as of now all on and off road Diesel is ULSD. ultra Low Sulfur Diesel. Less that 15ppm. Now some Marine diesel fuel has higher sulfur concentrations. But most of it is still under 500ppm. Now many people overlook the very few advantages of Acid rain, actually most people dont know there are advantages. Certain plants such as alfalfa, require sulfur as a nutrient. Acid rain always provided this, but with acid rain gone, we now have to apply it to fields. The above is true, but somewhat of a joke. Acid rain is bad, its not very hard to apply sulfur to fields, it just gets mixed in with other fertilizers. As for NOX. That is also controlled now. That is what the 2010 emissions standards focused on for on-road diesels. Many OEs opted for the easy way out by using Selective Catalytic Reduction. (SCR). Know by many as Urea Injection. Basically Liquid Urea (Diesel Exhaust Fluid (DEF)) is injected into the exhaust stream in a catalyst after the Diesel Particulate filter. The urea reacts with the NOX and converts it to Nitrogen, Water and a small trace of CO2. Its a very simple setup. It does add an additional upfront cost due to the cost of the equipment and it does also require an additional maintenance cost throughout the vehicles life. DEF is $4-7 per gallon and on passenger vehicles, the tank gets refilled every oil change (manufacturers suggested miles). This is mandated by the EPA that the tank be large enough to allow this. On commercial trucks the tanks usually last for a few tanks of fuel which on a commercial truck is a minimum of 100 gallons of fuel on board and can be as high as 400 gallons. How much DEF these systems burn i really cant say, they are brand new in the US(except for the Mercedes Benz Diesels). But I do know the new Duramax has a 5.5 gallon tank, and the OCI is 7,500 miles. Thats on a 397hp/765lb tq engine. So the added cost isnt a lot. Now there is AdBlue, MBs DEF. Its something ridiculous like $35/gallon. But its no different than generic DEF. Truck stops are in the process of installing DEF pumps. Now if you are a farmer reading this, you cannot just put granular UAN urea into the tank. And for some of the people who payed attention in chemistry, no you cannot pee in your DEF tank. The tanks have sensors in them to determine what is in them ,and if the wrong fluid is in there it will shut down the vehicle. Same happens if you run out. Now it does give you a grace period to get to a DEF station. But it does this under reduced power. and if you run out in the middle of the desert you may be out of luck. Other manufacturers such as Cummins, relied on in cylinder technology on their 6.7L to meet the emissions standards. But in order to accomplish this they had to reduce the compression ratio, increase the EGR cooler size and put more Exhaust gas into the cylinder. All of this is done to reduce the combustion temperature. a cooler burn in the cylinder reduces NOX emissions, but it also reduces power and reduces fuel economy. Which is why the B series cummins jumped .8L. SCR will always provide better fuel economy than a large EGR system with lower combustion temps. A hotter burn is more efficient and SCR allows a very hot burn. A hotter burn also reduces particulate emissions meaning fewer DPF regens. Then there is the VW TDI. They went one step further and come out with the best of the best. They put cylinder pressure sensors in the glowplugs and used Piezo injectors to alter the amount of fuel put into each individual cylinder for each injection event. By only giving the cylinder the amount of fuel it needs, and by using piezo injectors to inject the fuel multiple times per event, they were able to meet the stringent 2010 emissions standards. Now for Off-Road vehicles the same emissions regs are coming. 2013 is the date. 2011 is when the NOX standards go into effect, 2013 is when the particulate emissions go into effect. Agco has already put SCR on their tractors. CNH announced it would also be using SCR, and Deere announced they would be going the rout of Large EGR coolers and lower compression. However currently, off road emissions regulations only cover engines up to 800hp. Engines over 800hp are exempt, thus why most large ships dont have emissions regs.