1. Council Directive 96/62/CE of 27 September of 1996 on ambient air quality assessment management.
2. Air quality guidelines for Europe, WHO regional publications, European series, No. 23, WHO Regional Office for Europe, Copenhagen, 1987.
3. World Health Organisation Regional Office for Europe, Concern for Europe's Tomorrow. Health and the Environment in the WHO European Region, Wissenschaftlishe Verlags. Ges. Stuttgart, 1995.
4. International Standard Organisation, ISO/DIS 10489, Ambient air — determination of sulphur dioxide — Ultraviolet Fluorescence method, International Standardisation Organisation, Geneva.
5. International Standard Organisation, ISO 7996: 1985, Ambient air — determination of the mass concentration of nitrogen oxides — Chemiluminescence method, International Standardisation Organisation, Geneva, 1985.