Measurement and modelling of the dynamics of NH3 surface-atmosphere exchange over the Amazonian rainforest

Ramsay, Robbie; Di Marco, Chiara F.; Heal, Mathew R.; Sörgel, Matthias; Artaxo, Paulo; Andreae, Meinrat O.; Nemitz, Eiko. 2021 Measurement and modelling of the dynamics of NH3 surface-atmosphere exchange over the Amazonian rainforest. Biogeosciences, 18 (9). 2809-2825.

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Local and regional modelling of NH3 surface exchange is required to quantify nitrogen deposition to, and emissions from, the biosphere. However, measurements and model parameterisations for many remote ecosystems – such as tropical rainforest – remain sparse. Using 1 month of hourly measurements of NH3 fluxes and meteorological parameters over a remote Amazon rainforest site (Amazon Tall Tower Observatory, ATTO), six model parameterisations based on a bidirectional, single-layer canopy compensation point resistance model were developed to simulate observations of NH3 surface exchange. Canopy resistance was linked to either relative humidity at the canopy level (RHz′0), vapour pressure deficit, or a parameter value based on leaf wetness measurements. The ratio of apoplastic NH+4 to H+ concentration, Γs, during this campaign was inferred to be 38.5 ± 15.8. The parameterisation that reproduced the observed net exchange of NH3 most accurately was the model that used a cuticular resistance (Rw) parameterisation based on leaf wetness measurements and a value of Γs=50 (Pearson correlation r=0.71). Conversely, the model that performed the worst at replicating measured NH3 fluxes used an Rw value modelled using RHz′0 and the inferred value of Γs=38.5 (r=0.45). The results indicate that a single-layer canopy compensation point model is appropriate for simulating NH3 fluxes from tropical rainforest during the Amazonian dry season and confirmed that a direct measurement of (a non-binary) leaf wetness parameter improves the ability to estimate Rw. Current inferential methods for determining Γs were noted as having difficulties in the humid conditions present at a rainforest site.

Item Type: Publication - Article
Digital Object Identifier (DOI):
UKCEH and CEH Sections/Science Areas: Atmospheric Chemistry and Effects (Science Area 2017-)
ISSN: 1726-4170
Additional Information. Not used in RCUK Gateway to Research.: Open Access paper - full text available via Official URL link.
NORA Subject Terms: Atmospheric Sciences
Date made live: 11 Aug 2020 10:11 +0 (UTC)

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