Building, road surfaces help create smog, UCI chemist says

The Orange County Register

July 20th, 2009

By Pat Brennan, green living, environment editor

Buildings and roads might be hotbeds of smog formation, playing host to chemical reactions that lead to higher levels of harmful ozone gas, according to a new study by a UC Irvine chemistry professor.

UCI Chemist Barbara Finlayson-Pitts

These surfaces could account for a significant portion of the state’s legal limit for ozone in outdoor air, says UCI chemist Barbara Finlayson-Pitts. The reactions were previously unknown, so are not factored into computer models used by regulators to predict air pollution patterns.

“When we put this into the model, it does predict that it would lead to increased ozone levels in Southern California,” Finlayson-Pitts said Monday. “Exactly how much we are not in a position to quantify well.”

The study is to be published this week in the Proceedings of the National Academy of Sciences.

Concrete, asphalt and even plants provide ideal platforms for tailpipe pollutants called nitrogen oxides to react with sea salt, Finlayson-Pitts’s study shows.

That results in the release of highly reactive chlorine atoms, which speed up formation of the ground-level ozone that can cause lung and throat irritation and worsen asthma and other respiratory illnesses.

After the reaction was confirmed in the laboratory by postdoctoral researcher Jonathan Raff, UCI professor Donald Dabdub and graduate student Wayne Chang plugged an extreme version of the chemistry into an air-pollution computer model. It yielded a prediction of 40 parts per billion of ozone resulting from the reactions. That’s nearly half the 90 parts-per-billion air-quality standard for California, Finlayson-Pitts said.

In the real world, she said she was almost certain that ozone resulting from reactions on surfaces would never reach such a high level. But even at the more likely lower levels, ozone formation from building, road and other surfaces could make up a significant part of the air we breathe, she said.

“What it does say is that this is potentially a contribution worth understanding,” she said.

Finlayson-Pitts, an acknowledged expert on the role of sea salt in smog formation, said many scientists expected that road and building surfaces would destroy nitrogen oxides.

The discovery that they instead provide a friendly environment for important smog-related reactions could force a revision of computer models, which provide much of the basis for efforts to reduce ozone pollution.

And the reactions might be taking place indoors as well as out.

Outdoors, hydrochloric acid from sea salt and other sources reacts with nitrogen oxides on buildings, roads and airborne particles. Indoors, hydrochloric acid from cleaning products reacts with nitrogen oxides from appliances, such as gas stoves, again leading to release of reactive chlorine atoms.

In this case, the result would not be ozone; sunlight is needed for that. Instead, it could result in fine particle pollution, another worry for regulators. The odd chemistry also could increase corrosion of things like electronics.

The new and unexpected findings were supported by theoretical work by UCI professor Benny Gerber and postdoctoral researcher Bosa Njegic; they collaborated with professor Mark Gordon of Iowa State University.