The Transformations of Sulfur And Nitrogen in the Remote Atmosphere Background Paper

Abstract

Many, if not most, sulfur and nitrogen compounds are introduced into the troposphere as gases (see Chapters 1 and 2) and a portion of these compounds are removed directly to the earth’s surface. Before their removal, most of the remaining fraction undergo both chemical transformation to another molecular form and physical transformation to a condensed phase, either in aerosol particles or in cloud droplets. Simultaneously, all the substances are mixed by eddy motions into the planetary boundary layer and, in some cases, throughout the troposphere and into the stratosphere. Volcanoes sporadically inject relatively small but important amounts of some species directly into the stratosphere where transformations also occur before slow transport back to the earth’s surface via the troposphere. Because three physical states are involved (gas, solid or liquid aerosol particles, and solute in cloud droplets), the transformations occurring in each phase and between the three phases need to be described.