National Trends in Sulfur_Dioxide Concentrations in 1980 - 2014

Year	Mean	Number of Trend Sites	10th Percentile	90th Percentile
1980	159.757777777777	45	50	340
1981	151.878888888888	45	40	271
1982	137.177777777777	45	25	250
1983	147.228888888888	45	34	300
1984	134.693333333333	45	30	263
1985	138.613333333333	45	40	249
1986	137.174444444444	45	30	248
1987	134.077777777777	45	25	280
1988	140.085185185185	45	30	267
1989	134.771851851851	45	30	261
1990	120.154074074074	45	26	226
1991	113.662222222222	45	30	218
1992	110.711851851851	45	28	210
1993	101.642962962962	45	40	200
1994	103.896296296296	45	32	181
1995	94.8244444444444	45	27	217
1996	87.6777777777777	45	28	160
1997	92.6488888888889	45	29	187.2
1998	89.7088888888889	45	28	192
1999	91.2259259259259	45	28	195.5
2000	82.7162962962963	45	26	163
2001	85.5466666666666	45	29	203
2002	74.2296296296296	45	22	145
2003	78.8059259259259	45	18	176
2004	75.6266666666666	45	20	172
2005	74.914074074074	45	16	158
2006	68.8548148148148	45	21	138
2007	64.7177777777777	45	19	139
2008	58.9548148148148	45	17	122
2009	50.8151851851852	45	13	100
2010	46.2503703703703	45	10.9	100
2011	37.9851851851851	45	9.83333333333333	68
2012	36.6725925925926	45	8	71.6
2013	30.0818518518518	45	7	64
2014	32.06	45	8.3	77