Year Lower than 10 000 (µg/m³)•h 10 000-20 000 (µg/m³)•h 20 000-30 000 (µg/m³)•h 30 000-50 000 (µg/m³)•h Greater than 50 000 (µg/m³)• h
2004 2 49.3 20.1 21.3 7.2
2005 24.7 18 18.9 28.7 9.7
2006 0.2 31.8 18 39.8 10.2
2007 40.3 14.6 13.6 24.5 6.9
2008 21.7 31.2 21.5 25.1 0.5
2009 34.7 19.3 18.4 24.2 3.3
2010 38.9 15.1 25.1 19 2
2011 32.9 16.3 25.8 21.9 3
2012 36.7 18.7 18.2 22.9 3.6
2013 34.4 24.2 19.3 18.3 3.7