A review of ammonia emission measured using wind tunnels compared with micrometeorological techniques

Abstract

Ammonia (NH3) emission from livestock manure constitutes a loss of crop‐available nitrogen (N) and poses a threat to the environment. Therefore, low NH3 emission slurry application technologies have been developed, the reduction efficiency of which has typically been estimated through measurements using wind tunnels or integrated horizontal flux (IHF) micrometeorological techniques. A recovery of 100% of released NH3 can be obtained if wind tunnels are designed to avoid pulses of wind into the tunnel through the canopy opening and leaks from the tunnels. The NH3 emission measured with wind tunnels adjusted to an air flow of 1 m/s deviated significantly (P < 0.05) from the emission measured using IHF methods, which are generally considered to give reliable emission estimates for ambient conditions. If wind tunnel air flow was adjusted to the ambient wind speed at height 0.25–0.30 m, then measured emissions were not significantly different from those measured using IHF methods. Wind tunnels influence the air flow pattern and cause turbulent convection in the air layers above the emitting surface, so the similarity in measured emissions for the two measuring techniques is perhaps surprising. This may be because the soil surface resistance to NH3 transport is often the most important rate‐regulating variable, so that the absence of a laminar boundary air layer resistance as caused by wind tunnels is of minor importance. It is concluded that the wind tunnels are well suited to test the emission reduction efficiency of new technologies.

Improved acid trap methodology for determining ammonia volatilization in wind tunnel experiments

“…1a), which was determined by field sonic anemometers, placed 0.25 m above the soil surface, in 2013 and 2014 to be representative of average near-surface wind speeds at the field site (data not shown). Adjusting wind speed to represent ambient conditions (at 0.25 m) can provide ammonia volatilization values in statistical agreement with IHF results (Sommer and Misselbrook 2016). Wind speed can directly affect ammonia volatilization rates within wind tunnels.…”

“…Sommer et al (1991) showed a positive increase in losses, from cattle slurry, up to 2.5 m s −1 , whereas increases in wind speed beyond 2.5-4 m s −1 did not influence loss. Sommer and Misselbrook (2016) suggested having relatively high wind speeds will increase the likelihood of agreement with the IHF method, as the laminar boundary layer resistance will no longer be the controlling factor for ammonia volatilization loss.…”

“…Dynamic wind tunnel field chambers developed by Lockyer (1984) continue to be the recommended NH 3 -N volatilization sampling method for comparing multiple treatments (and replicates) within field studies (Shah et al 2006;Sommer and Misselbrook 2016) that examine fertilizer and (or) manure sources, placement methods, timing of application, and other ammonia volatilization reduction strategies (Misselbrook et al 2005b;Rochette et al 2009;Drury et al 2017). Ammonia volatilization emissions based on data from wind tunnel field studies are being used in the Intergovernmental Panel on Climate Change greenhouse gas inventories and synthesis publications (Pan et al 2016).…”

Can the agronomic performance of urea equal calcium ammonium nitrate across nitrogen rates in temperate grassland?

“…Overall the current study suggests that ammonia losses from urea usage in a temperate maritime climate are much lower than the values obtained from wind tunnels. This is perhaps not so surprising when one considers that Ryden and Lockyer () reported that wind tunnels can overestimate ammonia losses by a factor of 2.4–6 during rainfall and that Sommer & Misselbrook () report that wind tunnels which are adjusted to match ambient airflow could give results similar to integrated horizontal flux for periods without rainfall. In the parallel study of Forrestal et al .…”

An Assessment of Low-Cost Techniques to Measure Ammonia Emission from Multi-Plots: A Case Study with Urea Fertilization

“…In the last decades, most of the tests performed on NH 3 volatilization from manure and mineral fertilizers at field-scale or in in agronomic plots, were measured with the Integrated Horizontal Flux (IHF) technique, the ZINST method, the inverse dispersion modelling (IDM) coupled with concentration measurements, or with wind tunnels [13][14][15]. Agronomic plots of 20 m in radius treated with manure are the most common design in the tests of low emitting spreading technologies [14], and the IHF is often considered as a reference method to assess NH 3 emissions [12,16]. In the typical tests, IHF is used to measure emission from relatively large plots (radius of 20 m) which demands a large distance between coexisting plots to avoid advection interferences; consequently, few or no replications at plot-level are carried out.…”