year pollutant_name index
2000 PM2.5 100.0
2001 PM2.5 99.0
2002 PM2.5 96.9
2003 PM2.5 98.1
2004 PM2.5 99.4
2005 PM2.5 97.6
2006 PM2.5 94.3
2007 PM2.5 92.0
2008 PM2.5 87.9
2009 PM2.5 82.1
2010 PM2.5 77.4
2011 PM2.5 73.5
2012 PM2.5 68.0
2013 PM2.5 63.1
2014 PM2.5 61.0
2015 PM2.5 57.3
2016 PM2.5 58.3
2017 PM2.5 56.3