Concerns

Some Concerns about the 8-Hour Ozone Standard

In 1994, Drs. Allen S. Lefohn and Paul J. Lioy, who have published extensively in the peer-review literature on exposure-response, described in a New Directions Column, in the distinguished journal Atmospheric Environment, their concerns about the form of the 8-hour ozone standard. One of the several concerns measured was the use of averaging to develop a standard to protect vegetation. The concerns are real and important. In addition, the "piston" effect, as described elsewhere on the web pages, may make it difficult to attain the 8-hour ozone standard.

The figures below show the effect of using averages to describe ozone exposure.

Both figures summarize the ozone data that were collected on August 24, 1998. The figure on the right identifies many more areas of concern than the figure on the left. The hourly average ozone concentrations are the same in the two figures. The difference is that the figure on the right averaged the hourly concentrations over an 8-hour period, while the figure on the left shows the maximum hourly values for the day. By applying averages, the data are smoothed and provide the appearence of greater areas of concern. Laboratory studies show that the peak concentrations are more important than the average concentrations. Thus, the figure on the right may not be as relevant as the figure on the left. Yet, the figure on the right uses the average concentrations similar in the manner that the 8-hour ozone standard is determined.

Scientists and engineers around the world are becoming aware that the United States 8-hour ozone standard may present a problem that is called "unattainability." We discussed this in our peer-review paper published in 1997. In November 1998, the topic was discussed at an international meeting in Beijing, China. The unattainability issue has been raised by A.S.L. & Associates and others. In the coming years, policymakers will find that the 8-hour ozone standard will be difficult to attain and control strategies will not work as planned. Mid-range hourly average concentrations decline slower than the higher hourly average concentrations and make it difficult to attain the standard. Independent analyses have confirmed the "piston effect". EPA reports and papers published in 1985, 1995, and 1996 confirm the effect. A slide presentation summarizing the "piston effect" is available. More detailed information about the effect can be found by clicking here.

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%

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. 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 2001-2003, 2002-2004, and 2003-2005 periods for the 4th highest 8-hour ozone concentration.

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)

As of June 2, 2008, there were 57 nonattainment areas for ozone. Sixty-nine of the original 126 nonattainment areas have been redesignated as attainment. These 69 areas are

Clarksville-Hopkinsville, TN-KY
Fredericksburg, VA
Madison and Page Counties (Shenandoah NP)
Jackson County, IN
Greene County, IN
Muncie, IN
Terre Haute, IN
Birmingham, AL
Charleston, WV
Evansville, IN
Rocky Mount, NC
Hancock, Knox, Lincoln, and Waldo, ME
Portland, ME
Kent and Queen Anne's, MD
Fort Wayne, IN
Parkersburg-Marietta, WV-OH
Steubenville-Weirton, OH-WV
Wheeling, WV-OH
Benton Harbor, MI
Canton-Massillon, OH
Flint, MI
Grand Rapids, MI
Kalamazoo-Battle Creek, MI
Lansing-East Lansing, MI
Lima, OH
Muskegon, MI
Benzie Co, MI
Cass Co, MI
Huron Co, MI
Mason Co, MI
Norfolk-Virginia Beach-Newport News
Richmond-Petersburg, VA
Louisville, KY-IN
Lancaster, PA
Tioga Co, PA
South Bend-Elkhart, IN
La Porte, IN
Harrisburg-Lebanon-Carlisle, PA
Franklin Co, PA
Altoona, PA
Johnstown, PA
Toledo, OH
Dayton-Springfield, OH
Reading, PA
Huntington-Ashland, WV-KY
Macon, GA
Erie, PA
Murray Co (Chattahoochee Nat Forest), GA
Indianapolis, IN
Youngstown-Warren-Sharon, OH-PA
State College, PA
Scranton-Wilkes-Barre, PA
Raleigh-Durham-Chapel Hill, NC
York, PA
Greensboro-Winston Salem-High Point, NC
Berkeley and Jefferson Counties, WV
Chattanooga, TN-GA
Columbia, SC
Fayetteville, NC
Frederick Co, VA
Greenville-Spartanburg-Anderson, SC
Hickory-Morganton-Lenoir, NC
Johnson City-Kingsport-Bristol, TN
Nashville, TN
Roanoke, VA
San Antonio, TX
Washington Co (Hagerstown), MD
Allentown-Bethlehem-Easton, PA
Kewaunee Co, WI

The figure below illustrates the current 57 nonattainment areas and the 69 areas that were previously designated as nonttainment for the 8-hour ozone standard.

Although more than half of the originally designated nonattainment areas have been redesignated to attainment, many of the areas that are the most populated still remain in nonattainment. Five nonattainment areas were recently reclassified (i.e., bumped up) from Marginal (June 2007) to Moderate (June 2010) because the areas did not reach attainment within the designated time periods. The five areas are:

Atlanta, GA
Imperial Co, CA
Memphis, TN-AR
Baton Rouge, LA
Beaumont-Port Arthur, TX

On June 19, 2008, the Ventura County nonattainment area will be reclassified from Moderate (June 2010) to Serious (June 2013).

As indicated above, the "piston effect" will make it difficult to attain the 8-hour standard and remain in attainment. In 1997, we published a paper indicating that nonattainment areas would go into and out of attainment because of the "piston effect." The previous Birmingham, Alabama nonattainment area violated the 8-hour ozone standard for the 2004-2006 period. The summer of 2007 was extremely hot in the United States, especially during the month of August. In our preliminary review of the ozone data for 2007, we have noted that several of the areas that were originally designated nonattainment but had been changed to attainment had violated the 8-hour standard for the 2005-2007 period. This is consistent with the predictions discussed in our 1997 peer-reviewed paper.

The "piston" effect as described in the peer-review literature and on this web site affects the ability of the nation to atttain the 8-hour ozone standard and in some cases, the 1-hour standard. 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) The figure below illustrates the "piston" effect as it affects ozone in Fairfield County, CT.

From 1980 through 1994, significant decreases occurred. However, since 1994, no significant trend in decreasing ozone has occurred. When one compares the Fairfield County figure with the results described in EPA's latest trends report, the similarities are observed. The slight downward pattern observed for the periods 2002-2004, 2003-2005, and 2004-2006 is a result of the 0.081 ppm 4th highest annual 8-hour average value experienced in 2004. The year-by-year figure below illustrates what is happening.

The 0.081 ppm value that occurred in 2004 is the lowest 4th highest annual 8-hour average value recorded between 1980 and 2007. The 4th highest values recorded in the years 2005 and 2006 were 0.090 and 0.095 ppm, respectively. The effect of the 0.081 ppm value was to depress the 3-year average of the 4th highest 8-hour concentration for the 2004-2006 period. As noted in the previous figure, the 4th highest 8-hour average increased from 0.089 for the 2004-2006 period to 0.092 for the 2005-2007 period. The elimination of the 2004 contribution of the 0.081 ppm value (as a result of including only the years 2005, 2006, and 2007) resulted in a higher 3-year average for the 4th highest 8-hour concentration for the 2005-2007 period. It appears that the "piston" effect is affecting, in a large degree, the nation's ability to improve its air quality.

What is the cause of the "piston" effect? Research appears to point to the possibility that natural causes are partly responsibile for it. Possible reasons for it have been discussed in the literature (Reynolds et al., 2003; Reynolds et al., 2004). The authors commented on possible chemical explanations for the observation that more prominent trends in peak 1-h O3 levels than in peak 8-h O3 concentrations or in occurrences of mid-level (i.e., 0.06 to 0.09 ppm) concentrations have been reported. The authors noted that when anthropogenic VOC and NOx emissions are reduced significantly, the primary sources of O3 precursors are biogenic emissions and CO from anthropogenic sources. Chemical process analysis results indicated that a slowly reacting pollutant such as CO could be contributing on the order of 10 to 20% of the O3 produced. The authors recommended that further work focus on the need to confirm that biogenic emissions have not been significantly overestimated in the most recent emission inventories and on the examination of the effects of CO reductions.

Is there a way to get around the "piston" effect. Probably not. We must realize its existence and deal with it in implementing our national ozone standards. If we do not, then it is possible that the 8-hour ozone standard promulgated in 1997 will be a "goal" instead of an attainable standard and demands for further emission reductions because of the unattainability of the ozone standard will be resisted not just by many in our society but also by the "piston" effect itself. To learn more about the "piston" effect, please click here.

References

Reynolds, S. D.; Blanchard, C. L.; Ziman, S. D. (2003) Understanding the effectiveness of precursor reductions in lowering 8-hr ozone concentrations. J. Air & Waste Manage. Assoc. 53: 195-205.

Reynolds, S. D.; Blanchard, C. L.; Ziman, S. D. (2004) Understanding the effectiveness of precursor reductions in lowering 8-hr ozone concentrations - Part II. The Eastern United States. J. Air & Waste Manage. Assoc. 54: 1452-1470.

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