Assessment of the Effects of the Tier 2/Low Sulfur and Other Mobile Source Emission Control Strategies on Ozone Nonattainment using High-Resolution Photochemical Modeling

摘要

In support of EPA's Tier 2/Low Sulfur mobile source control rulemaking, EPA performed photochemical modeling using three Ozone Transport Assessment Group (OTAG) databases to assess the effects of the mobile source rule on ozone concentrations in the eastern U.S. Mobile source emissions have the highest density in urban areas. The OTAG photochemical modeling databases were designed to assess regional ozone transport so a coarse horizontal resolution (36/12-km) was used that inadequately characterizes urban photochemistry. In this paper we discuss the application of high-resolution photochemical modeling of the Tier 2/Low Sulfur and other alternative mobile source technology and fuel control strategies focusing on the Northeast Corridor, lower Lake Michigan, and Houston areas. The Comprehensive Air-quality Model with extensions (CAMx) was used with fine grids (4-km) covering the Northeast Corridor, Lake Michigan and Houston areas. The ozone impacts in the three urban areas due to alternative mobile source control scenarios were assessed for the year 2007 and three different motor vehicle technologies, NLEV, Tier 2, and the Alliance of Automobile Manufacturers (AAM) alternative to Tier 2. In addition, the ozone impacts due to three different gasoline sulfur contents, current, 30 ppm at 5 ppm were also analyzed for the year 2007. The effects of the alternative control strategies on 1-hour ozone nonattainment was assessed using design value scaling methods similar to EPA's draft 8-hour ozone modeling guidance. The effects of the alternative mobile source control strategies on 2007 peak ozone and daily maximum ozone concentrations in the Northeast Corridor, Lake Michigan, and Houston areas and vicinities were also examined. The study found that the AAM alternative to Tier 2 motor vehicle control technology provided the same 1-hour ozone attainment benefits as Tier 2 and that use of lower sulfur fuel results in more ozone benefits than Tier 2. The high-resolution (4-km) grids provided a better characterization of urban photochemistry including a better representation of the effects of NOx emission reductions on urban ozone concentrations.