FIRS The Smithsonian Astrophysical Observatory
Far-Infrared Spectroscopy Group
March 11, 1999

Current work:

We observe the stratosphere in thermal emission which enables us to make abundance measurements during both day and night, in any azimuth heading. We can retrieve mixing ratio profiles for most species from the balloon altitude (35-40 km) down to the tropopause (10-16 km, depending on latitude). The 15 micron band of CO2 is used to retrieve temperature and pressure profiles, and then we retrieve the vertical mixing ratio profiles for other species. For balloon flights between 1989 and 1993 we have retrieved mixing ratio profiles for H2O (including HDO, H2(17)O, and H2(18)O, CO2, O2, O3 (including symmetric and asymmetric (49)O3 and (50)O3), N2O, HCN, CO, HF, HCl, HOCl, NO2, HNO3, OH, H2O2, HO2, and HBr, as well as a meaningful upper limit for HOBr. By changing the beamsplitter for our May 1994 flight we were able to retrieve ClNO3 and N2O5 in addition to the above species. We have been using an improved beamsplitter since 1996 which not only improves measurements of all species observed on previous flights but also allows us to measure C2H6, C3H6O (acetone), HNO4, CFC12, CFC11, HCFC22, CCL4, CH3Cl, SF6, OCS, and CH4. In the following table we list the species measured during our most recent flight.

FIRS precision table

We have retrieved constituent profiles for balloon flights on May 12, 1988; September 26, 1989; June 4, 1990; May 29, 1992; September 29, 1992; March 23, 1993; May 22, 1994; and April 30, 1997. Measurements of some species for our 1997 Alaska flight extend to as low as 10 km. Column amounts for H2O, HCl, HF, O3, and HNO3 have also been obtained from observations made during AASE II (January-March, 1992). The measurements in 1992-94 were made as part of the UARS correlative measurement campaign, and the balloon flight in 1997 was part of the Alaska Balloon Campaign in support of the ILAS instrument on board ADEOS.

By comparing our measurements with model calculations we determine the relative rates of destruction of ozone via the HOx, NOx, Clx, and Brx cycles over nearly the full range of the measurements, roughly 20-40 km. The large suite of molecules measured simultaneously by the FIRS-2 allows us to place tight constraints on the photochemical models used to analyze our data, making the model calculations more meaningful and highlighting discrepancies in reaction rates and missing chemistry. In the figure below the symbols represent rates calculated directly from our measurements of radical species, and curves represent results of a photochemical model calculation constrained by our measurements of precursors.

April 1997 Alaska O3 loss rates

More recently, we have begun using our measurements of water vapor and isotopes to explore issues of stratosphere-troposphere exchange. Measurements of H2O in the lower stratosphere are important for understanding climate change and the feedback between global warming and water vapor. In addition, our measurements of HDO and H2(18)O place tight constraints on models of stratospheric dehydration.

David Johnson (