1. measures O 2 concentration (reported as O 2 /N 2 ratio) using a vacuum-ultraviolet absorption technique based on earlier shipboard and laboratory instruments, but designed specifically for airborne use to minimize motion and thermal sensitivity and with a pressure and flow controlled inlet system flew on the Wyoming King-Air during ACME-2007 switches between sample gas and air from a high-pressure reference cylinder every 2 seconds and has a precision of +/- 5 per meg on a 5-second measurement consists of a pump module, a cylinder module, an instrument module, and a dewar NCAR Airborne Oxygen Instrument (AO2)

2. Contact name :Britton Stephens, NCAR EOL/TIIMES, 303-497-1018, stephens@ucar.edu Dimensions : 19" rack wide X 30" tall X 22" deep plus a 6" diameter X 14" tall dewar Instrument weight :200 lbs. Power:110 AC Hazmat : 4 kg of solid CO 2 (dry ice) Inlet(s) : dedicated aft facing 1/4" inlet, unheated stainless steel or Synflex secondary inlet to rule out fractionation Number of operators :1 (eventually planned for 0 as instrument matures) Altitude requirements :max. alt 60,000 feet Ground requirements :30 minute preflight NCAR Airborne Oxygen Instrument (AO2) [Stephens, B.B., R.F. Keeling, and W.J. Paplawsky, Shipboard measurements of atmospheric oxygen using a vacuum-ultraviolet absorption technique, Tellus Series B, 55, 857-878, 2003.]

3. collects cryogenically dried air into 16 1.5 L glass flasks under actively controlled flow and pressure conditions designed to sample for laboratory measurements of O2/N2, Ar/N2, 13CO2, and C18OO earlier version flew on the UND Citation II (COBRA-2000 and 2003) and on the NCAR C130 (IDEAS, ACME-2004) integrated control and data acquisition system logs housekeeping variables every second consists of a pump module, a flask module, and a dewar NCAR MEDUSA Flask Sampler

4. Contact name : Britton Stephens, NCAR EOL/TIIMES, 303-497-1018, stephens@ucar.edu Dimensions : 19" rack wide X 27 " high X 18 " deep, plus a 6" diameter X 14" high dewar Weight : 100 lbs. Power : 28 VDC Hazmat : 4 kg of solid CO 2 (dry ice) Inlet : dedicated forward facing 3/8" inlet, unheated stainless steel or Synflex Number of operators : 1 (can be shared) Altitude requirements : max. alt 52,000 feet Ground requirements : 30 minute preflight NCAR MEDUSA Flask Sampler [Graven et al., Causes of Observed Summertime Variability in Tropospheric O 2 /N 2 above North America, manuscript in preparation, 2008] COBRA-NA 2003

5. nominal flow rate is 3.3 SLPM and the flask volume is 1.5 L, resulting in a 30-second quasi- integrated sample. GV cabin throughflow ~ 24,000 SLPM (unofficial value fromGulfstream) Flask rupture would lead to an addition of < 3 SLPM of air into cabin (~ + 0.01 % change) Flask rupture combined with upstream flow-controller failure to full-closed and downstream flow- controller failure to full-open would lead to a removal of < 4 SLPM of air from cabin (~ - 0.015%) NCAR MEDUSA Flask Sampler