Trends in Ammonium Concentrations in Relation to Local-Scale Agriculture and Regional Sulfur Dioxide Emissions

Ammonium concentrations (in precipitation and atmospheric particles) at the Institute of Ecosystem Studies in Dutchess County, New York declined during the 12-year period between 1988-1999, but have increased between 1999 and 2002. The decline between 1988 and 1999 parallels 1) a decline in the number of cattle and calves, and especially the total milk production in Dutchess County, and 2) a decline in the concentration of particulate SO4 in the air. Concentrations of particulate ammonium correlate better with particulate sulfate concentrations than with agricultural statistics, suggesting that changes in air concentrations of ammonium are controlled more by changes in particulate sulfate concentrations, which are a product of regional SO₂ emissions, than by changes in agriculture in this area. In particular, the period after 1999 is characterized by increasing particulate NH4 and SO4, but continually declining milk production. Concentrations of ammonium in precipitation correlate with sulfate concentrations in precipitation, but not as well as air concentrations of ammonium and sulfate. In this poster we will discuss the mechanisms and implications of the observed trends.

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