title: Trends in atmospheric ammonium concentrations in relation to atmospheric sulfate and local agriculture.
abstract: Ammonium (NH(4)(+)) concentrations in air and precipitation at the Institute of Ecosystem Studies (IES) in southeastern New York, USA declined over an 11-year period from 1988 to 1999, but increased from 1999 to 2001. These trends in particulate NH(4)(+) correlated well with trends in particulate SO(4)(2-) over the 1988-2001 period. The NH(4)(+) trends were not as well correlated with local cattle and milk production, which declined continuously throughout the period. This suggests that regional transport of SO(4)(2-) may have a greater impact on concentrations of NH(4)(+) and subsequent deposition than local agricultural emissions of NH(3). Ammonium concentrations in precipitation correlated significantly with precipitation SO(4)(2-) concentrations for the 1984-2001 period although NH(4)(+) in precipitation increased after 1999 and SO(4)(2-) in precipitation continued to decline after 1999. The correlation between NH(4)(+) and SO(4)(2-) was stronger for particulates than for precipitation. Particulate NH(4)(+) concentrations were also correlated with particulate SO(4)(2-) concentrations at 31 of 35 eastern U.S. CASTNet sites that had at least 10 years of data. Air concentrations of NH(4)(+) and SO(4)(2-) were more strongly correlated at the sites that were located within an agricultural landscape than in forested sites. At most of the sites there was either no trend or a decrease in NH(4)(+) dry deposition during the 1988-2001 period. The sites that showed an increasing trend in NH(4)(+) dry deposition were generally located in the southeastern U.S. The results of this study suggest that, in the northeastern U.S., air concentrations of NH(4)(+) and subsequent deposition may be more closely linked to SO(4)(2-) and thus SO(2) emissions than with NH(3) emissions. These results also suggest that reductions in S emissions have reduced NH(4)(+) transport to and NH(4)(+)-N deposition in the Northeast.
authors.affiliation: Institute of Ecosystem Studies, Millbrook, NY 12545, USA. kellyv@ecostudies.org
authors.forename: Victoria R
authors.initials: VR
authors.lastname: Kelly
authors.forename: Gary M
authors.initials: GM
authors.lastname: Lovett
authors.forename: Kathleen C
authors.initials: KC
authors.lastname: Weathers
authors.forename: Gene E
authors.initials: GE
authors.lastname: Likens
mesh_terms: D000383:Agriculture; D000393:Air Pollutants / Q000032:analysis*; D000818:Animals; D001272:Atmosphere / Q000032:analysis*; D002417:Cattle; D011232:Chemical Precipitation; D004784:Environmental Monitoring / Q000379:methods; D008892:Milk; D009518:New York; D000644:Quaternary Ammonium Compounds / Q000032:analysis*; D013431:Sulfates / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D000644:Quaternary Ammonium Compounds; D013431:Sulfates