Climate change is expected to exacerbate ground-level ozone pollution in many densely populated areas, leading to more severe impacts in regions with higher concentrations. The increased frequency and intensity of ozone episodes pose a threat to both human health and environmental progress.
However, accurately evaluating these changes is challenging due to the uncertain climate sensitivity, closely tied to the response of climate models, and the internal variability in simulations forecasting the influence of climate on air quality.
A recent study suggests that by 2050, climate change will likely worsen ground-level ozone spikes, potentially causing widespread non-compliance with air quality standards in numerous parts of the United States and posing greater risks to public health.
Ozone, a reactive gas composed of three oxygen atoms, is often formed at ground level through the interaction of volatile organic compounds (VOCs) and nitrogen oxides (NOx) – both of which are air pollutants, although ozone can also occur naturally.
“Climate change affects ozone formation through a complex set of factors, but warmer temperatures are correlated with increases to ozone in polluted areas,” says James East, first author of a paper on the study and a former Ph.D. student at North Carolina State University who is now a researcher at Harvard University.
“That means areas that already have higher levels of air pollution of VOCs and NOx will likely see increases in ozone as average temperatures go up. What’s more, climate change is expected to increase naturally occurring VOC emissions in some parts of the U.S., such as the Southeast, exacerbating the challenge.”
Rising ozone levels pose a serious threat to public health, leading to a myriad of respiratory issues and contributing to a significant number of deaths annually.
“It’s pretty well-established that climate change will increase ozone pollution, but there has been a tremendous amount of uncertainty regarding what that increase might look like,” says Fernando Garcia Menendez, corresponding author of the work and an associate professor of environmental engineering at NC State. “Our goal with this work was to quantify the range of outcomes and get a much clearer picture of how climate change will affect ozone pollution events in the U.S.”
“Atmospheric chemistry is complex, and climate change affects the rate of chemical reactions, the amount of ozone precursors present, and how long the ozone will linger in the environment,” Garcia Menendez says. “We built on a variety of existing models and incorporated statistical tools that allow us to account for this wide array of variables to look at ozone pollution in the years ahead.”
Researchers have examined the potential impact of exceeding air quality standards and overshooting ozone levels by 2050. The study’s outcomes are presented with a degree of uncertainty, as climate scientists are still determining the sensitivity of the climate to greenhouse gas concentrations.
In the best-case scenario, where the climate shows low sensitivity to carbon dioxide, the study suggests that high ozone measurements would increase by less than 0.3 parts per billion on average. Despite this increase, many locations may still fall within existing air quality standards.
“However, even in this best-case scenario, we found that more variability in ozone levels is projected for 2050 – meaning that we’d still expect to see an increase in the number of days where there is an exceptionally high increase in ozone, violating the air quality standard,” says East.
In the worst-case scenario, a highly sensitive climate to carbon dioxide could lead to an average increase of more than 2.3 ppb in ozone measurements, according to the study. This could result in a significant rise in the number of days when ozone levels exceed air quality standards in many parts of the country, especially when coupled with increased variability.
“In practical terms, our study finds that between 5 million and 13 million additional people will be exposed to dangerously high levels of ozone in 2050,” East says.
“Right now, state and federal governments are trying to manage ozone levels by reducing emissions of air pollutants,” says Garcia Menendez. “This work suggests that the current emissions reductions efforts may be less effective for helping meet ozone standards for many parts of the country, particularly those that are already struggling to meet air quality standards.”
“This work is important for two reasons,” East says. “First, it contributes to our understanding of how climate change will affect ground-level air quality and, by extension, human health. Among other things, this contributes to the way we estimate cost/benefit analyses of climate regulations and related technologies.
“Second, by clarifying the range of climate impacts on ozone, we’re providing critical information that can inform policy decisions – such as EPA’s ongoing review of the air quality standard for ozone.”
Journal reference:
- James D. East, Erwan Monier, Rebecca K. Saari, Fernando Garcia-Menendez. Projecting Changes in the Frequency and Magnitude of Ozone Pollution Events Under Uncertain Climate Sensitivity. Earth’s Future, 2024; DOI: 10.1029/2023EF003941