1Department of Environmental Science, Aarhus University, P.O. Box 358, Frederiksborgvej 399, 4000 Roskilde, Denmark
2Department for Environmental, Social and Spatial Change (ENSPAC), Roskilde University, 4000 Roskilde, Denmark
3Department of Physical Geography and Ecosystems Science, Lund University, Sölvegatan 12, 223 62 Lund, Sweden
4Centre for Ecology & Hydrology (CEH), Bush Estate Penicuik Midlothian EH26 0QB, UK
5Energy Research Centre of the Netherlands (ECN), Biomass, Coal & Environmental Research, P.O. Box 19, 1755 ZG Petten, The Netherlands
6School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston Birmingham B15 2TT, UK
7Department of Environmental Sciences/Center of Excellence in Environmental Studies, King Abdulaziz University, P.O. Box 80203, Jeddah, 21589, Saudi Arabia
8EMEP MSC-W, Norwegian Meteorological Institute, Henrik Mons Plass 1, 0313 Oslo, Norway
9Department of Earth & Space Sciences, Chalmer University of Technology, SE412 96 Gothenburg, Sweden
10University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
11Department of Physics, University of Helsinki, Finland
12Earth and Climate, VU university Amsterdam and Louis Bolk Institute, Hoofdweg 24, 3972 LA Driebergen,The Netherlands
Received: 15 Jul 2012 – Discussion started: 27 Jul 2012
Abstract. Reactive nitrogen (Nr) compounds have different fates in the atmosphere due to differences in the governing processes of physical transport, deposition and chemical transformation. Nr compounds addressed here include reduced nitrogen (NHx: ammonia (NH3) and its reaction product ammonium (NH4+)), oxidized nitrogen (NOy: nitrogen monoxide (NO) + nitrogen dioxide (NO2) and their reaction products) as well as organic nitrogen compounds (organic N). Pollution abatement strategies need to take into account the differences in the governing processes of these compounds when assessing their impact on ecosystem services, biodiversity, human health and climate. NOx (NO + NO2) emitted from traffic affects human health in urban areas where the presence of buildings increases the residence time in streets. In urban areas this leads to enhanced exposure of the population to NOx concentrations. NOx emissions generally have little impact on nearby ecosystems because of the small dry deposition rates of NOx. These compounds need to be converted into nitric acid (HNO3) before removal through deposition is efficient. HNO3 sticks quickly to any surface and is thereby either dry deposited or incorporated into aerosols as nitrate (NO3−). In contrast to NOx compounds, NH3 has potentially high impacts on ecosystems near the main agricultural sources of NH3 because of its large ground-level concentrations along with large dry deposition rates. Aerosol phase NH4+ and NO3− contribute significantly to background PM2.5 and PM10 (mass of aerosols with an aerodynamic diameter of less than 2.5 and 10 μm, respectively) with an impact on radiation balance as well as potentially on human health. Little is known quantitatively and qualitatively about organic N in the atmosphere, other than that it contributes a significant fraction of wet-deposited N, and is present in both gaseous and particulate forms. Further studies are needed to characterise the sources, air chemistry and removal rates of organic N emissions.
Revised: 29 Oct 2012 – Accepted: 14 Nov 2012 – Published: 04 Dec 2012
Hertel, O., Skjøth, C. A., Reis, S., Bleeker, A., Harrison, R. M., Cape, J. N., Fowler, D., Skiba, U., Simpson, D., Jickells, T., Kulmala, M., Gyldenkærne, S., Sørensen, L. L., Erisman, J. W., and Sutton, M. A.: Governing processes for reactive nitrogen compounds in the European atmosphere, Biogeosciences, 9, 4921-4954, doi:10.5194/bg-9-4921-2012, 2012.