Unlike a new engine, the lubricating oil is a dominant contributor to particulate matter (PM) emissions in aged engines. The obvious strategy to control / reduce hydrocarbon emissions is to reduce oil consumption. This, of course, points to a strategy of reducing abrasion and wear. According to projections by Barris of Donaldson Co. after 12,000 hours of service, an off-road diesel engine can produce nearly six times more exhaust emissions due to wear associated with particles and other causes.
Reference: Jim Fitch 'Clean Oil Reduces Engine Fuel Consumption'