Proposal Title: Airborne Measurement of New and Important Trace Gases in Support of Chemical Studies
Two principal concerns regarding atmospheric trace gases are the effects of hydrocarbons (i.e. acetone) and peroxyacetyl nitrate (PAN) on ozone in the upper troposphere and lower stratosphere (UT/LS), and the growth of the new chlorofluorocarbon (CFC) substitutes in the atmosphere. PAN is a major component of reactive nitrogen and a reservoir for nitrogen oxides in the global troposphere. Furthermore, acetone is a key intermediate product of hydrocarbon oxidation and a precursor for PAN formation. The instrument name PANTHER, PAN and Trace Hydrohalocompounds ExpeRiment, will reflect the wide diversity of compounds that can be measured. PANTHER can be easily reconfigured with different columns to measure almost any hydrocarbon, any halocompound, all the methyl halides, N2O, H2, and CH4.
We have reached the highest frequency of one sample every 70 seconds using packed columns and electron capture detectors (ECDs) on our current gas chromatographs (GC), Airborne Chromatograph for Atmospheric Trace Species-IV (ACATS-IV) and Lightweight Airborne Chromatograph Experiment (LACE). Unfortunately, we can not measure these new compounds with the existing GCs.
We propose to build an airborne, three channels, rapid sampling chromatograph with one mass spectrometric detector (MSD) and two highly sensitive ECDs. The MSD can measure acetone, some CFCs and CFC substitutes, like hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbon (HFCs). For the ECDs, one can measure SF6 and N2O every 70 seconds without sample preconcentration, and the other one can measure PAN with cryogenic preconcentration. The MSD channel, never flown on a UT/LS airborne platform in combination with other detectors, will contain high resolution wide bore capillary columns that could permit a high sampling rate as frequent as once every 4 minutes for a couple of molecules. In the first year, we plan to purchase a commercial GC-MSD and build a custom PAN GC to develop the chromatography for rapid sampling. We will complete the airborne system designed for the NASA ER-2 aircraft in the second year, and will be ready for a field demonstration on a NASA aircraft in the third year.
Elkins, J. W. et al., Geophys. Res. Lett., 23, 347, 1996
Volk, C. M., J. W. Elkins, D. W. Fahey, et al., Science, 272, 1763, 1996