High resolution spectra in the region of the 2nu(9) band of nitric acid have been obtained for selected portions of the HNO(3) spectrum using tunable diode laser techniques. Continuous spectra are presented from 891.25 cm(-1) to 898.77 cm(-1), with a spectral resolution =0.001 cm(-1) (30 MHz). Absolute line intensities and line positions are presented. Absolute wavelength calibration was obtained by frequency mixing the diode laser with a C(13)O(2)(16) isotope laser. Self and foreign gas (N(2)) broadening coefficients were iteratively calculated from the experimental data and were determined to be alpha(a) = 0.8 cm(-1)/atm and alpha(f) = 0.13 cm(-1)/atm, respectively.
Measurements of NH(3) absorption coefficients are presented for several transitions of a C(13)O(2)(16) laser for small concentrations of NH(3) (p = 1 Torr) for absorption lines broadened to 1 atm with N(2). NH(3) absorption coefficients were determined for laser transitions R(8) (920.2194 cm(-1)) to R(28) (933.8808 cm(-1)) of the 00 degrees 1 - [10 degrees 0,02 degrees 0](I) band. The strongest absorption coefficient [K = 36.09 +/- 1.43 (atm-cm)(-1)] was measured for the R(18) transition for the NH(3) line, aQ(6,6), and is larger than has been found in any previous measurements with a CO(2) laser. The dependence of K on total pressure was also obtained for select transitions, and the frequency separation between the R(18) laser transition and the neighboring NH(3) line [aQ(6,6)] was determined to be 550 +/- 50 MHz. These results are significant for long path absorption monitoring of NH(3) with CO(2) lasers since the path length can be reduced by approximately 40% and for heterodyne mdetection of NH(3) since the relative position of the laser transition to the NH(3) absorption line is well within the bandpass of Hg-Cd-Te photomixers (B >/= 1.5 GHz).
The chemical composition of the troposphere is controlled by various biogeochemical cycles that couple the atmosphere with the oceans, the solid Earth and the biosphere, and by atmospheric photochemical/chemical reactions. These cycles and reactions are discussed and a number of key questions concerning tropospheric composition and chemistry for the carbon, nitrogen, oxygen and sulfur species are identified. Next, we review various remote sensing techniques and instruments capable of measuring and monitoring tropospheric species from the ground, aircraft and space to address some of these key questions. We also consider future thrusts in remote sensing of the troposphere.
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