A suspension of droplets or particles in a gas; more precisely, of particles with a maximum diameter of 1 μm (fog and mist are thus aerosols). In meteorology, the term is often used to describe the particles suspended within the air, such as minute fragments of sea-salt, dust, organic matter, and smoke. These enter the atmosphere by natural processes such as vulcanicity, and by human agency such as burning fossil fuels. Aerosols have a role in the radiative forcing of climate; they can absorb and scatter both infrared and solar radiation in the atmosphere; and they can affect and change the processes that control cloud and precipitation formation through their role as condensation nuclei. See I. T. Houghton, Y. Ding, and D. I. Griggs, et al. (2001) on aerosols and climate change. NASA posts a daily global aerosol map on the web.