Year	micrograms per cubic meter
1990	52.24964201700479
1995	49.07816392668681
2000	51.4509807250405
2005	50.90861027034643
2010	54.37589881818793
2011	55.578960175513835
2012	59.211355398540704
2013	60.57828054368385
2014	62.94649461571737
2015	60.05563593157189
2016	61.30824237950635
2017	55.68342332131681
2018	56.32170647399748
2019	56.31191926720347