The chief executive of Volkswagen AG said Wednesday that he is stepping down in the wake of the scandal that broke Friday over the company’s use of special software to thwart U.S. emissions standards. “I am shocked by the events of the past few days,” Winterkorn said in a statement. “Above all, I am stunned that misconduct on such a scale was possible in the Volkswagen Group.” Volkswagen shares rose on the news and were last up 7.5%. The stock has lost about 30% of its value since the Environmental Protection Agency said Volkswagen used a sophisticated software algorithm that detected when cars underwent emissions tests, turning on full emission controls only during the tests but not during normal driving conditions. Winterkorn said the company needs a fresh start, “also in terms of personnel.” Volkswagen said about 11 million cars are affected and apologized to its customers for breaching their trust.