Year	micrograms per cubic meter
1990	43.904463989819895
1995	46.0035932813364
2000	46.57413264571428
2005	46.07225332199164
2010	50.08627365184133
2011	47.48952946301501
2012	47.535979173292844
2013	48.38566572385567
2014	46.57884507054225
2015	48.551367376084194
2016	45.79102546317512
2017	45.92904025905915
2018	46.10334477285499
2019	45.77674200494411