Influence of different meteorological parameters on the development of an ozone gradient between the soil surface and a level of 250 cm

In the present study the percentage ratio of the ozone concentration within and above a grass layer of 5 cm height were measured with respect to the o zone concentration at a level of 250 cm. In addition the influence of sever al meteorological parameters (global radiation, wind speed, temperature, re lative air humidity) was determined. To this end ozone concentrations were measured at levels of 1 cm, 5 cm, 10 cm, 50 cm and 250 cm above ground at t he meteorological station of the University of Hohenheim (Stuttgart, German y) during a period from August to October 1999. The registered vertical pro files of ozone clearly show lower ozone concentrations within the vegetatio n layer than at the 250-cm level. It could be noticed that the ozone concen trations at the different levels measured have a typical ratio compared to the ozone concentration at the 250-cm level, the absolute amount of which h ad no influence on the percentage ratios close to the soil surface. At the 1-cm level the ozone concentration amounted to about 53% of the one measure d at the 250-cm level, whereas this amount increased to 92% at the 50-cm le vel already. The percentage ratio of the ozone concentration is influenced by different meteorological factors analysed for the 1-cm level. The most i mportant factor of influence is the wind speed which causes a logarithmic i ncrease of the concentration ratio. A rise of the relative air humidity by about 10% results in a decline of the concentration ratio of about 4%. The influence of global radiation can be observed mostly in the mornings and ev enings whereas the influence of temperature remains rather slight. As reaso ns for the concentration ratios observed turbulent mixing processes as well as the stomatal behaviour of plants are discussed.