Los Angeles pollution
May 6, 2014

Summer Ozone Pollution Expected To Worsen Due To Global Warming

redOrbit Staff & Wire Reports - Your Universe Online

Rising temperatures in the United States could result in a 70 percent increase in unhealthy summertime ozone levels by the year 2050, according to new research appearing this week in the American Geophysical Union’s Journal of Geophysical Research-Atmospheres.

The study, which was funded by the National Science Foundation (NSF) and the US Department of Energy showed that global warming, higher atmospheric methane levels, and other climate-related changes could result in chemical reactions that increase the overall levels of ozone, NSF officials explained on Monday.

Without drastic cuts in the pollutants associated with ozone formation, nearly all parts of the continental US will experience at least a handful of days with unhealthy air during the summer months, the researchers reported. Locations in the East, Midwest and West Coast – already heavily polluted because ozone levels frequently exceed recommended levels – could experience unhealthy air during nearly all of the season, they added.

“It doesn’t matter where you are in the United States – climate change has the potential to make your air worse,” lead author Gabriele Pfister of the National Center for Atmospheric Research’s Earth System Laboratory, said in a statement Monday. “A warming planet doesn’t just mean rising temperatures, it also means risking more summertime pollution and the health impacts that come with it.”

The study, which the authors said was one of the first of its kind to be conducted with advanced geosciences supercomputing capabilities, showed that a sharp reduction in the emissions of some types of pollutants would lead to drastically decreased ozone levels, even as temperatures grow warmer.

“Understanding future changes in surface ozone over the summer has tremendous implications for air quality and human health,” said NSF Division of Atmospheric and Geospace Sciences program director Anjuli Bamzai, whose organization funded the work through its Decadal and Regional Climate Prediction using Earth System Models (EaSM) Program.

“Through a series of 'what if' simulations, atmospheric chemists, climate modelers, regional modelers and developers of emissions scenarios demonstrate that a balance of emission controls can counteract the increases in future temperatures, emissions and solar radiation that in turn lead to decreases in surface ozone,” she added.

Ozone pollution is not emitted directly, the researchers explained. Rather, it forms as the result of chemical reactions between nitrogen oxides and volatile organic compounds in the presence of sunlight – gases resulting from human activities such as oil and coal combustion, as well as natural sources such as emissions from plants.

“Unlike ozone in the stratosphere, which benefits life on Earth by blocking ultraviolet radiation from the Sun, ground-level ozone can trigger a number of health problems. These range from coughing and throat irritation to more serious problems, including aggravation of asthma, bronchitis, and emphysema,” the NCAR said. “Even short periods of unhealthy ozone levels can cause local death rates to rise. Ozone pollution also damages crops and other plants.”

In order to gauge the impact of climate change on ozone pollution levels, the study authors examined a pair of scenarios, each of which assumed continued greenhouse gas emissions with significant global warming. In the first one, emissions of nitrogen oxides and volatile organic compounds from manmade activities maintained their current levels through 2050. In the second one, those emissions would be reduced by 60 to 70 percent.

Pfister and her colleagues discovered that, in the first scenario, the number of eight-hour periods during which ozone levels would exceed 75 parts per billion (ppb) would increase by a nationwide average of 70 percent by 2050. That 75 ppb level over eight hours is the threshold that is deemed unhealthy by the Environmental Protection Agency (EPA), though the agency is considering tightening those standards to 65 to 70 ppb over eight hours.

The study also found that, 90 percent of the time, ozone levels in 2050 would range from 30 ppb to 87 ppb, compared to estimated present-day levels of 31 ppb to 79 ppb. While the range itself increases only slightly under the research team’s estimates, the result is a drastic rise in the number of days above the current threshold considered unhealthy.

One of the reasons for this increase in ozone with climate change is the fact that chemical reactions associated with atmospheric ozone production tend to occur more rapidly at higher temperatures. Likewise, plants emit a higher amount of volatile organic compounds at higher temperatures, and increased amounts of atmospheric methane have also been associated with increased baseline ozone levels throughout the US.

“In the second scenario, Pfister and her colleagues found that sharp reductions in nitrogen oxides and volatile organic compounds could reduce ozone pollution even as the climate warms,” the NCAR said. “In fact, 90 percent of the time, ozone levels would range from 27 to 55 ppb. The number of instances when ozone pollution would exceed the 75 ppb level dropped to less than 1 percent of current cases.”