• On EPA's web site (www.epa.gov/airtrends/ozone.html), the Agency in April 2008 summarized trends for the periods 1980-2007 and 1990-2007. Figures 1 and 2 below have been reproduced from the Agency's current website. There has been a flattening effect over time, where the peak O3 concentrations were reduced in the early years but then most modest improvements in the mid-level values since the 1990s. Based on EPA's calculations, on a national basis, O3 levels have not changed over the past several years. Table 1 below lists the changes over the past several years.

Figure 1. National 8-hour Ozone Air Quality Trend, 1980-2007, 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, 1990-2007, 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 three time periods.

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

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. Our prediction apparently has been verified by the EPA's analysis. 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 and in some cases, the 1-hour 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 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 our ability to attain the 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.

Trends in 8-hour design values are calculated using three consecutive years of air monitoring data. EPA compares design values to its national air quality standards to determine whether they are met. Figure 3 illustrates trends for the original 126 designated nonattainment areas for ozone for the 3-year periods from 1999 to 2005. As of December 20, 2007, there were 74 nonattainment areas for ozone.

Figure 3. Eight-hour ozone design value trends for the original 126 designated ozone nonattainment areas for the 3-year periods from 1999 to 2005.
(Source: www.epa.gov/airtrends/ozone.html)

Because the design value is calculated as a three-year average of the 4th highest 8-hour value, the effects of the low ozone years of 2003 and 2004 appear to be affecting the 2002-2004 and the 2003-2005 design value calculations. A map has been created that compares for the U.S. and Canada the 2002-2004, 2003-2005, and 2004-2006 periods for the 4th highest 8-hour ozone concentration.

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• On March 12, 2008, the EPA Administrator made the final decision on the human health and vegetation ozone standards. 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 W126 cumulative exposure index. Although the EPA Administrator recommended the W126 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). For additional information concerning the implementation schedule for the revised 8-hour ozone standard, please click here. A list of design values for the 2004-2006 period identifying the violating counties with monitors for the 0.075 ppm ozone standard can be viewed by clicking here. Please note that many counties, which do not currently monitor ozone, may be included when EPA makes its final nonattainment designations. for the revised ozone standard. A map is available for downloading that identifies the violation counties with monitors that exceeed the 0.075 ppm design value for the period 2004-2006. Please remember that additional counties without monitors may be included when nonattainment designations are made.

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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 January 31, 2007, the final version of the OAQPS Staff Paper: National Ambient Air Quality Standards for Ozone: Policy Assessment of Scientific and Technical Information was issued by the EPA. The EPA staff recommended: (1) considering a standard level within the range of somewhat below 0.080 parts per million (ppm) to 0.060 ppm; (2) retaining the 8-hour averaging time and giving consideration to retaining the form of the current standard (i.e., the 4th maximum 8-hour average, averaged over 3 years) or an alternative form within the range of 3rd to 5th maxima, averaged over 3 years; and (3) specifying the level of the standard to the nearest thousandth ppm (3rd decimal place). For the secondary ozone standard (i.e., to protect vegetation), EPA recommended a more biologically relevant form than the 8-hour average standard. Specifically, the EPA recommended a cumulative form to adjust for the differences in the way plants respond to ozone exposure as compared to humans. In agreement with EPA's Clean Air Scientific Advisory Committee (CASAC), staff recommended considering a form of the standard known as the W126 exposure index. The range of suggested values for the W126 was 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 Staff recommended 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. Staff recommended a range of levels from 21 down to 7 ppm-hrs (parts per million –hours). Our analyses and peer-reviewed published papers indicated 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. It is interesting to note that in February 1996, the EPA made the decision to recommend the SUM06 exposure index to protect vegetation from ozone exposure. Similar to the decision made on March 12, 2008 on the revision of the secondary ozone standard, in 1997 the EPA decided not to establish a secondary ozone standard different from the primary standard. You can learn more about the subject of vegetation effects by visiting our Table of Contents web page.

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• As of March 12, 2008, EPA announced that the number of nonattainment areas are 72 ozone (8-hour), 14 ozone (1-hour), 3 carbon monoxide, 10 sulfur dioxide, 47 PM-10, 39 PM-2.5, and 2 lead in the United States. There are no NO2 nonattainment areas in the United States. Maps of the ozone, carbon monoxide, sulfur dioxide, PM-10, and PM-2.5 nonattainment areas are available for review and download.

• Canada has identified the ozone concentrations for the 4th highest 8-hour levels for 2004-2006 for the U.S. and Canada. Maps are available that compare the U.S. and Canada for the 2002-2004, 2003-2005, and 2004-2006 periods for your review.

• EPA released its design value findings on air quality in 2006 on October 1, 2007 and concluded for the period 2004-2006:

	45 of the 126 areas originally designated nonattainment for the 8-hour O3 National Ambient Air Quality Standard (NAAQS) failed to meet the NAAQS in 2004-2006 (see Table);
	2 of the areas originally designated nonattainment have incomplete data (see Table);
	As of August 13, 2007, 43 of the 126 areas originally designated nonattainment for the 8-hour O3 NAAQS have been redesignated to attainment (see Table);
	1 additional unclassifiable/attainment area failed to meet the O3 NAAQS in 2004-2006 (Gregg, Texas) (see Table);
	32 of the original 39 areas designated nonattainment for the PM2.5 NAAQS in April, 2005 (using 2001-2003 data) violated the annual PM2.5 NAAQS in 2004-2006 (see Table);
	29 of the original 39 nonattainment areas violated the 24-hour NAAQS in 2004-2006 (see Table);
	6 of the original 39 designated nonattainment areas met the PM2.5 annual NAAQS in 2004-2006. [In the Philadelphia nonattainment area, all the sites with complete data for 2004-2006 showed attainment but several other monitors which previously showed nonattainment have incomplete data for 2004-2006.] 10 nonattainment areas met the 24-hour PM2.5 NAAQS for 2004-2006. 2 nonattainment areas (Evansville, IN and Wheeling, WV-OH) met both the annual and 24-hour PM2.5 NAAQS for 2004-2006 (see Table);
	The single area (Greenville-Spartanburg, SC) designated as unclassifiable for the PM2.5 NAAQS in April, 2005 again failed to meet the PM2.5 NAAQS (annual standard) in 2004-2006 (see Table); and
	6 additional areas (counties not part of nonattainment areas) also failed to meet the annual PM2.5 NAAQS for 2004-2006. Thirty two additional counties violated the 24-hour PM2.5 NAAQS in 2004-2006. In summary, 39 counties outside of nonattainment areas violated one or both PM2.5 NAAQS in 2004-2006.(see Table); and

In previous discussions about ozone trending, the EPA has noted that the summers of 2003 and 2004 in the East have been cooler than normal. The cooler weather may have influenced the mathematical determination that resulted in the reduction in the number of violation areas, based on 2004-2006 data, in comparison to the 2002-2004, 2003-2005, and 2001-2003 periods. The year 2002 was a high exposure year in the East and affected the number of violation areas determined for the 2001-2003 and 2002-2004 periods. With the year 2004 being a very mild exposure year in some locations in the United States, the 2004-2006 violation determinations are influenced by the low year. The ozone exposures in 2005 were generally higher in the East when compared to 2003 and 2004, but not as high as those experienced in 2002. The summer of 2007 was extremely hot in the United States, especially during the month of August. We shall be reviewing the ozone data for 2007 with interest.

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• On EPA's web site (http://www.epa.gov/airtrends/sixpoll.html), the Agency summarizes emission trends for the period 1980-2006. The table below is a composite of the April 2007 and the most current estimates provided by EPA on its web page.

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

Percent Change in Air Quality

Pollutant	1980 versus 2006	1990 versus 2006
CO	-75	-62
Ozone (8-hour)	-21	-9
Lead	-96	-54
Nitrogen Dioxide	-41	-30
PM10 (24-hour)	--	-30
PM2.5 (Annual)	--	-14
PM2.5 (24-hour)	--	-15
Sulfur Dioxide	-66	-53

Percent Change in Emissions

Pollutant	1980 versus 2006	1990 versus 2006
CO	-50	-38
Lead	-97	-40
Nitrogen Oxides	-33	-29
VOC	-52	-37
Direct PM10	-28	-20
Direct PM2.5	--	-31
Sulfur Dioxide	-47	-38

-- Trend data not available.
PM2.5 air quality based on data since 2000.
Direct PM10 emissions for 1980 was based on data since 1985.
Negative numbers indicate improvements in air quality or reductions in emissions.

• 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 was revising the level of the 24-hour PM2.5 standard to 35 micrograms per cubic meter (µg/m3) and retaining 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 is retaining the 24-hour PM10 and revoking the annual PM10 standard. With regard to secondary PM standards, EPA is making them identical in all respects to the primary PM standards, as revised. The issue of reliability of the epidemiological time-series methodologies continues 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 15, 2006, public health and environmental groups filed suit against the U.S. EPA for refusing to strengthen the PM-2.5 annual standard.

• A.S.L. & Associates has estimated the nonattainment areas for a daily PM-2.5 standard of 35 ug/m3. For the 2004-2005 period, A.S.L. & Associates estimates that there will be 441 counties that violate a possible short-term standard of 35 ug/m3. A map is provided to illlustrate the violation areas. To review the map, please visit our maps web page.

• 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.

• For several years, A.S.L. & Associates has had on-going efforts to better understand the range and frequency of occurrence of background ozone levels that may not be affected by emission reduction strategies. A paper was published in May 2001 by a research team, consisting of Allen Lefohn, Samuel Oltmans, Tom Dann, and Hanwant Singh, confirming that background ozone levels are higher and that the natural short-term variability is more frequent and greater than previously believed. Although spatially low-resolution models (2 degrees by 2.5 degrees, several hundred kilometer spatial resolution) have been exercised and indicate that the conclusions reached by Lefohn et al. (2001) are incorrect, our current research continues to indicate that the conclusions reached by Lefohn et al. (2001) are valid and that the low-resolution models are underestimating policy relevant background concentrations at both high- and low-elevation monitoring sites. 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 can be found in the Air Quality Analyses section of our Table of Contents. In-depth discussions are provided on this very important topic.

• On June 15, 2005, the 1-hour ozone standard was revoked for all areas except the 8-hour ozone nonattainment Early Action Compact Areas (EAC) areas. These areas do not yet have an effective date for their 8-hour designations. To review a map of the 1-hour violating EAC areas, please visit our maps web page.

• Review the areas that exceeded the EPA's PM-2.5 standards based on 2004-2006 data.

• Review the areas that exceeded the EPA's 8-hour ozone standard based on 2004-2006 data.

• Our research team has used ordinary kriging to develop surface ozone models for the years 1982 to 2006. 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 10 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.

• On April 5, 2005, the Environmental Protection Agency (EPA) modified its original 225 nonattainment counties (including the District of Columbia) for the PM-2.5 standard. The number of nonattainment counties has been changed to 208. A map is available that identifies the nonattainment areas. Further information can be obtained from EPA's web site.

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.