Aerodynamic gradient measurements of the NH<sub>3</sub>-HNO<sub>3</sub>-NH<sub>4</sub>NO<sub>3</sub> triad using a wet chemical instrument: an analysis of precision requirements and flux errors

Abstract

Abstract. The aerodynamic gradient method is widely used for flux measurements of ammonia, nitric acid, particulate ammonium nitrate (the NH 3 -HNO 3 -NH 4 NO 3 triad) and other water-soluble reactive trace compounds. The surface exchange flux is derived from a measured concentration difference and micrometeorological quantities (turbulent exchange coefficient). The significance of the measured concentration difference is crucial for the significant determination of surface exchange fluxes. Additionally, measurements of surface exchange fluxes of ammonia, nitric acid and ammonium nitrate are often strongly affected by phase changes between gaseous and particulate compounds of the triad, which make measurements of the four individual species (NH 3 , HNO 3 , NH + 4 , NO − 3 ) necessary for a correct interpretation of the measured concentration differences.We present here a rigorous analysis of results obtained with a multi-component, wet-chemical instrument, able to simultaneously measure gradients of both gaseous and particulate trace substances. Basis for our analysis are two field experiments, conducted above contrasting ecosystems (grassland, forest). Precision requirements of the instrument as well as errors of concentration differences and micrometeorological exchange parameters have been estimated, which, in turn, allows the establishment of thorough error estimates of the derived fluxes of NH 3 , HNO 3 , NH + 4 , and NO − 3 . Derived median flux errors for the grassland and forest field experiments were: 39% and 50% (NH 3 ), 31% and 38% (HNO 3 ), 62% and 57% (NH + 4 ), and 47% and 68% (NO − 3 ), respectively. Additionally, we provide the basis for using Correspondence to: V. Wolff (veronika.wolff@art.admin.ch) field data to characterize the instrument performance, as well as subsequent quantification of surface exchange fluxes and underlying mechanistic processes under realistic ambient measurement conditions.

Semi-continuous gas and inorganic aerosol measurements at a Finnish urban site: comparisons with filters, nitrogen in aerosol and gas phases, and aerosol acidity

“…9). These diurnal cycles resemble those observed at other sites, for instance Zürich (Fisseha et al, 2006), Pittsburgh (Wittig et al, 2004), and Oensingen, Switzerland (Wolff et al, 2010): the peak nitrate concentration is a few hours earlier than that of HNO 3 . The time lag can be explained by the temperature dependent partitioning of ammonium nitrate between the gas and aerosol phase (e.g., Fisseha et al, 2006).…”

“…The reason is that the diurnal cycles depend both on the site and the time of the year. For example, in Oensingen in the late summer of 2006, the maximum HNO 3 concentration was clearly later in the afternoon (16:00-17:00) (Wolff et al, 2010), which is about 4 h later than in our spring period in Helsinki. In our study the HNO 3 concentration decreased in the afternoon, probably due to dry deposition and heterogeneous formation of nitrate, as suggested for example by Fisseha et al (2006) for the similar cycle in Zürich.…”

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

“…This is due to the fact that dry N r exchange constitutes a variety of compounds with different exchange patterns and that in general, concentration and flux measurements of N r species are challenging from a metrological point of view (e.g. von Bobrutzki et al, 2010;Wolff et al, 2010a). Well-established measurement techniques (e.g.…”

Determination of field scale ammonia emissions for common slurry spreading practice with two independent methods

“…Two adjacent fields cultivated as cropland (wheat) and intensively managed grassland (grass-clover mixture) were fertilised with liquid cattle slurry. The grassland is one of the level 3 sites of the NitroEurope project (www.nitroeurope.eu) and NH 3 concentrations as well as exchange patterns had been investigated here previously (Norman et al, 2009;Spirig et al, 2010;Wolff et al, 2010;Flechard et al, 2010Flechard et al, , 2011. The climate is temperate continental with mean annual temperature and rainfall of 9.5 • C and 1200 mm, respectively.…”