1986 - Sulfur Dioxide Deposition to Snowpack Research

Left: Department of Hydrology graduate student Deena Stanley catches a few rays while monitoring in-situ deposition of sulfur dioxide to snow. Pictured, left to right, is a tank of nitrogen, an air pump, an ozone generator, an ozone monitor, and a chart recorder. The in-situ device that delivers sulfur dioxide to the snow is just off-camera, to the right.

Interesting things about the pine forest in the background. In northern Arizona, and along the Mogollon Rim, one can find many clusters of very small trees. Almost all these trees sprouted in the unusual spring of 1919, when growing conditions were just right. Nevertheless, none of these trees could grow very well because every single sprout survived and provided killer competition, so you could find many trees, no bigger round than your wrist, that were nevertheless older than your grandparents. A perfect, brushy thicket for catching fire during summer lightning strikes!

There was other research going on at Fort Valley as well. The U.S. Forest Service was looking at the process of cold-hardening of Ponderosa Pine trees. Trees have to prepare for winter: take a pine tree in July and freeze it, and it will die. This preparation process, called cold-hardening, generates lots of gas (ethylene, I believe) and can be monitored with a gas chromatograph.

The first ozone generator we worked with really cranked out the fresh-smelling stuff. I remember thinking, "Hey, this smell's great! I could sniff this all day!" I inhaled big lungfuls of the ozone. Unfortunately the concentration was 1 to 2 parts per million, 10 to 20 times the hourly federal health standard, and ten minutes later, I had the worst sore throat - ever!

Left: The snow reaction vessel. Sulfur dioxide abstracted either from a tank, or from a solution, was passed over snow in the vessel, and taken up by that porous medium.

The lid of this vessel was composed of a special glass that transmitted ultraviolet (UV) radiation. Normally, glass bars UV light from passing through (that's why you don't get a sunburn driving around on a sunny day). We did experiments looking at whether UV light had any effect on the uptake, but we didn't note any effect.

The reaction vessel is placed in a cooler and chilled by antifreeze passing through the copper tubing surrounding it. The antifreeze is pumped from an external refrigeration unit.

Left: Taking the snow and sectioning it into centimeter-thick slices with a handy-dandy snow coring and sectioning tool assembled by Richard Milliron at the University of Arizona's Department of Atmospheric Sciences. Afterwards, the snow is melted and passed through an ion chromatograph for chemical analyses.

Results of this research (Principal Investigators: Roger C. Bales and George A. Dawson) were published in the Journal of Geophysical Research:

"Gaseous Deposition to Snow: I. Experimental Study of SO2 and NO2 Deposition," J. Geophys. Res., 92, 9779-9787, 1987.

Left: The San Francisco Peaks of northern Arizona.