title: Changing chemical composition of precipitation in Wilmington, North Carolina, U.S.A.: implications for the Continental U.S.A.
abstract: The H+(aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% during the preceding two decades, similar to trends seen nationwide. The decrease in acidity is important because solution pH plays a key role in atmospheric reactions, and because the change is so large. This study presents the first long-range study of dissolved organic carbon (DOC) levels in precipitation which demonstrates that DOC concentrations have decreased by approximately half in Wilmington, NC, precipitation. The concentrations of H+(aq) and DOC are highly correlated primarily because small organic acids contribute to both DOC and H+(aq) in precipitation. Ammonium ion concentrations in precipitation have increased due to increased agricultural activities, and this also affects precipitation pH. The reduction of SO2 emissions in 1995 imposed by the Clean Air Act Amendment, better control of emissions of volatile organic compounds, and the increase in ammonia emissions all contribute to the decreasing H+(aq) in precipitation nationwide. These compositional changes in precipitation have many environmental implications, such as decreased acid deposition to lakes, changing speciation for trace metals in precipitation, increased ammonium deposition to coastal waters, and decreased DOC transport to the open ocean.
authors.affiliation: Department of Chemistry and Biochemistry and Marine Science Program, University of North Carolina Wilmington, Wilmington, North Carolina 28403-5932, USA. willeyj@uncw.edu
authors.forename: Joan D
authors.initials: JD
authors.lastname: Willey
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Kieber
authors.forename: G Brooks
authors.initials: GB
authors.lastname: Avery
mesh_terms: D015258:Acid Rain; D002244:Carbon / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009657:North Carolina; D009930:Organic Chemicals / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D011891:Rain / Q000737:chemistry*
chemical_list: D015258:Acid Rain; D002712:Chlorides; D009930:Organic Chemicals; D000644:Quaternary Ammonium Compounds; D002244:Carbon