Year	micrograms per cubic meter
1990	9.310192174647783
1995	9.558915835248053
2000	10.967702260434121
2005	11.088000516750125
2010	11.27001027560406
2011	11.146679784230434
2012	11.13453703598903
2013	11.349953072082494
2014	11.211130178105734
2015	11.21988191564124
2016	11.543873042535349
2017	11.34962889552479
2018	11.459482479084983
2019	11.50018691207713