Open AccessBi‐directional air‐surface exchange of atmospheric ammonia: A review of measurements and a development of a big‐leaf model for applications in regional‐scale air‐quality models
Author(s) -
Zhang L.,
Wright L. P.,
Asman W. A. H.
Publication year - 2010
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2009jd013589
Subject(s) - environmental science , atmospheric sciences , canopy , nitrogen , air quality index , vegetation (pathology) , deposition (geology) , vegetation type , ammonia , hydrology (agriculture) , agronomy , meteorology , grassland , ecology , chemistry , geography , medicine , paleontology , geotechnical engineering , organic chemistry , engineering , pathology , sediment , biology , geology
The air‐surface exchange of atmospheric ammonia (NH 3 ) and measurements of the canopy and stomatal compensation points ( χ cp and χ st , respectively) and the stomatal and soil emission potentials (Γ st and Γ g , respectively) are reviewed. A database of these values has been developed, to be used for the development of input parameters and for model evaluation. The compensation points are dependent on canopy type, nitrogen (N) status, temperature, growth stage, and meteorological conditions. Canopies that receive high atmospheric nitrogen input generally have high χ cp values. χ cp values also tend to be higher over intensively managed vegetated surfaces than semi‐natural vegetation, due to the higher nitrogen content in these surfaces. Increased nitrogen concentrations from fertilization and cutting practices have been observed to increase the compensation points and therefore the emission from these canopies. The decomposition of litter leaves has been found to play a dominant role and significantly increase the values of χ cp over agricultural vegetation and fertilized grasslands. By modifying an existing big‐leaf dry deposition model to allow NH 3 emission from leaf stomata and soil surfaces, a bi‐directional air‐surface exchange model has been developed for applications in regional‐scale air‐quality models. The model predicts χ cp values that vary with canopy type, nitrogen content, and meteorological conditions. χ cp values predicted by the model are around 1–2 μ g m −3 over forest canopies and 4–10 μ g m −3 over grasslands and agricultural canopies during a typical summer daytime; χ cp values are ∼10 and ∼3 times lower over forests and agricultural lands, respectively, in nighttime and/or winter conditions. These results are similar to the range of measured values. The new bi‐directional air‐surface exchange model will reduce the dry deposition fluxes by 20–100 ng m −2 s −1 compared to the original dry deposition model over low‐N forests and agricultural lands during typical summer daytime conditions, which can be the difference between whether deposition or emission occurs. For example, this new model produces emissions fluxes of 0–90 ng m −2 s −1 over croplands when the atmospheric NH 3 concentrations are below 10 μ g m −3 .