title: Trends of nitrogen in air and precipitation: model results and observations at EMEP sites in Europe, 1980--2003.
abstract: We analyze trends of some nitrogen compounds using long-term measurements and results from the EMEP (co-operative programme for monitoring and evaluation of the long-range transmissions of air pollutants in Europe) chemical transport model at EMEP sites. We find statistically significant declines at the majority of sites for NH(x) (sum of ammonia and ammonium) in air and for nitrate and ammonium in precipitation, but only at a few sites for xNO3 (sum of nitrate and nitric acid) in air. Model calculations and measurements give similar results. We demonstrate that the lack of trends for xNO3 in air at least partly can be attributed to a shift in the equilibrium between nitric acid and ammonium nitrate towards particulate phase, caused by reductions in the sulfur dioxide emissions.
authors.affiliation: Norwegian Meteorological Institute, Research and Development Department, P.O. Box 43, Blindern, N-0313 Oslo, Norway. h.fagerli@met.no
authors.forename: Hilde
authors.initials: H
authors.lastname: Fagerli
authors.forename: Wenche
authors.initials: W
authors.lastname: Aas
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000032:analysis / Q000706:statistics & numerical data*; D000641:Ammonia / Q000032:analysis; D011232:Chemical Precipitation; D004784:Environmental Monitoring / Q000379:methods / Q000706:statistics & numerical data; D005060:Europe; D015233:Models, Statistical; D009566:Nitrates / Q000032:analysis; D017942:Nitric Acid / Q000032:analysis; D009584:Nitrogen / Q000032:analysis*; D000644:Quaternary Ammonium Compounds / Q000032:analysis; D012621:Seasons; D013458:Sulfur Dioxide / Q000032:analysis
chemical_list: D000393:Air Pollutants; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D013458:Sulfur Dioxide; D017942:Nitric Acid; D000641:Ammonia; D009584:Nitrogen