Increased atmospheric ammonia over the world's major agricultural areas detected from space.

This study provides evidence of substantial increases in atmospheric ammonia (NH3) concentrations (14-year) over several of the worlds major agricultural regions, using recently available retrievals from the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite. The main sources of atmospheric NH3 are farming and animal husbandry involving reactive nitrogen ultimately derived from fertilizer use; rates of emission are also sensitive to climate change. Significant increasing trends are seen over the US (2.61% yr-1), the European Union (EU) (1.83% yr-1), and China (2.27% yr-1). Over the EU, the trend results from decreased scavenging by acid aerosols. Over the US, the increase results from a combination of decreased chemical loss and increased soil temperatures. Over China, decreased chemical loss, increasing temperatures, and increased fertilizer use all play a role. Over South Asia, increased NH3 emissions are masked by increased SO2 and NOx emissions, leading to increased aerosol loading and adverse health effects.

Experimental investigation of the self- and N(2)-broadened continuum within the ν(2) band of water vapor.

We present an experimental study of the self- and N(2)-broadened H(2) O continuum in microwindows within the ν(2) fundamental centered at ~1600 cm(-1). The continuum is derived from transmission spectra recorded at room temperature with a BOMEM Fourier transform spectrometer at a resolution of ~0.040 cm(-1). Although we find general agreement with previous studies, our results suggest that there is significant near-wing super-Lorentzian behavior that produces a highly wave-number-dependent structure in the continuum as it is currently defined.

Comparison of neural networks and regression-based methods for temperature retrievals.

Two methods for performing clear-air temperature retrievals from simulated radiances for the Atmospheric Infrared Sounder are investigated. Neural networks are compared with a well-known linear method in which regression is performed after a change of bases. With large channel sets, both methods can rapidly perform clear-air retrievals over a variety of climactic conditions with an overall RMS error of less than 1 K. The Jacobian of the neural network is compared with the Jacobian (the regression coefficients) of the linear method, revealing a more fine-scale variation than expected from the underlying physics, particularly for the neural net. Some pragmatic information concerning the application ofneural nets to retrieval problems is also included.

Line mixing effects in solar occultation spectra of the lower stratosphere: measurements and comparisons with calculations for the 1932-cm(-1) CO(2) Q branch.

Line mixing effects have been observed in a CO(2)Q branch recorded in 0.01-cm(-1) resolution IR solar occultation spectra of the lower stratosphere. The spectral data were obtained by the Atmospheric Trace Molecule Spectroscopy Fourier transform spectrometer during the Spacelab 3 shuttle mission in the spring of 1985. Analysis of the 1932.47-cm(-1) (11102)?(00001) band Q branch of (12)C(16)O(2) shows absorption coefficients below the band origin approximately 0.62 times those calculated using a standard Voigt line shape function. Calculations of line mixing using the Lorentz halfwidths of the lines and a simple energy gap scaling law to parametrize rotational energy transfer reproduce the observed absorption coefficients to ~10%. The present results provide the first quantitative information on air-broadened line mixing effects in a Q branch at low temperatures (~210 K) and show that these effects are significant even at the low pressures of the lower stratosphere (~100 mbar).

Effect of line mixing on atmospheric brightness temperatures near 15 microm.

The effect of line mixing on the effective blackbody brightness temperature of the earth in the region of the 15microm nu (2)Q branch of CO(2) is calculated. The procedures used to compute line mixing follow those used to successfully model mixing observed in laboratory spectra of two near-infrared CO(2)Q branches. The atmospheric radiances are calculated between 664 and 670 cm(-1), a spectral region that is of interest for sounding the upper troposphere and the stratosphere. Mixing was found to lower the observed brightness temperatures by as much as 3 K for some temperature profiles. Ignoring this effect would significantly impact the ability of advanced sounders to produce temperature retrievals which meet the projected accuracy requirement of 1 K/km.

Observation of nuclear quadrupole hyperfine structure in the infrared spectrum of hydrogen iodide using a tunable-diode laser.

Nuclear quadrupole hyperfine structure has been observed in the 1-0 vibration-rotation band of hydrogen iodide with a tunable-diode laser. The measured splittings agree well with microwave measurements of the HI molecule. Evidence for a slight change in the iodine nuclear quadrupole coupling constant from the ground to first excited vibrational state in hydrogen iodide was found.