Emissions of volatile organic compounds have fallen while gasonline usage has risen

See Energy Fact of the Week: Gasoline Consumption and Emissions of Volatile Organic Compounds by Steven F. Hayward of AEI.

Excerpt:

"...much of this reduction would have occurred as a result of market forces in the absence of a regulatory mandate. One large chunk of VOC reductions from cars came from the move to fuel-injected engines, which vastly improve engine efficiency and combustion. What would not have occurred without a mandate are the sealed caps on auto fuel tanks that prevent evaporation, and the evaporation abatement nozzles on gas pumps. This is why, for example, a pre-1970 car parked in the driveway with its engine shut off will emit more VOCs through evaporation than a new car running at 60 mph on the highway."