Indeed, the EPA has steadily increased the stringency of particulate matter (PM) standards over the years (these have an impact on car/engine design and fuel (s

Indeed, the EPA has steadily increased the stringency of particulate matter (PM) standards over the years (these have an impact on car/engine design and fuel (sulphur and nitrogen content)); you can find more information here: http://www.epa.gov/pm/ http://www.epa.gov/pm/