Measurements and estimates of leaf wetness over agricultural grassland for dry deposition modeling of trace gases

• Published in: Atmospheric environment (1994) Vol. 42; no. 21; pp. 5304 - 5316
• Main Authors: Wichink Kruit, R.J., Jacobs, A.F.G., Holtslag, A.A.M.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-07-2008; Elsevier Science
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agricultural and forest meteorology; Agronomy. Soil science and plant productions; ammonia; Biological and medical sciences; canopy; estimating dew duration; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Generalities, techniques; Generalities. Techniques. Climatology. Meteorology. Climatic models of plant production; Leaf wetness; Leaf wetness grid sensor; Leaf wetness measurements; Leaf wetness modeling; Leaf wetness sensor; leaves; moisture; periods; sensor; water films; Leaf wetness; Leaf wetness measurements; Leaf wetness grid sensor; Leaf wetness modeling; Leaf wetness sensor; Grassland; Air environment; Moisture sensor; Environmental factor; Modeling; Dry deposition; Moisture measurement; Plant part; Agricultural region; Physical model; Humidity; Moisture meter; Mathematical model; Instruments; Wetness duration; Estimation; Measurement sensor; Trace compound; Air quality; Plant leaf; Empirical model; Agroecosystem; Measuring instrument; Gases; Aeronomy; Applied mathematics; Measurement technique; Vegetative apparatus; Metrology; Above ground plant part; Agrometeorology
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2008.02.061

Leaf wetness is an important and frequent phenomenon for the surface–atmosphere exchange of some atmospheric trace gases that are well soluble in water, such as ammonia (NH
3 and SO
2), as well as for plant disease epidemiology. This study shows a comparison of two different techniques to measure leaf wetness; namely a painted flat-plate grid sensor and a system of four clip sensors. Although both techniques gave comparable results, the flat-plate grid sensor was favored, because of its stable signal and its ease of use. In this technique, the measurement height turned out to be of great importance for the leaf wetness duration (LWD); the flat-plate sensor at 1.0
m systematically underestimated LWD, while the flat-plate sensor at 0.1
m better represented the actual LWD. To obtain a representative signal, leaf wetness should be measured close to the surface. Using the available leaf wetness measurements, a comparison was made between three physical and four empirical leaf wetness models. Without any optimization, the physical model that calculates the potential condensation at the leaf surface gave the best results. However, after optimizing the humidity thresholds in the empirical leaf wetness models, the optimized model based on the difference between the actual and saturated specific humidity at the surface gave best results. For practical applications in atmospheric transport models, like for the calculation of dry deposition of well-soluble gases, the relative humidity (RH) threshold model might be easiest to implement. This study showed that different thresholds should be used for different vegetation types. In this study, an optimized RH threshold of 71% was derived for agricultural grassland.