Remember the disappearing ozone layer that was being eaten up by spray can propellants and threatening us all with skin cancer? Well, maybe it's not a worry after all. A University of Southern California chemistry professor thinks that space dust that rockets into the Earth's atmosphere might be preventing destruction of the layer by spray can gases. Sidney Benon says that a million pounds of heaven-sent debris burn up each year in the atmosphere. The debris is made of specks of sand, aluminum, iron and other metals from outer space -- the "shooting stars" that light up the heavens for a split second.

But it's more than celestial fireworks to Benson, who believes that the chemicals the debris adds to the atmosphere scrub away impurities that were thought to be destroying ozone. "If you put metals in the upper atmosphere, they sweep up chlorine," Benson said. Chemical chlorine is a basic ingredient of flurocarbons or Freon, used as a spray can propelant until such aerosol products were banned in the United States in April 1979. The ban was based on scientific warnings that spray can chemicals drifted into the atmosphere and began eating away at the Earth's protective ozone layer 20 miles up. Ozone shields Earth from harmful ultraviolet rays, which can cause skin cancer. Benson said atmospheric chemical changes caused by solar system debris "have been completely ignored. The conclusion scientists have reached on the destructive effects of Freon on ozone have left out the whole chemistry of chemicals. "Essentially, we've discovered natural protection against chlorine in the atmosphere. No one knows how effective it is; it hasn't been studied." Lester Machta, air resources director for the National Oceanic and Atmospheric Administration, said he doubts Benon's theory although he would not rule it out. But Machta admitted there is a great deal of uncertainty among scientists on the ozone question. "The flurocarbon increase [in the atmosphere] has been documented," he said. It increases at the rate of 5 or 8 percent a year as a result of continued Freon and spray can use in other countries. "Everyone who has made the measurements sees that," Machta said. "The ozone change is what we don't see. It's gone up and it's gone down. There seem to be natural fluctuations."