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Multiple Air Toxics Exposure Study-II Final Report

SYNOPSIS: 

At its November 5, 1999 meeting, the Board released a draft version of the Multiple Air Toxics Exposure Study-II final report for a 90-day public review and comment period. Also, staff has conducted a special public informational session on "Diesel Emissions as a Toxic Air Contaminant" as well as a public workshop on the draft report. Based on public comments received, and input at the public sessions, staff has incorporated appropriate changes into the final report. This version includes a summary of the comments and questions received along with staff responses. The general conclusions presented to the Board in November have not changed, but a number of amplyifying or clarifying statements have been added to address the comments received.

Barry R. Wallerstein, D.Env.
Executive Officer

Background

In 1997, the Board approved a set of Environmental Justice Initiatives, which included a major air toxics monitoring program, referred to as MATES-II (Multiple Air Toxics Exposure Study-II). The program included air monitoring of over 30 toxic pollutants, both gaseous and particulate. MATES-II included two key monitoring elements: 10 fixed sites characterizing neighborhood-scale conditions over a one-year period; and a complementary microscale study using three mobile platforms for approximately one month at each of 14 additional locations. In addition to the monitoring, the toxics emissions inventory was further developed, and computer models were utilized to depict toxic risks for the entire Basin. In total, the MATES-II project represents one of the most comprehensive air toxics monitoring programs ever conducted in a major urban area in the country, and an extraordinary level of national and international interest has focused on this study.

Last November, staff presented the Draft Final Report of MATES-II to the Board, and released it to the public for review and comment over a 90-day period, ending February 1, 2000. Due to the high level of public interest and comment, the comment period was extended to February 22, 2000. At the request of the Board, a special informational session on "Diesel Emissions as a Toxic Air Contaminant" was held on February 2, 2000, featuring noted national experts on health impacts of diesel emissions, and developing technologies to reduce diesel emissions. Over 200 people attended the event, which was video-taped. Copies of the tapes have been made available to Board members.

Also, a special public workshop was held on February 22, 2000 to provide the public and interested stakeholders with an opportunity to present additional comments to staff prior to the finalization of the draft report. There were 38 people in attendance, and 10 people provided comments, which were included along with the written comments in the preparation of the final report.

Summary of Key Comments

A total of 24 comment letters were received, many with very detailed remarks and suggestions. A list of the commentors is provided in the Attachment to this letter. Staff is appreciative of the quality of comments received, and revisions to the report reflect many of these comments, and staff believes the revisions improve the clarity and technical foundation of the MATES-II report. A summary of the response-to-comments is provided as an added chapter, so that the public input becomes a part of the document itself. Some of the key comments are provided below:

1. Comment: There is a large uncertainty in the diesel risk factors, and there is little scientific basis for the risk factor used.
   
   Response: AQMD staff recognizes that there are inherent uncertainties associated with the quantified risk factors established in California, and that on a national level, there has not been any recommendation for a quantified value. The AQMD further understands the concerns about earlier studies which contributed to the California assessment. However, AQMD staff relies upon the medical expertise within the CalEPA for establishing pollutant toxicity factors (as well as the state ambient air quality standards for criteria pollutants) and believes adequate evidence is available currently. Therefore, AQMD staff accepts risk factors established by CalEPA as applicable to the entire state at this time, and will continue to monitor activities at the state and federal level.
   
   
2. Comment: The use of "average cancer risk" in describing the basin-wide conditions is not correct, since risk estimates are based on upper limit confidence levels.
   
   Response: The term "average" was used to convey the average of the conditions across all fixed monitoring sites. AQMD staff recognizes that the term "average cancer risk" may misconstrue the fact that potency factors are taken to reflect the upper limit of the confidence intervals, not the average. To avoid confusion, the term "basin-wide cancer risk" will be used instead of "average cancer risk," and this term will be explained to represent the risk derived from the average concentration of pollutants measured at the fixed monitoring sites.
   
   
3. Comment: There is no definition of "hot spot."
   
   Response: AQMD staff will seek to develop an appropriate definition with input from the Air Toxic Study Technical Review Group (ATSTRG) in the near future. However, absent such a definition, the report can still be finalized and provides timely information regarding air toxics levels in Southern California.
   
   
4. Comment: The use of elemental carbon as a surrogate for diesel particulates is based on a study conducted in the 1980’s, and changes in emissions since then indicate that a lower estimating factor is more appropriate.
   
   Response: AQMD staff recognizes many limitations with the use of one factor as a surrogate to estimate diesel particulates, from which cancer risk estimates can be determined. A number of commentors criticized the use of a factor which was determined based on 1982 emissions inventories, when in fact, emissions data have changed over time. To address this concern, staff has recalculated the estimating factor using the 1998 inventory as determined specifically for PM2.5 emissions, thus eliminating confounding difficulties from coarse particulate emissions. Then, ambient data from the AQMD’s TEP-2000 study, which measured both PM10 and PM2.5 elemental carbon during much of the same sampling period as the MATES-II sampling, was used to determine the fraction of the total PM10 elemental carbon which is made up of measured PM2.5 elemental carbon. Adjusting elemental carbon to PM2.5 levels, and then applying the PM2.5 inventory-derived factor, does provide a recent-year methodology for estimating diesel particulates. The results are very consistent with the original factor, and in fact, indicate that even greater levels of diesel particulate may be occurring. Staff believes that diesel particulates are not overestimated as a result of using the 1982 estimating factor.

Release of Final MATES-II Report

The Final MATES-II Report was released to the public March 2, 2000 to allow the public an opportunity to review the document prior to the presentation to the Board. The major conclusions as presented in the draft report have not changed, but a number of amplifying and clarifying statements have been added to improve the report. Also, a summary of public comments has been added as an additional chapter. The Final MATES-II Report is also being made available to the public on our website.

Attachment

List of Commentors on MATES-II Draft Report

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