Results from the Balloon Ozone Intercomparison Campaign (BOIC)

The purpose of the Balloon Ozone Intercomparison Campaign (BOIC) is to assess the accuracy and precision of various ozone measurement systems under development and those flown operationally. Several in situ UV absorption photometers, two solar UV absorption photometers, electrochemical sondes, and a mass spectrometer were intercompared in three flight missions. Concurrent data from Umkehr and satellite observations are also intercompared. Ozone calibration procedures are also being reviewed as a part of BOIC and the National Bureau of Standards (NBS) provided a “standard” ozone source for intercomparing the in situ instruments at ground pressure. The following are some preliminary results. The standard deviation of the sensitivities among 17 instruments against the NBS reference was about 11%. These differences appear in flight at the lower levels, however changed at higher altitudes indicating height dependent errors. The difference among 5 in-situ UV photometers flown together ranged by ±8% during ascent to about 41 km. During float at 42 km the difference nearly doubled. During descent the difference decreased to about 4% which is much closer to the expected accuracy of these instruments. A complement of electrochemical sondes flown with the UV photometers agreed with them in range of 0–20% depending on the sonde and altitude. Some electrochemical sondes gave lower ozone values at pressures lower than 10 mbar (31 km). Balloon sondes also showed systematically lower values than concurrent Umkehr and SBUV satellite observations at altitudes above 10 mb. Intercomparisons among the instruments in the troposphere showed 30% differences.