The International Council on Clean Transportation

Since the mid-1990s, developed countries have steadily tightened limits on passenger vehicle emissions of NO_x, SO_x, carbon monoxide, particulates and other toxic pollutants. Developing countries have followed suit, usually basing their standards on either US or European regulations. Similarly, regulators in most of the 10 largest motor vehicle markets have decreased the concentration of sulfur allowable in gasoline and other fuels, both to reduce SO_x emissions and improve the performance of catalytic converters and other pollution control devices that are fouled by the contaminant. These charts show the progression of existing and proposed standards for toxic pollutants and gasoline sulfur content from 2005 to 2014 for the world's top 10 vehicle markets, plus Thailand.