A quantitative assessment of the impact of gas phase toxic emissions from motor vehicles on public health and welfare

Gas-phase mobile sources air toxic (MSAT) emissions were measured for gasoline, diesel vehicles and engines and investigated in a number of studies dating back to the 1970s and early 1980s. Data reported here showed large reductions in the airborne toxic emissions over the years as a result of improved emissions control technology and the introduction of cleaner fuels. It is expected that the emissions of these compounds will continue to be reduced further in the future with the introduction and proliferation of even more advanced technology vehicles. For gasoline vehicles, the catalytic converter provides about 50 to 80% reductions of MSAT emissions for oxidation catalysts (OCs) and 80 to 99%+ for three-way catalysts (TWCs) vehicles compared to non-catalyst (NC) vehicles, with conversion efficiencies for today's modern vehicle reducing toxics by >98%. A decrease of 69 to 85% in MSATs emissions is observed for diesel vehicles equipped with OCs compared to uncontrolled diesel vehicles. The reduction of MSAT emissions is more than 70% for diesel vehicles equipped with catalyzed diesel particulate filters (DPFs). Gas-phase toxic emissions also showed a strong dependence on driving conditions. Generally, fuel effects are smaller than those that can be obtained with more advanced aftertreatment. The emission rates for each of these MSATs will remain a reasonably constant percentage of the total organic gases (TOG) regardless of control technology, certification level and in-use emission rate.; The average ambient concentrations for MSATs were measured for indoor and outdoor air in Mira Loma, California and analyzed for Los Angeles, New York City, Washington DC, Atlanta, and Houston from 1987 to 2002, respectively. The indoor concentrations of air toxic compounds were higher than the outdoor concentrations. Formaldehyde, acetaldehyde, and acrolein concentration levels in indoor air exceeded the California chronic reference level (REL) or the EPA reference concentration (Rfc). The ambient concentrations of these compounds were relatively consistent for all of the cities. The ambient concentrations of benzene, 1,3-butadiene, and acetaldehyde were considerably below the EPA RfC. Acrolein was the only compound that has ambient concentrations above the EPA threshold. The MSATs concentrations are expected to be reduced as emissions of hydrocarbons are reduced in the future. Finally the MSATs emission inventories and ambient concentrations are estimated for the Los Angeles Basin for next 20 years and the continuous decreases of MSAT emissions and ambient concentrations are expected in future.