9 and in the wall 14 39 located behind the metal block 9 supporting same the top of the sensor casing 1 is closed with a lid to enclose all the operational parts and the air passage not shown behind the metal block 9 housed in the venturi shaped channel structure 2 airflow channel 18 indicated schematically in fig1 is installed in the upper portion of the casing 1 and connected to a fan 13 on its right end shown in fig1 the fan 13 may be for example a sunol model 1212 pfb2 which is rated for operation at 12 v but was operated at 16 v in the ozone sensor according to the invention the fan has an optimized nozzle geometry i e a design in which the ratio of inlet opening cross section to exit opening cross section is approximately 2 1 in an implemented embodiment of the invention the cross section of the inlet opening is 110 mm 2 and the cross section of the fan outlet opening is 62 mm this ensures that the required minimum speed of 80 cm s across the chemiluminescence disc is attained at the same time the created nozzle geometry also results in an optimization between a maximum speed attainable with this type of fan and a flow resistance which increases with a smaller nozzle outlet cross section fig2 illustrates the integral electronic components of a circuitry for signal processing and monitoring.