Gases are purified for the purpose of further using the gases themselves or the impurities contained in them; industrial gases discharged into the atmosphere are purified to prevent pollution of the air by noxious substances. Until the second half of the 19th century the struggle against the harmful effect of discharging industrial gases into the atmosphere consisted only of banning or restricting the construction of certain enterprises; however, these measures were rendered ineffective by the growth of industry, transportation, and large cities. The problem of purification of industrial gases arose precisely because of rapid industrial development, the concentration of industries, and increased scales of production. In industrially developed countries, the saturation of areas with industries and transportation was such that local pollution of the atmosphere became universal and led to the pollution of the entire air basin, or at least a huge part of it.