Where Does Ozone Come From?
What you see coming out of the tailpipe on that truck isn’t ozone, but the raw ingredients for making ozone. Like some types of particle pollution, ozone is formed by chemical reactions in the atmosphere from two gases that do come out of tailpipes, smokestacks and many other sources. These essential raw ingredients for ozone are nitrogen oxides (NO_X) and hydrocarbons, also called volatile organic compounds (VOCs). They are produced primarily when fossil fuels like gasoline or coal are burned or when fossil fuel-based chemicals, such as paints, evaporate. When they come in contact with both heat and sunlight, these molecules combine and form ozone. NO_X is emitted from power plants, motor vehicles and other sources of high-heat combustion. VOCs are emitted from motor vehicles, chemical plants, refineries, factories, gas stations, paints and other sources.

The recipe for ozone is simple and, like any recipe, the ingredients must all be present and in the right proportions to make the final product.

NO_X + VOC + Heat + Sunlight = Ozone

You may have wondered why “ozone action day” warnings are sometimes followed by recommendations to avoid activities such as mowing your lawn or refilling your gas tank during daylight hours. Lawn mower exhaust and evaporating gasoline vapors turn into ozone in the heat and sun. If you take away the sunlight, then ozone doesn’t form, so refilling your gas tank after dark is better on high ozone days. In the same way, if we reduce the chemical raw ingredients (NO_X and VOCs) in the right proportions, ozone doesn’t form. Since we can’t control sunlight and heat, we must reduce the chemical raw ingredients if we want to reduce ozone.

How Ozone Pollution Harms Your Health 

Scientists have studied the effects of ozone on health for decades. Time and time again research has confirmed that ozone harms people at levels currently found in the United States. In the last few years, we’ve learned that it can also be deadly.

Breathing ozone may shorten your life 

Strong evidence arrived late in 2004, when two large investigations documented that short-term exposure to ozone can shorten lives. Numerous earlier studies had linked short-term exposure to ozone to an increased risk of premature death, so these probes focused directly on that question. One of them looked at 95 cities across the United States over a 14-year period. That study compared the impact of ozone on death patterns during several days after the ozone measurements. Even on days when ozone levels were below the current national standard, the researchers found that the risk of premature death increased with higher levels of ozone. They estimated that over 3,700 deaths annually could be attributed to a 10-parts-per-billion increase in ozone levels.¹  Another study, published the same week, looked at 23 European cities and found similar effects on mortality from short-term exposure to ozone.²

Confirmation came in the summer of 2005. EPA commissioned three groups of researchers working independently to review all the research surrounding deaths associated with short-term high levels of ozone. The three teams—at Harvard, Johns Hopkins and New York University—used different approaches and conducted additional research, all published in the journal Epidemiology. All three studies reported a small but robust association between daily ozone levels and increased deaths.³ Writing a commentary on these reviews, David Bates, MD, explained how these premature deaths could occur:

“Ozone is capable of causing inflammation in the lung at lower concentrations than any other gas. Such an effect would be a hazard to anyone with heart failure and pulmonary congestion, and would worsen the function of anyone with advanced lung disease.”⁴

Groups at risk 

Five groups of people are especially vulnerable to the effects of breathing ozone: Children, senior citizens, people who work or exercise outdoors, people with preexisting respiratory disease (e.g., asthma or COPD) and “responders” who are otherwise healthy but have an enhanced reaction to ozone.

Ozone’s effect on an individual’s health can depend on many factors, including whether they are part of a susceptible population group, how much ozone is in the air, how rapidly they breathe and how long they are exposed to the ozone.

Other risks from breathing ozone 

Many areas in the United States produce enough ground-level ozone during the summer months to cause health problems that can be felt right away. These immediate problems are:

• shortness of breath
• chest pain when inhaling deeply
• wheezing and coughing
• increased susceptibility to respiratory infections

Exposure to ozone increases:

• risk of premature mortality;
• pulmonary inflammation;
• the risk of asthma attacks;
• the need for people with lung diseases, such as asthma or chronic obstructive pulmonary disease (COPD), to receive medical treatment and to go to the hospital.

Two studies published in 2005 explored ozone’s ability to reduce the lung’s ability to work efficiently, a term called “lung function.” Each study looked at otherwise healthy groups who were exposed to ozone for long periods: outdoor postal workers in Taiwan and college freshmen who were lifelong residents of Los Angeles or the San Francisco Bay area. Both studies found that the long exposure to elevated ozone levels had decreased their lung function.⁶

Short-term exposure to ozone also has been linked to aggravation of chronic obstructive pulmonary disease (COPD).⁷ Repeated inflammation due to exposure to ozone over a period of years can lead to a chronic “stiffening” of the lungs.