Unhealthy ozone days could increase by more than a week in coming decades

April 21, 2016

If emission rates continue unchecked, regions of the United States could experience between three and nine additional days per year of unhealthy ozone levels by 2050, according to a new study from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) published in Geophysical Research Letters.

"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.

California, the Southwest, and the Northeast would be the most affected, each possibly experiencing up to nine additional days of dangerous ozone levels, with much of the rest of the country experiencing an average increase of 2.3 days.

This increase could lead to more respiratory illness with especially 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."

While temperature has long been known as an important driver of ozone episodes, it's been unclear how increasing global temperatures will impact the severity and frequency of surface level ozone.

To address this question, Shen and Mickley -- with coauthor Eric Gilleland of the National Center for Atmospheric Research (NCAR) -- developed a model that used observed relationships between temperature and ozone to predict future ozone episodes.

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.

"Typically, when the temperature increases, so does surface ozone," said Mickley.

"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."

However, at extremely high temperatures -- beginning in the mid-90s Fahrenheit -- ozone levels at many sites stop rising with temperature. The phenomena, previously observed only in California, is known as ozone suppression.

In order to better predict future ozone episodes, the team set out to find evidence of ozone suppression outside of California and test whether or not the phenomena was actually caused by chemistry.

They found that 20 percent of measurement sites in the US show ozone suppression at extremely high temperatures. Their results called into question the prevailing view that the phenomenon 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," said Shen. "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," 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."
-end-
This research was supported by the NASA Air Quality Applied Sciences Team and the National Institute of Environmental Health Sciences.

Harvard John A. Paulson School of Engineering and Applied Sciences

Related Ozone Articles from Brightsurf:

Investigating the causes of the ozone levels in the Valderejo Nature Reserve
The UPV/EHU's Atmospheric Research Group (GIA) has presented a database comprising over 60 volatile organic compounds (VOC) measured continuously over the last ten years in the Valderejo Nature Reserve (Álava, Basque Country).

FSU Research: Despite less ozone pollution, not all plants benefit
Policies and new technologies have reduced emissions of precursor gases that lead to ozone air pollution, but despite those improvements, the amount of ozone that plants are taking in has not followed the same trend, according to Florida State University researchers.

Iodine may slow ozone layer recovery
Air pollution and iodine from the ocean contribute to damage of Earth's ozone layer.

Ozone threat from climate change
We know the recent extreme heat is something that we can expect more of as a result of increasing temperatures due to climate change.

Super volcanic eruptions interrupt ozone recovery
Strong volcanic eruptions, especially when a super volcano erupts, will have a strong impact on ozone, and might interrupt the ozone recovery processes.

How severe drought influences ozone pollution
From 2011 to 2015, California experienced its worst drought on record, with a parching combination of high temperatures and low precipitation.

New threat to ozone recovery
A new MIT study, published in Nature Geoscience, identifies another threat to the ozone layer's recovery: chloroform -- a colorless, sweet-smelling compound that is primarily used in the manufacturing of products such as Teflon and various refrigerants.

Ozone hole modest despite optimum conditions for ozone depletion
The ozone hole that forms in the upper atmosphere over Antarctica each September was slightly above average size in 2018, NOAA and NASA scientists reported today.

Increased UV from ozone depletion sterilizes trees
UC Berkeley paleobotanists put dwarf, bonsai pine trees in growth chambers and subjected them to up to 13 times the UV-B radiation Earth experiences today, simulating conditions that likely existed 252 million years ago during the planet's worst mass extinction.

Ozone at lower latitudes is not recovering, despite Antarctic ozone hole healing
The ozone layer -- which protects us from harmful ultraviolet radiation -- is recovering at the poles, but unexpected decreases in part of the atmosphere may be preventing recovery at lower latitudes.

Read More: Ozone News and Ozone Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.