1.3 - Uncertainties in the Atmospheric Chemical System

Abstract

This chapter focuses on processes that affect the budget of ozone in the troposphere at the global scale. Without human-induced perturbations, the chemical composition of the atmosphere would be strongly determined by biological processes at the earth's surface. Photosynthesis, respiration, matter decomposition, and microbial activity produce intensive exchanges of chemical elements at the earth's surface with a deep influence on the atmospheric composition. Volcanic eruptions that have played a major role in the evolution of the earth's atmosphere at geological time scales have limited effects in the contemporary. An interesting example of the biological influence on the atmospheric composition is provided in the chapter by the processes affecting the formation and destruction of atmospheric ozone in the natural atmosphere. Global chemical transport model of the troposphere called “images” is described to assess the importance of various factors that influence the global ozone budget. Images model incorporates several basic elements: surface emissions, atmospheric transport, chemical transformations, and surface deposition. The images model has been used to assess the impact of human activities on the chemical composition of the global troposphere. To quantify past, current, and future changes in tropospheric composition, images was used to simulate the preindustrial atmosphere and a future atmosphere, respectively.