Highway motor vehicles as sources of atmospheric particles: Projected Trends 1977 to 2000

Abstract

Highway motor vehicle emissions contribute to the total atmospheric particulate matter burden. The possible health and welfare effects of these emissions depend upon their composition and concentration in the atmosphere, the exposure of man and materials, and in some instances the length of time of the exposure. The characteristics of long-term national and mesoscale (citywide) exposures and short-term localized (congested freeway, city street canyon) exposures to mobile source particles were examined for 1977 and 1988, and estimated for 2000. Because of interest in the possible impact of passenger car dieselization on atmospheric particle concentrations, three degrees of diesel penetration (5%, 10% and 20% of light-duty sales by 2000) were examined with and without an assumed scenario of particulate matter emissions regulation. Generally, urban concentrations of mobile source particles ranged from about 2 to 10 μg/m 3 in 1977; lower concentrations occurred in suburban areas and higher concentrations occurred in city central core areas. However, concentrations of nearly 80 μg/m 3 could be experienced on congested freeways with low velocity, near parallel winds. Due primarily to decreases in the number of vehicles using leaded gasoline, the mobile source particulate matter burden is projected to be less in 1988 and 2000 than in 1977; the degree to which the burden will lessen depends upon the level of dieselization and the degree of regulation. The compositional characteristics of the particles will also change. The outyear fractions of lead will decrease and the fraction of elemental and organic matter carbon will increase. Heavyduty diesel motor vehicles will become the single most important source of mobile source particles. Knowledge of vehicle usage patterns will then become important for classical dispersion model estimation of emissions impact, since truck kilometer traveled will likely not be uniformly distributed across cities.