Meteorological Variability Conference Call

May 7, 1997

1:00 - 2:30 pm

Attendees:

David Chock	Ford Motor Company

Bill Cox	U.S. EPA/AQMG

Cyril Durrenberger	TNRCC

S.T. Rao	New York

David Sanders	U.S. EPA/OPSG

John Silvasi	U.S. EPA/OPSG

Steve Ziman	Chevron

Contractor Support:

Bob Wayland

Summary of the Call

S.T. Rao questioned if we were simply trying to answer question #3 from NRSWG, or if there was some alternative agenda? Mr. Rao continued, that if we were trying to answer question #3, then this answer could be a simple "yes or no". He advocated avoiding getting into the details in a conference call format. He said that it was very difficult to get into the detail in this type of forum.

John Silvasi suggested that he re-read the actual question, as submitted by the NRSWG. He read question #1, as contained in the original minutes of last week's call:

As discussed in item #1, there is a desire to assess air quality metrics at pre-determined intervals in order to determine if the emissions reduction program being implemented are bringing an area towards attainment at the planned rate. In general, the philosophy is "the shorter interval the better" so that if a mid-course correction is needed it can be implemented rapidly so the attainment dates are met. However, it is also recognized that meteorology may exert a short-term influence on these metrics that may have no bearing on whether or not the emissions reduction programs being implemented are having the desired influence on air quality. Is there a valid method for identifying meteorological events that result in ozone or PM-fine concentrations that should be considered "statistical outliers" in an air quality analysis? Also, are there tools that can be applied to "remove" the effect of meteorology in order to better understand true air quality trends? This would include tools not only to eliminate the influence of meteorology that increased concentrations of PM-2.5 and/or ozone but also meteorology that depresses concentrations (i.e., cool summers, etc.).

David Chock stated that this was a very lengthy question. However, he continued that some parts could be answered very quickly and tersely. He said that a short-term interval would not be acceptable for determining a trend, and that a minimum of 5-6 years was most preferable. He stated the believed that most of the group would agree on this. Mr. Chock also cautioned the group not to exclude outliers, and suggested that tools do exist to adequately assess meteorological variability.

David Sanders questioned the phrase "removal of meteorology" - exactly how much are we interested in removing?

S.T. Rao suggested that he would rephrase this question all together. Mr. Rao suggested the following: "Do we have tools that enable us to discern changes in ozone air quality due to control policies in the presence of meteorological variability?" Or, stated another way, "Do we have tools to detect the efficiency of our ozone management policies in the presence of meteorological variability?" Mr. Rao contended that the answer to both of these would be yes, that there are lots of tools for assessing/quantifying these types of processes.

John Silvasi asked if the answer was "yes", would this group feel that it needed to provide EPA some recommendations on what these tools are and how they might be used appropriately?

S.T. Rao responded that this would be appropriate. Mr. Rao stated that David Chock had already identified several references in his response to last week's minutes. He continued stating that both himself and Bill Cox had worked on this issue and had published numerous papers on the topic.

David Chock agreed with Mr. Rao.

S.T. Rao continued saying that he agreed with Mr. Chock on the first part of the question, and that a minimum of 5-6 years of data were required to account for any climatic fluctuations.

John Silvasi suggested that the group ask the Contractor to draft a response for the group in light of the discussions held today and last week. Mr. Silvasi suggested that this response contain a list of potential tools.

S.T. Rao cautioned that the tools available would always be in a state of flux - work would continue to sharpen and refine these existing tools; that this was a work in progress. He concluded stating that our ability to detect these types of changes would be improving in the future, and thus, we should be too prescriptive in defining a list of tools.

Cyril Durrenberger cautioned Mr. Rao that one tool may work in one area, but not work so well in another area.

S.T. Rao responded that the tool he considered to be the right tool, was the tool that adequately addressed the physics and chemistry of the individual situation.

Cyril Durrenberger responded that he was not arguing with that point, rather he did not want to see a prescriptive list of tools distributed for use everywhere. As an example, Mr. Durrenberger discussed the correlations between ozone and temperature, which work in some locations quite well, and not so well in other regions.

Steve Ziman stated that the group would agree that the metric would not be uniform across the board. Mr. Ziman said that we simply did not have a prescriptive method here.

David Chock suggested that we could only provide the methodology, not the details.

Steve Ziman suggested that the group provide a reference set of choices which could be evaluated and then developed further for individual applications. However, Mr. Ziman concluded that the STSWG response to the RFP group did not have to be a detailed answer.

David Chock agreed with Mr. Ziman, stating that this was not the proper scientific forum to discuss these types of details.

Steve Ziman suggested that any guidance information that was generated should be reviewed by the STSWG, prior to its release.

David Sanders questioned if it made any difference to insert the word "extreme" into the second sentence, prior to the word meteorology (e.g., extreme meteorology)?

S.T. Rao responded that this was not necessary, and stated that he would phrase this question another way: "Are there tools which would enable us to relate changes in ozone to our ozone management efforts in the presence of meteorological variability?"

Steve Ziman replied that this was excellent wording of the issue.

John Silvasi stated that in light of this discussion, he would ask the contractor draft a response for the subgroup (minus the list of tools), which could be distributed to the subgroup members for review, prior to going to the full STSWG in time for next Tuesday's call.

S.T. Rao suggested that the group did need to discuss the issue of statistical outliers, which was raised earlier by David Chock. Mr. Rao stated that we could not ignore this issue, because there really were no outliers. He said that our role as scientists should be to adequately explain the meaning of the data. Mr. Rao continued that every piece of data had a meaning, and we should be able to explain this, in terms of what was signal and what was noise. Mr. Rao suggested that this question should restated as follows: Can we explain the variance in the data?

David Chock agreed with Mr. Rao.

S.T. Rao stated that we needed to explain the variance in terms of the chemistry and physics represented by the data. He said that it was beyond the scope of this effort to attempt to compile a list of references of the available tools. He concluded that it should be sufficient to say that the STSWG has enough tools for them (e.g. RFP group) to begin to move forward on this issue.

David Sanders questioned if the group had adequately dealt with the third part of question #1?

S.T. Rao and David Chock indicated that this had been sufficiently covered.

Jay Rosenthal joined after the group the call was over, and Mr. Silvasi gave him a brief recap of the agenda.