VARIATIONS IN THE ABSORPTION SPECTRA OF ATMOSPHERIC DUST
ARMY ELECTRONICS COMMAND WHITE SANDS MISSILE RANGE NM ATMOSPHERIC SCIENCES LAB
Pagination or Media Count:
Six impactor and 99 membrane filter samples of atmospheric dust were collected atop a mountain in south central New Mexico during April and May 1968. Qualitative analysis of these samples by infrared absorption spectroscopy in the 4000 to 250cm wavenumber 2.5 to 40 micron wavelength range revealed that the positions and relative intensities of the absorption bands were dependent on the size fraction of the dust and on the time the sample was taken. Within the 1250 to 770cm 8 to 13 micron atmospheric window, the micron-sized giant particles exhibited a peak absorption at 1027cm 9.7 micron, whereas the submicron large particles had their peak absorption at 1108cm 9.0 micron. These two absorption bands are induced, respectively, by silicate clays and by ammonium sulfate. A temporal variation was observed in the ratio of the intensities of the 1027cm 9.7 micron silicate and the 1425cm 7.0 micron carbonate absorption bands of the giant particles. This ratio was high during the early morning, at times of convective activity and precipitation and at times of cold frontal passage from the east it was low during the afternoon and at times of convective inactivity and no precipitation. The low ratio dust is attributed to advection of fresh soil particles from the exchange layer over the adjacent basin and mountains and the high ratio dust to advection of fresh soil particles from the Great Plains and aged soil particles from the overlying free atmosphere.
- Guided Missile Launching and Basing Support