Air quality guidelines : 

 - Copenhagen, Denmark :  World Health Organization,  c2006. 
 - ix, 484 p. :  ill. (chiefly col.) ; 
<br/><br/><label>ISBN: </label>9789289021920  9289021926  
<br/><br/><label>Subjects--Topical Terms: </label><br/>Air<br/>Air quality.<br/>Air Pollution.
<br/><br/><label>LC Class. No.: </label>TD883  / .A47844 2006