Gas-particle interactions above a Dutch heathland: II. Concentrations and surface exchange fluxes of atmospheric particles
Item
Title (Dublin Core)
Gas-particle interactions above a Dutch heathland: II. Concentrations and surface exchange fluxes of atmospheric particles
Description (Dublin Core)
Size-dependent particle number fluxes measured by eddy-covariance (EC) and continuous fluxes of ammonium (NH<sub>4</sub><sup>+</sup>) measured with the aerodynamic gradient method (AGM) are reported for a Dutch heathland. Daytime deposition velocities (<i>V<sub>d</sub></i>) by EC with peak values of 5 to 10 mm s<sup>-1</sup> increased with particle diameter (<i>d<sub>p</sub></i>) over the range 0.1–0.5 µm, and are faster than predicted by current models. With a mean <i>V<sub>d</sub></i> of 2.0 mm s<sup>-1</sup> (daytime: 2.7; night-time 0.8 mm s<sup>-1</sup>) NH<sub>4</sub><sup>+</sup> fluxes by AGM are overall in agreement with former measurements and NH<sub>4</sub><sup>+</sup>-N dry deposition amounts to 20% of the dry input of NH<sub>3</sub>-N over the measurement period. These surface exchange fluxes are analyzed together with simultaneous gas-phase flux measurements for indications of gas-particle interactions. On warm afternoons the apparent fluxes of acids and aerosol above the heathland showed several coinciding anomalies, all of which are consistent with NH<sub>4</sub><sup>+</sup> evaporation during deposition: (i) canopy resistances for HNO<sub>3</sub> and HCl of up to 100 s m<sup>-1</sup>, (ii) simultaneous particle emission of small particles (<i>D<sub>p</sub></i><0.18 µm) and deposition of larger particles (<i>D<sub>p</sub></i>>0.18 µm), (iii) NH<sub>4</sub><sup>+</sup> deposition faster than derived from size-distributions and size-segregated EC particle fluxes. These observations coincide with the observations of (i) surface concentration products of NH<sub>3</sub> and HNO<sub>3</sub> well below the thermodynamic equilibrium value and (ii) Damköhler numbers that indicate chemical conversion to be sufficiently fast to modify exchange fluxes. The measurements imply a removal rate of volatile NH<sub>4</sub><sup>+</sup> of 3−30×10<sup>-6</sup> s<sup>-1</sup> averaged over the 1 km boundary-layer, while NH<sub>3</sub> deposition is underestimated by typically 20 ng m<sup>-2</sup> s<sup>-1</sup> (28%) and flux reversal may occur.
Creator (Dublin Core)
Nemitz, E.
Sutton, M. A.
Wyers, G. P.
Otjes, R. P.
Mennen, M. G.
Putten, E. M.
Gallagher, M. W.
Date (Dublin Core)
2018-06-28
Type (Dublin Core)
Text
Format (Dublin Core)
application/pdf
Identifier (Dublin Core)
10.5194/acp-4-1007-2004
https://acp.copernicus.org/articles/4/1007/2004/
Source (Dublin Core)
eISSN: 1680-7324
Language (Dublin Core)
eng
