F. Sherwood Rowland

Trace Gas Chemistry in the Cities and Over the Oceans


Abstract

Migrating smog has begun to pollute the skies over oceans in the southern hemisphere, resulting in tropospheric ozone levels near remote islands that would "trigger a first-stage smog alert" in Los Angeles. Tropospheric ozone thus may be reffered to a major atmospheric problem for the 21st century. Long-lasting plumes from biomass burnings -- the practice of burning to clear woodland or brush from the land -- travel across Africa and Australia to bring higher smog levels within rage of remote loca7ions in the southern oceans, such as Fiji. Tropospheric ozone is a key, harmful part of the photochemical smog found in major cities throughout the world, often as the result of congested vehicular traffic. However, in some cities such as Mexico City and Santiago, Chile, use of liquefied petroleum gas for heating and cooking also can contribute significantly to ozone formation. At elevated levels, it can cause breathing difficulties, increase the risk of asthma attacks, and adversely affect the growth of trees, shrubs, and cash crops ranging from vegetables to orchids. Wheter you're in a congested city such as Los Angeles or the seemingly pristine environment of the south seas, the chemistry behind tropospheric ozone remains the same: You need hydrocarbons, nitrogen oxides and sunlight. In the tropics, burning forests give off hydrocarbons and the high temperatures create nitrogen oxides, and there is plenty of sunlight. The data reported stem from a variety of studies, many of which have not yet been published. Some surprising findings have originated from comprehensive NASA aircraft experiments involving a dozen different research groups. In locations more famous for their isolation than their air pollution -- such as Easter. Island, the Galapagos Islands, and Ascension Island -- the NASA researchers detected significant ozone concentrations that can be traced back to biomass burnings on distant continents, indicating that the smog created by the burning is long-lasting and migrates great distances. In 1996, for example, two research planes flying in the South Pacific encountered ozone from biomass burning on 50 percent of their flights. One airplane flew through a plume of Smog about 500 miles north of Fiji in which ozone readings reached 131 parts per billion (ppb). The pollution had traveled over Australia, with the major contributors of ozone likely coming from as far away as Africa. Yet, by the time it reached the south seas, its ozone concentration was high enough that you would say this is a violation of the EPA regulations, if it occurred in the continental U.S. Harmful ozone levels remain higher in the northern hemisphere around the world, compared to the southern hemisphere.


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