Chemistry of air pollution Tamil revision mind map as a four-quadrant grid: the major air pollutants carbon monoxide sulphur dioxide nitrogen oxides particulates and hydrocarbons with their sources and harm, the greenhouse effect where greenhouse gases carbon dioxide methane and water vapour absorb outgoing infrared radiation causing enhanced global warming, stratospheric ozone depletion where CFCs release chlorine free radicals that catalytically destroy ozone in a regenerating cycle, and photochemical smog where nitrogen oxides and unburnt hydrocarbons react in sunlight to form ground-level ozone and other secondary oxidants that irritate eyes and damage lungs and plants.