Year	micrograms per cubic meter
1990	47.65728152507983
1995	45.02792958512046
2000	49.23700564431792
2005	46.177810845307825
2010	45.90630503062154
2011	47.30009359491296
2012	48.49785819568757
2013	44.97807559499876
2014	44.26191607225983
2015	51.638150412900764
2016	48.632680688483426
2017	47.191965049737206
2018	47.247863994386236
2019	47.04563195512429