The emission standards prescribed by the European Parliament specify emission limits for HC (hydrocarbons), CO (carbon monoxide), NOx (nitrogen oxides), and particulates with regard to all newly registered vehicles in Europe. Different limits apply to diesel and gasoline engines. The Euro 6 standard, which introduces much stricter limits on nitrogen oxides in diesel-powered vehicles, came into force for passenger cars in 2014. As from September 1, 2017 the new standards 6c and 6d-TEMP have been in force. These stipulate more stringent test procedures. Effective from 2014, Euro 6 also imposed drastic reductions on heavy truck emissions of NOx, in particular, but also HC and CO.