Year	NH3	NOX	PM2.5	SO2
1990	0.1	2.1	6.5	3.0
1991	0.1	2.0	3.2	2.9
1992	0.1	2.0	2.7	2.9
1993	0.1	2.1	2.5	3.1
1994	0.1	2.1	2.3	3.0
1995	0.1	2.1	1.6	3.0
1996	0.1	2.0	1.3	2.9
1997	0.1	2.0	1.4	2.8
1998	0.1	2.1	1.5	3.0
1999	0.1	2.0	1.3	2.9
2000	0.1	2.0	1.2	2.8
2001	0.1	1.9	1.0	2.8
2002	0.1	1.9	1.0	2.7
2003	0.1	1.3	0.9	1.8
2004	0.1	1.4	0.9	1.9
2005	0.1	1.5	0.9	2.0
2006	0.1	1.4	1.1	2.0
2007	0.1	1.4	1.0	1.9
2008	0.1	1.3	1.4	1.7
2009	0.1	1.2	1.1	1.6
2010	0.1	1.2	1.2	1.6
2011	0.1	1.1	1.1	1.4
2012	0.1	1.1	1.1	1.4
2013	0.1	1.1	0.8	1.3
2014	0.1	1.0	0.8	1.2
2015	0.1	1.0	0.9	1.2
2016	0.1	1.0	0.9	1.2
2017	0.1	1.0	0.9	1.2
2018	0.1	1.0	0.9	1.2