From the L.A. Times:
Farm equipment manufacturers are rolling out cleaner tractors to meet stricter new federal air regulations, but many in the industry say the challenge will be getting farmers to put the high-priced models into fields during hard economic times.
The rules that went into effect Saturday apply to tractors, construction vehicles and other so-called nonroad equipment. The U.S. Environmental Protection Agency says the vehicles are major sources of particulate-matter emissions — the stuff that makes smoke black and air difficult to breathe.
Federal air standards have been tightening since the mid-1990s. The 2011 regulations are the latest step, requiring that diesel engines built starting this year produce even fewer of the nitrous oxides that can cause acid rain.