A Relaxed Eddy Accumulation System for the Automated Measurement of Atmospheric Ammonia Fluxes |
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Authors: | Nemitz E. Flynn M. Williams P. I. Milford C. Theobald M. R. Blatter A. Gallagher M. W. Sutton M. A. |
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Affiliation: | (1) Centre for Ecology and Hydrology (CEH), Edinburgh Research Station, Bush Estate, Penicuik, Midlothian, U.K.;(2) Physics Department, UMIST, Manchester, U.K;(3) Centre for Ecology and Hydrology (CEH), Edinburgh Research Station, Bush Estate, Penicuik, Midlothian, U.K;(4) Federal Research Station for Agroecology and Agriculture (FAL), Berne-Liebefeld, Switzerland |
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Abstract: | A continuous relaxed eddy accumulation system ispresented for the automated measurement of surface/atmosphere exchange fluxes of atmospheric ammonia (NH3) at a single height. The new system features sampling by parallel plate denuder inlets, online chemical analysis using the conductivity cell of a commercially available NH3 analyzer and online flux calculation. The effective detection limit of the system for air concentrations is 0.2 g m-3 and it is estimated to resolve fluxes > ± 20 ng m-2 s-1, depending on the NH3 concentration and turbulence. The performance of the system was tested in two measurement campaigns above agricultural grassland, in which it was compared with a 3-point continuous gradient system. During the first campaign, after urea application of 47 kg N ha-1 in autumn, the REA system derived fluxes which were on average twice as large as the gradient fluxes, while concentrations agreed closely (on average within 4%). Possible reasons include differences in the footprint and an over-correction of the gradient flux in stable conditions. Due to wet and cold conditions, only 0.3% of the fertilizer N was volatilized as NH3 during the first week. Results from the deployment of an improved system are presented for a summer day, 6 days after fertilization with calcium ammonium nitrate. The agreement of both concentrations (on average within 13%) and fluxes (26%) was very encouraging and similar to the agreement found between two state-of-the-art gradient systems with online analysis. |
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Keywords: | ammonia volatilization conditional sampling technique diffusion scrubber surface/ atmosphere exchange urea |
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