Motor vehicles have been recognized as an important contributor to air quality problems for over 40 years, almost as long as air pollution itself has been considered a public health problem instead of simply a nuisance.

Attempts to control mobile emissions began in the United States, Japan and northern Europe around 1970, amid growing concerns about unhealthy air. Until about a decade ago, direct public health impacts were the focus of auto emissions policies, which were designed to reduce emissions of the so-called “conventional” pollutants, carbon monoxide (CO), volatile organic compounds (VOCs), oxides of nitrogen (NOx) and lead, substances that either alone or upon reaction with other pollutants can cause respiratory disease, elevated cardiovascular disease risk, high blood pressure, photochemical smog formation, reduced visibility and acid deposition. Of these, the most serious (and fortunately the easiest to deal with) was lead, an additive that raised octane levels in gasoline. Today, gasoline is leadfree in most of the developed world and is being steadily phased out almost everywhere else.