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CHICAGO, IL 60604-3590

DATE: April 25, 1997

SUBJECT: Proposed Treatment of Monitoring Data For Particulate Matter

FROM: David Kee, Director /s/
Air and Radiation Division

TO: John Seitz, Director
Office of Air Quality Planning and Standards

The proposed changes to the ozone and particulate matter air quality standards have been widely and properly recognized as one of the key environmental decisions being made by our agency this year.  There has been less recognition of the significance of a critical shift in treatment of monitoring data, applied exclusively to particulate matter, wherein valid monitoring data indicating exposures to concentrations above the particulate matter standards need not be treated as indicating nonattainment.

The new approach appears in several forms in the proposals.  Most starkly, the proposals explicitly provide that for monitors placed near sources, where violations are most likely, data from the next 3 years may be disregarded in evaluating whether any of the particulate matter standards are being attained.  Second, the proposals provide that evaluation of the attainment of one of the particulate matter standards is to be based on a subset of monitors and thus is again to disregard high concentrations at any other monitor.  Third, as has been more broadly noted, one of the particulate matter standards is based on spatial averaging, which inherently allows some subpopulations to be exposed to concentrations above the standard so long as other subpopulations are exposed to concentrations that are sufficiently low.  

We have a long history for all pollutants of applying nonattainment designations to areas if concentrations are above the standard anywhere in the area (or even, where applicable, anywhere downwind if caused by the area’s emissions).  I believe that we cannot defend any other policy, nor can we explain why it should be acceptable for anyone to be exposed to concentrations above the level of any air quality standard.  One of the clearest principles we have maintained recently concerning redesignations is that areas with concentrations above the standard cannot be redesignated, and yet the proposed policies would clearly contradict that principle.  I understand that the proposed particulate matter standards are conceptually based on average population exposures, and I understand the urge to revamp the regulatory program to conform to the conceptual basis of the standards.  I find it more difficult to understand the justification for one of these standards to reflect greater disregard for excessive concentrations than is reflected in the other standards.  We have a policy on ambient air that defines areas of potential exposure, currently applicable to all standards.  While we may wish to consider revisions to that policy, it is critical for successful implementation of all our air quality standards that any valid data indicating exposure above any standard must be treated as indicating nonattainment.

In addition to my general concern about disregarding data indicating unhealthful concentrations, I have several more detailed comments on the specific policies just identified.  I will first address the "moratorium" that would provide that we disregard any violations recorded at source-oriented monitors during the 3 years following promulgation of the standards.  The purpose of the moratorium is to encourage monitoring that will help characterize contributions of individual sources.  However, I view such monitoring as being quite analogous to monitoring under current policy within plant boundaries. In both cases, the purpose of collecting the data would be the same and the data would be ignored in attainment reviews.  In practice, States find little value in such monitoring, they rarely if ever devote their resources to such monitoring, and to my knowledge they have never used such information for characterizing sources’ impacts in lieu of analyses based on best available emissions data.  The main difference is that the proposed moratorium would sanction disregarding violations where routine exposure can occur.  Moreover, without such incentives, States have generally done far more monitoring than we required in 40 CFR 58.  In short, I believe that the proposed moratorium would have little benefit and yet would represent a significant policy shift against public health protection.

A second context in which data are to be ignored is in the use of only a subset of monitors in evaluating annual average fine particle concentrations.  I understand that derivation of a concentration representing average exposure across a broad population requires that only certain kinds of data be considered.  However, I do not view this as a defense for ignoring evidence that a subpopulation is exposed to unduly high concentrations; instead, I view this as an adverse, direct consequence of choosing in the first place to address only the average exposure of a broad population.

A third context in which data indicating concentrations above the standard do not induce regulatory action is spatial averaging.  This provision puts us in the position of arguing that exposure at one location to concentrations above the standard is acceptable so long as the exposures at other locations are low.  It is important here to note that the most sensitive populations tend to have very localized daily lives, so for example a child that lives in a high concentration area will only experience those high concentrations.

Aside from the untenability of arguing that concentrations above the standard are acceptable, I would like to add my concern about implementation difficulties that would arise with spatial averaging. The proposal recognizes that concentrations will vary within metropolitan areas, and accordingly recommends subdividing metropolitan areas into "spatial averaging zones".  This subdivision and the identification of monitors to be included in determining each area’s average concentration will likely be arbitrary exercises, with substantial latitude for States to gerrymander the zone definitions and monitor selections.  The proposal presents a vision in which the spatial averaging zones are both relatively uniform in concentration and contain considerable population, and yet in many areas that are likely to be of greatest concern these are mutually incompatible goals.  In the area of Granite City, IL, for example, even if background accounts for half of the average observed concentration, we cannot expect to achieve the target uniformity of concentrations without subdividing this area’s modest population into many small parts.  It will also be difficult to refute or deny after the fact justifications for revised (and less constraining) rezonings that the States would "demonstrate to be necessary" using the air quality data.

In this discussion, I have focussed on the use of monitoring data. Please recognize that many parallel problems would arise in conducting modeling analyses.  Although we as an agency have not focussed the same attention on these issues as they relate to modeling, I expect that we will find that the problems of defining spatial averaging zones and of disregarding or discounting concentrations above the standards will be just as difficult in a modeling context as they are in a monitoring context.

Notwithstanding our reliance for particulate matter on epidemiological evidence, i.e. "community average" health statistics, I believe it is feasible and necessary for us to identify an annual average fine particulate matter concentration that we recommend no individual’s exposure to exceed, as we have done for the other particulate matter standards and for standards for other pollutants. I defer to the judgment of health experts how best to identify such a concentration, at which exposure is reasonably unlikely to cause adverse health effects.  My experience relates more to how we should run our regulatory program to achieve such concentrations.  On the basis of that experience, I urge that we we maintain our longstanding policy that any valid data at any monitor (or any valid modeling result) that indicates exposure to concentrations above the level and frequency of a standard shall be treated as nonattainment of that standard.

Please feel free to contact me if you have any questions or desire any clarification of these views.

cc:  Air Division Directors, Regions 1-4, 6-10

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This Information Last Modified On: 09/18/2008 03:58 PM