Three generations of ACATS instruments have been built at NOAA/ESRL/GMD since 1991. Each
instrument was designed specifically to make autonomous measurements of
chlorofluorocarbons
and other long-lived atmospheric tracers on board
the high altitude NASA ER-2 aircraft. The succession of instruments reflects the
incorporation of additional channels to the
gas chromatograph (GC)
, measurements of more atmospheric tracers, and faster measurement rates.
Below we describe the lineage of ACATS instruments and their utility in NASA upper atmosphere science missions
since 1991.
ACATS-I, a one-channel gas chromatograph (GC) with
electron capture detection (ECD)
, was designed and constructed in 1990-1991 for operation on the high-altitude NASA ER-2 aircraft
during the October 1991 - March 1992 AASE-II mission. The GC resided inside the
NOAA Aeronomy Laboratory Reactive Nitrogen Instrument (NOy) and its operation and data acquisition were handled
by the host instrument computer. ACATS-I measured chlorofluorocarbon-11
(CFC-11, CCl3F) every 120 seconds during this mission,
providing key information about ozone-depleting chlorine in the lower stratosphere.
The original instrument was upgraded to a two-channel GC-ECD for the April-May 1993
SPADE mission. The new ACATS-II incorporated measurements of
chlorofluorocarbon-113 (CFC-113, CCl2FCClF2) on the original CFC-11 channel
and added a second channel using a nitrous oxide
(N2O)-doped ECD to measure methane (CH4). Both
channels reported data at 120 second intervals. Instrument control and data acquisition were handled by the
host NOy instrument.
A new instrument, ACATS-IV, was constructed in 1993 for the 1994 ASHOE/MAESA
mission. ACATS-IV is a four-channel GC-ECD designed to operate external to and independent of the NOy
instrument. The new instrument added measurements of 1,1,1-trichloroethane
(methyl chloroform, CH3CCl3) and
carbon tetrachloride (CCl4) to the CFC-11 and CFC-113 channel, measurements
of hydrogen (H2) to the CH4 channel, and
incorporated two new channels: one to measure N2O and
sulfur hexafluoride (SF6), the other to measure
halon-1211 (CBrClF2) and
chlorofluorocarbon-12 (CFC-12, CCl2F2).
Measurement intervals for the four channels ranged from 3 to 6 minutes.
ACATS-IV was part of the ER-2 payload for the 1995-1996 STRAT, 1997
POLARIS, and 2000 SOLVE missions. Improvements to the
instrument during 1997-2000 were primarily advances in chromatography that increased the frequency of
measurements. In general,
chromatography columns
were shortened, column inside diameters were decreased,
sample loop
volumes were reduced, and
carrier gas
flows were programmed to decrease retention times while
maintaining peak separation. Stacked sample injections, where a new sample is injected before all peaks of
interest from the previous sample have eluted, were also incorporated. Improved chromatography allowed the
detection of chloroform (CHCl3) on the CFC-11 channel.
In March 2001 ACATS-IV was configured as a ground-based instrument for the
TROICA-7 expedition along the trans-Siberian railway in Russia. Detection of
carbon monoxide (CO) was added to the H2 and CH4 channel in
April 2002.
A simple description of ACATS-IV is available along with a general description
and glossary of gas chromatography terms.
For details of the current instrument configuration, operation, data handling methods, and a full schematic of
ACATS-IV please follow this detailed descriptions link.