A Proposed Standard Fog Collector for Use in High-Elevation Regions

The collection of fog droplets by vegetation is an important wet deposition process. It can, in fact, dominate the chemical and hydrological input to certain high elevation watersheds. However, measurements of fog deposition are rarely made and, where they do exist, comparisons of deposition rates in different locations have been hampered by the use of innumerable types of collection devices. A simple, inexpensive, 1-m2 fog collector that can produce measurements of the deposition of fog water to a vertical surface is described here. The collector has been used successfully in five countries to investigate the variation of fog deposition in complex terrain and to estimate the deposition to trees and to much larger fog collectors. It is proposed that it be employed widely as a standard to quantify the importance of fog deposition to forested high elevation areas and to measure the potential collection rates in denuded or desert mountain ranges. The standard fog collector costs about the same as a rain gauge ($100 U.S.) to construct and can be used with a variety of recording devices. It is a flat panel made of a durable polypropylene mesh and mounted with its base 2 m above ground. Fog collection rates are typically 1–10 L m−2 of vertical collecting surface per day but can reach values of 30–40 L m−2 day−1. The presence of drizzle or light rain with the fog, coupled with 10 m s−1 winds, has produced collection rates as high as 300 L m−2 day−1. If a standard fog collector is installed at a site with wind speed measurements and a conventional rain gauge, a reasonable estimate can be made of the proportions of fog and rain being deposited on the vertical mesh panel. This information is fundamental to the understanding of acidic wet deposition at higher elevations and to comprehensive hydrological calculations in watersheds.