But several studies indicate that the biggest share of ammonia emissions is from animal wastes and fertilizers. Areas with highest emissions were Pennsylvania's Lancaster and Lebanon counties, other parts of southcentral Pennsylvania, the Shenandoah Valley in Virginia and West Virginia, and parts of Maryland. By contrast, ammonia releases in agriculture have been fairly well studied because farmers who apply manure or fertilizer need to take potential losses into account to make sure their crops are getting enough nitrogen. Though most agree that agriculture is the main source of ammonia emissions, many suspect that other sources have been undercounted. Ammonia also comes from wastewater treatment plants, industrial refrigeration units, tailpipes and smokestacks.
Some industries add ammonia to reduce NOx emissions.
Ammonia concentrations in Baltimore are twice that in rural Kent County, MD, said Baker, of the Chesapeake Biological Laboratory, though he noted that Kent County is not in a heavy agricultural area. But frankly, I think it's a population density kind of deal. Nor is anyone certain where ammonia goes once it gets into the air. For years, the conventional wisdom has been that ammonia does not travel far from its source - perhaps only a few hundred yards or a few miles. The implications from the agricultural activity, of course, is that those concentrations should be going up, along with the transport and deposition.