Development and Comparison of 1990 and 1996 Mobile Source Hazardous Air Pollutant Emissions Estimates

摘要

In support of a variety of regulatory and policy activities, a hazardous air pollutant (HAP) mobile source inventory was developed for inclusion into the National Toxics Inventory (NTI). This inventory includes estimates for onroad, aircraft, and nonroad equipment for 21 HAPs for the years 1990 and 1996 (1995 for commercial aircraft, because 1996 data were not available). During this period, overall HAP emissions from U.S. mobile sources declined 10 percent, with the greatest decline associated with onroad emissions. Despite a 16 percent increase in national vehicle miles traveled (VMT), total onroad emissions declined by 16 percent. This decline in onroad emissions was attributed to the introduction of winter oxygenated and reformulated fuels, as well as the phase-out of leaded onroad fuels. The reduction in HAP emissions for individual HAPs, except methyl tertiary butyl ether (MTBE), was even greater. (In 1990, MTBE was included in premium gasoline and in some oxygenated gasoline programs in the Southwest, but overall, its use was very limited; therefore, 1990 MTBE emissions were not quantified.) Total aircraft emissions increased by 6 percent between 1990 and 1996, despite the fact that aircraft activity increased quite significantly in that same time frame. This is true especially for commercial aircraft, which accounted for 84 percent of aircraft emissions in 1996. Though commercial aircraft activity increased by approximately 17 percent during this period, the emissions for this type of aircraft increased by only 8 percent. This decrease is a result of a Federal Aviation Administration (FAA) mandate to reduce noise pollution by year 2000 by phasing out older, less efficient aircraft, which also tend to be the higher polluting types of aircraft. Of the three mobile categories included in this inventory, nonroad emissions had the largest percent increase. Between 1990 and 1996, nonroad emissions increased by approximately 7 percent. Many of the individual pollutants showed declines which paralleled the decline in volatile organic compounds (VOC) and particulate matter (PM) emissions, but several pollutants showed increases in emissions. One such pollutant was MTBE, which was not quantified in 1990, but accounted for 12 percent of the total nonroad HAP emissions in 1996. Most of the other increases in nonroad emissions were attributed to increased diesel emissions. Though total nonroad VOC emissions declined, diesel nonroad VOC emissions increased during this period.