Exchange of reactive nitrogen compounds: concentrations and fluxes of total ammonium and total nitrate above a spruce canopy

Abstract

Abstract. Total ammonium (tot-NH3 ) 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 wetchemical two-point gradient instrument, the GRAEGOR. Median concentrations of NH 3 , HNO 3 , NH + 4 , and NO − 3 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 on occult deposition (fog water interception) at the study site, the total N deposition in September 2007 was estimated to 5.86 kg ha −1 .

Eddy covariance measurements with high-resolution time-of-flight aerosol mass spectrometry: a new approach to chemically resolved aerosol fluxes

“…To our knowledge, the measurements described here include the first direct eddy covariance flux measurements of particulate ammonium. Availability of instrumentation has limited past studies to indirect flux methods (Nemitz et al, 2004b;Trebs et al, 2006;Wolff et al, 2010). Ammonium is an unusually challenging aerosol component for which to interpret fluxes, as one subset of ammonium is irreversibly tied to sulphate ions, while another is in equilibrium with gas-phase species: NH 3(g) + HNO 3(g) ↔ NH 4 NO 3(particle)…”

“…Fluxes of total or size-resolved aerosol number (without chemical information) have been performed for some time (e.g., Katen et al, 1985;Sievering, 1987;Buzorius et al, 1998;Dorsey et al, 2002;Mårtensson et al, 2006;Vong et al, 2010). However, total and chemically-resolved particle mass fluxes have lagged behind because most instruments measuring mass or aerosol chemical composition are far from meeting the rigorous requirements for EC, and most chemically-resolved aerosol flux measurements have been indirect with slower time resolution approaches (e.g., Nemitz et al, 2004b;Trebs et al, 2006;Myles et al, 2007;Thomas et al, 2009;Wolff et al, 2010).…”

Observations of reactive nitrogen oxide fluxes by eddy covariance above two midlatitude North American mixed hardwood forests

“…Other studies using eddy covariance have applied novel instruments to directly determine the contribution of individual species over short-term (several months or less) intensive field campaigns at a number of sites across North America (Horii et al, 2004;Turnipseed et al, 2006;Farmer and Cohen, 2008;Wolfe et al, 2009;Min et al, 2012;Zhang et al, 2012). Gradient methods above forest canopies have also been used to determine the contributions of certain species to NO y deposition or emission budgets (Sievering et al, 2001;Pryor et al, 2002;Neirynck et al, 2007;Wolff et al, 2010).…”

TRANC – a novel fast-response converter to measure total reactive atmospheric nitrogen

“…Meixner, 1994) and gas-aerosol particle interactions (e.g. Wolff et al, 2010b), and therefore the necessity to measure several parameters simultaneously, and (c) the complexity and labour-intensity of flux measurements of the individual compounds.…”