However, problems may arise in distant areas that receive the pollution. Temperature inversions can enhance the severity of a photochemical smog episode. Normally, during the day the air near the surface is heated and as it warms it rises, carrying the pollutants with it to higher elevations. However, if a temperature inversion develops pollutants can be trapped near the Earth's surface. Temperature inversions cause the reduction of atmospheric mixing and therefore reduce the vertical dispersion of pollutants.
Inversions can last from a few days to several weeks.
Topography is another important factor influencing how severe a smog event can become. Communities situated in valleys are more susceptible to photochemical smog because hills and mountains surrounding them tend to reduce the air flow, allowing for pollutant concentrations to rise. In addition, valleys are sensitive to photochemical smog because relatively strong temperature inversions can frequently develop in these areas. A possible solution to the problem of photochemical smog is to enforce stricter emission laws all over the globe. Many countries have varying laws on the legal limits of NOx, Carbon Dioxide, and Sulfur Dioxide.