Aircraft C-130 Chemistry: Ozone and Fast Ozone Ian Faloona & Teresa Campos NCAR P.O. Box 3000 Boulder, Colorado 80307-3000 (303)497-1445, (303)497-1048 faloona@ucar.edu, campos@ucar.edu 1. Data Set Overview: The data files described herein are separate for the two instruments (slow and fast ozone) named according to the convention: TECO - 131RF??TO3.nc, Fast - 131RF??FO3.nc. Keeping with RAF protocol they are in 1 and 25 Hz NetCDF format, respectively, and all units are parts per billion by volume (ppbv). The data represent all 10 research flights based out of North Island Naval Air Station, San Diego, CA between July 10 and July 28, 2001. 2. Instrument Description: Ozone was measured by two different techniques onboard the C-130. The first instrument was a modified TECO (Thermo Environmental Instrument, http://www.thermoei.com/ambairsm.htm) 49C. This UV photometric ozone analyzer has been developed for criteria pollutant monitoring and is based on ozone's strong absorption of 254 nm light. The detection cell windows have been replaced with high quality Sapphire to reduce water vapor nucleation which results in a documented water vapor interference. The second instrument was developed in-house at NCAR using a chemi- luminescence technique (the reaction of NO and O3 yields a channel which emits red to near IR radiation). This technique responds on a much faster time scale than the TECO. A description of a very similar instrument design can be found in Ridley et al., J. Atmos. Ocean. Tech, v9 n2, 142- 148, 1992. 3. Data Collection & Processing: The final TECO (slow ozone) data differ from the preliminary data by no more than 5% due to an altitude bias in our in-field calibration. In addition, the slow ozone data have been shifted backwards in time anywhere from 25-30 seconds because of transport delays in the inlet coupled with the relatively slow instrumental response time. The accuracy of the slow ozone is estimated as the larger of 2% or 1 ppbv taken as a 60 second average. Averaged to 30s the slow and fast measurements typically agree to within 3% (1 standard deviation.) In addition to calibrations both directly before and after the mission, two in-field calibrations were performed in the field with a portable transfer standard. These calibrations indicated a very steady instrument performance with no discernible drift in the sensitivity over the course of the mission. 4. Data Format: The data files are in netCDF format to conform to NCAR/RAF protocol. If ASCII is preferred simply send a request to the PI's listed at the top of this file. The missing data flags are -32767, and will be ignored when viewing the data in ncplot. 5. Data Remarks: We recommend that fast ozone data be used wherever available, especially during relatively rapid air mass transitions (e.g. altitude profiling). We only report here the data collected within a few seconds of takeoff and landing. In many cases the PI's can accommodate requests for additional data from any of the periods flagged as missing. This is the final ozone data. Submitted 10/24/02.