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.