A new EPA standard for the sulfur content in diesel fuel sold in the United States beginning in 2006. This applies to all diesel fuel sold for use in road-going vehicles. The allowable sulfur content (15 ppm) is much lower than the previous U.S. standard (500 ppm), which not only reduces emissions of sulfur compounds (blamed for acid rain), but also allows advanced emission control systems to be fitted that would otherwise be poisoned by these compounds. These systems can greatly reduce emissions of oxides of nitrogen and particulates.