Year	micrograms per cubic meter
1990	57.10921851812784
1995	52.631764953252286
2000	57.316723022244716
2005	53.30685372600772
2010	54.01350571277655
2011	55.576123799859886
2012	58.649183294744276
2013	56.32313170116462
2014	57.64398728171865
2015	62.353566299558324
2016	60.464309803823284
2017	57.15262732074424
2018	57.56236991250276
2019	57.69883301693019