[Encyclios]

Effects of weathering on pollution

Concentrations of pollutants in the air depend not only on the number and intensity of pollution sources and the distance from these sources, but especially on local meteorological conditions (for local-scale pollution phenomena) and local and large-scale meteorological conditions (for pollution phenomena at large distances from the sources). For local-scale pollution phenomena, the greatest influence on the transport and atmospheric diffusion of pollutants is due to wind intensity, turbulence conditions (mechanical and thermodynamic) of the lower atmospheric layers, and particular meteorological effects such as breezes (sea or mountain), wind channelling in narrow valleys, or in roads in urban areas, etc.

For large-scale pollution phenomena, the greatest influence on pollutant transport and diffusion is due to wind variations with altitude (wind shear), barotropic or baroclinic conditions in the atmosphere, and large-scale turbulence determined by cyclonic and anticyclonic areas. In general, with the same emission of pollutants from sources, concentrations in small-scale air (urban areas, industrial areas, etc..) are lower when the wind is moderate or strong and the atmosphere is unstable in the lower layers, or when the wind is weak or absent but there is strong insolation with clear skies and sun high on the horizon. Vice versa, concentrations become high when there is inversion of the vertical thermal gradient or in conditions of high pressure at night and with weak wind, or in conditions of persistent fog that causes processes of accumulation of pollutants in the air, sometimes very dangerous for human health.