22 Jul 2020

22 Jul 2020

Review status: this preprint is currently under review for the journal BG.

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

Robbie Ramsay1,2, Chiara F. Di Marco1, Mathew R. Heal2, Matthias Sörgel3,a, Paulo Artaxo4, Meinrat O. Andreae3,5, and Eiko Nemitz1 Robbie Ramsay et al.
  • 1UK Centre for Ecology and Hydrology (UKCEH), Bush Estate, Penicuik, EH26 0QB, UK
  • 2School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, UK
  • 3Biogeochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 4Instituto de Física, Universidade de São Paulo, São Paulo, Brazil
  • 5Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
  • anow at: Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany

Abstract. 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 one 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 bi-directional, 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 NH4+ 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.

Robbie Ramsay et al.

Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Robbie Ramsay et al.

Robbie Ramsay et al.


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Short summary
The exchange of the gas ammonia between the atmosphere and the surface is an important biogeochemical process, but little is known of this exchange for certain ecosystems, such as the Amazon Rainforest. This study took measurements of ammonia exchange over an Amazon rainforest site, and subsequently modelled the observed deposition and emission patterns. We observed emissions of ammonia from the rainforest, which can be simulated accurately by taking a canopy resistance modelling approach.