New measurements of ammonia (NH 3) loss after slurry application on grassland in Swi tzerland were carried over the last two years. They yielded NH 3 emissions being by approximately 50% lower compare d to earlier published values in the 1990s. A reasses sm nt of the previous experiments revealed experimental shortcomings that do explain most of t he difference. Introduction The Swiss model Agrammon [1] for the calculation of the national emissions of ammonia (NH 3) within the framework of the UN Convention on Long-range Tr ansboundary Air Pollution [2] uses currently an average emission factor (EF) of 50% of the applied total ammoniacal nitrogen (TAN) for broadcast application which is considered as the reference te hnique. For low emission application techniques su ch as trailing hose and trailing shoe, specific factor s for emission reduction (70% and 50% of broadcast, respectively) are used. The EF for broadcast applic ation is mainly based on the ALFAM model [3] and on measurement in Switzerland from the 1990s [4,5]. Re cent measurements for Swiss conditions exhibited significantly lower emissions [6,7] that could not be explained and the hypothesis of a potential plot scale influence on EF was stated [8]. Consequently, a new measurement campaign was launched at different sites in Switzerland to reveal potential influences of used plot scales and to clarify the differences . This study presents the results from the current campaig n nd discusses the reasons for the discrepancy between the previous and the new results. Material & Methods Field sites and agronomical issues A first series of trials (module 1) examined whethe r an influence of the plot scale on the EF’s exists . The slurry was applied with slurry tankers equipped wit h a splash plate, or a trailing hose. Plots of medi um size (30m x 30m) were compared to field size plots of 0.5 ha. A second series (module 2) was devoted t investigate the influence of application technique, type of slurry and seasonality on medium size plot s (30m x 30m). All experiments were carried out on gr assland and application rates amounted to approximately 30 t/ha. The ammonia loss was measure d fo 2-3 days. Table 1 shows a compilation of the trials. Measuring technique At the centre of each plot, an impinger based sampl ing device measured the NH 3 concentration at two heights (approx. 0.9m and 1.6m). Additionally, the background concentration was sampled up wind of the manured areas. The impinger sampling systems [6] we re operated at a flow rate of approx. 0.7 L/min and sampling intervals between 10 min at application st art and several hours over night. Wind velocity and temperature fluctuations were measured with 3D soni c devices. The measurements were terminated when an emission flux could no longer be detected (i.e. when the concentrations above the plots were equal or below the inflow concentrations). WindTrax approach For each NH3 sampling device, the ratio of the measured concent ration to the related emission rate (C/E) was calculated using the backward Lagrangian stocha sti Model (bLS) WindTrax [9]. The model input was given by 10 minute averages of the wind directi on, the friction velocity (U*), the Obhukov-Length (L) and the roughness length (Zo), as well as the s andard deviations of the rotated high frequency wi nd velocities. Emission rates were then calculated by dividing the measured NH 3 concentrations less the measured background concentration by the C/E ratios veraged over the sampling intervals.

Reassessment of Swiss ammonia emission factors after slurry application.

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Reassessment of Swiss ammonia emission factors after slurry application.