Review of the NARSTO Draft Report: An Assessment of Tropospheric Ozone Pollution--A North American Perspective (2000)

This is the first report prepared by the National Research Council (NRC) Committee to Assess the North American Research Strategy for Tropospheric Ozone (NARSTO) Program. (Biographical information on the committee members is presented in Appendix A). According to its statement of task, the committee's responsibilities include the review of the strategy and draft products produced under the auspices of NARSTO. Further, it is charged to offer guidance on scientific questions, integration and assessment, as well as short- and long-term balance issues and research priorities. The committee is also charged to monitor NARSTO program activities, progress, and products over time. The committee is expected to consider the regional programs of NARSTO, including the Southern Oxidants Study¹ and others formed in various regions of the United States, Canada, and Mexico. The committee is charged to place within its purview all such programs, not just those of the U.S. Environmental Protection Agency (U.S. EPA). Notwithstanding this broad charge, this report, at the request of NARSTO, is more-narrowly focused on a review of a draft document prepared under NARSTO, “An Assessment of Tropospheric Ozone Pollution: A North American Perspective.”²

The committee met three times to consider matters brought before it and to develop guidance and reactions to NARSTO program participants. At each of those meetings, open sessions were held during which committee members heard presentations from NARSTO representatives and obtained information used in preparation of this first report. At its second meeting, the committee heard presentations regarding lessons learned from past science-policy assessments.

This committee's report comes at an important juncture in the NARSTO program. Substantial research has been motivated by previous reviews of the state of atmospheric science that were conducted in the early 1990s and presented, among other places, in the NRC document Rethinking the Ozone Problem in Urban and Regional Air Pollution (NRC 1991 ). As an update of those efforts, 24 critical review papers were prepared under NARSTO summarizing research developments. (The titles and authors of those papers are presented in Appendix B.) One of those papers (Solomon et al. In press) estimates that upwards of $600 million was spent over the past decade in North America and Europe to understand the atmospheric production and transport of ozone and to analyze the opportunities for control of ambient ozone concentrations. Much of those efforts involved large-scale field studies designed to test the new understandings that have developed. Substantial progress in achieving scientific understanding has occurred.

Ambient ozone concentrations continue to exceed ozone air-quality standards or objectives at many locations in Canada, Mexico, and the United States. According to the NARSTO assessment document, it is estimated that 14 million people in Canada, more than 20 million people in Mexico, and about 70 million people in the United States lived in or near areas where ozone concentrations violated the respective national ozone target concentrations in 1995. (Those are concentrations that, if exceeded, are considered to be detrimental to human health or to cause significant damage to plants.)

Throughout the 1990s, the United States has aggressively implemented an expansive and costly control system to lessen emissions of ozone precursors, and has been successful in reducing ozone concentrations substantially below what they would have been without regulation. Nonetheless, in many locations, that system has failed to achieve compliance with applicable ozone standards. Furthermore, based on a reading of the NARSTO assessment document, one gets the sense that there is little prospect that continuation of similar efforts would change this picture markedly. One of the primary motivations for NARSTO is to advance scientific understanding to increase the efficacy and efficiency of emissions-control efforts.

Complicating this task, in July 1997, the United States altered its ozone-control regime and compliance targets in response to findings that longer-term exposures can have health impacts at concentrations below those at which short-term exposures were expected to result in negative health effects.³ These changes result in ozone target concentrations that are even more difficult to reach than those replaced. Also in July 1997, standards for airborne particulate matter with diameters at or below 2.5 microns have been established, even further complicating the picture.⁴ Particulate matter is a pollutant related in origin and in control mechanisms to ozone.

In May, 1999, a panel of the U.S. Court of Appeals for the District of Columbia Circuit remanded the 1997 changes in the National Ambient Air Quality Standards for ozone and particulate matter.⁵ The court has required U.S. EPA to provide more explanation of its decision-making process and criteria in setting the standards. In October 1999, U.S. EPA

proposed reinstating its 1-hr standard for ozone while it appeals the court's remand decision.⁶ There is some uncertainty as to the potential impact of the court 's decision. Whatever the resolution of such legal proceedings, public health and environmental concerns about ozone and particulate matter will remain. Efforts to pursue important scientific research on ozone and particulate matter continue to be important.

In Canada and Mexico, the emissions-control strategies are different but the problem is the same: continuing failure to provide air quality that meets health goals. Special problems exist in some major urban areas, such as Mexico City, where ozone concentrations are frequently high and where efforts to reduce them have been generally unsuccessful. Although maximum ozone levels have been lower in recent years than they were, for instance, in 1992, the ozone concentrations were below the Mexican air-quality standard for only 12% of the days in 1997 and 13% of the days in 1998 (Aldana et al. 1999). The ozone problem is complicated because coordinated efforts are required within the frameworks of control adopted by the individual countries, especially in the border areas where Canada and Mexico join the United States.

It is at this juncture, where future research must be planned and where emissions-control systems are in flux, that the NARSTO assessment document was produced. Chapter 2 of this report discusses the intended roles of NARSTO as reflected in the assessment document. Chapter 3 reviews the NARSTO assessment document—and the scientific activities on which it reports—from the perspective of its contribution to resolving the challenges of ozone control and providing a clear direction for future effort. Chapter 4 considers opportunities for strengthening ozone management. Chapter 5 presents the committee's observations concerning a path forward for NARSTO and for ozone management.