Meghan Hodges
Ozone pollution, also known as smog, is a powerful respiratory irritant that causes serious health issues, especially in children, older adults, and people with lung diseases. It is one of the most dangerous and widespread pollutants in the United States, affecting nearly half of the population. In recent years, the US has seen a worrying increase in ground-level ozone pollution, with more than 125 million people exposed to unhealthy levels, leading to a range of negative health impacts. This trend has particularly affected states in the Midwest, Plains, and Texas. While there have been improvements in some western states, the overall worsening of ozone pollution in the US raises concerns about the effectiveness of current measures to address this issue.
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What You'll Learn
- The US has high levels of ozone pollution, but it is unclear if it is leading worldwide
- Ozone pollution is a powerful respiratory irritant that can cause shortness of breath and trigger asthma attacks
- Ground-level ozone is formed by chemical reactions between nitrogen oxides and volatile organic compounds (from cars, power plants, etc.)
- Ozone pollution is especially harmful to children, the elderly, and those with lung diseases like asthma
- Ozone pollution is linked to an increased risk of premature birth and low birth weight
The US has high levels of ozone pollution, but it is unclear if it is leading worldwide
Ozone pollution, also known as smog, is a powerful respiratory irritant that can cause serious health issues. Inhaling ozone can lead to shortness of breath, coughing, asthma attacks, and even premature death. It is one of the six common air pollutants identified in the Clean Air Act, and its levels in outdoor air need to be limited based on health criteria. While the US has made significant progress in reducing ozone pollution through the implementation of the Clean Air Act, recent reports suggest that nearly half of the population in the US, approximately 125 million people, were exposed to dangerous levels of ground-level ozone pollution from 2021 to 2023. This is an increase of 24.6 million people compared to the previous year.
The American Lung Association's "State of the Air" report for 2025 revealed that 37% of the US population lived in areas with unhealthy ozone pollution levels. This includes infants, children, older adults, and individuals with lung diseases, who are particularly vulnerable to the harmful effects of ozone. The report also showed that nine states, including Indiana, Illinois, and Missouri, experienced an increase in the number of unhealthy days for ozone levels. However, it is important to note that the list of the 25 worst cities for ozone pollution remained relatively stable compared to the previous year's report.
While the US is facing significant challenges in addressing ozone pollution, it is unclear if it leads the world in this regard. Ozone pollution is a global issue, and many countries are struggling to reduce their ozone levels. Climate change, extreme heat, and wildfires contribute to the increase in ozone levels, and these factors are not unique to the US. Additionally, ozone formation is not limited to major urban areas or large countries. Smaller cities and rural areas can also experience high ozone concentrations due to the transport of pollutants downwind.
To effectively tackle ozone pollution, both nationwide and worldwide, it is crucial to implement and enforce air quality standards and regulations. The US Environmental Protection Agency (EPA) plays a vital role in protecting people's health from ozone pollution and providing essential information about air quality. By working together and taking individual actions to reduce air pollution, we can strive for cleaner air and improved health outcomes for all.
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Ozone pollution is a powerful respiratory irritant that can cause shortness of breath and trigger asthma attacks
Ozone pollution is a serious issue in the United States, affecting the health of millions of Americans. Ozone (O3) is a gas molecule composed of three oxygen atoms. While stratospheric ozone is beneficial as it shields us from the sun's harmful ultraviolet rays, ground-level ozone is a dangerous pollutant. Ground-level ozone is formed when gases from sources like cars, power plants, and industrial boilers react with sunlight. It is the main component of smog, often invisible but highly dangerous.
Ozone pollution is a powerful respiratory irritant. When inhaled, ozone chemically reacts with and aggressively attacks lung tissue. This can lead to a range of respiratory issues, including shortness of breath, coughing, and inflammation and damage to the airways. People with pre-existing respiratory conditions, such as asthma, are particularly vulnerable. Ozone pollution can trigger asthma attacks and exacerbate symptoms, leading to increased medication use, doctor visits, and hospital admissions. Long-term exposure to ozone pollution is linked to an increased risk of developing asthma and other respiratory illnesses.
The impact of ozone pollution is widespread, with 37% of the US population (approximately 125 million people) exposed to unsafe ozone levels in 2021, 2022, and 2023. This includes vulnerable groups such as infants, children, older adults, and individuals with lung diseases. Certain regions, such as the Midwest, the Plains, and Texas, have been particularly affected by worsening ozone levels.
The severity of the ozone pollution problem is evident in the “State of the Air" reports, which grade counties based on their air quality. In 2025, 211 counties across 35 states received an "F" grade for ozone levels, indicating a significant decline in air quality. While some western states, such as California and New Mexico, have shown improvements, the overall trend highlights the urgent need for action to protect public health.
To address ozone pollution and mitigate its respiratory impacts, various measures can be implemented. These include reducing emissions from power plants, industrial sites, and vehicles, as well as enforcing air quality standards and regulations. Individual actions, such as checking air quality forecasts and limiting outdoor activities on high-ozone days, can also help reduce exposure and protect respiratory health.
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Ground-level ozone is formed by chemical reactions between nitrogen oxides and volatile organic compounds (from cars, power plants, etc.)
Ozone is a gas molecule composed of three oxygen atoms. It can be “good” or “bad” depending on where it is found in the atmosphere. Stratospheric ozone is “good” because it protects living things from the sun's ultraviolet radiation. Ground-level ozone, on the other hand, is “bad” because it can trigger a variety of health problems, especially for children, the elderly, and people with lung diseases such as asthma. It is the main ingredient in "smog" and is formed by chemical reactions between nitrogen oxides and volatile organic compounds (VOCs).
Tropospheric, or ground-level ozone, is not emitted directly into the air but is instead created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs). These reactions occur in the presence of sunlight, with higher concentrations typically forming during warmer temperatures. While ground-level ozone is less concentrated than stratospheric ozone, it is of concern due to its health effects and contribution to global warming.
The primary sources of NOx are power plants, industrial furnaces, boilers, and motor vehicles. VOCs, on the other hand, originate from chemical plants, gasoline pumps, oil-based paints, auto body shops, and print shops. These pollutants are released into the atmosphere through activities such as combustion, vehicle emissions, and industrial processes.
In the United States, ozone air pollution has been identified as one of the six common air pollutants by the Clean Air Act. Despite efforts to reduce ozone pollution, it remains a persistent issue, with 37% of the population (approximately 125.2 million people) exposed to unhealthy levels in recent years. This has particularly impacted vulnerable groups, including infants, children, older adults, and people with pre-existing health conditions.
To address ground-level ozone pollution, various measures can be implemented. These include vehicle and transportation standards, regional haze and visibility rules, and regular reviews of national ambient air quality standards (NAAQS). Additionally, states can develop implementation plans (SIPs) to outline specific actions for improving air quality in areas that do not meet the standards.
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Ozone pollution is especially harmful to children, the elderly, and those with lung diseases like asthma
Ozone pollution is a serious issue in the United States, affecting the health of millions of people. In 2021, 2022, and 2023, about 37% of the US population, or 125.2 million people, were exposed to dangerous levels of ozone. This includes tens of millions of children, the elderly, and those with lung diseases, who are especially vulnerable to the harmful effects of ozone pollution.
Ozone pollution, particularly at ground level, is a harmful air pollutant that can trigger a range of health problems. It is formed by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. This occurs when pollutants are emitted by cars, power plants, industrial boilers, refineries, and other sources. As a result, ozone pollution is often worst in urban areas, especially on hot sunny days.
Children are particularly vulnerable to ozone pollution due to their developing lungs and higher likelihood of spending time outdoors when ozone levels are typically higher. In addition, children are more prone to asthma, which can be aggravated by ozone pollution. Ozone can cause the muscles in airways to constrict, making it difficult to breathe, and can also damage the lining of the airways, leading to inflammation similar to sunburn.
The elderly are also at increased risk from ozone pollution. Research has shown that older adults are more susceptible to the harmful effects of ozone, even at levels below the current national standard. They may experience an increased risk of premature death and other health issues associated with ozone exposure.
People with lung diseases, such as asthma, are especially vulnerable to ozone pollution. Long-term exposure to ozone can aggravate asthma symptoms and may even contribute to the development of the disease. Ozone pollution can trigger asthma attacks and cause inflammation of the airway lining, making it difficult to breathe.
Overall, ozone pollution poses a significant health threat to children, the elderly, and those with lung diseases like asthma. It is important for individuals in these vulnerable groups to monitor air quality forecasts and take precautionary measures to protect their health when ozone levels are expected to be high.
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Ozone pollution is linked to an increased risk of premature birth and low birth weight
The US has seen a worrying increase in ozone pollution in recent years, with 37% of the population (125.2 million people) exposed to dangerous levels of ozone in 2021, 2022, and 2023. This includes millions of infants and children, the elderly, and those with pre-existing health conditions. This is a significant deterioration from previous years, where clean-up measures had successfully reduced ozone pollution.
Ozone pollution is a serious health threat, and ground-level ozone is particularly harmful. It is a strong oxidizing agent and a key ingredient in smog, which can cause respiratory issues and trigger asthma attacks. It is formed through chemical reactions between oxides of nitrogen and volatile organic compounds, emitted by cars, power plants, industrial boilers, and other sources, in the presence of sunlight.
Ozone pollution is indeed linked to an increased risk of premature birth and low birth weight. Studies have shown a direct correlation between maternal ozone exposure and these adverse birth outcomes. For example, a study in Guangzhou, China, examined 444,096 singleton live births and found that maternal ozone exposure may be associated with low birth weight, particularly during the 15th to 26th gestational weeks.
Additionally, research in Ahvaz, Iran, over a ten-year period, found a significant relationship between exposure to air pollutants, including ozone, and low birth weight. This research also highlighted the sensitivity of pregnant women and fetuses to air pollution due to physiological changes during pregnancy.
Furthermore, a systematic review and meta-analysis of 19 studies concluded that increased ozone exposure during early pregnancy is associated with preterm birth. This review analyzed the effect of a 10 ppb increase in ozone exposure, demonstrating the impact of even relatively small increases in exposure on birth outcomes.
The link between ozone pollution and premature birth and low birth weight is a critical public health concern, particularly in areas with high levels of air pollution. It underscores the importance of taking precautionary measures to protect maternal and infant health, as well as implementing measures to reduce air pollution and improve air quality.
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Frequently asked questions
Ozone (O3) is a gas molecule composed of three oxygen atoms. Ozone in the upper atmosphere shields us from much of the sun's ultraviolet radiation. However, ozone at ground level is a harmful air pollutant and the main ingredient in "smog".
The US is one of the leaders in ozone pollution, with 37% of the population (approximately 125 million people) exposed to levels of ozone that put their health at risk.
Ground-level ozone is formed from gases emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources. These gases react with sunlight to form ozone.
Ozone pollution can cause serious health problems, especially for vulnerable groups such as infants, children, and older adults. It can narrow a person's airways, making it harder for the lungs to provide oxygen to the body. Ozone can also increase the risk of premature death, even at levels below the current national standard.
