The OZ photometer is a small, low power, dual beam instrument that measures ozone (O3) mixing ratios in the air stream every 10 s. The instrument, which resides inside the UCATS GC box, is nearly self-contained, having its own air pump, instrument control software, and data acquisition board, needing only its power from the GC power distribution system. The photometer requires its own Teflon inlet tubing (absolutely void of wetted metal surfaces) to provide an air flow of ~1 L min-1 with a downstream diaphragm pump. The ozone measurements are based on the absorption of UV light (254 nm) by ozone present in the air drawn through one of two 15-cm long absorption cells, as measured by a photodiode detector. Ozone-free (scrubbed) air is simultaneously drawn through the other 15-cm long absorption cell to provide a reference signal (IO) at the other photodiode detector. Solenoid valves regularly switch the whole air and scrubbed air streams to the two cells, minimizing systematic errors in the dual cell, dual detector configuration. The ozone mixing ratio is determined through a simple Beer-Lambert Law calculation of ozone concentration, combined with the measured cell temperature and pressure. Calibration is performed in the laboratory before and after each mission. The instrument is re-zeroed before each flight. Data are recorded on a PCMCIA compact flash card which is removed post-flight for data processing, and are also logged by the GC data acquisition system.
Data Interval: 10-s average
Accuracy: Greater of ±2 ppb or ±3%
Precision: Greater of ±1 ppb or ±2%
UCATS
Dual-Beam Ozone Photometer (OZ)