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| Titel |
Gas-particle interactions above a Dutch heathland: II. Concentrations and surface exchange fluxes of atmospheric particles |
| VerfasserIn |
E. Nemitz, M. A. Sutton, G. P. Wyers, R. P. Otjes, M. G. Mennen, E. M. Putten, M. W. Gallagher |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 4, no. 4 ; Nr. 4, no. 4 (2004-07-02), S.1007-1024 |
| Datensatznummer |
250001835
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| Publikation (Nr.) |
 copernicus.org/acp-4-1007-2004.pdf |
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| Zusammenfassung |
| Size-dependent particle number fluxes measured by eddy-covariance (EC) and
continuous fluxes of ammonium (NH4+) measured with the aerodynamic
gradient method (AGM) are reported for a Dutch heathland. Daytime deposition
velocities (Vd) by EC with peak values of 5 to 10 mm s-1 increased
with particle diameter (dp) over the range 0.1–0.5 µm, and are
faster than predicted by current models. With a mean Vd of 2.0 mm s-1 (daytime: 2.7; night-time 0.8 mm s-1) NH4+ fluxes
by AGM are overall in agreement with former measurements and
NH4+-N dry deposition amounts to 20% of the dry input of
NH3-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 NH4+ evaporation
during deposition: (i) canopy resistances for HNO3 and HCl of up to 100 s m-1,
(ii) simultaneous particle emission of small particles
(Dp<0.18 µm) and deposition of larger particles (Dp>0.18 µm), (iii) NH4+ 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 NH3 and HNO3 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 NH4+ of 3−30×10-6 s-1 averaged over the 1 km boundary-layer, while NH3 deposition is underestimated by typically 20 ng m-2 s-1 (28%) and flux reversal may occur. |
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