| Instrument: | Tropospheric Ozone and Tracers from Commercial Aircraft Platforms (TOTCAP) |
| Principal Investigator: | Linnea Avallone |
| Organization: | Laboratory for Atmospheric and Space Physics University of Colorado Campus Box 392 Boulder, CO 80309-0392 |
Instrument Description: TOTCAP is a prototype instrument suite designed to fly for long durations unattended on commercial aircraft, to obtain extensive data about the dynamics of the UT/LS region. TOTCAP has been modified slightly to fly on the DC-8 and will make its first appearance as a complete system during SOLVE. The instrument package comprises sensors to measure ozone, water vapor, carbon dioxide, and halocarbons, as well as a common gas-handling system and computer/data acquisition system.
Ozone is measured in a dual-beam ultraviolet (254 nm) absorption analyzer. Ambient air flows through one absorption cell while air scrubbed of ozone flows through an adjacent one. This allows continuous measurement of both background and absorption signals. Flows are switched between cells by a pair of solenoid valves, which permits monitoring of optical changes. Water vapor is detected with a tunable diode laser spectrometer designed and built by Randy May. This sensor employs a room-temperature near-infrared laser (single mode at about 1.37 microns) and second harmonic detection, rather than direct absorption. Unlike the JPL water instrument, this sensor has an internal absorption path, optimized for the mid-troposphere. Carbon dioxide is measured by its absorption in the infrared (4.25 microns) using a LiCor NDIR instrument. This is also a dual-cell device, in which the absorption caused by the ambient air sample is compared to that from a reference gas of known composition. Halocarbons are monitored with a custom-built gas chromatograph, using short, packed columns and small ovens, and HP micro-electron capture detectors. Ambient sample and standard will be run simultaneously on paired columns to reduce errors associated with drift in ECD response. For SOLVE, compounds such as CFCs -11, -12, - 113, and carbon tetrachloride will be measured.
Weight: 165 lbs., exclusive of mounting hardware
| Ozone | Water | CO2 | GC | |
|---|---|---|---|---|
| Precision: | 1 ppb | 1-2% | 0.1 ppm | 10% |
| Detection Limit: | 1 ppb | 10 ppm | 0.1 ppm | 1 ppt |
| Response Time: | 4 sec | 1 sec | 1 sec | < 5 min |