Year 0-6 000 (μg/m3).h 6 000-12 000 (μg/m3).h 12 000-18 000 (μg/m3).h Greater than 18 000 (μg/m3).h
1996 7.6 25.6 23.1 43.7
1997 9.8 29.7 30.7 29.9
1998 15.2 16 27.5 41.3
1999 4.5 17.1 40.3 38.1
2000 16.1 24.9 20 38.9
2001 10.6 23.6 20.7 45.1
2002 10.6 24 22.2 43.1
2003 8.5 13.6 12.6 65.2
2004 20.4 23.9 21.4 34.3
2005 12.7 16.6 25.2 45.4
2006 2.4 7.2 21.7 68.7
2007 23.7 25.3 18.8 32.2
2008 4.7 28.3 31.6 35.4
2009 20.1 33.6 24.1 22.3
2010 15.4 28.8 34.6 21.2
2011 12.6 26.8 42.4 18.2
2012 14.2 32.4 26.3 27.1
2013 19.8 36.6 22.9 20.7