AIR MONITORING


Measurement Performance Based on the calibration method described above, the ULTRA.sens® highly accurate O3


Application Example can be used to perform gas analyses. Fig. 8 shows the measurement results for a gradual change in O3


concentration in the ppb range. This enables a measuring range of 0-1000 ppb with a resolution of approx. 5 ppb (Fig. 9). For long-term stable O3


(AZF) is recommended. This option allows long-term stable gas analyses to be performed over an unlimited period of time. Drift is completely compensated for (Fig. 10). There is no cross- sensitivity to other gases in the ambient air (water vapour, carbon dioxide, etc.). Other substances such as sulphur dioxide (SO2


), nitrogen oxides (NOx with the ULTRA.sens® ), etc. can also be measured simultaneously , thus compensating for cross-sensitivities if necessary. The concentration


measurement is compensated for gas density via an integrated temperature and pressure sensor, so that this infl uence can also be neglected.


gas analyses, the integration of an AutoZeroFunction


One current example of the wide range of possible applications for this innovative gas measurement technology will be cited here. Plant growth (plant physiology) depends on many external factors such as light, humidity, temperature, CO2


concentration and also the O3 concentrations. These O3


in the ambient air. For this purpose, the respiratory activity of plants is analysed in special test facilities [7]. One stress factor is the O3


content, which is supplied to the plants in small concentrations can be measured and regulated very precisely using the


setup described above. Fig. 11 shows such a setup from the company Plant Invent (Estonia). The device allows parallel non-destructive measurements of stomatal conductance, photosynthesis and transpiration of multiple plants. Parallel measurements speed up the workfl ow while also providing more comparable gas exchange data. The cuvette conditions are precisely controlled, and various stimuli can be applied.


content


Fig. 11: Jyrkki MAX is a multi-cuvette stationary gas exchange device designed to measure bigger plants like cereals, ferns, tomatoes etc. (Plant Invent Estonia)


Fig. 8: Gradual change in O3 concentration using a voltage-controlled ozone generator (silent discharge) Summary


The ULTRA.sens gas measurement module from Wi.Tec-Sensorik GmbH described above is characterised by its precise determination of ozone concentrations from trace levels (ppb) up to the industrial vol.% range. This is achieved through exact mathematical calibration in accordance with ISO 13964. Multi-channel measurement enables high dynamic ranges (ppb to vol.%), which can open up completely new areas of application. It is also possible to measure other gases (e.g. NO2


)


in addition to ozone in the same setup. This is helpful in plasma technology application engineering. The versatility of this gas measurement technology was demonstrated using an application example from plant physiology.


References


[1 ] Batakliev et al. : Ozone decomposition. Interdicip. Toxicol. 2014 ; Vol. 7(2) ; 47-59 doi : 10.2478/intox-2014-0008


[ 2] Daumont, D. et al.: Ozone UV spectroscopy I: Absorption cross-sections at room temperature., J. Atmos. Chem.15(2), 145–155 (1992). doi:10.1007/bf00053756


[3 ] Meyer, C. P. et al.: Water vapor interference in the measurement of ozone in ambient air by ultraviolet absorption. Rev. Sci. Instruments. 62(1), January 1991, 223-228.


Fig. 9: Determination of the detection limit as 3 times the standard deviation of the O3 measurements at zero point


[4 ] ISO 13964 (1998) Air quality- Determination of ozone in ambient air – Ultraviolet photometric method


[5 ] Wiegleb, G.: Einsatz von LED-Strahlungsquellen in Analysengeräten. Laser- und Optoelektronik No.3/1985, 308-310


[6] Wiegleb, G.: Gas Measurement Technology in Theory and Practice, Springer Verlag Wiesbaden 2023


[7] Merilo, E., et al.: PYR/RCAR Receptors Contribute to Ozone-, Reduced Air Humidity-, Darkness-, and CO2-Induced Stomatal Regulation. Plant Physiology, July 2013, Vol. 162, pp. 1652–1668,


Prof. Dr. Gerhard Wiegleb Wi.Tec-Sensorik GmbH


Fig. 10: Periodic exposure (15-minute intervals) of the structure to zero gas, followed by adjustment of the zero point. The variation in the fi nal value of ±10ppb O3


is due to the unstable generation of the O3 ozone generator. concentration in the


Schepersweg 41-61, D-46485 Wesel, Germany Email: ge.wiegleb@witec-sensorik.de Web: www.witec-sensorik.com


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