Year	micrograms per cubic meter
1990	67.63582184578512
1995	62.16205835620581
2000	66.57331820082254
2005	66.57128131935218
2010	71.77793687436707
2011	74.70462129040553
2012	80.97158024361003
2013	83.26781207707178
2014	88.83596039165947
2015	82.75943777087443
2016	85.6833112815973
2017	76.38704397725172
2018	77.42768615051168
2019	77.563400343277