EPA’s New Ozone Rule: Part 8

Posted on July 23, 2012 | Leave a comment

In 2008, the EPA under George W. Bush reduced the maximum allowable concentration of ground-level ozone from 80 ppb to 75 ppb1. Two years later, the EPA decided to reduce the limit still further to 70 ppb.2. What made the EPA decide to do so in only two years? This was unusual because the Clean Air Act only requires the EPA to review its policy on ozone once every five years, the next review required in 20133. What was the rush?

In April 2008, soon after the EPA lowered the standard, the Clean Air Scientific Advisory Committee (CASAC, EPA’s scientific advisory board on clean air4) sent the EPA a letter strongly disagreeing with the new standard, claiming that the new ozone standard was not low enough to provide a margin of safety. It wanted a primary standard between 60 and 70 ppb. In addition, CASAC felt that a different secondary standard should be established to protect property and the environment. This standard should be cumulative rather than be based on highest average readings5.

A month later, a number of groups challenged EPA’s standards in court. Some of them felt the standard went too far: business interests and some states. Other petitioners felt the standard did not go far enough: environmental organizations, public health organizations, and other states. These lawsuits were consolidated into one: State of Mississippi et al v. U.S. Environmental Protection Agency. In March 2009, the EPA filed an unopposed motion to hold the lawsuit in abeyance while it reviewed the new standard. 6 The revised standard, which lowered the maximum allowable concentration from 75 ppb to 70 pbb, was published in July 20117. In September 2011, the Obama administration requested that the EPA rescind its new standard8.

The document which lays out this new standard, National Ambient Air Quality Standards for Ozone, Final Preamble published July 7, 2011, lays out a detailed explanation of EPA thinking: why it didn’t think 75 ppb was a good enough standard, why 60 ppb was too low and 70 ppb was about right, and why it felt a new secondary standard to protect property and the environment was necessary9. I am going to try to summarize that thinking here.

Footnotes:

  1. U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Third External Review Draft, June 2012, p.lxxiii.
  2. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, p.6.
  3. United States Code, Title 42, Chapter 85, §7409 (d)(1). To view, click here.
  4. The Clean Air Act requires that an independent scientific body review the NAAQS at five-year intervals and make recommendations. CASAC currently fulfils this role. See United States Code, Title 42, Chapter 85, §7409 (d)(2). To view, click here.
  5. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, p.18.
  6. ibid.pp.29-30
  7. This is the National Ambient Air Quality Standards for Ozone, Final Preamble, 2011 that has been referred to above.
  8. Statement by the President on the Ozone National Ambient Air Qualities Standards. White House website. To view, click here.
  9. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011. The rationale for the primary standard (section II) starts on p. 34 and the rationale for the secondary standard (section III) starts on p. 192.

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EPA’s New Ozone Rule: Part 7

Posted on July 19, 2012 | 1 comment

Before discussing why EPA should lower the limit on maximium ground-level ozone concentration from 75 ppb to 70 ppb, we need to explain why EPA needs to regulate ozone in the first place. Just to clarify, we are not dealing with stratospheric ozone high above the earth’s surface 10 miles up that protects us from harmful ultraviolet radiation from the sun. Rather, we are strictly speaking about ground-level ozone, the only ozone that people have direct exposure to.

Ozone is a highly corrosive chemical, one of the most chemically active known (reaction potential = 2.07 volts in an acid solution at 25°C)1. When breathed in, it attacks the upper respiratory tract and the lungs2. Breathing 100% ozone is quickly fatal, in fact, breathing air with as little as 50 ppm (50,000 ppb) ozone will likely kill a human within a half-hour3. It has been observed that people inhaling 9 ppm ozone along with other air pollutants developed pulmonary edema3.

Ozone at much lower concentrations can also cause problems. To quote EPA’s Integrated Science Assessment:

…short-term O3 exposures induced or were associated with statistically significant declines in lung function. An equally strong body of evidence from controlled human exposure and toxicological studies demonstrated O3-induced inflammatory responses, increased epithelial permeability, and airway hyperresponsiveness. Toxicological studies provided additional evidence for O3-induced impairment of host defenses. Combined, these findings from experimental studies provided support for epidemiologic evidence, in which short-term increases in O3 concentration were consistently associated with increases in respiratory symptoms and asthma medication use in children with asthma, respiratory-related hospital admissions, and ED [emergency department – MHK] visits for COPD [chronic obstructive pulmonary disease, including chronic bronchitis and emphysema – MHK] and asthma. Additionally, recent evidence supports the range of respiratory effects induced by O3 by demonstrating that short-term increases in ambient O3 concentrations can lead to respiratory mortality. The combined evidence across disciplines supports a causal relationship between short-term O3 exposure and respiratory effects4.

The decrease in lung function caused by short-term exposure to ozone quickly fade when the ozone is removed5. However, repeated exposure to ozone over a long period of time may cause more chronic problems such as reduced lung function6. Ozone has also been implicated in causing problems to the cardiovascular, central nervous, and reproductive systems, although these have not been conclusively proven. 6. There is not enough evidence to suggest that ozone causes cancer6.

The EPA’s National Ambient Air Quality Standards 2011 document on ozone states these concerns with some passion:

These physiological effects [inflammation and damage to the respiratory system and impaired host defense capabilities – MHK] have been linked to aggravation of asthma and increased susceptibility to respiratory infection, potentially leading to increased medication use, increased school and work absences, increased visits to doctors’ offices and emergency departments, and increased hospital admissions. Further, pulmonary inflammation is related to increased cellular permeability in the lung, which may be a mechanism by which O3 exposure can lead to cardiovascular system effects, and to potential chronic effects such as chronic bronchitis or long-term damage to the lungs that can lead to reduced quality of life. These are all indicators of adverse O3-related morbidity effects, which are consistent with and lend plausibility to the adverse morbidity effects and mortality effects observed in epidemiological studies.7

Ozone has also been shown to injure plants and reduce their growth. This reduces agricultural yields and the productivity of ecosystems8. Ozone is a significant greenhouse gas, and is probably contributing to global warming9. However, I would think that it would be less than a threat than carbon dioxide, because ozone tends to quickly decompose into oxygen whereas carbon dioxide can linger in the atmosphere for a century or more10. Nevertheless, if society is constantly generating more ozone, the contribution to climate change could be significant. If it reduced its ozone production, this contribution would fade almost instantaneously.

To demonstrate the extent of scientific research documenting the effects of ozone on human health, I excerpted the reference section of Chapter 6 of EPA's Integrated Science Analysis, the chapter that discusses the health effects of short-term ozone exposure. This reference section lists some 500 scientific papers on the effects of ozone. I have not read these papers except for one, so I cannot vouch for them; nevertheless, the list taken together is formidable. Take a look yourself by clicking on the link below. You can click on any reference in the list to see the paper’s abstract.

Reference Section of Chapter 6

The next question we must discuss is: Granted that trace amounts of ozone in the ground-level atmosphere is injurious to human welfare, how do we know that 75 ppb (the former limit) is still injurious? Why wasn’t that level good enough? Why did the EPA think it should lower it?

Footnotes

  1. Rein Munter, Ozone: Science and Technology,Encyclopedia of Life Support Systems. To view, click here.
  2. U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Third External Review Draft, Section 6.2: Respiratory Effects, p. 6-1ff.
  3. Ozone Levels and Their Effects, edited by Den Rasplicka, OzoneLab Instruments website. To view, click here.
  4. U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Third External Review Draft, Chapter 1: Executive Summary, p.1-6.
  5. Ibid., Chapter 6: Integrated Health Effects of Short-Term Ozone Exposure, pp. 6-14, 6-27, 6-165.
  6. Ibid., Table 1-1: Summary of ozone causal determinations by exposure duration and health outcome, p. 1-5. Table 2-2: Summary of evidence from epidemiologic, controlled human exposure, and animal toxicological studies on the health effects associated with short- and long-term exposure to ozone, pp 2-25 — 2-26.
  7. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, p.40.
  8. U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Third External Review Draft, Table 1-2: Summary of ozone causal determination for welfare effects, p. 1-8. Table 2-3: Summary of ozone causal determination for vegetation and ecosystem effects, p.2-40.
  9. Ibid., Section 2.7.1: Tropospheric Ozone as a Greenhouse Gas, pp. 2-49 — 2-50.
  10. I don’t have a single source for this. Wikipedia quotes M.Z. Jacobson in a 2005 letter to the Journal of Geophysical Research, 110 pp. D14105, as estimating the atmospheric lifetime of carbon dioxide as 300 years (click here to view the Wikipedia article). David Archer, in his article Fate of Fossil Fuels in Geologic Time, Journal of Geophysical Research, Volume 110 C09S05, argues, “A better approximation of the lifetime of fossil fuel CO2 for public discussion might be ‘300 years, plus 25% that lasts forever.'” He claims that when additional carbon dioxide is added to the atmosphere, some of it lingers for tens of thousands of years. To see the article, click here. See also Archer, David et al, Atmospheric Lifetime of Fossil Fuel Carbon Dioxide, Annual Review Earth Planet Sci. 2009 37:117-34 (click here to view). For a lively discussion of the topic, see the Skeptical Science website, which you can read by clicking here.

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EPA’s New Ozone Rule: Part 6

Posted on July 11, 2012 | 2 comments

Let’s look at EPA’s proposed ozone rule to see exactly what it entails. Unlike previous ozone rules, it has two distinct parts1:

  • A primary standard to protect human life and health.
  • A secondary standard to protect property, agriculture, and the environment.

Technically speaking, EPA rules always had primary and secondary standards, but up to now, the ozone primary and secondary standards were identical2. This is the first time that the two standards were made distinct, done at the urging of EPA’s Clean Air Scientific Advisory Committee (CASAC)3.

The two standards are different in character. The primary standard is based solely on averages4. If the average ozone concentration rises above a certain level, that location is in non-attainment. The secondary standard is based on cumulative exposure to ozone1. It is more focused on the effects caused by long-term exposure to ozone.

The new rule is making an interesting statement: it appears that with regards to human health we are more interested in the acute effects of high exposure. With property and agriculture, we seem more concerned with ozone’s long term effects. Yet the EPA is aware of that long-term exposure to ozone can degrade human health over time.

Now if a locale is to be in attainment, it presumably must meet both the primary and secondary standards. Sometimes one standard will be more stringent, sometimes the other. Consider locales which meet one standard and not the other. In one locale, ozone levels are usually very low. Occasionally, they peek to high levels, just often enough so that the locale does not meet the primary standard, yet the cumulative exposure to ozone remains low. In another locale, ozone levels are consistently high causing large cumulative exposure, but they fall just shy of breaking the primary standard. State and Federal authorities will need to keep track on two sets of numbers for each locale to enforce both standards.

The primary standard in the proposed rule is actually the same as in current rule, just a little stricter, the maximum concentration lowered from 75 ppb in the current rule to 70 ppb. The air is sampled frequently at a measuring station, and readings are averaged out over an eight-hour period. This yields 1,095 such averages in a calendar year (1,098 in a leap year). The three highest averages are thrown out and the fourth-highest average is used to represent the year’s maximum. The maximums from three consecutive years are then averaged together. If this composite average exceeds 70 ppb, that locale is considered in nonattainment1.

The secondary standard is a little more complicated but easily understandable if you remember your high school algebra. The values to be summed are not the ozone concentrations themselves but a calculation based on each reading of ozone concentration, called the W126 index5. To determine, the cumulative index, hourly readings of ozone concentrations are taken at an individual station 12 hours a day, starting at 8 a.m. and finishing at 7 p.m. A value Wi is then calculated as follows:

                                     Wi =        Ci                 

                                             1 + 4403e –ACi

where:

Ci (read as “C sub i”) is the reading of ozone concentration measured in parts per million (ppm) taken at hour i. Because the W126 index is cumulative, Ci is in units of ppm-hours.
e is the base of natural logarithms, approximately equal to 2.71828.
A is a constant equal to 126/ppm-hour.

For example, suppose at 2:00 in the afternoon we measured an ozone concentration of .083 ppm. We would then calculate a W value for 2 pm this way:

             W2pm =                              .083 ppm-hours                   
                                1 + (4403)(e – (126/ppm-hour)(.083 ppm-hours))

This can easily be calculated with the help of a scientific calculator6 (note that the ppm-hours units cancel in the exponent as they should), yielding a value of 0.74 ppm-hours. This means that the ozone concentration at 2 pm will contribute slightly less to the cumulative total than if we did not use the formula (.074 ppm-hours versus .083 ppm-hours).

The Wi values are summed each day, giving a daily cumulative total:

Wdaily = ΣWi

summed from the first reading of the day at 8 am to the last reading at 7 pm.

The Wdaily values are themselves summed over a three-month period. As I understand it, these are running totals: January-February-March, February-March-April, March-April-May, and so on.

W126 = ΣWdaily

summed from the first day of each three-month period through the last day.

Thus, each calendar year produces ten W126 values, from January-February-March through October-November-December. The highest W126 value for the year is selected. This process is carried out for three consecutive years, producing three yearly maximum W126 values. The average of these three values is the final W126 value. If it is higher than 13 ppm-hours, then the area where the readings were taken is declared to be in non-attainment5.

For example, the following are fictitious highest W126 totals summed up during each of 2008, 2009, and 2010. All values are in ppm-hours:

Year Highest Value Period Summed
2008 15.2 Apr-May-Jun
2009 14.3 May-Jun-Jul
2010 12.9 Mar-Apr-May

The average of these three values is 14.1 ppm-hours. Since this is above the standard of 13 ppm-hours, the area from where these readings were taken is in non-attainment.

Why is the W126 index used? To quote A.S.L. & Associates, a Montana company whose founder developed the W126 index:

The W126 index is a cumulative exposure index that is biologically based. The W126 ozone index focuses on the higher hourly average concentrations, while retaining the mid- and lower-level values. By applying a continuous weighting, the W126 index has the advantage of not utilizing an artificial “threshold.”

In 1985, A.S. Lefohn proposed the use of the W126 ozone exposure index for predicting vegetation effects. The cumulative W126 exposure index uses a sigmoidally weighted function (i.e., “S” shaped curve) as described by Lefohn and Runeckles (1987) and Lefohn et al. (1988). The W126 index is a cumulative exposure index and not an “average” value. It is a biologically based index, which is supported by research results (i.e., under both experimental and ambient conditions) that show that the higher hourly average ozone concentrations should be weighted greater than the mid- and lower-level values. The W126 index is accumulated over a specified time period.7

Let’s look again at the equation that defined the individual hourly W126 values, designated as Wi:

                                     Wi =        Ci                 

                                             1 + 4403e –ACi

Let’s plot the Wi values on a graph as a function of the original hourly ozone concentrations that generated them, Ci:

Graph of Wi values plotted against the ozone concentrations used to calculate the values.

As the graph shows, when the ozone concentration Ci is less than .035 ppm-hour, Wi values are negligible. As Ci increases, the Wi values quickly climb, but are still always less than Ci. As Ci increases beyond about .085 ppm-hour, the growth rate of Wi subsides somewhat until about .10 ppm-hour, when Ci nearly equals Wi (within 1%), and the graph becomes linear. This shows that for ozone concentrations less than 0.035 ppm, the W126 values contribute almost nothing to the cumulative total. For concentrations greater than than .100 ppm, the W126 values are almost identical to the ozone concentrations. In between 0.035 ppm and .100 ppm, the contribution varies, with larger concentrations contributing much more to the cumulative total than smaller concentrations.

You can also see this in a table that I prepared of oxygen concentrations in increments of .010 ppm and their corresponding W126 values:

Ozone   Percent of Ozone
Concentration (ppm) W126 Value Concentration
0.01 0.0000 0.08%
0.02 0.0001 0.28%
0.03 0.0003 0.99%
0.04 0.0014 3.39%
0.05 0.0055 11.01%
0.06 0.0182 30.36%
0.07 0.0424 60.59%
0.08 0.0675 84.42%
0.09 0.0855 95.03%
0.10 0.0985 98.54%

Footnotes:

  1. U.S. Environmental Protection Agency, National Ambient Air Quality Standards, 2010, pg. 1 and pg. 6
  2. U.S. Environmental Protection Agency website, Ozone (O3) Standards – Table of Historical Ozone NAAQS. To view, click here.
  3. U.S. Environmental Protection Agency, National Ambient Air Quality Standards, 2010, pg. 17.
  4. ibid., pg. 34
  5. ibid., pg. 193.
  6. It is even easier using Microsoft Excel® or similar spreadsheet program. If an ozone concentration in ppm is in cell A1, then this formula typed in cell B1 will give the corresponding W126 value:

    = A1 / (1 + 4403 * EXP(-126*A1))

  7. A.S.L. & Associates website, How the W126 Ozone Exposure Index Was Developed. To view, click here.

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EPA’ s New Ozone Rule: Part 5

Posted on July 2, 2012 | Leave a comment

On September 2, 2011, the Obama administration rescinded an EPA proposal to tighten standards on ozone in the atmosphere at ground level1.   This proposal would have:

  • Lowered the maximum allowable concentration of ground-level ozone from 75 parts per billion (ppb) to 70 ppb2. This is the primary standard whose purpose is to safeguard human health.
  • Introduced a secondary standard based on a cumulative total of ozone exposure, 13 parts per million-hours (ppm-hour) in a three month period2. One ppm-hour is the exposure one receives from breathing an atmosphere of 1 ppm ozone for one hour. Two ppm-hours is the exposure of 1 ppm for 2 hours or 2 ppm for 1 hour. The purpose of the secondary standard is to protect property, quality of life, and wildlife habitat.

The question we want to consider is: Did it serve the public interest to rescind the proposed regulation or would it have been better to allow the regulation to become law? Does the benefit that the regulation provides the public outweigh the costs or vice versa?

Some might argue that a regulation that is shown to save lives offers a benefit that outweighs all costs, but that isn’t necessarily true. We put a finite price on human life all the time: insurance companies, the courts, the medical profession, governments. To show why we must do this, ask yourself this question: suppose a single person was in grave danger but could be rescued for a billion dollars. Should the government pay a billion dollars to rescue that individual? There is a raging debate how about much money to spend on medical care for the poor at a cost much less than a billion dollars per life. There are limits to how much we can spend to rescue people, especially when the costs can affect the business and economic climate3.

Another example: suppose we want to institute environmental regulation X. X will save the lives of 1000 people but will cause 10,000 people to be laid off from their jobs. Is it worth it? What if it will save the lives of 5,000 people? 10,000 people? 100,000 people? What if X will reduce tax revenues needed for schools, sanitation, police and fire services? When the question is phrased as a matter of extremes (X will save a million lives at an economic cost of ten million dollars, or X will save a handful of lives but will wreak economic havoc), most of us would find the question easy to answer. But when the costs and benefits are more balanced, that’s when it becomes tricky.

Of course, saving lives are not the only benefits of environmental regulations4. Tougher ozone standards promise to reduce the amount and severity of respiratory illness5, even to increase general wellness, helping to keep our lung function from deteriorating over long periods of time. The atheletes among us will be able to retain their abilities longer, but even ordinary people may be able to retain their vigor longer into their old age.

Lower ozone levels could particularly benefit those with pre-existing respiratory conditions, such as asthma, chronic bronchitis, and emphysema5. While people with these conditions represent just a fraction of the population, they still deserve our consideration. We have a legislative precedent: the Americans with Disabilities Act (ADA) has made life easier for millions of people6. If we demand accommodations for the blind, the deaf, and wheelchair-bound, we should also make accommodation for those with breathing difficulties.

There are also economic benefits from tougher ozone standards. If even low concentrations of ozone make some people ill, then maintaining lower concentrations will mean less illness. That means lower health care costs, less productivity lost at work, less absences at school. Ozone also damages plant life7; lower ozone levels will benefit agriculture as well as protect other forms of property (ozone is murder on certain types of rubber8). Less tangible is the damage that can be prevented to our national parks and other wildlife habitat.

On the other hands, there could be substantial costs. Ozone is not emitted directly by industry but is formed from other chemicals released into the air9. To reduce ozone, industry (as well as private cars and trucks) must curtail these emissions, and that can be expensive. If the costs are too great, companies will become less profitable, will need to cut back on hiring, will yield less tax revenue, may be tempted to move to other jurisdictions with less onerous regulation. The EPA is prohibited by law from allowing cost considerations to influence its decision to impose new and stricter regulations10. But we are not so prohibited, and we need to weigh costs against benefits to determine how society’s interests are best served.

Footnotes:

  1. Statement by the President on the Ozone National Ambient Air Qualities Standards. White House website. To view, click here.
  2. U.S. Environmental Protection Agency, National Ambient Air Quality Standards, 2010, p. 1. To view the document, click here.
  3. A related concept is the value of statistical life (VSL), which is a measure of how much people are willing to pay for reduction of danger to life. For a discussion on determining VSL in three provinces in China, see the paper The Value of Statistical Life by Jie He and Hua Wong, World Bank eLibrary, which you can view by clicking here. See also the Wikipedia article Value of Life which you can view by clicking here.
  4. For discussions of mortality associated with ozone exposure, see the U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Second External Draft, September 2011, Sections 2.6.2, 6.6, 7.4.10, and 7.7. To view the document, click here, then click the button “Get the Report.”
  5. For discussions of health conditions associated with ozone exposure, see the U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Second External Draft, September 2011, Sections 2.6, 6.2 through 6.5, and 7.3 through 7.6. To view the document, click here, then click the button “Get the Report.”
  6. For discussions of the effect of ozone on lung health, see the U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Second External Draft, September 2011, Sections 6.2 and 7.2. To view the document, click here, then click the button “Get the Report.”
  7. The U.S. Equal Employment Opportunity Commission maintains a website with a good summary of the ADA, which you can view by clicking here.
  8. For discussions of the effect of ozone on vegetation and the environment, see the U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Second External Draft, September 2011, Sections 2.7 and 9. To view the document, click here, then click the button “Get the Report.”
  9. See my post “EPA’s New Ozone Rule, Part 4” which you can view by clicking here.
  10. U.S. Environmental Protection Agency, National Ambient Air Quality Standards, 2010, p. 9. To view the document, click here.

    Actually, this prohibition is not actually stated by the Clean Air Act, but has been inferred by the courts. It is based on Section 109 of the Clean Air Act (United States Code, Title 42, Section 7409, which you can read by clicking here) which states in subsection (b)(1): “National primary ambient air quality standards…based on such criteria and allowing an adequte margin of safety, are requisite to protect the public health.” Similarly, it states in subsection (b)(2): Any national secondary ambient air quality standard…is requisite to protect the public welfare from any known or anticipated adverse effects associated with the presence of such air pollutant in the ambient air.” The Supreme Court in its ruling in the case Whitman v. American Trucking Associations, Inc. (which you can read by clicking here) inferred from the lack of mention of cost as a criteria in determining NAAQS that cost was excluded. This is because in other places, the Clean Air Act explicitly does allow cost as a criteria. As an Orthodox Jew, I take great pleasure from this argument — it could have come straight from the Talmud.

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EPA’s New Ozone Rule: Part 4

Posted on December 15, 2011 | 1 comment

This post is based on information provided by two websites:

  • Washington University in St. Louis, Missouri. Chemistry 152: How Does Ozone Form? Unfortunately, the link to this website has been broken and the website is no longer available. (A shame, as it was really well done.)
  • NASA Earth Observatory, Chemistry in the Sunlight: The Chemistry of Ozone Formation To view, click here

See also Geoffrey Tyndal, Peroxy Radicals: Big Players on Ozone Production, website hosted by the project Stratopheric Processes And Their Role in Climate (SPARC) (University of Toronto). To view, click here.

Special thanks to Dr. Tyndal who graciously answered my questions regarding ozone formation. He explained to me how the VOC molecule whose peroxy radical had surrendered a oxygen atom to nitric oxide could continue to form more ozone, allowing concentrations to grow.

See also the website Environmental Science Published for Everybody Round the Earth (ESPERE), Lower Atmosphere: Oxidation in the Atmosphere. To view, click here.

If I am misunderstanding or misinterpreting the information, readers are urged to correct me. First, I want to describe the chemicals that we will be discussing here:

Nitrogen oxides consist of some combination of nitrogen and oxygen. We will be discussing two here. The first is nitric oxide, whose molecule consists of one nitrogen atom bonded to one oxygen atom:

NO

Nitrogen dioxide is a gas whose molecules consist of one nitrogen atom bonded to two oxygen atoms:

NO2

Volatile organic compounds (VOCs) are organic compounds (compounds containing carbon) that can exist as a gas or vapor in the atmosphere. Examples include natural gas, drinking alcohol, gasoline, fresh paint, nail polish remover, cooking aromas, women’s perfume.

Radicals are fragments of molecules that have one or more unpaired electrons. This makes them highly reactive: they are desperate to attach themselves to any molecule that will take them. They can have a positive, negative, or neutral charge. We will mention three types of radicals in this post, all of them neutral:

  • hydroxyl radicals consists of a hydrogen atom bonded to an oxygen atom, the chemical formula being (the mid dot [·] after the formula denotes electric neutrality):

    OH·

  • Peroxyl radicals consists of two oxygen atoms. Normally, O2 is ordinary oxygen gas, but it can act as a radical, as we shall see.
  • Hydroperoxyl radicals consists of a hydrogen and two oxygen atoms bonded together:

    HO2

    • In my last post, I wrote about the formation of stratospheric ozone that it is primarily produced by ultraviolet radiation from the sun. The ozone there does an excellent job in absorbing the radiation, so that very little ultraviolet radiation (of the type that forms ozone) reaches the ground. Ground-level ozone, by contrast, forms as the result of the chemical reactions of atmospheric nitrogen oxides. These nitrogen oxides are mostly formed by the burning of fuel in the presence of nitrogen and oxygen, the two most prevalent gases of Earth’s atmosphere. The high temperature of combustion fuses the nitrogen and oxygen into one molecule. This is why the exhaust of cars and coal-burning electric plants can be laden with nitrogen oxides. Lightning and chemical processes in the soil are also sources.

    There are many forms of nitrogen oxides; the two that are relevant here are nitric oxide (NO) and nitrogen dioxide (NO2). Only nitrogen dioxide directly produces ozone. A nitrogen dioxide molecule struck by a photon of sunlight (represented here as hv) will break down into nitric oxide and a free oxygen atom:

    NO2 + hv → NO + O    (1)

    The free oxygen atom is highly reactive and will quickly combine with a nearby oxygen molecule to form ozone.

    O2 + O → O3    (2)

    If that was all there was to it, the ozone problem would be much more manageable. Ozone is not a stable molecule: it reacts with surrounding chemicals to break down into ordinary oxygen. For example, ozone recombines with nitric oxide to reform nitrogen dioxide and ordinary oxygen:

    O3 + NO → NO2 + O2    (3)

    The amount of ozone would be much lower than it actually is, because it would be destroyed soon after being formed. There is a complicating factor, however.

    Volatile organic compounds (VOCs) can convert nitric oxide back into nitrogen dioxide with the help of the hydroxyl radical, a substance that composes a tiny proportion of the atmosphere (parts per trillion!) but can have a significant impact nonetheless. Suppose we represent a VOC molecule with the single chemical symbol R. Now VOC molecules usually have several hydrogen atoms. What we will do is exclude a single hydrogen atom from what is represented by R, such that the entire molecule is represented by the symbol:

    R-H

    where H represents the single hydrogen atom.

    When the VOC molecule contacts a molecule of ordinary oxygen and a hydroxyl radical (OH·), the single hydrogen atom is replaced with a peroxy radical (O2·). A water molecule is also formed. The reaction is:

    R-H + HO· + O2 → RO2· + H2O    (4)

    When the VOC molecule with the peroxy radical attached encounters a molecule of nitric oxide (NO), the peroxy radical gives up one atom of oxygen to the nitric oxide, converting it into nitrogen dioxide:

    RO2· + NO → RO· + NO2    (5)

    The nitrogen dioxide is then free to form more ozone.

    But it doesn’t stop there. If the VOC molecule with the extra oxygen atom has another hydrogen atom (and it usually does), it can react with an oxygen molecule to form a carbonyl compound (a compound where an oxygen and a carbon atom share a double bond) plus a hydroperoxyl radical (HO2·). I represent the VOC molecule in the following equation as RCHO· to emphasize the presence of a carbon atom, a hydrogen atom, and an oxygen atom radical, and I represent the carbonyl compound as RC=O:

    RCHO· + O2 → HO2· + RC=O    (6)

    The hydroperoxyl radical can then react with nitric oxide to form the hydroxyl radical plus nitrogen dioxide, both of which can participate in further reactions to form more ozone:

    HO2· + NO → HO· + NO2    (7)

    This description is an oversimplification. There are other chemical pathways for ozone to form. Also, small amounts of ozone can drift down from the stratosphere. But this gives a good idea how much of ground-level ozone is created. The main point is that ozone creation is a cycle. Nitrogen dioxide reacts with ordinary oxygen to form nitric oxide and ozone. Nitric oxide is converted back to nitrogen dioxide by the peroxy radical in VOC molecules. It is then free to convert more oxygen to ozone, and on the cycle goes. The presence of VOCs in the atmosphere, therefore, maintains a level of ozone in that vicinity.

    Why is this information important to our question of ozone regulation? We need to sit down with industry and discuss what needs to be done to reduce ozone concentrations at ground level. Industry emits very little ozone; it does emit ozone precursors and these need to be controlled. By knowing how much these precursors need to be reduced, we can work with industry to set up best practices while minimizing the burden, trying to keep both necessary capital expenditures and additional operational costs as low as possible.

    Finally, it appears that a small amount of ground-level ozone (below 15 ppb, perhaps?) is actually beneficial, because it generates the hydroxyl radical. The hydroxyl radical has been called the detergent of the atmosphere, because it is very good at eliminating many atmospheric pollutants. The hydroxyl radical constantly needs to be replenished, because its atmospheric lifespan is only a few seconds. See the article written by Phillip Ball entitled Fast-Acting Atmospheric Detergent (starting with the fifth paragraph) in the journal Nature, November 3, 2000, which you can view by clicking here.

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EPA’s New Ozone Rule: Part 3

Posted on December 15, 2011 | Leave a comment

To understand atmospheric ozone, it is important to know how it is formed. In a previous post, I pointed out how ground-level ozone affects humans differently than the higher-up stratospheric ozone (thus the quip, “Good on high, bad nearby”1.) The way they are formed is different as well. Stratospheric ozone is formed when solar ultraviolet radiation strikes ordinary oxygen molecules (O2) and disassociates them into single atoms of oxygen. The ultraviolet energy is absorbed by the oxygen and does not reach the ground. These single atoms are extremely reactive and combine with nearby oxygen molecules to form triatomic oxygen or ozone (O3)2.

The ultraviolet radiation that forms ozone also destroys it when the radiation strikes an ozone molecule and breaks it up into an ordinary oxygen molecule and a free atom of oxygen. Thus ozone in the stratosphere is constantly being created and destroyed so that it does not accumulate past a certain amount3. In my next post, I’ll discuss how ground-level ozone is formed.

Footnotes:

  1. For example, see the Almanac of Policy Issues. To view, click here.
  2. NASA Earth Observatory, Chemistry in the Sunlight: The Chemistry of Ozone Formation To view, click here. You can see an excellent YouTube video of the process by clicking here.
  3. NASA Earth Observatory, Chemistry in the Sunlight: The Chemistry of Ozone Formation To view, click here.

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EPA’s New Ozone Rule Part 2

Posted on December 8, 2011 | Leave a comment

Recently, the Obama administration withdrew a proposal to reduce the maximum allowable level of ground-level ozone concentration in the atmosphere1. The question that I wish to address is whether the benefits that might accrue to our nation from such a reduction are greater than the costs, particularly to industry. To analyze this problem, we need to understand what ground-level ozone is, how it is formed, what man-made processes promote ozone formation, and what industry must do to reduce the level of ozone.

Ozone is a form (called an allotrope2) of oxygen, the eighth element in the chemical periodic table3. Pure oxygen usually exists as molecules consisting of two oxygen atoms each, represented by the chemical formula O2. Ozone consists of molecules of three oxygen atoms each, represented by the chemical formula O3. Despite the fact that ozone consists of nothing but oxygen atoms, it is far more chemically reactive than ordinary oxygen4. For example, one cannot breathe pure ozone: breathing ozone in concentrations fifty parts per million or higher is probably fatal within 60 minutes5. Likewise, ozone can dissolve far more readily in water than ordinary oxygen6 and attacks substances (such as certain rubbers) that are not touched by ordinary oxygen7.

Breathing ozone is harmful to health even in low concentrations. Breathing air with 1.5 parts per million (ppm) of ozone for more than two hours can result in severe lung irritation with fluid-buildup, chest pain and cough, and extreme fatigue5. Ozone is known to attack and injure the tissues in the upper respiratory system, although the damage can be repaired by the body in a matter of weeks8.

It is important to distinguish between ozone in the troposphere (that part of the atmosphere that rests on the surface of the Earth) and the stratosphere (that layer of the atmosphere between about 6 and 31 miles above the surface at temperate latitudes). About 90% of all ozone in the atmosphere is in the stratosphere where it performs the very important function of absorbing high-energy ultraviolet radiation from the sun (all of the UV-c rays, most of the UV-b rays, and about half of the UV-a rays)9, preventing them from reaching the surface of the Earth where they would harm life. This ozone poses no dangers to humans; on the contrary, it helps make life possible. It is the 10% of the ozone in the atmosphere that exists in the troposphere (called tropospheric or ground-level ozone) that poses problems and is the subject of the proposed government regulation.

According to NASA, ground-level ozone levels without the presence of human activity should be about 10 to 15 parts per billion (ppb, one part per million equals 1000 ppb)10. Industrial activity has boosted those levels significantly such that the Environmental Protection Agency has established a limit of 80 ppb10. It appears to me that most people are able to breathe in that level of ozone without ill effects, or respiratory illnesses would be much more common than they are now. The question is whether people with respiratory problems, the very young, and the very old are adversely affected. If they are, is it cost effective to lower levels of ozone to improve their quality of life? Also, could long-term exposure to 80 ppb of ozone cause any significant health effects?

In my next post, I want to discuss how ozone is produced.

Footnotes:

  1. Statement by the President on the Ozone National Ambient Air Qualities Standards. White House website. To view, click here.
  2. For a good explanation of allotropes, see the Diffen website, Oxygen vs Ozone.
  3. See the WebElements Periodic Table on oxygen.
  4. Rachel Cassiday and Regina Frey, Washington University.Chemical Properties of Ozone. To view, click here.
  5. Ozone Levels and Their Effects, edited by Den Rasplicka, OzoneLab Instruments website. To view, click here.
  6. Bruce Mattson, Janel Michels, Stephanie Gallagos, Creighton Univerisity.Microscale Gas Chemistry, Part 28 Mini-Ozone Generator: 800 nanomoles/minute p.7 paragraph “Office Paper.” To view, click here.
  7. Bassam Z. Shakhashiri, University of Wisconsin – Madison.Chemical of the Week: Ozone paragraph 7. To view, click here.
  8. U.S. Environmental Protection Agency website, Ground-Level Ozone: Health. To view, click here. For a more detailed treatment, see Health Effects of Ozone in the General Population, which you can view by clicking here.
  9. U.S. National Aeronautics and Space Administration Ozone Hole website, Ozone Facts tab, paragraph 2. To view, click here.
  10. Jeannie Allen, The Ozone We Breathe, NASA Earth Observatory website. To view, click here.

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Topic: The EPA’s New Ozone Rule Part I

Posted on September 25, 2011 | 2 comments

Welcome to the very first topic of this blog, The EPA’s New Ozone Rule. It’s a rather long topic, consisting of 24 posts. If you arrived at this post via a link, you can navigate between posts using the arrows that appear above each post heading. Click on the right arrow (→) to go to the next post. Click on the left arrow (←) to go to the previous post.

On September 2, 2011, the White House released a statement that President Obama had requested the Director of the Environmental Protection Agency (EPA) Lisa Jackson to withdraw a recent EPA proposal to tighten standards for ground-level ozone1.  This proposal would lower the maximum allowable concentration of ground-level ozone from the current standard set in 1997 of 0.08 parts per million (ppm)2 3 to somewhere in a range between 0.060 and 0.070 ppm4.

This change in policy evoked cheers from political conservative and business circles and outrage from the environmental community. Jack Gerard, president of the American Petroleum Institute, was quoted by the newspaper USA Today as saying, “The president’s decision is good news for the economy and Americans looking for work. EPA’s proposal would have prevented the very job creation that President Obama has identified as his top priority.”5 The same article quotes Michael Steel, spokesperson for Speaker of the House John Boehner as saying, “We’re glad that the White House responded to the speaker’s letter and recognized the job-killing impact of this particular regulation.”6 On the other hand, environmentalists were furious. Gene Karpinski, president of the League of Conservation Voters, was quoted by the USA Today article as saying, “The Obama administration is caving to big polluters at the expense of protecting the air we breathe. This is a huge win for corporate polluters and huge loss for public health.”7  Conservatives and business interests, then, see the new rule as an undue burden on business. Environmental groups regard the rule as vital in protecting the public health. Who is correct?

It is possible that both sides have valid points and that the truth lies somewhere between them. I suspect that the rule would place a heavy burden on business, but not as heavy as its opponents make it out to be. Similarly, the rule would probably contribute to public health, although not as critically as its proponents think it will. Perhaps it would be wise to delay implementing the rule, but not to postpone it indefinitely.

I hope in my next postings to analyze the proposed rule, spell out exactly what claims are being made for it, and examine closely the claims of its opponents.

Footnotes:

  1. Statement by the President on the Ozone National Ambient Air Qualities Standards. White House website. To view, click here.
  2. National Ambient Air Quality Standards. EPA website. To view, click here.
  3. The 1997 standard is widely quoted as being 0.084 ppm rather than 0.08 ppm. This is because the EPA only demands an accuracy of 0.01 ppm. Therefore, any reading of ozone concentration between 0.075 ppm and 0.084 ppm would be rounded to 0.08 ppm and be considered in compliance. However, a reading of 0.085 ppm would be rounded to 0.09 ppm and would not be considered in compliance. Practically speaking then, 0.084 is the highest reading possible that remains in compliance. See EPA’s March 2008 National Ambient Air Quality Standards for Ground-Level Ozone: General Overview, p. 3. To view, click here. By the way, this is an excellent review of the case against ground-level ozone.
  4. Federal Register Vol. 75 No. 11, p. 2938 Tuesday, January 19, 2010. Docket no. EPA-HQ-OAR-2005-0172. To view, click here.
  5. USA Today, “Obama decides against tougher ozone standards” September 2, 2011, paragraph 14. To view, click here.
  6. Ibid. Paragraph 7
  7. Ibid. Paragraph 26

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