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EPA research on ammonia prompts satellites and surface measurements to converge

New technique transforms satellite data to tools that find and track ammonia around the globe

Posted: April 6, 2011

Google Earth image of ammonia levels across North and South America as measured by the Tropospheric Emission Spectrometer (TES) on NASA’s Aura satellite.

A ground-level sampler in Lillington, N.C.

What circles the Earth in 98 minutes, advances 2,500 miles westward on every trip, and returns to the same location every 16 days? It’s the NASA Aura satellite, which carries the Tropospheric Emission Spectrometer (TES). Who knew? Researchers at the U.S. Environmental Protection Agency (EPA) knew. And they used the satellite, the spectrometer, and their expertise and creativity to solve some of the problems associated with identifying sources of ground-level ammonia on Earth.

For the first time, EPA scientists and their collaborators have demonstrated that ammonia measurements taken via satellite closely resemble those routinely measured via monitors on Earth. The results of this research were published Feb. 18, 2011, in Geophysical Research Letters in a paper titled "Quantifying spatial and seasonal variability in atmospheric ammonia with in situ and space-based observations."

Why use satellites?
The TES satellite on the Aura mission provides rich, reliable data on the composition, chemistry, and dynamics of the atmosphere miles above the Earth’s surface. Since satellites cover the globe each day, they can provide a perspective vastly more telling than what can be delivered via a limited number of surface measurements taken from the Earth. The satellite-based sensors are even able to capture seasonal and spatial ammonia patterns on the Earth’s surface.

Where does ammonia come from?
Much of the ammonia comes from livestock waste and fertilizer that are continually broken down and converted to ammonia by microorganisms. The U.S. Department of Agriculture estimates that confined animals in the United States alone excrete three times more waste than the entire American population each year.

What is the impact of ammonia on the environment and human health?
Ammonia can contribute to the formation of particulate matter — a form of air pollution that has been linked to adverse respiratory and cardiac effects in humans. When deposited in sensitive ecosystems, ammonia can also contribute to algae blooms which can deplete oxygen in lakes and streams and induce reductions in specific fish or other animal populations.

How was the study conducted?
EPA researchers gathered measurements from surface-level monitors for ten months and coordinated collection of satellite measurements with collaborators at the University of Colorado (Boulder), the Jet Propulsion Laboratory (Pasadena, Calif.), Atmospheric and Environmental Research Inc. (Lexington, Mass.), and Environment Canada. Surface-level monitors were placed in a designated study area in eastern North Carolina to gather measurements from the ground. As the satellites passed over the study area, the satellite-based sensors took measurements at 25 locations, each approximately 3-miles long by 5-miles wide.

Why was the study conducted in eastern North Carolina?
Eastern North Carolina was selected for the study because ammonia sources there are plentiful. Between 1990 and 2000, North Carolina’s ammonia emissions increased 66 percent, mostly attributable to agricultural animal populations. This location was also selected because the counties immediately surrounding the study area have designated wilderness areas, significant seasonal changes, and much lower ammonia emissions than the study area itself.

The bottom line
The techniques developed and tested by EPA researchers provide sustainable solutions for monitoring air quality, determining sources of pollution, and providing information to inform the development of mitigation strategies that can protect public health and the environment.

For complete study details, see the Feb. 18, 2011 issue of Geophysical Research Letters. (Pinder, R., Walker, J., Bash, J., et.al., "Quantifying spatial and seasonal variability in atmospheric ammonia with in situ and space-based observations," Vol. 38, L04802, Feb. 18, 2011).

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