Policy Summary: The Major Policy-Relevant Findings of SOS

Ozone Abatement in the South:

• Ozone managment strategies that focus on decreasing nitrogen oxide emissions will be more effective in decreasing ozone concentrations in the rural South and in Atlanta and similar urban centers than strategies that focus on decreasing anthropogenic emissions of volatile organic compounds.

Regional Chemical Climatology:

• No significant change was obxerved in the average ozone concentration in most rural and urban areas of the South from 1980 to 1992. This occurred despite the sizable investments made in volitile organic compound emissions controls in the region, and possibly because of the significant economic growth of the region over the period.
• During the summer months of many of these years, high concentrations of ozone occurred in rural as well as urban areas of the South.
• Ozone concentrations in rural areas of the south were not as high as in urban areas, but they frequently were high enough to inhibit photosynthesis in the region's extensive crops, forests, and ornamental plants.
• Because of these high rural ozone concentrations, revision of the current ozone standard, or promulgation of a secondary ozone standard based on longer averaging time but a lower ozone concentration, could cause large portions of the rural South to be designated for ozone non-attainment.
• Because of the different temporal patterns of ozone episodes in rural and urban areas of the South, the promulgation of an ozone standard based on longer averaging times will tend to shift the regulatory focus in the South from urban centers to more rural areas.

Urban Non-Attainment:

• Maximum ozone concentration in Atlanta can occur downwind of the city center but within power plant or similar point-source plumes as they emerge from the city. These point-source plumes occur within a more general urban ozone plume from biogenic, mobile, and other area sources, which, in turn, is embedded within a wide spread regional tide of enhanced ozone concentrations.
• This phenomenon of plume coverage suggests that ozone non-attainment events in the South can occur when enhanced ozone concentrations within the region, the urban plume, and smaller-scale point-source plumes intersect, producing a cumulative ozone concentrtion in excess of the standard.

Emissions:

• The primary source of nitrogen oxides in the South is the burning of fossil fules in power plants, industrial boilers, motor vehicles, and other internal combustion engines. Nitrogen oxides also are emitted during the burning of biomass -- in open fields, recovery furnaces of pulp mills, other space and water heating furnaces stoves, incinerators, etc. and from well fertilized crop lands, pastures and lawns. Under some meteorological conditions, nitrogen oxide production from lighting may be significant.
• Natural emissions from vegetation, principally trees, are the dominant source of volatile organic compounds in the rural South and a significant source of those compounds in many southern cities. Isoprene is typically the most significant biogenic ozone precursor.
• On-road measurements in two interstate highway tunnels indicate that the latest vehicle emissions models developed by EPA's Office of Mobile Sources (MOBILE 4.1 and MOBILE 5.0) provide reasonably good estimates of volatile organic compound, carbon monoxide, and nitrogen oxide emissions from a fleet of well maintained vehicles operating under highway conditions. It is therefore likely that these emissions models underestimate the emissions of the fleet of vehicles operating under urban conditions.
• On-road tests in Atlanta suggest that severe power enrichment caused by acceleration and other heavy engine loads is a major souce of carbon monoxide and a significant source of volatile organic compound eissions from motor vehicles.

Attainment Demonstration For Atlanta Using UAM:

• Urban Airshed Model (UAM) simulations for the Atlanta metropolitan area using EPA State Implementation Plan guidelines suggest that a 90% decrease in nitrogen oxide emissions will be required to bring Atlanta into attainment with the present ozone standard. These simulations also suggest that complete elimination of anthropogenic volatile organic compounds emissions will decrease peak ozone concentrations in Atlanta, but still leave parts of the metropolitan area about 20 ppbv above the present ozone standard under some meteorological conditions.
• Analysis of the UAM simulations for the Atlanta metropolitan area using EPA State Implementation Plan guidelines indicates that the model, and/or its application following these guidelines, have significant technical deficiencies. These deficiencies include: An inability to simultaneously reproduce observed concentrations of oxone and its precursors, and an inaccurate representation of urban wind fields and thus an inaccurate reproduction of the direction, altitude, and dispertion of the urban ozone and precursor plumes. Because of these deficiencies, the conclusions drawn from UAM simulations using EPA State Implementation Plan guidelines cannot yet be viewed with confidence.