A new project titled Lightweight Airborne Chromatograph Experiment (LACE) is a 2-channel GC designed to measure CFC-11, CFC-113, and SF₆. It was built to fly on a balloon and take data from altitudes up to 32 km. This will complement the lower altitude NASA ER-2 data, help solidify understanding of atmospheric dynamics, and provide a comparison for midlatitude and tropics chemistry. NOAH scientists used the ACATS-IV instrument as a starting point; however, several key differences have been introduced. The balloon´s fast decent of 2.5 m s^-1 imposes a faster data sample rate of 1 minute to acquire reasonable coverage of data every 150 m. Sample rates for the ACATS-IV instrument are currently 3 and 6 minutes with the exception of one recent flight where the new 1-minute chromatography (Figure 5.24) was successfully flown. Because of the higher altitude, clean air samples must be loaded from an ambient pressure of only 10 mb compared to an ambient pressure of 50 mb or higher for the ACATS instrument. Finally, in contrast to the ER-2's Q-bay, which is pressurized to a minimum of 300 mb and houses the ACATS instrument, the balloon platform required a self-pressurized, lighter-weight instrument that uses less power.

Fig. 5.24. Simultaneous 1- and 3-minute chromatograms and a correlation plot of the 1-minute CFC-11 versus the 3-minute CFC-11 data for this flight.

Problems solved in building this GC for a balloon platform were similar to those that will occur when placing an instrument in a remotely piloted aircraft (RPA) like Perseus. When an operational RPA becomes available, LACE can be easily modified for flight on this type of platform.

[back] [contents] [next]