Sulfur in the Stratosphere

[SUNSHADE #1: THE VOLCANO EFFECT] Sulfur in the Stratosphere Past volcanic eruptions have cooled the earth substantially by injecting sulfur dioxide (SO2) gas into the upper atmosphere. Atmospheric scientists have proposed that SO,-already emitted in vast quantities into the lower atmosphere by burning fossil fuels-could have the same cooling effect if it were lofted into the stratosphere. Light is scattered by clouds of sulfate droplets DEPLOYMENT BY BALLOON Lighter-than-air craft would require very little energy to raise a cargo of So, at least six miles high. DEPLOYMENT BY PLANE Running on "dirty," high-sulfur fuel at cruising altitudes, airplanes could add plenty of SO2 to the stratosphere. THE DOWNSIDES STRATOSPHERE UNPREDICTABLE CHANGES in regional wind and rainfall patterns REDUCED EVAPORATION, lead- ing to reduction in global rainfall HOW IT WORKS When SO, reaches the stratosphere, a series of chemical reactions that involve such molecules as the hydroxyl radical (OH), diatomic oxygen (0,) and water, either in its vapor form or condensed into a liquid droplet, give rise to sulfate particles about a micron across. The particles-made up of sulfuric acid (H2S04), water and trace amounts of impurities-deflect some of the incoming sunlight. The diagram below shows some of the molecules involved, but none of the specific chemical pathways are portrayed. INCREASING ACID RAIN, possi- bly polluting pristine ecosystems ACCELERATED DESTRUCTION of ozone layer, causing higher incidence of skin cancer Cunce CHEAP ENOUGH to be done unilaterally, without inter- national agreements, which could increase global tensions H20 Pastvokank eruption CONTINUAL MAINTENANCE required; the earth would warm quickly if maintenance was OH- DEPLOYMENT BY MISSILE Shells charged with S02 and fired from ships atsea could respond quickly to changing conditions in the upper atmo- sphere, provided atmospheric scientists gain a better understanding of the details of aerosol formation there. so deferred and carbon emissions continued unabated H,S0. Нао