NASA - National Aeronautics and Space Administration

Alpha Jet (O₃) Ozone instrument details

Measurements of ozone (O₃) mixing ratios are performed using a commercial O₃ monitor (2B Technologies Inc., model 205 (http://www.twobtech.com/model_205.htm)) based on ultraviolet (UV) absorption techniques and modified for flight worthiness. The dual-beam instrument uses two detection cells to simultaneously measure UV light intensity differences between O₃-scrubbed air and un-scrubbed air to give precise measurements of O₃. The monitor has been modified by upgrading the pressure sensor and pump to allow measurements at high altitudes, including a lamp heater to improve the stability of the UV source, and the addition of heaters, temperature controllers and vibration isolators to control the monitor’s physical environment.

Ozone inlet

The air intake is through Teflon tubing (perfluroalkoxy-polymer, PFA) with a backward-facing inlet positioned on the underside of the instrument wing pod. Air is delivered through a 5 µm PTFE (polytetrafluroethylene) membrane filter to remove fine particles prior to analysis.

Ozone instrument calibrations:

The O₃ monitor has undergone thorough instrument testing in the laboratory to determine the precision, linearity and overall accuracy. Eight-point calibration tests (ranging from 0 – 300 ppbv) are typically performed before and after each flight using an O₃ calibration source (2B Technologies, model 306 referenced to the WMO scale). The calibration of all 2B Technologies Ozone Calibration Sources is traceable to NIST through an unbroken chain of comparisons and is sent back to the vendor annually for calibration. Calibrations in a pressure- and temperature-controlled environmental chamber have also been carried out using the O₃ calibration source over the pressure range 200 - 800 mbar and temperature range -15 to +25 ⁰C; typical pressure and temperature ranges observed in the wing-mounted instrument pod during flight.