RITS Program Background

The Climate Monitoring and Diagnostics Laboratory ( CMDL) of the National Oceanic and Atmospheric Administration ( NOAA) operates four baseline observatories at Barrow, Alaska (71.3° N), Mauna Loa, Hawaii (19.5° N), Cape Matatula, American Samoa (14.2° S), and South Pole, Antarctica (90.0° S). A fifth site at Niwot Ridge, Colorado (40.4° N) is run cooperatively with the University of Colorado. Since 1977, pairs of air samples collected weekly in flasks at these sites have been transported to Boulder and analyzed by CMDL's HATS (Halocarbons and other Atmospheric Trace Species) group for several compounds known to play an active role in the chemistry of stratospheric ozone.

In 1985, the Radiatively Important Trace Species (RITS) program was launched to provide concurrent in situ monitoring of several of the same ozone-depleting chemicals measured in the HATS flask program. Gas chromatographs with electron capture detectors (ECDs) were installed at five sites over a period of five years for the purpose of measuring nitrous oxide (N₂O), the chlorofluorocarbons (CFCs) CFC-11 (CCl₃F) and CFC-12 (CCl₂F₂), and the chlorocarbon solvents methyl chloroform (CH₃CCl₃) and carbon tetrachloride (CCl₄). Secondary calibration standards referenced to primary gravimetric standards were prepared in the laboratory and shipped to the field sites for interleaved sampling with the outdoor environment. During the early stages of the RITS program sample injections occurred once every 60, 90, or 120 minutes depending on the station. This yielded environmental sampling rates of 6 to 12 measurements per day. By the end of 1991 the RITS systems at all stations had been modified to inject samples every 30 minutes to give an environmental sampling rate of 1 per hour.

Since the establishment of the flask and in situ monitoring programs, many new compounds have been added to the list of those measured and analyzed by the HATS group. These include several hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) developed as alternatives to CFCs banned by the United Nations' Montreal Protocol. The addition of these and other gases of interest (e.g. halons, methyl halides) has necessitated the replacement of aging RITS systems with newer and more capable 4-channel CATS system GCs.

Between June, 1998 and October 2000, CATS systems were installed at each of the five field sites occupied by RITS sytems. Data continuity was insured by allowing the RITS systems to run for a period of several months overlap with the new CATS systems until data from the latter showed equal or better precision. The last of the RITS systems, at Niwot Ridge, was shut down in August of 2001. Click here for a chronicle of RITS/CATS field installations. Table I summarizes only the RITS system field installations by individual channel.