National Center for Atmospheric Research
Science Update
Winter 2006
Air Quality Research
The air we breathe can contain pollutants from numerous sources around the globe, ranging from cars on a nearby highway to a forest fire in Alaska to a factory in Asia. Although largely invisible, these chemicals and particles have detrimental effects on our health and our environment.
Scientists at the National Center for Atmospheric Research (NCAR), using computer models and sophisticated observing instruments, are making new discoveries about air pollutants and their movements worldwide. This research may help society take targeted steps to improve air quality. In addition, the work is shedding light on the subtle interactions between air pollution and climate.
Scientists for the first time are achieving the goal of observing pollution on a global scale and tracking in detail the movement of pollutants in
the atmosphere.
Their accomplishment is due to a landmark instrument designed and built by a team at NCAR and the University of Toronto, Canada. The satellite-borne Measurements of Pollution in the Troposphere (MOPITT), launched in 1999, makes continuous measurements of carbon monoxide, which is both a pollutant and a key indicator of the presence of other pollutants.
The instrument has enabled researchers to create worldwide maps of carbon monoxide and to analyze the impacts of wildfires, industrial facilities, and even climate shifts on atmospheric pollution. Scientists have used MOPITT to help establish the sources of air pollution, determining, for example, that almost a third of Europe's pollution arrives from North America and Asia. They have also discovered that pollution varies significantly from one year to the next because of emissions from wildfires.
Thanks to extended funding from NASA, the instrument over the next several years will help researchers learn more about the impact of drought and other climatic events on the year-to-year variability of pollution. Scientists also hope to glean new insights into how various pollutants, in turn, affect climate—both by influencing rainfall patterns and by affecting the amount of solar radiation in the atmosphere.
 James Smith. (Photo by Carlye Calvin, UCAR) |
Among the pollutants that are most hazardous to human health are tiny particles known as ultrafine aerosols. These particles, which are smaller than 100 nanometers or about a thousandth the diameter of a human hair, can be inhaled deeply into the lungs, evading the body's protective mechanisms and causing respiratory problems and other ailments. Ultrafine aerosols also influence climate by affecting water droplets and cloud formation.
A team of scientists from NCAR and the University of Minnesota has developed an instrument that can measure the chemical composition of particles as small as four nanometers. Deploying the instrument in Atlanta, NCAR scientist James Smith and colleagues found that the particles form suddenly across large regions when levels of sulfuric acid, which is a key ingredient in ultrafine aerosols, reach a critical threshold in the atmosphere.
The team hopes to answer such crucial questions as what causes ultrafine aerosols to form and whether they have a different composition in cities than in remote areas. Such research ultimately may help society better protect itself from these particles, as well as enable atmospheric scientists to interpret their impact on climate.
A recent data analysis by NCAR scientist Elisabeth Holland and colleagues at the University of New Hampshire indicates that the United States is sending nitrogen pollution beyond its borders, with some of it likely ending up in Western Europe.
Nitrogen pollution, which degrades air and water quality and alters ecosystems, has profound consequences for human health and agriculture. Various nitrogen compounds, including nitrogen oxides and ammonia, are a major ingredient in smog and acid rain.
The research team analyzed data between 1978 and 1994. Only 40% of nitrogen released into the atmosphere from U.S. factories, cars, power plants, and other sources was found deposited within U.S. boundaries. The remaining nitrogen was unaccounted for, and evidence indicates that a portion of it reached Western Europe.
 Alaskan wildfire. (Courtesy Alaska Fire Service.) |
Wildfires loft enormous amounts of pollutants into the atmosphere, but only recently have scientists been able to use observing instruments and computer models to quantify the pollutants' far-flung impacts.
A recent study by Gabriele Pfister and other NCAR scientists showed that unusually intense wildfires in Alaska and Canada in 2004 emitted about as much carbon monoxide as did human-related activities in the continental United States during the same time. The fires increased atmospheric concentrations of ground-level ozone—a pollutant formed from reactions involving carbon monoxide and other chemicals—by 25% or more in parts of the United States and by 10% as far away as Europe.
Another study by NCAR scientist David Edwards and colleagues determined that emissions from massive peat fires in 2002 near Moscow and intense wildfires in 2003 in Siberia circled the Northern Hemisphere.
Wildland fires, including fires set deliberately by farmers to clear land, are responsible for about half the world's emissions of carbon monoxide.
Air pollution from the world's growing megacities can travel far downwind, adversely affecting human health, agriculture, natural ecosystems, regional visibility, and possibly even the global environment. Because the pollution is highly complex, researchers have not been able to fully quantify its movement or chemical composition.
To get a better understanding of what happens to air pollution after it leaves a large city, NCAR scientist Sasha Madronich and a team of researchers in the United States and Mexico are launching a major field campaign in Mexico City. The team hopes to answer three broad questions:
• How will future urban growth affect atmospheric composition on regional and global scales?
• What are the impacts of pollutants on regional and global climate?
• Can better urban design and planning reduce these impacts?
Known as MIRAGE (Megacity Impacts on Regional and Global Environments), the Mexico City project is especially important because computer models of air pollution were developed mainly for cities in industrialized nations. The models may not accurately depict pollutants in cities like Mumbai, India, where many people burn coal and wood and drive vehicles that emit more harmful chemicals than those in the United States.
Smog in Mexico City. (© Julio Etchart) |
