Information on the vertical distribution of ozone is obtained from ozone soundings. During an ozone sounding a special ozone sensor (see the following scheme) is coupled to a radio sonde measuring pressure, temperature, humidity and wind. The instrumentation is carried aloft with a balloon. The signals of the sensors are transmitted by a radio signal to the ground receiving equipment at the institute. More information on the radiosonde technique can be downloaded in Dutch (pdf: 1.5Mb) or in French (pdf: 1.5Mb)
Scheme of the ECC ozone sensor.
The ozone sensor itself consists of a miniature pump (see figure). Ambient air is then bubbled through an Electrochemical Concentration Cell (ECC), which is filled with Potassium Iodide solutions. If the air contains ozone, the ozone molecules react with the solution producing a current in the cell. This current can be measured and transmitted to the ground through the radio-sonde by the use of an interface.
The picture above shows release of the balloon train for an ozone sounding.
Such an ozone sounding reveals a lot of information: as a function of altitude we obtain not only the ozone profile, but also the temperature, the relative humidity, wind direction and wind speed. In the following plot all the information of such a sounding is shown.
Result of an ozone sounding (at 8 July 2015). The magenta line shows the vertical distribution of ozone. During an ozone sounding also temperature (°C, red), relative humidity (%, green), wind direction (°, cyan) and wind speed (m/s, blue) are recorded. Also the temperature inside the insulating box that contains the ozonesonde (°C, sand color) is measured. Full lines denote the balloon ascent profiles, while dashed lines are the descent profiles.
The data of these soundings are used for several studies, mostly related to projects. They can be used to study the troposphere, the stratosphere or for validation of satellite products. Instrumental effects have also been studied extensively to remove artificial variations.
Since mid 2007, the most up-to-date Vaisala radiosonde receiving system is used to perform ozone soundings three times a week with the newest generation of radiosondes. More information can be found in Dutch or in French.