Posted by: greeningwashington | April 28, 2009

Houston: Ground-Level Ozone Part One

Ozone Haze in Houston

Ozone Haze in Houston

In an attempt to provide my reader’s with more in-depth analysis I will provide, in a three part series, my research on the problem of Ground-Level Ozone in Houston, Texas.


Ever since 1999, Houston, Texas has competed with large cities like Los Angeles, California for the title of the most polluted air in the United States, as measured by the number of days each city is in violation of federal air quality standards.[i] While air quality is certainly not the only environmental problem affecting Houstonians, it is arguably one of the more widespread and endangering problems. According to a 2004 study done by the American Lung Association, Houston was ranked fifth in the nation as a metropolitan area with the worst ozone air pollution.[ii] Due to the widespread ozone pollution problem in the Houston area, the specific air quality problem I will focus on is ground-level ozone pollution.

In analyzing this problem, it is important to first define ozone and then distinguish between “good” ozone and “bad” ozone, like the kind affecting the Houston area. Ozone is a gas that occurs naturally in the upper atmosphere, or the stratosphere, and in the lower atmosphere at ‘ground-level’, or the troposphere. According to the Environmental Protection Agency (EPA), ground-level ozone is the primary constituent of smog.[iii] On the other hand, “good” ozone occurs naturally in the upper atmosphere and forms a thin layer that protects Earth from the sun’s rays.[iv]

How is ground-level ozone, or ozone[1], formed? What causes it to become a harmful pollutant? According to the Texas Commission on Environmental Quality (TCEQ), ozone is not emitted directly into the air; instead, it is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC).[v] Motor vehicle exhaust, industrial plants, including power plants, chemical solvents, and other sources emit the oxides (NOx) and organic compounds (VOC) essential to ozone creation. To complete the equation, weather and climate factors such as, intense sunlight, warmer temperatures, constant high-pressure systems, and low wind speeds are necessary for the accumulation of large quantities of ozone. Weather conditions such as these are certainly plentiful in Houston during the hot, summer months. Simply put, the equation for ‘bad’ ozone is as follows: pollutants from power plants, cars and trucks, refineries, chemical plants, and other sources create ground-level ozone when they chemically react in the sunlight.

The extent of the ozone problem in the immediate city of Houston, which includes Fort Bend County, Harris County, and Montgomery County, according to the U.S. Census Bureau, affects approximately 2.2 million people.[vi] However, some ozone models use the ‘Houston-Sugar Land-Baytown Metropolitan Statistical Area’, which includes Austin County, Brazoria County, Chambers County, Fort Bend County, Galveston County, Harris County, Liberty County, Montgomery County, San Jacinto County, and Waller County, according to the Office of Budget and Management’s Metropolitan Statistical Areas and Components Bulletin dated, November 2007.[vii] This area includes nearly 4.5 million people. Other models, however, use the ‘Houston, Galveston, Brazoria Area’, which includes Brazoria, Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery, and Waller counties. I will distinguish between the immediate Houston area, and other areas when discussing scientific data models.

Next, who is most affected by ozone pollution? Children, the elderly, those in urban areas, and those that spend a significant amount of time outside are most affected by ozone pollution. According to a study by the American Lung Association, “27.1 million children age 13 and under, and over 1.9 million children with asthma are potentially exposed to unhealthful levels of ozone.”[viii] Additionally, the American Lung Association reported that minority children are more likely to live in areas with high ozone levels. According to their numbers: 61.3% of black children, 69.2% of Hispanic children, and 67.7% of Asian-American children live in areas that exceed the 80 ppb ozone standard. Only 50.8% of white children live in areas with levels higher than federal standards (since this study, the air standards for ozone has been changed to 75 ppb). Although ozone pollution affects children and those who spend more time outdoors in greater proportions, no one is completely free from ozone exposure.[ix]

Why should Houstonians care about the build-up of ozone? There are several reasons related to both health and environmental quality. First, exposure to elevated amounts of ozone can cause a variety of health problems including coughing, throat irritation, congestion, wheezing, inflammation, and it can worsen asthma, bronchitis and other respiratory related diseases. [x] It can also “reduce lung function and inflame the linings of the lung” and even permanently scar lung tissue. [xi]

For my father, who is an avid outdoor runner and has run 600 miles since October, air quality in Houston, especially ozone levels, is of great concern to him. “It (ozone levels) certainly can be a huge problem for people who don’t have the best health and are outdoors often,” he told me in a phone conversation. “In order to avoid higher ozone levels, I run mostly in the mornings when there are lower levels, and I run longer distances in the winter when the weather is cooler,” he said. “You can definitely tell in the summer that the air feels less refreshing,” he added. “It’s something I want to see taken care of overtime.”[xii]

Ground-level ozone also affects public welfare. That is, crops, vegetation, plants, forest growth, and crop yields. According to the EPA, ozone can make certain plants more susceptible to certain diseases and insects.

How severe is the problem of ozone in Houston? Prior to answering this question, it is important to explain some key terms that the EPA and state agencies use when describing ozone levels. In order to measure air quality standards, the EPA came up with the Air Quality Index (AQI), which measures air quality from 0 (being the lowest) to 500. Therefore, the higher the AQI value, the greater the level of air pollution and ultimately the greater the health risk.[xiii] Air quality between 0 and 50 is considered good; fifty-one through 101 is moderate; one hundred and one through 151 is unhealthy for sensitive groups; and 151 and beyond is very unhealthy.

According to the ‘High Ozone Average’ table provided by TCEQ, in 2008, the immediate Houston area had 38 days in which the eight-hour ozone (O3) average exceeded the federal standard of 75 parts per billion (ppb) with an average of 106 ppb, which is considered unhealthy for the eight-hour averages. This number was higher than any other city in Texas. For the one-hour averages, Houston had six days, which registered 127 ppb, which is considered unhealthy for sensitive groups. Using the same chart for 2007, Houston had 46 days in which the eight-hour ozone (O3) average was 112 ppb and nine days the one-hour average was 166, which is considered unhealthy.[xiv] Judging from the table, the highest levels of ozone pollution were worse in 2007 than in 2008. According to the TCEQ, ozone formation is typically highest between May and October.

How serious is the problem of ozone pollution in Houston and around the country? Serious enough for the EPA to set national ambient air quality standards (NAAQS) for ozone and other air pollutants. The potential risk to the health of children and people with asthma and other lung diseases is serious and can lead to complications and even death. According to a recent nationwide study led by researchers at the University of California, Berkeley, the estimated relative risk of death from respiratory causes that were associated with an increment in ozone concentration of 10 ppb was 1.040 (95% confidence interval, 1.010 to 1.067), which is statistically significant. The researchers also found that there exists a significant increase in the risk of death from respiratory causes associated with an increase in ozone concentration.[xv] The study, which followed almost 450,000 people for 20 years in over 96 U.S. metropolitan regions, found that people living in areas with the highest concentrations of ozone, such as Houston, had a 25 to 30 percent greater annual risk of dying from respiratory related diseases compared with people from regions with much lower levels of ozone. The study also found that there is a 4 percent increase in risk of death from respiratory causes, such as pneumonia, for every 10 ppb increase in ozone level. [xvi] The fact that ozone pollution has been linked to premature death, shortness of breath, inflammation of the lungs, and increased risk of asthma attacks speaks to the seriousness and severity of this problem not only in Houston but nationwide.

[1] For the purpose of this paper, unless stated otherwise, all references to ‘ozone’ refer to ground-level ozone.

[i] Wilson, James. “Getting the Big Picture on Houston’s Air Pollution.”

[ii] American Lung Association. “State of the Air: 2004.”

[iii] Environmental Protection Agency. “Ground Level Ozone: Basic Information.”

[iv] Environmental Protection Agency. “Ground Level Ozone.”

[v] Texas Commission on Environmental Quality. “Rapid Economic and Population

Growth Create a Potent Blend for the Region’s Environment.”

[vi] U.S. Census Bureau. “State and County Quick Facts: Houston, Texas.”

[vii] U.S. Census Bureau. “State and County Quick Facts: Houston, Texas.”

[viii] American Lung Association. “Children and Ozone Air Pollution Fact Sheet.”

[ix] American Lung Association. “Children and Ozone Air Pollution Fact Sheet.”

[x] Environmental Protection Agency. “Ground Level Ozone.”

[xi] American Lung Association. “Children and Ozone Air Pollution Fact Sheet.”

[xii]Leveille, Greg. Interview.

[xiii] AIRNow. “Air Quality Index (AQI) – A Guide to Air Quality and Your Health.”

[xiv] Texas Commission on Environmental Quality. “High Ozone in Your Metro


[xv] Jerrett, Michael Dr., Dr. Richard T. Burnett, et al. “Long-Term Ozone Exposure

and Mortality.”

[xvi] Yang, Sarah. “Nationwide Study Finds Long-Term Ozone Exposure Linked To

Higher Risk Of Death.”


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