Year	micrograms per cubic meter
1990	47.26235873
1995	43.86978315
2000	48.62243832
2005	43.50002991
2010	44.68925506
2011	48.88552552
2012	54.41184561
2013	51.40472879
2014	43.69608477
2015	48.33063334
2016	44.95047945
2017	46.44225626
2018	45.14403975
2019	44.46696713