A Relaxed Eddy Accumulation System for the Automated Measurement of Atmospheric Ammonia Fluxes

E Nemitz, M Flynn, P I Williams, C Milford, M R Theobald, A Blatter, Martin Gallagher, M A Sutton

    Research output: Contribution to journalArticlepeer-review


    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 µg 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.
    Original languageEnglish
    Pages (from-to)189-202
    Number of pages14
    JournalWater, Air, & Soil Pollution: Focus
    Issue number5
    Publication statusPublished - 2001


    • Biomedical and Life Sciences


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