Whole Air Sampler (WAS)

Measurement Description: The Whole Air Sampler (WAS) collects and stores up to 32 air samples along the ER-2 flight track. The air samples are analyzed on several gas chromatograph instruments each utilizing different detection techniques including flame ionization, mass selective, and electron capture detectors. The analysis includes halocarbons, hydrocarbons, and organic nitrates (see Table 1 below). Samples are shipped to the laboratory at NCAR and analyzed within 7 days of collection. Accuracy and precision of the analytical system is species dependent and, in general, averages 3-8% over the range of species reported. Some of the halogen containing compounds with low tropospheric mixing rations (i.e., less than 5 pptv) tend to have higher errors associated with their measurements (10-30%).

The WAS consists of 32 electropolished, 1.6 liter, stainless steel canisters connected in series through a manifold to a 4-stage metal-bellows compressor. The manifold is constructed of welded, 1/4-inch, electropolished, stainless steel tubing, and all interconnections are made with metal gasket fittings to eliminate contamination and/or loss of trace gases in the sample stream. Each can is connected to the manifold through a metal-seal valve. The compressor draws ambient air in through the instrument inlet and compresses the gas into the manifold. The sample valves are actuated by 28 Volt DC motors under computer control. The sample collection rate is controlled by a preset program, although the pilot can activate a second, faster sample sequence when required (during altitude profiles, for example). The cans are pressurized to 40 psia or approximately 4.4 standard liters. Can fill times depend on aircraft altitude, and range from approximately 45 seconds at 15 km to 180 seconds at 21 km. The WAS instrument is located in the center-line drop-dank attached to the belly of the ER-2 between the front and rear landing gear.

CFC-11 (CCl3F) Methane (CH4)

CFC-12 (CCl2F2) Ethane (C2H6)

CFC-113 (CCl2FCClF2) Propane (C3H8)

CFC-114 (CClF2CClF2) Butanes (C4H10)

CFC-115 (CF2ClCF3) Pentanes (C5H12)

Halon 1211 (CF2ClBr) Carbon Tetrachloride (CCl4)

Halon 1301 (CF3Br) Methyl Chloroform (CH3CCl3)

Halon 2402 (C2F4Br2) Tetrachloroethylene (C2Cl4)

Methylene Chloride (CH2Cl2)

Hydrochlorofluorocarbons

Trichloroethylene (C2HCl3)

HCFC-22 (CHF2Cl) Chloroform (CHCl3)

HCFC-141b (CH3CFCl2)

HCFC-142b (CH3CF2Cl)

Methyl Halides and related

Methyl Bromide (CH3Br)

Organic Nitrates
Methyl Chloride (CH3Cl)

Methyl nitrate (CH3ONO2) Methyl Iodide (CH3I)

Ethyl nitrate (C2H5ONO2) Methylene Bromide (CH2Br2)

Propyl nitrates (C3H7ONO2) Bromoform (CHBr3)