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Climate Change Penalty on Ozone

EPA scientist finds new metric to measure impacts of climate change on ozone air quality.

Sunset over the mountains

Summer sun and rising temperatures bring worries of sunburn and high heat. While hot summer months keep many people indoors, heat may not be the only cause for concern.

Rising temperatures also raise the risk of ozone exposure.

Ground level ozone forms when air containing hydrocarbons and nitrogen oxides (NOx) reacts with sunlight to form ozone. Ozone is an atmospheric pollutant and a health concern because of its harmful effects on the respiratory and cardio vascular systems. Unhealthy levels of ozone also have an effect on the environment, interfering with photosynthesis and damaging crop yields. High temperatures increase ozone formation, especially during the warm months of May to September, also known as “ozone season.” Average temperatures have been rising in the eastern United States and experts expect the trend to continue.

While many potential effects of climate change are hard to measure, EPA scientist Bryan Bloomer has found a way to estimate the amount of ozone in Earth’s future environment by using current and past data. Bloomer examined 21 years of ozone and temperature levels compiled by the U.S. EPA’s Clean Air Status and Trends Network (CASTNET) from rural areas in the eastern U.S. 

The data showed a steady rise in ozone amount as temperature increases.  He also discovered that decreases in nitrogen oxide (NOx) emissions from power plants around 2002—due to compliance with new emissions standards—appeared to lower the amount of ozone produced per degree of rising temperature. Bloomer was able to quantify this relationship between ozone and temperature using a measure that he calls the “climate penalty factor.” Bloomer found that the decrease in NOx emissions also led to a decrease in the climate penalty factor.

“We had evidence of the climate change penalty in ozone air quality from modeling studies but we wanted to find observational evidence of it with this study,” explains Bryan Bloomer. “We had a strong suspicion that the linear relationship did exist though we didn’t know what the numbers were.  What is surprising to see is that the relationship is so strong and the numbers are remarkably consistent over the entire rural eastern U.S. in the summertime.”

The ability to lower ozone production by reducing NOx emissions is welcome news to countries like the U.S., who have begun putting restrictions in place. The EPA recently made revisions to strengthen the health-based  National Ambient Air Quality Standards (NAAQS) for NOx. According to Bloomer, the benefits of the research are clear. “The Climate Penalty Factor is a good tool to estimate the impact of climate change on air quality in the presence of rising temperatures and constant emissions. It also shows us that NOx reductions are a good idea and effective both for the direct reduction of ozone amounts and for lowering the climate penalty factor.”

Understanding and using the climate penalty factor will benefit any community that wants to identify their potential risk for exposure to unhealthy levels of ozone in the future because of rising temperatures. Bloomer’s research is important to taking action on climate change and improving air quality, two EPA priorities. He is currently pursuing research on the climate change penalty and its effects on areas beyond the eastern U.S. and around the world.

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