Aircraft Laser Infrared Absorption Spectrometer (ALIAS) for  N₂O, CH₄, CO, HCl, NO₂, and Water Isotopes H₂¹⁶O, HDO, H₂¹⁷O, and H₂¹⁸O on the ER-2 and WB-57 Aircraft
Christopher R. Webster (PI), Lance Christensen, Gregory J. Flesch, 
Jesse Landeros, W. Steven Woodward

Previous contributors:  Ron Howe, Katy Modarress, David C. Scott, James E. Swanson, Randy D. May, Curtis A. Trimble, Robert G. Chave, Matthew A. Tuchscherer, James Kendall, Dr. Lyatt Jaegle, Dr. Hua Hu, Gwen Eknayan, Julie Jensen, Ronald Howe, George Mohler, Ted Brunzie, Alissa Fitzgerald, Scott Atkinson

The Aircraft Laser Infrared Absorption Spectrometer (ALIAS) instrument is a high resolution four-channel scanning Tunable Diode Laser (TDL) and Quantum-Cascade (QC) laser spectrometer (3.4 to 8 µm) that makes direct, simultaneous measurements of (e.g. HCl, NO₂, CH₄, N₂O, CO, water isotopes)  (including vertical profiles of the tracers) in the stratosphere and troposphere at sub-parts-per-billion sensitivities. The instrument weighs 160 lbs.

The measurement technique is based upon using TDL and QC lasers operating from 3.4 to 8 µm scanning over absorption lines recorded using second harmonic absorption spectroscopy over an 80-m pathlength in a 1-m multipass optical cell of the Herriott design. ALIAS has flown over 300 times in 7 major NASA missions: AASE-II, SPADE, STRAT, ASHOE/MAESA, POLARIS, SOLVE, and CRYSTAL-FACE.

For NASA's July 2002 CRYSTAL-FACE Mission out of Florida, ALIAS made the first true in situ measurements of H₂O, HDO, H₂¹⁷O, and H₂¹⁸O on NASA's WB-57F aircraft, as reported in a recent Science paper: 

"Water Isotope Ratios D/H, ¹⁸O/¹⁶O, ¹⁷O/¹⁶O in and out of Clouds Map Dehydration Pathways", C. R. Webster and A. J. Heymsfield, Science 302, 1742-1745, Dec 5 2003. 

"Quantum Cascade Laser Measurements of Stratospheric Methane and Nitrous Oxide", C.R. Webster, G.J. Flesch, D.C. Scott, J.E. Swanson, R.D. May, W.S. Woodward, C. Gmachl, F. Capasso, D.L. Sivco, J.N. Baillargeon, A.L. Hutchinson, and A.F. Cho, Applied Optics, 40, 321-326, 2001.

"Aircraft (ER-2) Laser Infrared Absorption Spectrometer (ALIAS) for In-situ Stratospheric Measurements of HCl, N₂O, CH₄, NO₂, and HNO₃", C.R. Webster, R.D. May, C.A. Trimble, R.G. Chave and J. Kendall, Applied Optics, 33, 454-472, 1994.

"Evolution of HCl Concentrations in the L. Stratosphere from 1991 to 1996 Following the Eruption of Mt. Pinatubo", CR Webster, RD May, HA Michelsen, DC Scott, JC Wilson, HH Jonsson, CA Brock, JE Dye, D Baumgardner, RM Stimpfle, JP Koplow, JJ Margitan, MH Proffitt, L Jaegle, RL Herman, H Hu, GJ Flesch, and M Loewenstein, Geophys. Res. Lett., 25, 995-998, 1998.

"Measurements of CO in the upper troposphere and lower stratosphere", RL Herman, CR Webster, RD May, DC Scott, H Hu, EJ Moyer, PO Wennberg, TF Hanisco, EJ Lanzendorf, RJ Salawitch, YL Yung, JJ Margitan, TP Bui, Chemosphere: Global Change Science, 1, 173-183, 1999.

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