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US EPA proposes Mobile Sources Air Toxics rule

20 July 2000

The US Environmental Protection Agency (EPA) has issued a Proposed Rule to Control Emissions of Hazardous Air Pollutants from Mobile Sources. The proposal identifies 21 substances that should be considered Mobile Source Air Toxics (MSATs). The list of MSATs includes diesel exhaust, as a whole, along with other compounds that result from fuel combustion in motor vehicle engines, as well as certain metal compounds.

Under the current US regulations, air toxics from motor vehicles are not identified or regulated. Unlike the provisions governing toxic emissions from stationary sources, the Clean Air Act does not include a list of pollutants that should be classified as motor vehicle toxics.

The proposal evaluates whether there are additional measures that could be put in place at this time to reduce highway MSAT pollutants. With regard to vehicle-based controls, the proposal concludes that the light-duty vehicle Tier 2 and proposed 2007 heavy duty standards, together with gasoline and diesel sulfur control, are the most stringent controls feasible at this time to reduce MSAT emissions from motor vehicles.

With regard to fuels-based controls, EPA proposes to set maximum limits on the amount of benzene that can be added to RFG and conventional gasoline. The proposed standards would require refiners to maintain their average 1998-1999 benzene levels. Benzene, classified as a known human carcinogen, is a common component of gasoline.

The proposal also sets out a Technical Analysis Plan whereby EPA will continue to conduct research and analysis and to revisit in 2003 the need for and feasibility of additional controls on toxic emissions from motor vehicles and fuels.

Proposed List of Mobile Source Air Toxics (MSATs)

Diesel Exhaust
Arsenic compounds*
Nickel compounds*
POM (Sum of 7 PAHs)*
1,3 Butadiene*
Lead compounds*
Chromium compounds*
Manganese compounds*
Mercury compounds*

Note: Substances marked with an asterisk (*) are also on the list of urban HAPs for the Urban Air Toxics Strategy, which was announced last year.

EPA Mobile Sources Air Toxics web site

Source: US EPA