Year	0 – 6000 (μg/m³).h	0-6000 (μg/m3).h	0–6000 (μg/m3).h	6000 – 12000 (μg/m³).h	6000-12000 (μg/m3).h	6000–12000 (μg/m3).h	12000 – 18000 (μg/m³).h	12000-18000 (μg/m3).h	12000–18000 (μg/m3).h	Greater than 18000 (μg/m³).h	Greater than 18000 (μg/m3).h
1996		7.63			25.61			23.11			43.65
1997		9.78			29.65			30.69			29.88
1998		15.24			16.01			27.46			41.28
1999		4.47			17.14			40.26			38.13
2000		16.14			24.93			20.0			38.93
2001		10.61			23.57			20.73			45.09
2002		10.63			24.04			22.2			43.13
2003		8.54			13.63			12.64			65.19
2004		20.39			23.88			21.43			34.29
2005		12.73			16.61			25.24			45.42
2006		2.43			7.17			21.66			68.74
2007		23.68			25.32			18.77			32.23
2008		4.72			28.27			31.58			35.44
2009		20.05			33.6			24.06			22.3
2010		15.39			28.83			34.58			21.2
2011		12.63			26.77			42.39			18.21
2012		14.18			32.4			26.29			27.13