RFP Metrics Conference Call

May 1, 1997

2:30 - 3:30 pm

Attendees:

Steve Ziman	Chevron

David Sanders	U.S. EPA/OPSG

Bob Stallings	U.S. EPA/OPSG

John Silvasi	U.S. EPA/OPSG

Contractor Support:

Bob Wayland	SAIC

Summary of the Call

David Sanders opened the call, explaining that when Cyril Durrenberger did the recap of last Wednesday's call for STSWG on Tuesday, he had mentioned five different metrics or indicators. Mr. Sanders asked if Steve Ziman could expand on these topics?

Steve Ziman responded this was their hierarchal approach to establishing an air quality metric and, in general, to RFP. Mr. Ziman said that the first concept was an iterative approach, and it looked at RFP from a prospective approach. He stated that you would need time to review your information, and to allow strategies to take effect, before you could determine whether you were in fact making progress. Mr. Ziman concluded that approximately 5-6 years of information would be preferable to make the determinations on meteorological variability and whether the emissions reductions were actually working.

David Sanders questioned the t-test method, which Mr. Durrenberger mentioned on Tuesday. Mr. Sanders indicated that was a basic restatement of David Chock's earlier work, and that it would be used in regions where robustness in the available data was lacking. Finally, Mr. Sanders stated the third concept had to do with design values, and that was all that he had in his notes.

Steve Ziman stated that the topics definitely relayed a hierarchy of air quality indicators that one would want to look at. He said that there may still be a need to look at an indicator which was based on the design value and how it changed with changes in emission reductions. However, he stated that the design value focused on a single monitor, and that this approach could be problematic. He continued saying that this approach restricted your analyses to a single monitoring location, and would in general tell you very little about the entire region (e.g., AOI or AOV). Thus, Mr. Ziman stated that the group needed to review metrics that were capable of capturing both the temporal and spatial characteristics components of the system.

Mr. Ziman continued that he and Mr. Durrenberger agreed to look at changes with respect to time and space. He said that Mr. Durrenberger refers to this approach as areal exposure, and involves calculating the change in ozone exposure in ppm-hours. Mr. Ziman continued that what you are actually calculating was the change in ppm-hours over an entire domain as the mechanism to judge your rate of progress. He indicated that ultimate indicator would be to incorporate into this calculations an assessment of exposure by using the door-step population relative. He stated that this latter approach would be the metric of choice, but that it was limited. Mr. Ziman said that this technique was limited because it required a monitoring network that was designed to equally assess population exposure within a region. He said the network would have to be designed such that no one monitor accounted for too much of the region's population. He concluded that EPA would need to provide more guidance on this methodology.

Mr. Ziman concluded his discussion of the five topics, saying that he and Mr. Durrenberger had concentrated on the final two indicators (e.g., areal exposure, and population exposure), because they covered both the temporal and spatial aspects of the metric.

David Sanders asked if the starter material for these two metrics could be found in the paper by Jim Smith and Cyril Durrenberger?

Steve Ziman responded that was a good starting point; but, that there were other pieces coming from California that would be applicable as well. Mr. Ziman indicated that he had faxed this material to John Silvasi. He said that in California, they were already using an air quality metric to look at population exposure. However, Mr. Ziman stated that this had only been done as a retrospective analysis. He said it utilized ambient air quality data from 1989 - 1992, and that he had previously shared these results with both John Silvasi and Nancy Mayer. He reminded the group that this research used only long-term monitoring locations and was based on ppm- hours per person.

He continued saying that in California, their efforts had been focused on retrospective analyses so far, and the results could show that California was meeting the goals. He indicated that they were now working with a prospective approach, and that this material had also been shared with both John Silvasi and Nancy Mayer. The retrospective approach did not allow you optimize and prioritize your strategies. With the prospective approach, we are trying to do the following: (1) You are going to model for your SIP, and most likely do more than one episode; (2) The episodes which you model should have recurrences of rather high ozone concentrations in your region; (3) Once you have adequate model performance for your base case, you can then try and make the determination of what control strategies you would like to try, and look at the ozone response surface; (4) This determination will help you determine where you are VOC or NOx limited; (5) Once you have this information, you can look at control measures which can move you toward attainment. The process allows you to optimize - similar to the schemes that Ted Russell has discussed previously. In this case, you can optimize for either areal exposure or population exposure. Thus, using the SIP process you have the ability to look at alternative strategies, and see how they move you towards your air quality metric, on your way to attainment. Mr. Ziman indicated that this was a very viable prospective approach. He said that this was why the STSWG prefers to call this an iterative approach. He stressed that you must go back and look at your air quality indicator and your rate of progress, and determine if in fact you were meeting these goals, and to determine how quickly you were getting there. However, he cautioned, that it was equally important to understand why you were meeting those goals.

David Sanders suggested that the next step was to look at the questions provided by NRSWG and determine if we had answered and of them. Mr. Sanders indicated that it was the consensus of the STSWG that emissions reduction metric was not acceptable to the membership.

Steve Ziman acknowledged that this was correct.

David Sanders stated that the remainder of this question dealt with the use of other types of metrics.

Steve Ziman replied that this was also discussed at the Falls Church meeting, and STSWG agreed that the emissions reduction metric was not appropriate. He stated that the group felt that this was the driver itself, and that it did not tell you anything about improvements to air quality.

David Sanders questioned if there were any other alternative metrics that should be discussed?

Steve Ziman responded that there may be others, but he thought these two were the most likely, because they attempted to look at changes in air quality and relate them to changes in emissions. He also stated that these two metrics attempted to account for what was happening in the entire area and not just at one location, and that they attempted to relate to exposure. He reminded the group that after all, we were looking at a health-based standard, and these metrics linked this to the standard. He concluded saying that this method also dealt with the associated risks.

Mr. Ziman continued saying that in terms of choosing an air quality indicator, the latter method at least attempted to try and use the suppositions that were used in the formulation of the standard. He referred the group to Harvey Richmond's work on the nine-cities study. He stated that there were definitely other metrics, but that in his opinion, these were the most viable, because the air quality indicator as a rate of progress should be linked to the standard.

Bob Stallings questioned that when a prospective approach is used, it implies some level of modeling, and would this not tie-in some degree of emissions reductions?

Steve Ziman responded that this was in fact correct; that you simply could not get around this issue.

Bob Stallings reminded Mr. Ziman that one question that would be raised was that the results of the prospective analysis would be based on emissions reductions that most likely could not be verified.

Steve Ziman again agreed with Mr. Stallings. However, he responded that Mr. Durrenberger and himself believed that it was incumbent as well to be able to look at your precursors and see if they too had been reduced, as well as dealing with meteorological variability. Mr. Ziman remarked that at this point we had no guarantees; even if we looked at emission reductions. Some people would still like to see reductions in precursors as well. He admitted that there was certainly a higher degree of uncertainty in doing this prospectively; however, that was why the retrospective analyses could be so useful. In the latter, you could determine whether the air quality changes were related to meteorological variability or true emissions reductions.

Bob Stallings continued to question Mr. Ziman about the necessity to have inventories to do gridded modeling runs.

Steve Ziman responded that the SIP process would contain all of these requirements (or at least should!). Mr. Ziman stated that if people were willing to accept air quality management as a process, and he believed that they were, then it was incumbent that the models be carefully evaluated (both diagnostically and mechanistically, as well as observationally). Thus, in accomplishing this level of evaluation, then your emissions inventory would also have to be evaluated properly.

Bob Stallings concluded that he did not see any other way to perform SIP planning with using numerical models.

Steve Ziman agreed, and said that it could not be done without models, because the process is so non-linear.

Bob Stallings stated that to run in a prospective mode, you would need to make projections, and that there was no indication on the validity of these projections.

Steve Ziman responded that this was the reason for including mid-course corrections; he indicated that this allowed you to challenge the system, and see if in fact you were making progress.

Bob Stallings offered that precursor atmospheric measurements could be a good surrogate for emission inventories.

Steve Ziman agreed, and mentioned the work of Eric Fujita and his colleagues, where they have shown this to be a positive approach, when coupled with Chemical Mass Balance (CMB) techniques.

Bob Stallings stated that unfortunately, there were not a lot of precursor models out there to choose from!

Steve Ziman agreed, and admitted that this was an issue that was larger than RFP. He said that NARSTO and others were researching this issue. However, he concluded that sooner of later, we simply needed to bite the bullet and fund some of this research.

David Sanders asked if the previous discussion helped us answer question #1, which dealt with the length or interval to determine the metric?

Steve Ziman responded absolutely; this falls into the discussion on meteorological variability, which David Chock and S.T. Rao were currently reviewing.

David Sanders questioned if this was not more closely related to question #3?

Steve Ziman said that this was correct, and that #1 and #3 were closely linked, in that they were both looking at determining the signal from the noise. He reminded the group that it was extremely difficult to separate the mitigating factors, and offered that this is why we utilize trend analyses. Mr. Ziman asked the group to look at the materials he had previously sent to John Silvasi, especially the document by Larson: Air Quality Related Indicators. Mr. Ziman concluded with two statements: (1) He stated that we had only talked about ozone in our discussions; but, conceptually you could do the same thing for PM, assuming you understood all the issues. However, he cautioned that we did not understand all of the issues, and thus we were dealing with a can of worms. (2) He said that one of the other reasons for considering an air quality indicator above and beyond the emissions indicator was that there would instances where one could not attain the standard. Mr. Ziman concluded saying that this approach would still provide an indicator that measures air quality, and also reduce your health risk at the same time.

(John Silvasi joined the call)

John Silvasi corrected Mr. Ziman stating that the problem with the RIA was not that the controls could not be found, it was just that the model did not accommodate the necessary controls. It was not that EPA did not have the controls, or that they were not available.

Steve Ziman responded that was not his understanding. Mr. Ziman indicated he was told that the control measures were simply not there to get the necessary reductions to get the region where they needed to go in terms of attainment.

John Silvasi replied that the Pechan-type model which was used, simply did not accommodate some of these additional control methods.

Steve Ziman said that was not his understanding, but that he was not interested in "beating a dead horse". He concluded that he did not believe that there were controls to get some areas of the country into attainment.

Bob Stallings replied that he believed what Mr. Ziman was saying was that using these latter two metrics, you were still reducing the health risk, while at the same time you were moving towards attainment, and he agreed with that approach.

Steve Ziman responded that was his approach.

Bob Stallings indicated that this approach would leave the determination up to the public on whether they wanted to live in a "bad air quality region or not"!

Steve Ziman indicated that this had not worked in California!

John Silvasi requested that the Contractor provide a written summary to David Sanders as soon as possible, such that it could be distributed prior to this group's next call, which would take place next Wednesday, Thursday or Friday.