"Dark clouds of soot and gases spewed by tractors, bulldozers and backhoes are becoming a thing of the past under new federal standards that have forced cleaner diesel engines this year.
While trucks and buses have been cleaned up, it’s taken years longer for farm and construction equipment to keep pace.
That’s because these diesel-powered vehicles come in many shapes and sizes, all with different workload demands, and there aren’t always convenient places to slap a filter on their engines.
A variety of new technologies are producing cleaner farm and construction machines. Included are lower-sulfur diesel fuel, particle-trapping filters and more efficient engines with fuel-injection software, recirculated exhaust systems or catalysts that prevent pollutants from forming."