A compact, fast UV photometer for measurement of ozone from research aircraft

In situ measurements of atmospheric ozone (O3) are performed routinely from many research aircraft platforms. The most common technique depends on the strong absorption of ultraviolet (UV) light by ozone. As atmospheric science advances to the widespread use of unmanned aircraft systems (UASs), there is an increasing requirement for minimizing instrument space, weight, and power while maintaining instrument accuracy, precision and time response. The design and use of a new, dual-beam, UV photometer instrument for in situ O3 measurements is described. A polarization optical-isolator configuration is utilized to fold the UV beam inside the absorption cells, yielding a 60cm absorption length with a 30-cm cell. The instrument has a fast sampling rate (2 Hz at < 200 hPa, 1 Hz at 200–500 hPa, and 0.5 Hz at ≥ 500 hPa), high accuracy (3 % excluding operation in the 300–450 hPa range, where the accuracy may be degraded to about 5 %), and excellent precision (1.1× 1010 O3 molecules cm−3 at 2 Hz, which corresponds to 3.0 ppb at 200 K and 100 hPa, or 0.41 ppb at 273 K and 1013 hPa). The size (36 l), weight (18 kg), and power (50–200 W) make the instrument suitable for many UASs and other airborne platforms. Inlet and exhaust configurations are also described for ambient sampling in the troposphere and lower stratosphere (1000–50 hPa) that control the sample flow rate to maximize time response while minimizing loss of precision due to induced turbulence in the sample cell. In-flight and laboratory intercomparisons with existing O3 instruments show that measurement accuracy is maintained in flight.