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 December 2010 summarized trends for the periods 1980-2009 and 1990-2009. Figures 1 and 2 below have been reproduced from the Agency's website. Table 1 below lists the changes over the past several years.

Figure 1. National 8-hour Ozone Air Quality Trend, 1980-2009. 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, 1990-2009. 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 the first and last year in the time sequence 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%

Maps have been created that compare for the U.S. and Canada the 2002-2004, 2003-2005, 2004-2006, 2005-2007, 2006-2008, and 2007-2009 periods for the 4th highest 8-hour ozone concentration.

As of December 14, 2012, there were 41 nonattainment areas for ozone. Eighty-five of the original 126 nonattainment areas have been redesignated as attainment. These 85 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
• Clearfield and Indiana Counties, PA
• Greene Co, IN
• Detroit-Ann Arbor, MI
• Cleveland-Akron-Lorain, OH
• Columbus, OH
• Haywood and Swain Cos (Great Smoky NP), NC
• Memphis, TN-AR
• Cincinnati-Hamilton, OH-KY-IN
• Door Co, WI
• Manitowoc Co, WI
• Beaumont-Port Arthur, TX
• Allegan Co, MI
• Knoxville, TN
• Baton Rouge, LA
• Chicago-Gary-Lake County, IL-IN
• Milwaukee-Racine, WI

As of December 14, 2012, the 41 nonattainment areas for ozone are as follows:

Extreme (June 2024)

• Los Angeles South Coast Air Basin, CA
• San Joaquin Valley, CA

Severe 15 (June 2019)

• Houston-Galveston-Brazoria, TX
• Los Angeles-San Bernardino Cos(W Mojave),CA
• Riverside Co, (Coachella Valley), CA
• Sacramento Metro, CA

Serious (June 2013)

• Baltimore, MD
• Dallas-Fort Worth, TX
• Ventura Co, CA

Moderate (June 2010)

• Amador and Calaveras Cos (Central Mtn), CA
• Atlanta, GA
• Boston-Lawrence-Worcester (E. MA), MA
• Boston-Manchester-Portsmouth(SE),NH
• Buffalo-Niagara Falls, NY
• Charlotte-Gastonia-Rock Hill, NC-SC
• Greater Connecticut, CT
• Imperial Co, CA
• Jamestown, NY
• Jefferson Co, NY
• Kern Co (Eastern Kern), CA
• Mariposa and Tuolumne Cos (Southern Mtn),CA
• Nevada Co. (Western Part), CA
• New York-N. New Jersey-Long Island,NY-NJ-CT
• Philadelphia-Wilmin-Atlantic Ci,PA-NJ-MD-DE
• Pittsburgh-Beaver Valley, PA
• Poughkeepsie, NY
• Providence (All RI), RI
• San Diego, CA
• Sheboygan, WI
• Springfield (Western MA), MA
• St Louis, MO-IL
• Washington, DC-MD-VA

Marginal (June 2007)

• Albany-Schenectady-Troy, NY
• Chico, CA
• Denver-Boulder-Greeley-Ft Collins-Love., CO
• Essex Co (Whiteface Mtn), NY
• Las Vegas, NV
• Phoenix-Mesa, AZ
• Rochester, NY
• San Francisco Bay Area, CA
• Sutter Co (Sutter Buttes), CA

The figure below illustrates the current 41 nonattainment areas and the 85 areas that were previously designated as nonttainment for the 8-hour 1997 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. Of the 152 million people residing in the original 126 nonattainment areas, there are 118 million people residing in counties that are still designated as nonattainment. Approximately 34 million people reside in counties that have been redesignated as attainment. (Source: http://www.epa.gov/oar/oaqps/greenbook/o8index.html

As indicated above, the "piston effect" makes it difficult to attain the 8-hour standard for many sites. 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 at many sites. 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. Note the rapid decrease in the early years and then a "flattening" of the curve in the later years. The year-by-year figure below illustrates the changes in the 4th highest daily maximum concentration. A rapid decrease in the early years occurred, but less of a decline occurred in the later years. For this monitoring site, a weaker statistically significant downward trend was observed for the 1994-2008 period than for the 1980-2008 period (-1.07 %/year versus -1.82 %/year, respectively) (Lefohn et al., 2010).

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 an 8-hour ozone standard may become 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

Lefohn, A.S., Shadwick, D., Oltmans, S.J. (2010). Characterizing Changes of Surface Ozone Levels in Metropolitan and Rural Areas in the United States for 1980-2008 and 1994-2008. Atmospheric Environment. 44:5199-5210.

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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