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Wolff, V; Trebs, I; Foken, T; Meixner, FX: Exchange of reactive nitrogen compounds: concentrations and fluxes of total ammonium and total nitrate above a spruce forest canopy, Atmospheric Chemistry and Physics, Discussion, 6, 10663-10706 (2009) [Link]
Abstract:
Total ammonium (tot-NH4+) and total nitrate (tot-NO3−) provide a chemically conservative quantity in the measurement of exchange processes of reactive nitrogen compounds ammonia (NH3), particulate ammonium (NH4+), nitric acid (HNO3), and particulate nitrate (NO3−), using the aerodynamic gradient method. Total fluxes were derived from concentration differences of total ammonium (NH3 and NH4+) and total nitrate (HNO3 and NO3−) measured at two levels. Gaseous species and related particulate compounds were measured selectively, simultaneously and continuously above a spruce forest canopy in south-eastern Germany in summer 2007. Measurements were performed using a wet-chemical two-point gradient instrument, the GRAEGOR. Median concentrations of NH3, HNO3, NH4−, and NO3− were 0.57, 0.12, 0.76, and 0.48 μg m−3, respectively. Total ammonium and total nitrate fluxes showed large variations depending on meteorological conditions, with concentrations close to zero under humid and cool conditions and higher concentrations under dry conditions. Mean fluxes of total ammonium and total nitrate in September 2007 were directed towards the forest canopy and were −65.77 ng m−2 s−1 and −41.02 ng m−2 s−1 (in terms of nitrogen), respectively. Their deposition was controlled by aerodynamic resistances only, with very little influence of surface resistances. Including measurements of wet deposition and findings of former studies at the study site on occult deposition (fog water interception), the total N deposition in September 2007 was estimated to 5.86 kg ha−1.
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last modified 2009-11-16