Particulate Matter Associated with Vehicles on the Road. II

Abstract

Experiments at the Allegheny and Tuscarora Mountain Tunnels of the Pennsylvania Turnpike in 1975–1979 have resulted in a comprehensive description of the airborne particulate matter associated with highway traffic. Because of strong variations of traffic composition with time, emission rates of most species were resolvable into emission rates for each of the two vehicle categories: gasoline-powered vehicles and heavy-duty diesels. Thirty-four elements were identified, accounting for all of the vehicle-derived airborne particulate mass. The principal component was carbon (elemental and organic) from exhausts of heavy-duty diesels, which comprised on the average 10%–15% of the traffic. Per vehicle-kilometer, diesels were the preponderant source of most of the other species as well. Other emissions resulted from oxidation of diesel-fuel sulfur to H₂SO₄ (5% of the particulate mass total for traffic overall), inorganic additives and adventitious components of fuels and motor oils (10% of the overall mass total, over half of it Pb), tire wear debris (1%), and soil dust (10%), leaving unidentified the origins of only ∼3.5% of the mass. Soil dust accounted fully for seven of the elements and a prominent share of at least nine more. Size distributions of the component species proved to be generally consistent with the putative origins. The gross mass median aerodynamic diameter was 0.15 μm, similar to diesel exhaust particles. Comparison of compositions reported here with compositions of urban and rural ambient-air particulate matter leads to estimates that the primary particulate matter from vehicles can account for most ambient airborne particulate Br and Pb; much of the C., H, Ba, and extractable organics; a measurable share of the Mn, Mg, Ca, Sr, CI, and P; and inconsequential amounts of the others. It appears to account for ∼ 11% of the airborne [pacute]articulate mass in cities and ∼2% in a remote rural area in the Northeast.