Prompted by accelerating auto sales , China’s oil refiners are ramping up gasoline output at the expense of diesel. The production shift away from the diesel used by trucks, power generators and farm vehicles in favor of the gasoline used by passenger autos coincides with a national drive to improve fuel standards and so curb vehicle emissions. Sharply higher motor-vehicle sales are one reason pollution is so bad in many of the Chinas cities. Vehicle emissions contribute as much as 30% of the fine particulate matter known as PM2.5—which is considered particularly hazardous—in urban air. Chinese motor-vehicle sales in 2013 were up 14% from 2012, the biggest increase in three years, according to the government-backed China Association of Automobile Manufacturers. Sales totaled nearly 22 million vehicles—including almost 18 million passenger cars, up 16%. Passenger-car sales have traditionally supported China’s gasoline demand, which was up 12% in the first 11 […]