There is some emissions regulation of older in-field equipment going on, most notably in California where the Air Resources Board has required the use of exhaust aftertreatment on machines within certain age ranges, and virtually banned some of the oldest machines (horsepower and age dependent). Those regs have been written about extensively on this forum.
Various other jurisdictions have regulated in-use diesel emissions (as opposed to just regulating new diesels) as well: the New York City metro area, New Jersey, Cook County, IL, and others.
The motivation for these regs comes from the Clean Air Act. EPA develops standards for air quality based on levels of pollution that do not threaten human health, monitors air quality throughout the nation, and has the authority to penalize states in which there are areas that do not meet the clean-air standards (so-called "nonattainment areas").
One of the penalties at EPA's disposal is withholding federal funding to a state with poor air quality. Not good. So the states pass the buck down to political authorities responsible for the nonattainment areas -- counties, municipalities, sometimes coalitions of local and regional governments -- to come up with plans to comply with EPA air-quality standards. When those with the most tenacious air-quality problems consider sources of regulated pollutants, they cannot overlook the amount of particulate matter and oxides of nitrogen (a component of smog) that older diesel engines emit.
The Feds have to walk the walk, so they've developed a process for limiting diesel emissions from projects with large federal funding elements taking place in nonattainment areas. Projects going back as far as Boston's Big Dig and Chicago's Dan Ryan Expressway rehab had limits on diesel emissions from contractors' equipment written into project specifications. They used similar specs the O'Hare Airport expansion on the Illinois Tollway authority adopted similar procedures for Chicagoland work. Retrofits of exhaust aftertreatment can satisfy those bid requirements.
I'm not familiar with exactly how those contract clauses are written, but I do know that contractors who worked out at O'Hare were buying new equipment to do the work in part because they had cleaner exhaust emissions. It helped them satisfy the bid specs.
I know the Chicagoland Cat dealer, Patten, has also been doing big business in machine repowers -- fitting older scrapers and big dozers and loaders with newer, cleaner-burning engines for a couple of years. They (and I'm sure other dealers in nonattainment areas) have helped Cat develop part-numbered repower procedures for specific machine models where the return on investment works.
The Feds have also supported engine upgrades and exhaust-aftertreatment retrofits with the
Diesel Emissions Reduction grants for the past five or six years. States like Texas (TERP, I thnk it's called) have had similar grant programs for a while. President Obama signed legislation early this year that authorizes up to $100 million each year for the DERA program for fiscal years 2012 through 2016. Not sure what any of those programs will look like in a year, given the current federal and state budget environments.
Don't get carried away by the scuttlebutt. It's hard to say what the long-term impact of emissions control technologies will be on diesel engines. While there are cases of equipment owners having problems that might be related to a diesel particulate filter or other emissions equipment an engine, there are LOTS of low-emissions diesel engines out there working pretty much like they did before the equipment was added; by and large, a technological non-event.
Here's what some were saying about on-highway engines that met EPA's 2007 emissions standards:
Truck Owners Testify to Green-Diesel Performance. The technologies used on-highway in 2007 -- diesel particulate filters and exhaust-gas recirculation for the most part, with some like Mercedes using selective catalytic reduction and an oxidation catalyst with injected DEF -- are very similar to what we're seeing now on the higher-volume 75 hp to 175 hp off-road diesels.
Hope this helps,
Larry