Every breath we take

08.24.07 -

By Trish Barker

Researchers at the Illinois State Water Survey and the University of Illinois use NCSA's systems to simulate how U.S. air quality will be affected by global climate and emission changes.

The prevailing scientific view is that emissions from our cars, planes, and the power plants that fuel our nearly infinite array of power-gobbling devices are changing the Earth's climate. Since the Industrial Revolution, our planet's temperature has edged higher. Data from the National Oceanic and Atmospheric Administration show that Earth's surface temperature has increased by about 1.2 to 1.4 degrees Fahrenheit since 1900, and the Environmental Protection Agency predicts a further increase of 2.5 to 10.4 degrees Fahrenheit above 1990 temperatures by the end of this century.

How this climate shift will affect plants, animals, and people—and what should be done about it—is a focus of much research (and political debate). For the past several years, a team of scientists at the Illinois State Water Survey (ISWS) and the University of Illinois at Urbana-Champaign has used high-performance computers at NCSA and the National Oceanic and Atmospheric Administration to examine the ways in which global climate change and human-driven emissions will affect future air quality. One focus has been ozone, which screens the Earth from damaging ultraviolet light in the upper atmosphere but becomes a pollutant closer to Earth.

The current EPA limit for ground-level ozone is 80 parts per billion (ppb), and the agency recently proposed lowering this standard to 70-75 ppb. In requesting the change, the EPA pointed to evidence that ozone causes health problems—such as reduced lung function and increased susceptibility to respiratory infections—at concentrations below the current standard. Recent scientific research also shows that repeated exposure to even low levels of ozone damages vegetation and trees and reduces crop yields.

ISWS researcher Xin-Zhong Liang is the principal investigator for the project; co-PIs are Water Survey scientists Michael Caughey, Ho‑Chun Huang, Kenneth Kunkel, and Allen Williams, and Donald Wuebbles, a University of Illinois professor of atmospheric science and the leader of the University's new School of Earth, Society and Environment. The goal of this EPA-funded project is to provide policymakers with the information they need to craft effective strategies to meet the agency's National Ambient Air Quality Standards in the decades to come.

The project encompasses numerous research areas, resulting in more than 10 articles published or accepted for publication in Geophysical Research Letters, the Journal of Climate, the Journal of Geophysical Research, the Journal of Applied Meteorology and Climatology, and other journals.

Modeling the big picture

The researchers applied a new modeling system, developed at the Water Survey, that integrates a regional climate model, an emissions model, and an air quality model nested within global climate and chemistry models. Using this integrated model to get a more complete picture of a highly complex system, the researchers homed in on four U.S. regions (Midwest, Northeast, California, and Texas) and four metropolitan areas (Chicago, St. Louis, New York City, and Washington, D.C.), looking at summers between 1995 and 2000. They found that the simulation results agreed well with recorded ozone levels, demonstrating the utility of the new model. This work has been accepted for publication in the Journal of Applied Meteorology and Climatology.

Again using the new ISWS modeling system, researchers considered two emission scenarios outlined by the Intergovernmental Panel on Climate Change (IPCC), labeled B1 and A1Fi. The B1 storyline describes a world in which resource use is dramatically reduced. The A1Fi storyline, on the other hand, depicts a future world of rapid economic growth under the fossil-intensive energy system. Liang describes the B1 scenario as "very clean," with drastic emissions cuts that would be quite difficult to achieve, and the A1Fi as "very dirty" with limited emissions controls.

The results were an intriguing mix. In the dirty scenario, ozone concentrations increased in large rural areas of the United States, but metropolitan areas experienced either small increases or decreases. In the clean scenario on the other hand, the reduction of nitrogen oxide emissions succeeded in decreasing surface ozone in the rural zones. But the opposite effect was found in metropolitan areas, where large reductions in nitrogen oxides actually increased the ozone level due to a short-term phenomenon known as the titration effect. The work has been accepted for publication in Geophysical Research Letters.

Emissions without borders

Emissions and air flow ignore national boundaries, so the researchers also considered how actions in other countries could impact U.S. air quality.

The Illinois researchers examined the effect of "transboundary emissions" from Mexico and Canada by comparing simulations that included precursor emissions from those countries with simulations that included emissions only from the 48 contiguous U.S. states. When emissions from across the southern and northern U.S. borders were included, ground-level ozone concentrations in northwest Washington state and along the south shore of Lake Ontario were elevated by as much as 16 ppb, with more moderate increases in other regions.

"Transboundary emissions must be considered when planning air quality control strategies," Liang explained. "If Canada and Mexico were committed to produce no emissions, then these influenced regions of the U.S. will be benefited significantly, with very little chance of violating the national ozone standard. However, if our neighboring countries produce more emissions (which is projected by various IPCC scenarios), then these sensitive regions will be further degraded."

And it's not just neighboring countries the United States must consider. U.S. air quality is also affected by pollutants from Europe and Asia. Using an improved version of the global Model for OZone And Related chemical Tracers (MOZART), the researchers examined the impact of transpacific transport (TPT) on U.S. ozone levels in 1999 and on to 2099. The projected increase in European and Asian emissions under the IPCCĂ­s A1Fi "dirty" scenario would need to be balanced by a drastic 50 percent cut in emissions in the northwest U.S. in order to maintain a stable ozone level. Under the "clean" B1 scenario, the drop in European and Asian emissions would allow a 25 percent increase in the northwest U.S. The researchers point out that this dramatic shift in regional air quality based on emissions originating half a world away points to the "necessity of global emission reductions for regional pollutant mitigation."

Putting more pollutants in the mix

While one EPA grant draws to a close this year, the team's work will continue and be expanded to include aerosols and mercury under a new grant that stretches until 2010. Using the integrated climate/air quality/chemical transport model, the researchers will examine aerosol-climate interactions. The plan is to increase the resolution of the modeling for the Northeast, Midwest, Southeast, California, and Texas, because of the high probability of air quality problems in those regions.

For further information

This research is supported by the Environmental Protection Agency's Science to Achieve Results program.

Team members
Michael Caughey
Katharine Hayhoe
Ho-Chun Huang
Kenneth Kunkel
Xin-Zhong Liang
Jintai Lin
Ken Patten
Zhining Tao
Allen Williams
Donald Wuebbles
Jinhong Zhu