A new study reveals that without proper steps to curb our emissions, the United States might experience anywhere between three and nine additional days of unhealthy ozone levels and smog per year by 2050.
"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, a graduate student at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and lead author of the study.
The results reveal that the areas most affected would be California, the Southwest and the Northeast, with each region experiencing up to nine additional days of dangerous ozone levels and the rest of the country an average of 2.3 additional days. These increases could cause increase in respiratory illness, which pose the most danger to children, seniors and those with asthma.
"Short-term exposure to ozone has been linked to adverse health effects," said Loretta Mickley, a research fellow at SEAS and co-author of the study. "High levels of ozone can exacerbate chronic lung disease and even increase mortality rates."
In order to reach their conclusions, the team created a model that observed relationships between temperature and ozone in order to better understand future ozone episodes and its connection to climate change and global warming. They measured ozone-temperature relationships at measurement sites all across the country and found that they are much more complicated than it seems.
"Typically, when the temperature increases, so does surface ozone," Mickley said. "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."
Despite this seemingly simple relationship, ozone levels actually stop rising at extremely high temperatures, a phenomenon known as ozone suppression.
The team set out to determine if this phenomena, previously observed in California, occurs outside of the state. It found that 20 percent of measurement sites in the country exhibit ozone suppression at very high temperatures, conflicting with the notion that it is caused by complex atmospheric chemistry.
"Rather than being caused by chemistry, we found that this dropping off of ozone levels is actually caused by meteorology," Shen said. "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."
"This research gives us a much better understanding of how ozone and temperature are related and how that will affect future air quality," Mickley said. "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."
The findings were published in the April 21 issue of Geophysical Research Letters.
