Most trace gases and particles that are brought into the atmosphere are not inert, i.e. are passive. They are chemically, or physically, transformed in the atmosphere, and are removed from the atmosphere by dry deposition – reaction with the surface – and wet deposition – taken up in water-droplets (rain-out) or removed by falling droplets (wash-out). The environmental impacts of the effects of chemistry relative to atmospheric dispersion are presented in this article by considering different spatial scales, namely local, regional and global.