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Determination of Fog-Droplet Deposition Velocity from a Simple Weighing Method

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DOI: 10.4209/aaqr.2016.11.0519
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Jackie Tav 1, Olivier Masson1, Frédéric Burnet2, Pascal Paulat1, Thierry Bourrianne2, Sébastien Conil3, Laurent Pourcelot1

  • 1 Institut de Radioprotection et de Sûreté Nucléaire (IRSN), LEREN, Cadarache, 13115 Saint Paul-Lez-Durance, France
  • 2 Météo-France/CNRS, CNRM/GAME, Toulouse 31000, France
  • 3 ANDRA/ OPE, Centre de Meuse/Haute-Marne, 55290 Bure, France

Highlights

A simple weighing method to estimate fog droplets deposition on plants.
For low wind speed, process governing fog droplet deposition on plants is turbulence.
Fog deposition on vegetation canopies is more important than deposition on bare soil.


Abstract

Fog water deposition can represent an important part of the atmospheric water, nutrient and pollutant inputs in specific areas such as mountainous or coastal regions (Shimadera et al., 2011). In order to determine the potential of fog water deposition on plants, a field experiment has been performed in the northeast of France to determine fog droplet deposition velocity on different types of plants. The main objective is to improve deposition models and make them prone to accurately take into account fog or low-cloud water inputs at ground level.

Flux of deposited fogwater was estimated by exposing plants to fog and weighing them with a precision balance. Contrary to other flux measurement methods, the weighing method is simple to set up. Three plant types (small conifers, grass and cabbages) plus a bare soil were used as impaction and deposition surfaces. A Particulate Volume Monitor (PVM-100) provides the liquid water content (LWC) to calculate fog droplet deposition velocities and a Fog Monitor (FM-120), the characterization of the droplet size distribution.

Two fog events with different features (visibility, LWC and droplet number) were compared with regard to deposition velocity.

When wind speed was below 4 m s–1, mean fog droplet deposition velocities ranged from less than 2.2 cm s–1 on bare soil to 40 cm s–1 on cypress. Thus impaction of fog droplets can be an important part of fogwater deposition on plants.

Keywords

Atmospheric aerosols Liquid water content Fog Droplets Aerosol deposition Measurement techniques Leaf area index


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