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Discovery
Every Breath You Take

Scientists search for an understanding of the air-water interface and its effect on air quality

Smog over San Jose, California

A thick layer of photochemical smog covers San Jose, California.
Credit and Larger Version

July 13, 2009

Traveling to Los Angeles can be a hazardous undertaking. The buzzing coastal city at the very edge of the American frontier has long been a symbol of exploration and progress. As planes land in L.A., they must first penetrate the dark, ominous cloud that hangs constantly above the skyscrapers. Smog lies over L.A. like a thick blanket, dimming the sunshine of the Golden State.

To some degree, scientists have been aware of air pollution for centuries, but it wasn't until the late 1940s that some of the causes were recognized. Since then, most atmospheric chemistry has focused on gas-phase interactions, as the majority of the atmosphere is a continuous gas phase, or reactions in the liquid phase, taking place within droplets of condensed matter. But these chemical models do not account for a significant portion of what is happening in the air above us.

A large number of atmospheric reactions occur under conditions we know very little about, and the Holy Grail of atmospheric chemistry has become developing a basic, molecular-level understanding of the reactions that occur in this mystery world--at the air-water interface, where the gas phase meets the liquid phase, and the reactions bear no resemblance to either phase alone.

In order to study these processes, Barbara Finlayson-Pitts and her team, first funded by the National Science Foundation's (NSF)Chemistry Division in 2002, have developed the Atmospheric Integrated Research for Understanding Chemistry at Interfaces (AirUCI) collaboration. The goal of AirUCI is to find that Holy Grail and develop the necessary understanding of the air-water interface and its effect on air quality. AirUCI uses an integrated approach, including experiments, theory and computer modeling to expand the very small amount of existing knowledge about reactions at interfaces.

The urgency of AirUCI's research comes from an understanding of how fragile the air we breathe truly is.

"Ninety-nine percent of the atmosphere is in the lowest 30 kilometers, concentrated in this tenuous layer we live in," says Mike Ezell, a senior researcher in Finlayson-Pitts's lab.

Ezell's work, like much of the work at AirUCI, focuses on aerosol particles, miniscule suspensions of matter in the air. The properties of aerosol particles have enormous implications for global climate change. Aerosol particles act as condensation nuclei for clouds, which need particles to form. Smaller particles result in smaller cloud droplets and longer-lived clouds, resulting in more reflected radiation and a greater cooling effect. Some larger particles, like soot, absorb light, causing a warming effect. In addition, the particles themselves scatter light, affecting the amount of radiation that reaches the Earth's surface.

"Climate change and air pollution are very closely linked," says Finlayson-Pitts. "One of the points people tend to miss in the debate on climate change is how much air pollution is really a factor. It isn't all about carbon dioxide."

Finlayson-Pitts' team is also concerned with the health effects of emissions, particularly in the production of ozone. Ozone, while a significant gas high in the stratosphere, is a health risk when produced in our tropospheric home. Researchers in the Nizkorodov lab at AirUCI are focused on the production of ozone from the commercial air purifiers that provide clean, safe air in our homes. Commercial air purifiers break up oxygen gas (O2) into single oxygen atoms, which can recombine into ozone (O3). Especially when placed in small rooms, these machines can rapidly increase the amount of the hazardous gas to a dangerous level, which has known severe effects on the lungs, causing cough, pain and shortness of breath.

The other source of ozone the team is studying, highlighted in 2000 and 2005 articles in Science, is the oxidation of chloride ions (Cl-) by hydroxide (OH) on the surface of particles, and producing chloride gas (Cl2). The gas photolyzes easily, splitting into chlorine atoms (Cl), which react very quickly with almost all organic particles, like those that we emit, producing a large amount of ozone as well as other pollutants. The AirUCI labs showed for the first time that this reaction occurs very quickly at the air-water interface, as chloride ions are readily available, demonstrated by theoretical models, and the surface reaction does not require the same conditions that the same reaction would require in the bulk of a liquid droplet.

The Hemminger lab works with AirUCI to develop a fundamental understanding of reactions at solution interfaces.  At the same time, other researchers in the lab are a part of an effort, funded by the Department of Energy and the California Community Foundation, to solve some energy issues. As demand for energy continues to outstrip the available supply, new technology to make clean, efficient energy possible becomes a more urgent need.

The vast majority of these technologies are simply not ready for the market; according to John Hemminger, widespread use of solar panels may be economically feasible in several decades, but even then, it may not be able to compete with oil in a free market. "Between us and feasible solar energy is either $200 per barrel oil, or fundamental science," says Hemminger.

In order to address this pressing need, the Hemminger lab is working on understanding radiation interactions on matter, focusing on radiation on surfaces, in the hopes of developing new, more efficient methods of harnessing the sun's energy.

Uncovering the secrets of air-water interfaces is not the only duty that AirUCI has taken on. "We are committed to conveying that to the public and K-12 educators," Finlayson-Pitts says. Each year, the AirUCI teacher workshop brings in middle and high school teachers, giving them lectures from leaders in the field of atmospheric chemistry as well as valuable experience using top-of-the-line lab equipment. Teachers then take the information they gain back to their classrooms.

"If we want to develop the next generation in science and technology, and if we want taxpayers to support us," says Finlayson-Pitts, "it is important that we interface with the public, invite them in, and show them what we are doing. It is an important responsibility."

AirUCI's research is illuminating a world of reactions that have powerful implications for each breath we take, as well as for projections of future conditions. Currently, the models used to predict future air and climate conditions do not account for air-water interface chemistry, because the fundamental understanding of these processes is not there.

"People know surface chemistry is happening, but it's not in the models. We need a molecular-level understanding of the processes occurring on surfaces in order to tell the modelers what to put in the models to accurately represent this chemistry and its potential effects," says Finlayson-Pitts.

And until we know what is truly happening in the air above us, there is no way to comprehend the full scope of effects and consequences our activities have on our world and on our future.

--  Efrat Rosenzweig, National Science Foundation

Investigators
Douglas Tobias
John Hemminger
Barbara Finlayson-Pitts

Related Institutions/Organizations
University of California-Irvine

Locations
California

Related Awards
#0431312 EMSI: Atmospheric Integrated Research Using Chemistry at Interfaces (AIRUCI)

Total Grants
$6,009,585

Related Agencies
Department of Energy

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