year	pollutant_name	index
1990	PM2.5	100.0
1991	PM2.5	100.0
1992	PM2.5	100.0
1993	PM2.5	100.0
1994	PM2.5	100.0
1995	PM2.5	100.0
1996	PM2.5	100.0
1997	PM2.5	112.5
1998	PM2.5	112.5
1999	PM2.5	112.5
2000	PM2.5	112.5
2001	PM2.5	100.0
2002	PM2.5	100.0
2003	PM2.5	100.0
2004	PM2.5	100.0
2005	PM2.5	100.0
2006	PM2.5	100.0
2007	PM2.5	100.0
2008	PM2.5	100.0
2009	PM2.5	100.0
2010	PM2.5	87.5
2011	PM2.5	87.5
2012	PM2.5	87.5
2013	PM2.5	75.0
2014	PM2.5	75.0
2015	PM2.5	62.5