HATS has been analyzing air samples collected in flasks since 1977. Originally set up under the auspices of the Geophysical Monitoring for Climatic Change (GMCC) division of NOAA's Air Resources Laboratory (NOAA/ARL), this program involved the analysis of flask samples from Point Barrow, Alaska (BRW), Niwot Ridge, Colorado (NWR), Mauna Loa, Hawaii (MLO), American Samoa (SMO), and the South Pole (SPO).
Electropolished, stainless-steel flasks (300 ml, Whitey with Nupro SS-4H metal bellows valves) were collected weekly in pairs, filled to 1.5 atm with a metal bellows pump to minimize contamination of CFC's by plastics or other elastomers, and shipped to Boulder for analysis. All samples were analyzed for N2O, CFC-11, and CFC-12 on a Hewlett Packard 5710A, electron-capture gas chromatograph (GC/ECD) equipped with a Porasil A column. In 1986, when GMCC became the Climate Monitoring and Diagnostics Laboratory and HATS was formed, efforts were initiated to increase the number of gases measured from each flask.
Larger flasks (850 ml, Biospherics) were obtained and KNF Neuberger diaphragm pumps (Model UN05SV1) were sent to the sampling sites so that the flasks could be pressurized to 4 atm absolute pressure. This allowed for the cryotrapping of larger quantities of air for detection of low concentration or weakly responding gases. Measurement of Halons by GC/ECD was begun in 1988 and analysis of flask samples for CFC's, N2O, CH3CCl3, and CCl4 was fully automated by 1992. In late 1991, HATS began analyzing flask samples for hydrochlorofluorocarbons (HCFC's), hydrofluorocarbons (HFC's), and other atmospheric halogens by gas chromatography with detection by mass spectrometry (GC/MS). Because of the need for additional air for some measurements, HATS has introduced 2.4 l flasks (Max Planck Institut für Chemie, Mainz) into the network.
Also in 1991, two cooperative sites were added to the sampling network -- Cape Grim Baseline Air Pollution Station, Tasmania (CGO) and Alert, Northwest Territories (ALT). Cooperative sampling sites are currently being set up at Harvard Forest, Massachusetts (HFM) and Grifton, North Carolina (ITN). Today, flasks are filled at nine sites, six of which are considered remote locations (ALT, BRW, NWR, MLO, SMO, CGO, SPO) and two of which were established to sample both polluted/source and clean air (ITN, HFM). HATS analyzes pairs of flasks collected weekly from these sites for over 20 gases. Calibration gases are prepared through HATS's Standards Program and measurements are coordinated with HATS's In Situ Station Program.
Instrumentation is a follows:
Automated Flask Analysis (GC/ECD) Shimadzu GC-8AIE, Poraplot Q Column (N2O) HP 5890 (2-channel), Porasil B Column (N2O, CFC-12, CFC-11) SP-2100 Column (CFC-11, CFC-113, CH3CCl3, CCl4) Halon Measurements (GC/ECD) HP 5890, DB-1 Column, Normal Detector (H1301, H1211, CH3Br) O2-doped Detector (CH3Cl)
Alternative Halocarbons (GC/MS) HP 5890, HP 5971, DB-5 HP 5890, HP 5971, Al2O3/KCl PLOT.