• measures O2 concentration (reported as O2/N2 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)

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 dewarInstrument weight : 200 lbs.Power: 110 ACHazmat : 4 kg of solid CO2 (dry ice)Inlet(s) : dedicated aft facing 1/4" inlet, unheated stainless steel or Synflex

secondary inlet to rule out fractionationNumber of operators : 1 (eventually planned for 0 as instrument matures)Altitude requirements : max. alt 60,000 feetGround 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.]

• 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

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 dewarWeight : 100 lbs.Power : 28 VDCHazmat : 4 kg of solid CO2 (dry ice)

Inlet : dedicated forward facing 3/8" inlet, unheated stainless steel or SynflexNumber of operators : 1 (can be shared)Altitude requirements : max. alt 52,000 feetGround requirements : 30 minute preflight

NCAR MEDUSA Flask Sampler

[Graven et al., Causes of Observed Summertime Variability in Tropospheric O2/N2 above North America, manuscript in preparation, 2008]

COBRA-NA 2003

• 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