2 January 2001

On 20 December 2000, the US EPA has signed the Final Rule to Control Emissions of Hazardous Air Pollutants from Mobile Sources, commonly known as the “Air Toxics” rule. Overshadowed by the coincident adoption of the 2007 emission standards and diesel fuel rule, the event went almost unnoticed. However, even though the air toxics rule does not implement any additional diesel fuel or diesel emission control measures, it does for the first time at the federal level identify diesel particulate matter and diesel exhaust organic gases (collectively DPM+DEOG) as a Mobile Source Air Toxic (MSAT).

Unlike the provisions governing toxic emissions from stationary sources, the Clean Air Act does not provide a list of motor vehicle air toxics. The new rule identifies 21 compounds as MSAT, as shown below.

List of EPA Mobile Source Air Toxics
AcetaldehydeDiesel Particulate Matter + Diesel Exhaust Organic Gases (DPM + DEOG)MTBE
AcroleinEthylbenzeneNaphthalene
Arsenic CompoundsFormaldehydeNickel Compounds
Benzenen-HexanePOM *
1,3-ButadieneLead CompoundsStyrene
Chromium CompoundsManganese CompoundsToluene
Dioxin/FuransMercury CompoundsXylene
* Polycyclic Organic Matter includes organic compounds with more than one benzene ring, and which have a boiling point greater than or equal to 100°C.

The new rule finds that the existing programs to reduce ozone and PM inventories, including the reformulated gasoline (RFG) program, national low emission vehicle (NLEV) program, emissions standards for passenger vehicles and gasoline sulfur control requirements (Tier 2), and the 2007 heavy-duty vehicle standards and highway diesel fuel sulfur control requirements, are expected to yield significant reductions of mobile source air toxics. With regard to fuels-based controls, the rule sets certain new gasoline toxic emission performance standards. With regard to vehicle-based controls, the rule concludes that the Tier 2 and heavy-duty 2007 standards are the most stringent controls feasible at this time to reduce MSAT emissions from highway vehicles and engines.

The rule also establishes a Technical Analysis Plan to continue research and analysis on mobile source air toxics. EPA will conduct a future rulemaking, to be completed by 1 July 2004, in which the feasibility and need for additional controls for MSATs will be revisited.

Regulatory documents from EPA

Source: US EPA