ABSTRACT
In order to test photochemical theories linking chlorofluorocarbon derivatives to ozone(O(3)) depletion at high latitudes in the springtime, several related atmospheric species, including O(3), chlorine monoxide(ClO), and bromine monoxide (BrO) were measured in the lower stratosphere with instruments mounted on the NASA ER-2 aircraft on 13 February 1988. The flight path from Moffett Field, California (37 degrees N, 121 degrees W), to Great Slave Lake, Canada (61 degrees N, 115 degrees W), extended to the center of the polar jet associated with but outside of the Arctic vortex, in which the abundance of O(3) was twice its mid-latitude value, whereas BrO levels were 5 parts per trillion by volume (pptv) between 18 and 21 kilometers, and 2.4 pptv below that altitude. The ClO mixing ratio was as much as 65 pptv at 60 degrees N latitude at an altitude of 20 kilometers, and was enhanced over mid-latitude values by a factor of 3 to 5 at altitudes above 18 kilometers and by as much as a factor of 40 at altitudes below 17 kilometers. Levels of ClO and O(3) were highly correlated on all measured distance scales, and both showed an abrupt change in character at 54 degrees N latitude. The enhancement of ClO abundance north of 54 degrees N was most likely caused by low nitrogen dioxide levels in the flight path.
ABSTRACT
Measurements in the stratosphere of gaseous constituents in the plume of Mount St. Helens were obtained during five flights of the NASA U-2 aircraft between 19 May and 17 June 1980. Mixing ratios from gas chromatographic measurements on samples acquired about 24 hours after the initial eruption show considerable enhancement over nonvolcanic concentrations for sulfur dioxide (more than 1000 times), methyl chloride (about 10 times), and carbon disulfide (more than 3 times). The mixing ratio of carbonyl sulfide was comparable to nonvolcanic mixing ratios although 3 days later it was enhanced two to three times. Ion chromatography measurements on water-soluble constituents are also reported. Very large concentrations of chloride, nitrate, and sulfate ions were measured, implying large mixing ratios for the water-soluble gaseous constituents from which the anions are derived. Measurements of radon-222 present in the plume are also reported.
ABSTRACT
A microparticle accelator of unique design, which produces high-velocity, micrometer-sized projectiles of any cohesive material, is described. In the source, an electrodynamic levitator, single particles are charged by ion bombardment in high vacuum. The vertical accelerator has four drift tubes, each initially at a high negative voltage. After injection of the projectile, each tube is grounded in turn at a time determined by the voltage and charge/mass ratio to give four acceleration stages with a total voltage equivalent to about 1.7 MV. The delay times may be set manually or controlled automatically by the particle's charge/mass ratio measured in the source by the operator just before ejection. At the entrance to the accelerator, the particle generates a signal that initiates the timing sequence. In the target chamber, detectors record the passage of the particle and provide information on charge, velocity, and position. Trajectories usually pass within a 1-mm-radius circle 1 m below the fourth drift tube. Velocities between 0.5 and 15 km/s have been attained with projectiles of various materials and shapes for cratering studies and calibration of micrometeoroid detectors. About 20 projectiles per day can be accelerated.
ABSTRACT
Micrometer-size silicate flakes do not accrete during impacts in the velocity range 1.5 to 9.5 kilometers per second. Conventional accretionary theories for silicate bodies are applicable only to particles whose orbits are similar. Metal-silicate fractionation in the solar system may have been affected by differences in the accretionary behavior of the metal and silicate particles.