What it is like around the rest of the world?
For customers and engine/machine manufacturers that operate on multiple continents, there will be new challenges. For North America and Europe, Tier 4a is very similar to Stage III B in Europe and Tier 4b is similar to Stage IV. NA and Europe are what is referred to as "harmonized" - when the emissions and implementation timeframes are the same (or close enough). Japan will likely introduce regulations similar to and in the same timeframe as the EU and North America.
Tier 4 regulations require the use of Ultra Low Sulfur Diesel (ULSD) (15ppm down from 500ppm sulfur). This of course is the same fuel required by 2007 on-highway truck and becomes effective for off-road in June 2010. Lower levels of sulfur produce less PM and sulfur dioxide. Generally ULSD is also required to allow the use of catalysts in some emissions control system. Emissions and fuel regulations are not the same and can very greatly around the world. As we move into Tier 4a, we will be forced to have different solutions in different parts of the world due to fuel availability.