In order to provide a hygiene evaluation of the degree of atmospheric pollution, one must have a scale which will show how much the given concentration exceeds the permissible limit. Such a scale is the maximum permissible concentration of the pollutants in the atmosphere. The maximum permissible concentrations enable the hygiene worker not only to estimate the degree of air pollution, but also to justify the need for particular measures -- purifying installations, gap zones, tall chimneys, etc. Moreover, sanitary norms of this type enable the hygiene worker to formulate his requirements in each concrete case quantitatively, indicating the size of the gap zone, the efficiency of the purifying installations in each concrete situation, etc. The norms also make it possible to find a quantitative expression for the degree of effectiveness of the environmental health measures that were implemented.