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

Although efforts to reduce emissions of ozone precursors have achieved much progress, ambient ozone concentrations continue to exceed ozone air-quality standards or objectives at many locations in Canada, Mexico, and the United States. It is estimated from the most recently available data that about 14 million people in Canada, more than 20 million people in Mexico, and more than 70 million people in the United States, lived in or near areas where ozone concentrations violated the respective national ozone target concentrations in 1995. Special problems exist in some major urban areas such as Mexico City, where ozone concentrations are frequently high and more-resistant to control efforts.

Over the past decade, substantial resources have been spent and significant progress has been achieved to improve understanding of the atmospheric production and transport of ozone and to analyze opportunities for control of ambient ozone concentrations. However, tropospheric ozone has proved a complex and refractory problem. The hot and dry summer of 1999 caused elevated ozone concentrations in many areas and the potential for adverse health effects to people living in those areas.

In the United States, the 8-hour National Ambient Air Quality Standard for ozone will be harder to meet than the one it replaces. However, prospects for the implementation of the new standard are uncertain because a U.S. Court of Appeals in May 1999 remanded it for reconsideration by the U.S. Environmental Protection Agency (U.S. EPA). In October 1999, U.S. EPA proposed reinstating its 1-hour standard for ozone while it appeals the court's remand. Public health and environmental concerns about ozone will remain, whatever the resolution of legal proceedings. The need for scientific research continues to be important.

The North American Research Strategy for Tropospheric Ozone (NARSTO) is a multinational public-private program to coordinate and enhance policy-relevant scientific research and assessment of tropospheric ozone behavior, with the central goal of determining workable, efficient, and effective strategies for ozone management in Canada, Mexico, and the United States. In addition, NARSTO expects to have a critical role in informing future policy debates concerning the ambient ozone levels that can be achieved at costs that the public is willing to bear.

This report was prepared by the National Research Council Committee to Assess the North American Research Strategy for Tropospheric Ozone Program. The committee was established to review the research strategy developed under the auspices of NARSTO. The committee is charged to offer guidance on scientific questions, integration and assessment, short- and long-term balance issues, and research priorities. Also, it is charged to monitor NARSTO program activities, progress, and draft products over time. At the request of NARSTO, this, the committee 's first report, reviews a draft document prepared under NARSTO entitled: “An Assessment of Tropospheric Ozone Pollution: A North American Perspective” (referred to in this report as the NARSTO assessment document).¹

In approaching this task, the committee took into consideration the objectives of the NARSTO assessment document as described in its preface and appendix, as well as those presented in NARSTO's 1997 Strategic Execution Plan. In addition, the committee is familiar with, but does not explicitly review in this report, the 24 critical review papers commissioned by NARSTO summarizing research developments and providing a scientific basis for the NARSTO assessment document.

The NARSTO assessment document is the first major synthesis report undertaken by NARSTO; it incorporates recent changes in scientific understanding. The prime audience is to be policy-makers in North America, who are charged with implementing workable and effective ozone-control strategies. The scientific community is also an important audience. The purpose of the NARSTO assessment document is summarized in four objectives stated in the NARSTO Strategic Execution Plan: (1) provide a synthesis and evaluation of policy-relevant scientific findings, methods, and recommendations that are timely and useful for regulatory initiatives and mid-course corrections; (2) provide guidance for setting NARSTO priorities for long-term research that will extend beyond the 2- to 3-year time frame; (3) examine alternatives to current technical approaches for achieving ozone compliance; and (4) ensure that information on ozone-precursor chemistry is well integrated with related pollutant issues, such as fine particulate matter, visibility impairment, and acid deposition. As noted in Chapter 3 of this report, the assessment document did not fully succeed in meeting those objectives.

In the judgment of this NRC committee, the NARSTO assessment document provides a commendable review of selected scientific issues related to urban and regional ozone problems. The topics covered are important, and the treatment of each is careful and includes critical information that has been developed since previous reviews were conducted. The document will be of substantial utility to scientists already acquainted with ozone problems, and they will benefit from this introduction to developments outside their own fields of expertise.

The NARSTO assessment document provides a reasonably thorough and candid

discussion of various specific topics, including the shortcomings in current emissions inventories, monitoring methods for precursor emissions and ambient concentrations, and the air-quality models used to design regulatory strategies. It describes well the conundrum posed by differing impacts of ozone-precursor emissions controls in geographically diverse urban settings.

Although emissions control strategies have reduced ambient ozone concentrations substantially below what they would have been without regulation, one gets the sense after reading the NARSTO assessment document that there is little prospect of meeting ozone-control goals through a continuation of current policies. Also, it does not offer any grounds for expecting that a system can be devised to more-effectively reduce ozone concentrations at acceptable costs by optimizing the control of volatile organic compounds (VOCs) and oxides of nitrogen (NO_x).

Most of the findings summarized in the Executive Summary of the NARSTO assessment document relate to the synthesis of scientific information. Recommendations are sometimes implicit, as in the document's discussions of ambient monitoring and the impact of lower ozone standards. The discussions in the document's Executive Summary come closer than those in most other sections to suggesting recommended actions or directions. However, the reader is not provided with a clear overall path for the research needed to gain the knowledge with which to devise a cost-effective control system that could meet ozone management goals. The NARSTO assessment document does not synthesize its assessments of relevant science to make recommendations for research priorities, for either the short or the long term. The authors state that they explicitly chose not to do so, and that this task is left to other NARSTO bodies.

The NARSTO assessment document falls short as a document useful for an audience of decision-makers and other stakeholders who must manage air quality in North America. Although it is not the role of the assessment document to prescribe policies, it should directly inform them. As a policy-relevant document it should contain an orderly presentation of the major elements of the ozone problem that starts with policy goals and then lays out the issues to be resolved. It should also note where scientific knowledge appears to be sufficient, where important uncertainties exist, and where and how further research advances would assist in ozone management. Such a framework would add perspective to the specific topics selected for discussion in the document. It would also guide the presentations on each topic, and in particular would direct the authors to explain better why their conclusions are important to the policy-making community. Further, such a framework would indicate what additional information could contribute to regulatory and other governmental decisions and thereby help build a constituency to support needed research. The reader of the NARSTO assessment document, as written, is largely left to infer why topics are presented, without much guidance as to the policy significance of the findings (or uncertainties) reported.

The findings summarized in the NARSTO assessment document will be of some use to those attempting to devise alternatives for achieving ozone compliance. For example, the use of inferences from atmospheric observations (observation-based modeling) is recommended in the document as a complementary approach to determining the efficacy of VOC and NO_x control. However, the reader would benefit from a more-structured approach to explaining policy relevance—an identification of the specific implications for action in ways he or she can understand, as they are presented in the document's individual sections.

By focusing on the difficulties of the ozone-control issue without more clearly indicating what might be done to make progress, the NARSTO assessment document will leave the reader (especially the policy-oriented reader) with the sense that there is little hope for progress in ozone control. Without accepted policy-relevant research objectives or clear criteria for setting them, there is little chance that NARSTO will be able to acquire either the policy support or funding it needs to fulfill its goals.

In developing its recommendations for improving the assessment document, the committee was aware that NARSTO may decide to retain a scientific-review focus for the assessment document, and perhaps address the necessary policy-relevant aspects through some other endeavor. However, to facilitate discussions in this report, the committee presents its recommendations as if the revised assessment document were intended to have the fullest policy-relevant perspective.

The NARSTO assessment document requires an Executive Summary that is written for nonscientists interested in policy implications. The introduction to the report should include a short summary of health and vegetation effects to explain why ozone pollution is a serious problem.

The committee suggests reorganizing the scientific information presented in the document so that it better informs environmental managers and regulators. One practical way to start this process is to address more substantially the many policy-relevant questions raised by NARSTO reviewers of the initial draft. The document would also be more effective with a closing chapter that points to an action plan and to resource needs. In addition, the abstracts of the critical review manuscripts should be provided in a consistent format as an appendix. The final version of the NARSTO assessment document should be published as widely as possible, perhaps on the World Wide Web with a discussion forum.

It is important for the NARSTO assessment document to show how NARSTO 's research objectives could contribute to the identification and design of new and better control strategies. For example, it could include a discussion of the measurement and monitoring needs for compliance assessment, as well as the need for baseline data sets. It could also identify the ambient data requirements to assess whether implemented emissions management strategies were actually having the predicted effects.

The discussion in the NARSTO assessment document reviews current source-characterization efforts and monitoring networks, but it does not address whether these are adequate to meet the needs of assuring compliance. Is there a need for new instrumentation? How well are such efforts linked to the air-quality models and their needs for verification? Although the primary focus of the document is on ambient concentrations of ozone, there should be more discussion of the need for exposure data to support modeling of health and environmental effects.

A more-explicit discussion is needed of research priorities, tying these to the decision-making process and showing how new knowledge will contribute to better decisions to improve air quality. Previous integrated assessments of other problem domains, such as the National Acid Precipitation Assessment Program, should be examined for relevant insights.

The removal of systemic obstacles to rational ozone management could improve compliance and increase the effectiveness and efficiency of control programs though improved design. The NARSTO assessment document cannot be expected to resolve these difficulties, but it can and should identify them for future attention. The following, presented in no particular order of priority, are among the key opportunities for strengthening ozone management that the document authors might consider in the final version of their report.

Uncertainty analysis would provide a more-rigorous rationale for setting priorities for research and data collection. Throughout the NARSTO assessment document, there are numerous references to uncertainties in the understanding of key physical processes as well as of many inputs to models. It is important to identify those uncertainties, following already established procedures, that contribute most to uncertainties in outcomes. This requires a process for determining the magnitude of the many uncertainties, and assessing how they influence one another, as well as the final results.

The NARSTO assessment document correctly identifies the crucial importance of addressing the many uncertainties associated with emissions characterization. A discussion is needed of the characteristics and dimensions of an effort to strengthen the source characterization measurement and modeling programs, to identify other methods to estimate emissions, and to structure emissions inventories so that they are more suited to the control-strategy design process.

Adequate investments in education and training are needed to address tropospheric ozone problems. Lack of adequately trained personnel would prevent the full utilization of data that have already been collected in approximately $600 million worth of field programs. There is also a need to engage a larger scientific and technical community by clearly identifying issues that might be of interest to other scientists and engineers in areas such as statistics and data analysis, applied mathematics for combinatorial optimization, instrumentation, and meteorology.

These needs are reinforced by NARSTO's agreement to extend its scope to the formation and atmospheric distribution of fine particles, only briefly addressed in the NARSTO assessment document. The draft is largely silent on the interconnections between tropospheric ozone pollution and climate change or acid deposition. The committee believes these connections are important.