Calculation of NH₃ Emissions, Evaluation of Backward Lagrangian Stochastic Dispersion Model and Aerodynamic Gradient Method

• Main Authors: Jesper Nørlem Kamp, Christoph Häni, Tavs Nyord, Anders Feilberg, Lise Lotte Sørensen
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Atmosphere
• Subjects: ammonia emission; backward Lagrangian stochastic model; micrometeorological techniques; differential optical absorption spectroscopy; cavity ring-down spectroscopy; grassland
• Online Access: https://www.mdpi.com/2073-4433/12/1/102

Two campaigns measuring ammonia (NH₃) emissions with different measurement techniques were performed on a large grass field (26 ha) after the application of liquid animal manure. The aim was to compare emissions from a confined area estimated from either (i) concentration measurements, both point and line-integrated measurements, combined with backward Lagrangian stochastic (bLS) dispersion modeling or by (ii) estimation of the vertical flux by the aerodynamic gradient method (AGM) with and without footprint correction approximated by the bLS model estimates of the flux footprint. The objective of the comparison is to establish the best practice to derive NH₃emissions from a large field. NH₃ emissions derived from bLS agreed well when comparing point and line-integrated measurements. Simple point measurements combined with bLS yield good emission estimations for the confined area. Without footprint correction, the AGM underestimates the emissions by up to 9% compared to the footprint-corrected AGM results. The sensitivity of the measurement methods makes it possible to quantify NH₃emissions with diurnal patterns even five days after a field application of liquid animal manure under wet conditions. The bLS model proves to be a strong tool to determine the NH₃emissions from point concentration measurements inside a large field after a slurry application.