Air quality in selected urban areas. 

 - Geneva :  World Health Organization. 
 - 1973/74- 
 - WHO offset publication ;  no. 30 WHO offset publication ;  no. 41 WHO offset publication ;  no. 57 WHO offset publication ;  no. 76 .
<br/><br/> On cover, 1973/74- : GEMS: Global Environmental Monitoring System. 
<br/><br/>Each volume covers two years. 
<br/><br/>Prepared in cooperation with the WHO Collaborating Centre on Environmental Pollution Control and the United States Environmental Protection Agency. Published under the joint sponsorship of the United Nations Environment Programme and the World Health Organization.