Year	micrograms per cubic meter
1990	43.78876512815989
1995	41.33111562898042
2000	45.32334441811591
2005	42.77783047278201
2010	42.641229528091834
2011	44.050442565529366
2012	45.24878748653791
2013	41.94316097601179
2014	41.13309874767386
2015	47.81735565868925
2016	45.35513431507842
2017	44.14107963761814
2018	44.19823842325815
2019	44.03506116674599