This Regulation of the Minister of Environment, which is composed of five articles and two Annexes, implements art. 86a point 1 of the Environment Protection Act and provides detailed provisions concerning calculating level of substances in ambient air. The present Regulation establishes way of: (1) calculation of the value of indicators of average exposure for agglomerations and cities with population greater than 100.000 (specified in Annex 1); (2) calculcation of the national indicator of average exposure (specified in Annex 2); (3) assessment of achieving the level of average exposure.