THE OZONE STANDARD TECHNICAL ISSUES
| Jurisdiction | United States |
(Nov 2007)
THE OZONE STANDARD TECHNICAL ISSUES
Senior Program Manager
ENSR International
Fort Collins, Colorado
Introduction
Compliance with the National Ambient Air Quality standard for ozone continues to be perhaps the most intractable ambient air quality problem. The complexities of ozone formation in the troposphere are still undergoing basic research regarding reactivity, the effect of specific emissions, transport, and modeling issues. The current standard is 0.08 parts per million (ppm) measured as the average of the fourth-highest readings over three years at any monitor in an affected region. A proposed rule reduces that standard to 0.070 or 0.075 ppm, and offers optional means of demonstrating compliance. Compliance with the current standard is still not attained in many locations, including the western United States, and a further tightening of the standard will bring added compliance concerns for a wide range of industries as well as agencies that regulate automobiles and traffic.
This paper summarizes key technical issues that are relevant to demonstrating compliance with the current and future standard. It discusses the proposed standards, and summarizes the U.S. Environmental Protection Agency's (USEPA) analysis of projected compliance based on current measurements.
For areas that are ultimately designated as non-attainment, the regulatory agency will be required to implement a plan that demonstrates that it will achieve attainment. An important aspect of that demonstration is the use of a meteorological and photochemical model which will be used to relate control strategies to the resultant ozone concentrations. The paper also summarizes technical issues related to modeling ozone concentrations based on specified source input data.
Summary of Proposed Standard and Projected Compliance
The proposed revisions to the ozone standard were published in the Federal Register on July 11, 2007.1 The proposed primary standard, 0.070 to 0.075 ppm, is set at a range wherein the USEPA is soliciting comments on the level of the standard. The proposal also specifies that the standard be evaluated at the nearest thousandth of a ppm. This is an important change from the past implementation which allowed a "rounding" to the hundredths of a ppm. In effect this proposal tightens the standard from 0.084 ppm to
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0.070 or 0.075 ppm, which is a reduction of some 18 percent of the current effective standard. The USEPA expects to use the measured levels for 2007-09 to evaluate attainment status as of 2010. States may submit requests for designations in 2009. Following attainment designations, agencies would have until 2013 to finalize a State Implementation Plan for non-attainment areas, with attainment dates scheduled to be achieved between 2013 and 2030, depending on the severity of the non-attainment.
The proposed regulation also solicits comment on the level of the ozone standard, ranging from 0.060 ppm up to the current standard, with its convention of rounding the levels (0.0849 would be in compliance). There is no indication that the classification levels for non-attainment (basic, marginal, moderate, severe 15, severe 17, or extreme) will change. Presumably the attainment dates ranging until 2030 will be based on the same compliance requirement for each classification level. Figure 12 shows the likely attainment status by county for the 0.075 ppm primary standard, across the country, based on the 2004-2006 data. The map clearly shows a concern in the Denver area as well as in northwestern New Mexico (San Juan, Sandoval, and Bernalillo [which includes Albuquerque] Counties) and Southeast Utah (San Juan County). All except Bernalillo County would be attainment under the higher 0.075 ppm standard. The urban Front Range of Colorado and the Salt Lake City metropolitan areas are slated for non-attainment status under both standards, with neighboring counties triggered only for the lower standard.
Figure 2 shows projected attainment status in 2020 (also footnote 2) based on projected development and trends, as well as evolving requirements for controls under the Clean Air Act. Note that USEPA could not make projections for some monitoring sites, including some cited above. It is also important to note for the minerals development industry that all of Wyoming and most of western Colorado are not slated for exceedances under either of the new standards. There are no current ozone monitoring sites in western Colorado. However, it is not clear that a solid trend in industrial development was included for these selected areas.
The proposal also includes a secondary ozone standard, which is promulgated based on ozone's effect on vegetation and crops. Since the effect on crops is essentially chronic, involving long-term exposure, EPA proposed a cumulative concentration-related form of the standard. The standard is expressed as a sum of weighted hourly concentrations, cumulated over the 12-hour daylight period (8 a.m. through 7 p.m., not specified as daylight or standard time), using the three month period with the highest index value. The formulation is based multiplying each hour's concentration by a weighting factor, and then summing the values using a Sigmoidal weighting function, where the weighting factor is as follows...
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