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Workshop on Mobile Source Air Toxics
HEI February 8, 2000

Date:  March 16, 2000
From: Dan Greenbaum, Chair

Re:     Presentations and Summaries from the Workshop

I am pleased to provide information from the workshop "Mobile Source Air Toxics: Exposure and Risk" held on February 8, 2000 in Washington, D.C. Included on this web site is the Agenda from the workshop, an attendees list, copies of the presentations made, and brief comments from our four Respondents. As chair of the workshop, I am pleased that so many individuals were able to participate in this important event. As a result of their active contributions, we were able to illuminate the key issues, opportunities, and needs for future decisions on mobile-source air toxics.

Below, I provide below a summary of the day's proceedings based on my comments at the meeting's conclusions. In brief, the workshop highlighted four key areas:

  • The Air Toxics Issue   It seemed clear from the presentations of both EPA and  the states that the issue of air toxics risk in general, and of mobile source air toxics in particular, has gained prominence and attention in recent years. The reasons for this are diverse but appear to be linked to, among other factors, the dissemination of the results of the Cumulative Exposure Project, continued ambient monitoring by some states of air toxics, and the finalizing by EPA of the Urban Air Toxics Strategy. A number of participants noted that the exposure and health risk database for these compounds is still limited. However, several of the state and local representatives indicated that the perceived risks are leading local communities to call for action to reduce emissions and exposure.

  • The Role of Mobile Sources   From the presentations and discussion it appears that, among the major toxics EPA is considering in its mobile-source air toxics rule-making (e.g. benzene, 1,3-butadiene, formaldehyde, and acetaldehyde), the proportion of exposure that is attributable to both on- and non-road mobile sources is significant.  Several participants noted that EPA's recent Tier 2 rule- making for vehicle emissions and fuels will substantially reduce emissions of some of these compounds. At the same time, some participants suggested that there are additional challenges / opportunities for reduction, particularly in the non-road area, and in benzene levels in non-RFG areas of the country.

  • Needs for New Information   While participants acknowledged EPA's efforts in
    applying the models and data currently available for predicting future ambient
    concentrations, there were several areas identified where additional data and
    assessment could substantially improve our ability to predict and characterize risk in the future. These included:

       Improved ambient monitoring - there was much sentiment that ambient
    monitoring would be a valuable way to assess actual exposure, and to validate
    current models.
       Personal exposure/time-activity patterns - there is very little data on the
    relationship of outdoor, indoor, and personal air toxics exposure today. Much
    of that which does exist is limited to adult middle class white populations, which
    may not reflect exposure of all sensitive populations, although studies are
    underway to improve this database.
       Future exposure modeling - several speakers noted the limitations of using
    CO-based HAPEM models for estimating personal exposure. Current efforts
    to improve these through the National Air Toxics Assessment (NATA) should
    help, but these efforts will only be as good as the ambient and personal
    exposure data which is available to validate them.
       Health risk - the data base for estimating human risk from air toxics has not
    expanded dramatically over the past ten years, resulting in substantial continuing
    uncertainties over the magnitude of risk from these compounds, and how that
    risk compares to other air pollution risks.

    There was general agreement that a comprehensive research strategy was needed.   EPA is currently preparing such a strategy, and the Health Effects Institute has made planning for and implementing a systematic investigation of the health effects of key air toxics an important part of its HEI Strategic Plan 2000 - 2005. Several participants urged that such strategies not just be planning exercises, but should actually be implemented.

  • Looking Forward    The workshop was not designed to come to conclusions about what specific regulatory steps EPA should or should not take to reduce exposure to mobile-source air toxics through its upcoming Notice of Proposed Rule Making, but rather to lay out what we do and do not know, and where we should go to improve future decisions. Having said that, a number of the participants and respondents shared their views on this point. Two of the respondents, while acknowledging substantial uncertainties, suggested that the potential risk merited proceeding with further action, even in the face of uncertainty. Another respondent suggested that the current health risks data is not sufficient for regulatory decisions, and that although the risk estimates
    may be sufficient for use in "technology-forcing" decisions, such decisions should be taken with caution..

    The state and local air agencies cited Section 202 (l)(2) of the Clean Air Act, in which the Agency was directed to set "reasonable requirements" for mobile-source air toxics, at a minimum for benzene and formaldehyde. They noted that in their view, these requirements were not necessarily to be based on health risk, but rather to "reflect the greatest degree of emission reduction achievable through the application of technology which will be available," taking into consideration existing standards, costs of the technology, noise, energy and safety factors, and lead time. EPA acknowledged these requirements at the workshop, while noting as well that any such additional requirements would be adopted under section 202 (a) or 211 (c) which require EPA to "set standards for emissions which may cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare."

         EPA Response     In closing comments, Merrylin Zaw-Mon of EPA's Office of Transportation and Air Quality, thanked the participants for their extensive and constructive input, and indicated EPA's desire to both incorporate as many of the thoughts as possible into upcoming decisions by the Agency and to seek continuing forums where the kind of dialogue that had begun today could be continued throughout the rulemaking process this year, and in the years to come as these issues continue to be considered.

Go to the Agenda to find the attendees list and Respondents' comments.  Copies of the presentations can be ordered from pubs@healtheffects.org.

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