Micrometeorological measurements of particle deposition velocities to moorland vegetation
article
Size-segregated particle number flux measurements using a micrometeorological technique, over the diameter (dp) range 0.1 to 3 ?m and total particle number fluxes (dp > 11 nm), are reported for Scottish moorland vegetation. Mean particle deposition velocities (Vd) range from 0.3 mm s-1 for 0.1 ?m particles to more than 10 mm s-1 for 3 ?m particles. On average, the measured size-dependence of Vd is almost identical with the prediction by the widely used Slinn model, using the original parameters derived from wind-tunnel studies. Within each size-band Vd increased linearly with the friction velocity (u*). Total particle number fluxes measured with a condensation particle counter are dominated by the high concentration of small particles; therefore, this provides the first estimate of Vd for particles smaller than those that can be sized by optical techniques, for short vegetation. Values of Vd ranged from 0.2 to 0.6 mm s-1 as u* increased from 0.15 to 0.55 m s-1. These deposition rates are one order of magnitude smaller than have been observed for a pine forest stand. The analysis shows that, at least for super-micron particles, the emission fluxes that were frequently observed at the study site need to be included in the computation of average values. At this site, upward fluxes are therefore more likely to be an artefact due to statistical constraints than a systematic physical phenomenon.
Topics
TNO Identifier
953643
ISSN
00359009
Source
Quarterly Journal of the Royal Meteorological Society, 128, pp. 2281-2300.
Publisher
Wiley
Pages
2281-2300
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