Year	micrograms per cubic meter
1990	43.78876512815989
1995	41.33111562898042
2000	45.32334441811591
2005	42.777830472782
2010	42.64122952809185
2011	44.05044256552936
2012	45.2487874865379
2013	41.94316097601178
2014	41.13309874767387
2015	47.81735565868924
2016	45.35513431507842
2017	44.14107963761814
2018	44.19823842325814
2019	44.03506116674599