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A coupled dispersion and exchange model for short‐range dry deposition of atmospheric ammonia
Author(s) -
Loubet Benjamin,
Cellier Pierre,
Milford Celia,
Sutton Mark A.
Publication year - 2006
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1256/qj.05.73
Subject(s) - atmospheric sciences , ammonia , dispersion (optics) , atmospheric dispersion modeling , environmental science , range (aeronautics) , deposition (geology) , meteorology , materials science , chemistry , physics , geology , air pollution , optics , geomorphology , organic chemistry , sediment , composite material
The MODDAS‐2D model (MOdel of Dispersion and Deposition of Ammonia over the Short‐range in two dimensions) is presented. This stationary model couples a two‐dimensional Lagrangian stochastic model for short‐range dispersion, with a leaf‐scale bi‐directional exchange model for ammonia (NH 3 ), which includes cuticular uptake and a stomatal compensation point. The coupling is obtained by splitting the upward and downward components of the flux, which can be generalized for any trace gas, and hence provides a way of simply incorporating bi‐directional exchanges in existing deposition velocity models. The leaf boundary‐layer resistance is parametrized to account for mixed convection in the canopy, and the model incorporates a stability correction for the Lagrangian time‐scale for vertical velocity, which tends to increase the Lagrangian time‐scale in very stable conditions compared with usual parametrizations. The model is validated against three datasets, where concentrations of atmospheric NH 3 were measured at several distances from a line source. Two datasets are over grassland and one is over maize, giving a range of canopy structure. The model correctly simulates the concentration in one situation, but consistently overestimates it at further distances or underestimates it at small distances in the two other situations. It is argued that these discrepancies are mainly due to the lack of length of one of the line sources and non‐aligned winds. Analysis shows that the surface exchange parameters and the turbulent mixing at the source level are the predominant factors controlling short‐range deposition of NH 3 . Copyright © 2006 Royal Meteorological Society