"The vast majority, 85 percent, of nitrogen deposition originates with human activities," explains principal investigator Daniel J. Jacob, Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering at the Harvard School of Engineering and Applied Sciences (SEAS). "It is fully within our power as a nation to reduce our impact."
Existing air quality regulations and trends in clean energy technology are expected to reduce the amount of harmful nitrogen oxides (NOx) emitted by coal plants and cars over time. However, no government regulations currently limit the amount of ammonia (NH3) that enters the atmosphere through agricultural fertilization or manure from animal husbandry, which are now responsible for one-third of the anthropogenic nitrogen carried on air currents and deposited on land.
"Ammonia's pretty volatile," says Jacob. "When we apply fertilizer in the United States, only about 10 percent of the nitrogen makes it into the food. All the rest escapes, and most of it escapes through the atmosphere."