The Dangers of Ozone
As our weather heats up this summer many of you may have noticed a decline in your local air quality. Where I live air quality alerts for ozone are becoming a routine part of summer. You probably assume that since there is an alert, high ozone levels are potentially dangerous, and you would be right. But what is the real danger of high ozone levels? Unfortunately, recent research suggests that there is a wide range of potentially severe health effects for those chronically exposed to high ozone levels. Most of us probably know what ozone is at this point. Ozone or O3, is formed from air pollutants that are commonly released by our cars and industries (often called ozone precursors). Its formation is catalysed by heat and sunlight, which is why we see higher ozone levels during the day and in the summer.
You have probably heard a lot about the importance of ozone. In fact, its existence is vital in protecting Earth’s life from dangerous levels of UV radiation. At first blush it may seem as though ozone formation would be good thing, the more ozone the better right? Unfortunately, while ozone is very beneficial when it's high in the stratosphere, ozone at ground level can have serious deleterious effects. Not only can it affect plant life by reducing photosynthesis, increasing disease susceptibility and vulnerability to insects, but it can have consequences for human health as well. Much like some of its precursors, ozone has a number of negative effects on our cardiopulmonary systems. Ozone can cause difficulty breathing, even in healthy adults, and exposure can lead to a reduction in lung function. Ozone also contributes to the development of asthma, and can worsen other respiratory conditions like emphysema and COPD and increase the possibility of stroke or heart attack. In a study of more than 11 million Americans, researchers were able to show that the hazard for being admitted to the hospital for a number of conditions including stroke, myocardial infarction, pneumonia, lung cancer, COPD, and heart failure, increases with greater ozone exposure.
Even worse than the above, there is a wide range of research that suggests that those living in areas that experience long term high levels of ozone may be at a greater risk of developing and dying from neurological diseases. Using data from 3.5 million Canadians, researchers were able to find “positive associations between ozone exposure and mortality due to Parkinson’s, dementia, stroke, and multiple sclerosis.” This effect becomes more pronounced as an individual ages, particularly for Parkinson’s disease with researchers noting that it is likely that aged nervous systems are simply less able to cope with the neuroinflammation that is caused by inhaled ozone. Studies in China parallel these findings. Researchers tracked more than 9500 adults over the age of 65 for a period of 6.5 years. Indeed they did find that those individuals that were exposed to higher levels of ozone suffered greater cognitive impairment than those who did not. Furthermore they were able to quantify the risk of developing cognitive issues. They found that for every 10 µg/m3 increase in ground level ozone concentration there is a 10.4% increase in the risk of cognitive impairment. This team's research also validates the WHO’s recommendation of average daily maximum 8-hour mean O3 concentration of 60 µg/m3, or roughly 30 ppb. Here in the United States a different metric is used based upon the 8 hour maximum ozone levels. Because ozone is so variable, the USEPA uses a rather cumbersome calculation to gauge compliance. The current standard is an 8 hour max ozone concentration of 70 ppb averaged over 3 years using the 4th highest reading for each of those years. This is called the “design value” or DV (perfectly straightforward right?). This level is a more strict standard than in the past, but despite ozone levels falling since the 1980s in the U.S., there are still multiple regions that currently do not meet this standard including the area where I live. Here on the Front Range of Colorado our DV is 81 ppb. This is equivalent to an ozone concentration 22 µg/m3 above the EPA standard. If the EPA’s standard is reflective of overall levels of ozone exposure, this means that those living in my region could be at a 20% greater risk of developing cognitive impairment than those living below the EPA standard.
Studies in the lab also confirm the negative effects of ozone in the mammalian brain. Studies in rats have shown that exposure to low levels of ozone affects rat brains with a condition similar to Alzheimer’s in humans. Effects include increased memory loss with an increasing concentration of ozone, neurodegeneration and loss of brain repair in the hippocampus, as well as the accumulation of beta-amyloid within the hippocampus (buildup beta-amyloid plaques are thought to be the primary cause of the cognitive degeneration in Alzheimer’s disease). Researchers believe these effects are caused by a chronic oxidative stress condition brought about by ozone deteriorating the antioxidant mechanisms in the brain.
Despite reductions in ozone causing compounds, and overall ozone levels in recent decades, over 90 million people in the U.S. lived in a county where the EPA’s 70 ppb standard was violated in 2021. Most of these counties naturally are near major cities, but many may be surprised to learn that, despite their often remote locations and seemingly pristine natural surroundings, that even our national parks experience high levels of ozone pollution. That “clean” air your breathing isn’t as clean as it seems, with researchers finding the ozone levels in many of the nation’s national parks are statistically indistinguishable from those found in major metropolitan areas.
The good new is we are releasing less ozone precursors. The bad news? The increase in global temperatures threatens to undo our air quality improvements with the higher temperatures increasing ozone formation. Experts are now worried that even with dramatic cuts in air pollution, ground level ozone levels may continue to rise. This is especially poignant considering Earth just had its hottest 4 day period in the last 100,000 years.
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