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Breathe Deeper: Ground Level Ozone Declining

Bill DiBenedetto | Friday March 15th, 2013 | 0 Comments

smog_kynantaitSometimes it seems like there’s nothing but trouble and bad news when it comes to reporting about climate change and the environment. But there is some good news regarding ground level ozone courtesy of research from Rice University and the EPA.

This stuff can get a bit technical, but thanks to the EPA the difference between ground level ozone and high-altitude ozone, in simple terms, is: ozone is “good up high, bad nearby.” We need that high altitude ozone layer to protect the atmosphere and, well, us. But ground level ozone, created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight, is harmful to breathe.

So here’s the good news on ozone: While dangerous ozone levels have fallen in places that have clamped down on emissions from vehicles and from industrial activity, the Rice University study suggests that a model—known as the Community Multiscale Air Quality (CMAQ)—that is widely used to predict the impact of remediation efforts has been too conservative.

In other words nasty ground ozone levels are declining, and even better, the decline is much more dramatic than the CMAQ assessment model otherwise  indicates.

The study, published online by the journal Atmospheric Environment, suggests the CMAQ model misjudged the reduction in ozone by 20 to 60 percent.

This ground level ozone decline  is particularly evident in Northeastern cities, where ozone levels dropped even beyond what was anticipated by cutting emissions of nitrogen oxides (NOx) from 2002 to 2006.

“The models have been under-predicting how much benefit we get from controlling NOx emissions in some instances,” says Daniel Cohan, an assistant professor of civil and environmental engineering and an author of the study with Rice graduate student Wei Zhou and Sergey Napelenok, a scientist in the Environmental Protection Agency’s Atmospheric Modeling and Analysis Division.

“Following major controls of NOx, ozone has come down more quickly than anticipated,” Cohan continues. “This is good news. But it also poses a challenge because states rely upon models to predict whether they’ll attain ozone standards in the future. If the models have key uncertainties that affect their responsiveness that can affect the states’ control strategies.”

That’s a good problem to have right? Maybe, but it can get complicated because modeling this complex chemistry is important in helping states comply with federal standards for ozone, which now stand at 75 parts per billion (ppb) and may be tightened by the Obama administration.

To place the importance of this type of measurement in some context, a recent Rice study showed a positive correlation between high ozone levels and cardiac arrest.

“How ozone responds to changes in NOx and hydrocarbons is a nonlinear chemistry,” Cohan says, “So it’s certainly possible that even the best models could be slightly inaccurate in defining those relationships. It tells us that, as modelers, we need to revisit the formulations, especially the chemistry.”

While, as Cohan says, it may be preferable for models to be a bit conservative rather than too aggressive in predicting ozone improvements, the models should represent air pollution as accurately as possible—it’s a matter of life and breath.

[Image: smog by kynan tait via Flickr CC]


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