Year	micrograms per cubic meter
1990	52.90993831
1995	51.64362616
2000	53.74695817
2005	55.06194439
2010	56.41649854
2011	60.5358739
2012	68.94271136
2013	66.42738113
2014	73.27082296
2015	68.97033719
2016	67.7673598
2017	62.75318316
2018	63.27546257
2019	63.4255285