Thomas Wrzesinsky

Ion fluxes from fog and rain to an agricultural and a forest ecosystem in Europe

The deposition fluxes of inorganic compounds dissolved in fog and rain were quantified for two different ecosystems in Europe. The fogwater deposition fluxes were measured by employing the eddy covariance method. The site in Switzerland that lies within an agricultural area surrounded by the Jura mountains and the Alps is often exposed to radiation fog. At the German mountain forest ecosystem, on the other hand, advection fog occurs most frequently. At the Swiss site, fogwater deposition fluxes of the dominant components SO 2- 4 (0.027 mg S m - 2 day - 1 ), NO - 3 (0.030 mg N m - 2 day - 1 ) and NH4 (0.060 mg N m - 2 day - 1 were estimated to be < 5% of the measured wet deposition (0.85, 0.70 and 1.34 mg m - 2 day - 1 , respectively). The corresponding fluxes at the forest site (0.62, 0.82 and 1.16 mg m - 2 day - 1 , respectively) were of the same order of magnitude as wet deposition (1.04, 1.01 and 1.36 mg m - 2 day - 1 ), illustrating the importance of fog (or occult) deposition. Trajectory analyses at the forest site indicate significantly higher fogwater concentrations of all major ions if air originated from the east (i.e. the Czech Republic), which is in close agreement with earlier studies.

Fog deposition fluxes of water and ions to a mountainous site in Central Europe

Fog and precipitation composition and deposition were measured over a 1-yr period. Ion concentrations were higher in fog than in precipitation by factors of between 6 and 18. The causes of these differences were less dilution of fog water due to non-availability of condensable water vapour, and more efficient transfer of surface emissions to fog water as compared to rain water or snow. Fogwater and dissolved ions depositions were measured with eddy covariance in combination with a bulk fogwater collector. Annual fogwater deposition was 9.4% that of precipitation. The annual deposition of ions through fog was of the same order as that for precipitation. Ammonium, representing local emission sources, had 46% more annual deposition through fog than through precipitation. The fog droplet number and mass size distributions are reported. Fog droplets of 15 μm diameter contribute most to the deposition flux. The variability of processes and parameters contributing to deposition of ions through fog (ion concentrations in fog water, liquid water content in air, fog duration and turbulence) is high.

Vertical divergence of fogwater fluxes above a spruce forest

Two almost identical eddy covariance measurement setups were used to measure the fogwater fluxes to a forest ecosystem in the ‘‘Fichtelgebirge’’ mountains (Waldstein research site, 786 m a.s.l.) in Germany. During the first experiment, an intercomparison was carried out with both setups running simultaneously at the same measuring height on a meteorological tower, 12.5 m above the forest canopy. The results confirmed a close agreement of the turbulent fluxes between the two setups, and allowed to intercalibrate liquid water content (LWC) and gravitational fluxes. During the second experiment, the setups were mounted at a height of 12.5 and 3 m above the canopy, respectively. For the 22 fog events, a persistent negative flux divergence was observed with a greater downward flux at the upper level. To extrapolate the turbulent liquid water fluxes measured at height

Development of a Land Surface Model Including Cloud Water Deposition on Vegetation

Abstract A land surface model including cloud (fog) water deposition on vegetation was developed to better predict the heat and water exchanges between the biosphere and atmosphere. A new scheme to calculate cloud water deposition on vegetation was implemented in this model. High performance of the model was confirmed by comparison of calculated heat and cloud water flux over a forest with measurements. The new model provided a better prediction of measured turbulent and gravitational fluxes of cloud water over the canopy than the commonly used cloud water deposition model. In addition, simple linear relationships between wind speed over the canopy (|U|) and deposition velocity of cloud water (Vdep) were found both in measurements and in the calculations. Numerical experiments using the model were performed to study the influences of two types of leaves (needle and broad leaves) and canopy structure parameters (total leaf area index and canopy height) on Vdep. When the size of broad leaves is small, they ...

Evaluation and Application of an Electrical Low Pressure Impactor in Disjunct Eddy Covariance Aerosol Flux Measurements

A micrometeorological application of an electrical low pressure impactor (ELPI) for the measurement of size-resolved particle fluxes between the surface and the atmosphere is proposed. Particles are introduced into the system for a very short time period through an inlet valve and analyzed in distinct size bins with the ELPI instrument for several seconds. Together with sonic anemometer measurements, size-resolved deposition velocities can be derived employing disjunct eddy covariance (DEC). Laboratory experiments studying ELPI instrument response indicate that a sampling interval of 0.3 s and a measurement interval of at least 5 s yield particle concentration data comparable to continuous sampling, and suitable for DEC. Calculations and Monte-Carlo simulations show that the finite length of the average period as well as Poisson and instrumental noise frequently introduce uncertainties in deposition velocities which may be an order of magnitude larger than the measurement value. In first field measurements with a prototype system, the measured fluxes were often below the detection limit as defined by the measurement uncertainties. At high particle concentrations, the DEC measurements could potentially extend current measurement capabilities to cover submicron particles fluxes in several size classes simultaneously.

Fog Deposition and its Role in Biogeochemical Cycles of Nutrients and Pollutants

It has been recognized for about 100 years now that the deposition of fog (occult deposition) can play an important role in the hydrological cycles of various mountainous ecosystems (Marloth 1906; Linke 1916; Grunow 1955; Baumgartner 1958, 1959). Considering the fact that the concentrations of trace substances in fog water are typically higher than those of comparable rain water, it becomes evident that the deposition of nutrients and pollutants through fog deposition may be as high as, or even higher than, the deposition through rainwater (e.g., Saxena and Lin 1990). There is a large variability in physical and chemical conditions of fog events, so that any estimates of their potential roles in biogeochemical cycles must be studied individually for each site and each time period of interest.

A Collector for Fog Water and Interstitial Aerosol

Abstract An active heatable cloud water collector for ground sampling is presented. The collector can be operated unattended for approximately one week, even in harsh winter conditions. The collection strands are Teflon tubes. A preset cycle of 15-min sampling followed by 250 s of mild heating using wires inserted into the tubes is used. The lower cutoff diameter for fog droplets is 7.3 μm, and its overall collection efficiency is 79% for the liquid water content of fogs at the experimental site in central Europe. It performed reliably during a 2-yr experiment. The collected fog water interacts exclusively with inert materials such as Teflon and Perspex so the collector is well suited for trace analyses of fog water. The collector can be upgraded with an interstitial aerosol collection unit, at the expense of unattended operation. The lower cutoff diameter of the fog water collection strands is 8.1 μm when the interstitial aerosol module is installed. The module efficiently collects particles with diamete...