The purpose of this chapter is to understand that air pollutants in the atmosphere can affect weather and even change the climate. One example is particulate matter that can affect light-scattering phenomena, reduce visibility, and increase atmospheric turbidity. Others concepts that are introduced include understanding of visibility phenomena such as smog, regional haze, plume blight, Arctic haze, and South Asian haze; awareness of what an urban heat island is and how it affects local and regional climate; understanding of processes that result in the formation of cloud and rain droplets and the role of pollutants in these processes; familiarity with the phenomenon of atmospheric deposition and its potential environmental impacts; understanding of O3 layer dynamics and how pollutants such as halogenated hydrocarbons and NOx catalytically destroy O3; understanding of how environmental factors and chemical reactions associated with anthropogenic air pollution cause the Antarctic O3 hole; recognizing that the earth’s climate undergoes natural variations associated with such phenomena as changes in solar luminosity and the earth’s orbit; understanding of how greenhouse gases such as CO2, CH4, N2O, O3, and chlorofluorocarbons affect radiative forcing and climatic change; awareness of global warming trends and model predictions; awareness of uncertainties involved in relating changes in greenhouse gas composition with changes in global climate; and understanding of scientific observations that are increasingly showing a pattern of significant global warming.