Seasonal and diurnal variation in the deposition velocity of ozone over a spruce forest in Denmark

K. Pilegaard, N.O. Jensen, P. Hummelshøj

    Research output: Contribution to journalJournal articleResearch

    Abstract

    The flux of O-3 was measured by the eddy-correlation method over Norway spruce in periods when the trees had a very low activity, periods with optimum growth, and periods with water stress. The aerodynamic resistance (tau(a)), viscous sub-layer resistance (tau(b)) and surface resistance (tau(c)) to O-3 were calculated from meteorological parameters and the deposition velocity. The canopy stomatal resistance to O-3 was calculated from measurements of the water vapour flux. The deposition velocities showed a diurnal pattern with night-time values of 3.5 mm s(-1) and day-time values of 7 mm s(-1), when the trees had optimal growth conditions. The surface resistance was highly dominating in day-time and the influence of meteorology low. In night-time the surface resistance to 0O was lower than the canopy stomatal resistance. A low surface resistance was also found in winter-time, when the activity of the trees was low. The surface resistance increased when the trees were subject to water stress. It is concluded that stomatal uptake is an important parameter for the deposition of O-3. However, other processes such as destruction of O-3 at surfaces, reaction with NO emitted from the soil, and reactions with radicals produced from VOC's emitted from the forest, should also be taken into consideration.
    Original languageEnglish
    JournalWater, Air and Soil Pollution
    Volume85
    Issue number4
    Pages (from-to)2223-2228
    ISSN0049-6979
    DOIs
    Publication statusPublished - 1995

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