft of the PM Staff Paper were submitted to EPA in October 2003. To read more about our concerns about the first draft, please visit our web page.

EPA announced on April 15, 2004 that it has designated 474 counties as nonattainment for the 8-hour ozone standard. There were 126 nonattainment areas. The most recent update shows an adjustment to these numbers. A map is available to view the locations of nonattainment counties. We do have concern that while the number of violation areas of the ozone standard is great, the public may not be at as much risk as the EPA estimates. In addition, the standard will be difficult and in many cases impossible to attain due to the "piston" effect. An Internet-based slide presentation is available that explains the effect. Additional information about the effect can be found in the Table of Contents section of this web site.

• Sometimes science and politics mixed together become science fiction. Such is the case that occurred, when in September 2002, many newspapers across the United States printed a story summarizing the report, Code Red: America's Five Most Polluted National Parks, which described The Great Smoky Mountains as the nation's most polluted national park, with air quality rivaling that of Los Angeles. For the period 1997-2001, the report claims that the annual ozone exposure was higher at Great Smoky Mountains National Park than at Los Angeles, California. There is a serious technical problem associated with the report and the report's conclusions are flawed. Please read "The Rest of the Story."

• In 2000, Haywood County, NC experienced its 4th highest 8-hour ozone concentration at 0.085 ppm. On May 1, a daily maximum 8-hour average concentration of 0.089 ppm was experienced. A detailed meteorological analysis suggests that stratospheric ozone played an important role in this ozone episode.