Response to suggested language for footnotes in the RIA and EO 12866 language in the 

preamble

Lydia Wegman to: James_A ._Laity, Dominic Mancini 06/01/2010 04:27 PM

Cc: "Ron Evans", "Kathy Kaufman", "Charlotte Bertrand", "Bridgid Curry", "Tricia 

Crabtree"

Please see our suggested edits below, as well as the explanation for the changes. Thanks.

Lydia

Ron Evans

 ----- Original Message -----

 From: Ron Evans

 Sent: 06/01/2010 04:23 PM EDT

 To: Lydia Wegman

 Cc: Bryan Hubbell; Ken Davidson; Neal Fann; Amy Lamson; Kathy Kaufman

 Subject: Fw: Our revisions to the OMB SO2 NAAQS RIA footnotes, REVISED

Lydia, we have reviewed the footnotes requested by OMB. Conceptually we are OK with adding them to 

the table and importing that table into the EO-12866 section of the preamble with appropriate caveats. 

That new preamble section is being developed. These footnotes would also appear in the same tables in 

the RIA.

We have some concerns with the characterization of the issues in the footnotes. Here is a summary of 

our concerns, as a rationale for our language changes

For the Threshold footnote:

o Based on the conclusions drawn from the literature in our Integrated Science Assessment for 

PM2.5 and concurred with by the CASAC, there is little scientific support for assuming a threshold in the 

calculation of benefits. We copied language we have used elsewhere in the benefits chapter to reflect 

this

o We do indicate that we have included a sensivity analysis in the body of the benefits chapter but 

given the little scienitific support for assuming a threshold we don't think the actual estimate is appropriate 

to appear in the Exectutive Summary or Benefit/Cost comparison tables. In addition, the threshold 

sensitivity analysis includes several other changes that cannot be disentangled . 

o On a technical note, the only estimate in the bar chart that includes thresholds is the lowest bar. 

Expert K specified that a C-R function with a 50% probability of no-threshold, 40% probability of a 

threshold below 5 ug/m3, and a 10% probability of a threshold between 5 and 10 ug/m3. Except for the 

sensitivity analysis, the Pope estimates in the chapter and figures do not include an assumed threshold. 

Footnote: The models used to generate these benefits estimates assume that the health impact function

for fine particles is log‐linear down to the lowest air quality levels modeled in this analysis causality

down to background levels of PM2.5 (i.e., there is no effect threshold).  Estimates that assume a

threshold in the concentration response functions between PM2.5 and premature mortality (see Table

5‐12, and the Figure 5.7 comparison between the bars on the far left with the other bars in the figure),

yield benefits estimates that are between 1/3 and 2/3 lower.  EPA's final Integrated Science Assessment

for particulate matter concluded that the scientific literature consistently finds that a no‐threshold

log‐linear model most adequately portrays the PM‐mortality concentration‐response relationship while

recognizing potential uncertainty about the exact shape of the concentration‐response function.  While
we have no evidence of a threshold at any specific concentration level, we include an estimate of the

sensitivity of the results to an arbitrary assumed threshold at 10 ug/m3 in conjunction with several other

changes in Table 5‐12 of the RIA.  While this sensitivity estimate shows decreased co‐benefits, we are

unable to estimate the difference due solely to thresholds.

For the chemical composition footnote

o We clarified the language to include that we reduce SO2 from EGUs, industrial sources, and area 

sources. However, we do not believe that the underlying science raised by this assumption is significant 

enough to warrent mention that this is rasies additional uncertainty.

Footnote: These models assume that all fine particles, regardless of their chemical composition, are

equally potent in causing premature mortality because there is no clear scientific evidence that would

support the development of are not clear scientific grounds for supporting differential effects estimates

by particle type.  However, it should be noted that this assumption raises additional uncertainty in an

analysis that specifically targets a single species or source, as in this analysis, which selects only controls

that reduce sulfur emissions from EGUs. Reductions in SO2 emissions from multiple sectors to meet the

SO2 NAAQS would primarily reduce the sulfate fraction of PM2.5.  Because this rule targets a specific

particle precursor (i.e., SO2), this introduces some uncertainty into the results of the analysis.

Minor issues:

o I prefer to leave the limitation discussion where it is currently located in the chapter. In the 

chapter, the uncertainty section follows the unquantified benefits section. This flow is logical because 

many of the limitations affect the unquantified benefits as well, and the fact that we were unable to 

quantify all the benefits is an important limitation of the analysis.

o The 1st bullet on page 5-23 uses language previously provided by OMB, and it is accurate. 

However, it may be more clear to revise it to say 2006-2009. These years refer to the time period during 

which we assumed a threshold of 10 ug/m3. 

Ron