Fourteen largest cities in the country, including the four metros, are scheduled to shift to which of the following vehicular emission norms from April 1, 2010?

India follows the Bharat Stage (BS) emission standards for vehicular pollution, which are based on European norms. The implementation was phased across major cities first. On April 1, 2010, fourteen largest cities including the four metropolitan cities (Delhi, Mumbai, Chennai, Kolkata) upgraded from Bharat Stage III to Bharat Stage IV norms. This was part of a planned environmental policy to reduce vehicular emissions in densely populated urban areas. BS-IV introduced stricter limits on pollutants like carbon monoxide, hydrocarbons, and nitrogen oxides.