North Dakota air pollution stats

County	First data available	Last data available
Billings Co	1997	2007
Burke Co	1998	2007
Burleigh Co	1997	2007
Cass Co	1997	2007
Dunn Co	1997	2007
Grand Forks Co	1997	2001
McKenzie Co	1997	2007
McLean Co	1997	2007
Mercer Co	1997	2007
Morton Co	1997	2005
Oliver Co	1997	2007
Stark Co	1997	2001
Steele Co	1997	2001
Williams Co	1997	2007