IMPACT-INDUCED PERTURBATIONS OF ATMOSPHERIC SULFUR

Asteroids and comets that are vaporized during hypervelocity impact ev ents can inject large masses of S into the stratosphere where it can p otentially affect the radiation budget of the Earth, alter the chemist ry of the ozone layer, and eventually be converted to sulfuric acid ra in. Relatively small carbonaceous asteroids, 0.3 km in diameter, conta in 5 times more S than the entire modern stratosphere and these object s hit the Earth at an average rate of 1 per 10,000 years. Larger impac t events, capable of injecting 10(15) g of S into the stratosphere, oc cur at an average rate of 1 per 1 million years. Calculations indicate there is sufficient O and H in the vapor plumes of most impact events to convert the S to sulfuric acid aerosols. If this conversion occurs , then the larger impact events could depress mean surface temperature s by more than 2 degrees C for 3 years or longer.