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Relative change in transportation air pollutant emissions from passenger cars and trucks between 1980 and 2014. The relative change is the annual change in million tons (Mt) emitted by passenger vehicles and trucks combined as a fraction of baseline 1980 emissions for CO, HC (VOC), NOx, and PM, which were 1.7, 0.2, 0.5, and 0.1 Mt, respectively.51
