Instrument: Airborne Chromatograph for Atmospheric Trace Species (ACATS IV)

Principal Investigators: James W. Elkins

Organizations:

NOAA Climate Monitoring Diagnostics Lab
R/E/CG1
325 Broadway
Boulder, CO 80303

Co-Investigators: Dale F. Hurst, Pavel A. Romashkin, and Geoff S. Dutton (all at Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder).

Principle of Operation:

ACATS-IV is a 4-channel gas chromatograph with electron capture detection (ECD) that measures a variety of halocarbons and other long-lived trace gases in the stratosphere. The instrument is currently configured to measure CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (CCl2FCClF2), methyl chloroform (CH3CCl3), carbon tetrachloride (CCl4), halon-1211 (CBrClF2), chloroform (CHCl3), methane (CH4), and hydrogen (H2) every 125 s, and nitrous oxide (N2O) and sulfur hexafluoride (SF6) every 250 s. Each channel is comprised of a sample loop (2-10 cm3 volume), gas sampling valve (GSV), chromatographic column pair, ECD, electrometer, and several flow, temperature, and pressure controllers. In-flight calibration is carried out every 625 s (1250 s for N2O and SF6) by injecting a dried, whole air standard containing approximately 80% of tropospheric mixing ratios. During field deployments, calibrations are also performed in the laboratory to quantitatively characterize any non-linearities and/or offsets in ECD resonses overthe range of trace gas mixing ratios in the lower stratosphere. Data acquisition and instrument control are handled by a 80486-based computer with a removable 40 MB flash disk.

Proposed Modifications for SOLVE:
We plan to implement rapid gas chromatography techniques on two channels that will permit measurements of CFC-12, halon-1211, N2O, and SF6 every 70 s. The increased number of ACATS N2O measurements during each flight will facilitate N2O data intercomparisons with the ARGUS and ALIAS instruments. Higher frequency measurements of SF6 will resuilt in a higher spatial resolution of mean ages calculated from ACATS SF6 data.
ACATS Instrument Diagram 



Precision: <1% for CFC-11, CFC-12, and N2O;
 <2% for CFC-113, CH3CCl3, and CCl4;
 <3% for CH4, SF6, and H2.
 About 5% for CBrClF2 and 10% for CHCl3.


Accuracy: < 3% plus precision


Response time:   125 s  (250 s for N2O and SF6).
 Proposed modifications will make response time 70s for CFC-12, halon-1211, N2O, and SF6, 140 s for others.


Location on the ER-2: Lower Q-bay rack