Trucks are the mules of China’s spectacularly expanding economy — ubiquitous and essential, yet highly noxious.

Trucks in China burn diesel fuel contaminated with more than 130 times the pollution-causing sulfur that the United States allows in most diesel.

The 10 million trucks on Chinese roads, more than a quarter of all vehicles in China are a major reason China accounts for half the world’s annual increase in oil consumption.

Cleaning up truck pollution presents complex problems for China’s leaders.

Forcing businesses and farmers to buy more expensive vehicles could put a drag on the economy. Oil giants like Sinopec, losing money on every gallon of diesel they refine because of the low sales cost, upgrade refineries slowly, if at all.

Evan Jia, a Sinopec spokesman said, ‘Sinopec is trying our best to purchase low-quality crudes - much heavier and more sulfur content. We buy those kinds of crudes to lower the purchasing cost.’

Low state-subsidized diesel prices frequently make trucks more cost-effective than trains, which pollute less. Demand for diesel at service stations is so great, and supplies are so tight, that rationing and shortages have become common.

Since 2000, sales of heavy-duty trucks have risen sixfold while car sales have risen eightfold.

Mainland Chinese atmospheric scientists concluded in an analysis this year in The Journal of Environmental Sciences that in Guangzhou, particles were the pollutant farthest out of line with air-quality norms 226 days a year.