Summary
Enhancement of the acidity of water on conifer needles, caused by evaporation even during the presence of cloud, is investigated. Field measurements of the acidity of droplets on polypropylene surfaces, shaped like needle bearing conifer shoots, and on Sitka spruce shoots, showed that surface droplet acidity varied significantly over a few hours, due to many causes. The acidity of the droplets commonly reached 800 μeq/l (pH = 3.1) and occasionally 1000 μeq/l (pH = 3.0). Increases in H+ ion concentration due to evaporation of pure water from the droplets occurred particularly around the end of cloud events. It was concluded that variation of H+ concentration of water on conifer needles due to evaporation during the presence of cloud is likely to be less important than that due to the other reasons. In particular the increase in H+ concentration from the reduction in droplet volume, due to evaporation, after the end of a cloud event is likely to be the most significant.
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References
Beswick KM, Hargreaves K, Gallagher MW, Choularton TW, Fowler D (1990) Size resolved measurements of cloud droplet deposition velocity at a forest canopy using an eddy correlation technique. Q J R Meteorol Soc (In Press)
Dollard GJ, Unsworth MH (1983) Field measurements of turbulent fluxes of wind-driven forces to a grass surface. Atmos Environ 17: 775–780
Frevert T, Klemm O (1984) Wie ändern sich pH-Werte im Regen- und Nebelwasser beim Abtrocknen auf Pflanzenoberflächen? Arch Meteorol Geophys Bioklimatol Ser B 34: 75–81
Fuzzi S, Orsi G, Mariotti M (1983) Radiation fog water liquid acidity at a field station in the Po Valley. J Aerosol Sci 14: 135–138
Gallagher MW, Choularton TW, More AP, Fowler D (1988) Measurements of the size dependence of cloud droplet deposition at a hill site. Q J R Meteorol Soc 114: 1291–1303
Jarvis PG, James GB, Landsberg JJ (1976) Coniferous Forest. In: Monteith JL (ed) Vegetation and the atmosphere, vol 2. Academic Press, pp 171–240
Klemm O, Riederer M, Frevert T (1987) pH response on leaves and isolated cuticles of Hedera helix L. after wetting with artificial rainwater. Environ Exp Bot 27: 349–355
Lovett GM (1984) Rates and mechanisms of cloud water deposition to a sub-alpine balsam fir forest. Atmos Environ 18: 361–371
Milne R, Crossley A, Unsworth MH (1988) Physics of cloudwater deposition and evaporation at Castelaw, SE Scotland. In: Unsworth MH, Fowler D (eds), Acid deposition at high elevation sites. Kluwer Academic, Dordrecht, pp 299–307
Schmitt G (1988) Measurements of the chemical composition in cloud and fog water. In: Unsworth MH, Fowler D (eds), Acid deposition at high elevation sites, Kluwer Academic, Dordrecht, pp 403–417
Shuttleworth WJ (1977) The exchange of wind-driven fog and mist between vegetation and the atmosphere. Boundary-Layer Meteorol 12: 463–489
Slinn WGN (1982) Predictions for particle deposition to vegetative canopies. Atmos Environ 16: 1785–1794
Unsworth MH (1984) Evaporation from forests in cloud enhances the effect of acid deposition. Nature, London 312: 262–264
Unsworth MH, Wilshaw JC (1989) Wet, occult and dry deposition of pollutants on forests. Agricultural For Meteorol 47: 221–238
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Milne, R., Crossley, A. & Henderson, C. Field measurements of the acidity of cloudwater deposited on polypropylene surfaces and Sitka spruce shoots. Trees 4, 205–210 (1990). https://doi.org/10.1007/BF00225317
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DOI: https://doi.org/10.1007/BF00225317