Year	micrograms per cubic meter
1990	60.737048
1995	53.45696804
2000	57.71889497
2005	55.20881643
2010	59.60870032
2011	59.98728468
2012	65.41081339
2013	66.84634548
2014	70.94474538
2015	66.9297544
2016	68.7176409
2017	61.75482212
2018	62.39700577
2019	62.57424987