Global warming will lead to spike in ozone pollution

Western U.S. Counties Violating Current and Proposed Ozone Air Quality Standards.
Western U.S. Counties Violating Current and Proposed Ozone Air Quality Standards. A new study suggests even more spikes in dangerous ozone levels as global temperatures increase. Map courtesy WildEarth Guardians.

New study tracks dangerous public health threat posed by rising temps

Staff Report

Along with catastrophic heatwaves, flooding and droughts, greenhouse gas emissions are likely to result in a big spike in the number of days when air quality is impaired by ozone, according to a new study from the Harvard John A. Paulson School of Engineering and Applied Sciences.

Left unchecked, global warming could lead to between three and nine additional days per year of unhealthy ozone levels by 2050, the researchers found.

“In the coming decades, global climate change will likely cause more heat waves during the summer, which in turn could cause a 70 to 100 percent increase in ozone episodes, depending on the region,” said Lu Shen, first author and graduate student at SEAS.

Hot regions, as well as those with pre-existing air quality issues, would be most affected, with the biggest increase in California, the Southwest, and the Northeast. Other areas could see an average increase of 2.3 unhealthy ozone days annually. Those numbers represent a huge public health issue because ozone contributes to respiratory illness with dangerous consequences for children, seniors, and people suffering from asthma.

“Short-term exposure to ozone has been linked to adverse health effects,” said Loretta J. Mickley, a co-author of the study. “High levels of ozone can exacerbate chronic lung disease and even increase mortality rates.”

The study was aimed at quantifying how global warming will affect the  severity and frequency of surface level ozone. The study used a model that analyzed relationships between temperature and ozone to predict future ozone episodes. Using the observational data helped make the projections more accurate.

Previous research had not relied so heavily on existing observations, making projections uncertain. Shen and co-authors analyzed ozone-temperature relationships at measurement sites across the US, and found them surprisingly complex.

“Ozone production accelerates at high temperatures, and emissions of the natural components of ozone increase. High temperatures are also accompanied by weak winds, causing the atmosphere to stagnate. So the air just cooks and ozone levels can build up,” Mickley said.

But when it gets extremely hot — the mid-90s — ozone levels at many sites stop rising with temperature. The researchers tracked the data for ozone suppression, finding that it occurred at 20 percent of measurement sites in the US. Their findings suggest that ozone suppression is caused by the weather than atmospheric chemistry.

“Typically, ozone is tightly correlated with temperature, which in turn is tightly correlated with other meteorological variables such as solar radiation, circulation and atmospheric stagnation. But at extreme temperatures, these relationships break down,” Shen said.

“This research gives us a much better understanding of how ozone and temperature are related and how that will affect future air quality,” said Mickley. “These results show that we need ambitious emissions controls to offset the potential of more than a week of additional days with unhealthy ozone levels.”

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