Year	micrograms per cubic meter
1990	43.79263059169571
1995	41.33435201521597
2000	45.326843598543256
2005	42.78073482897783
2010	42.64403735675223
2011	44.053105314757666
2012	45.25156201149098
2013	41.94561582660642
2014	41.1355193331923
2015	47.8203662322586
2016	45.35781839788414
2017	44.143625173154156
2018	44.200771479628656
2019	44.03753964704777