Year	micrograms per cubic meter
1990	46.63689526753511
1995	43.93642331859717
2000	47.386696971728824
2005	45.53841012950644
2010	46.406051160177604
2011	47.842001514368384
2012	50.460572888416564
2013	48.472017035840956
2014	48.96348249491595
2015	52.04942410889096
2016	50.51457601494655
2017	47.87450466243056
2018	48.03500246924873
2019	47.919628235748355