Exceptional EventsElements of an Effective Demonstration Darren Palmer US EPA Region 4
Exceptional Events RuleThe Basics • Sets criteria and process for EPA to agree to exclude event-influenced data when determining NAAQS compliance and design values. • Section 319 of the Clean Air Act, as amended by the SAFE-TEA-LU Act of 2005 required EPA to promulgate a rule to governthe review and handling of exceptional events data. • Final rule published March 22, 2007 (Effective date = May 21, 2007) • Scope: General rule which applies to all NAAQS. • CFR language defining NAAQS for ozone, PM2.5, PM10, and Pb explicitly provides for exclusion of event-influenced data. • Preamble states EPA intention to effectively apply same scheme for other NAAQS also, via 107(d)(3) discretion. • EPA will formally extend the rule to other pollutants as NAAQS are revised, in time for new mandatory designations. • Replaces previous EPA policy/practices.
How to Justify Data Exclusion40 CFR 50.14(a) • A State may request that EPA exclude data related to exceedances or violations of a NAAQS that are directly due to an exceptional event from use in regulatory determinations • Demonstration to justify data exclusion • May include any reliable and accurate data • Must demonstrate a clear causal relationship between the measured exceedance or violation of the affected standard and the event.
Notification of the Public and EPA • Notify public of the occurrence (or anticipated occurrence) of the event • Notify EPA by Flagging the data. • Flag data in AQS and provide event description by July 1 of following year. • Also provide initial event description • Give public notice and 30 day comment period.
The Exceptional Event Demonstration • Must be submitted to EPA not later than the lesser of: • 3 years following the end of the calendar quarter in which the event occurred • or 1 year before EPA plans to use the data for a regulatory decision. • A State must submit the public comments it received along with its demonstration to EPA. • In general, the type, amount, and detail level for presentation of evidence will vary by the circumstances for each event.
The Exceptional Event DemonstrationThe Four-Part Test [§ 50.14(c)(3)(iii)] • Demonstration to justify data exclusion shall provide evidence that: • The event satisfies the Statutory Definition of Exceptional Event • There is a clear causal relationship between the measurement under consideration and the event that is claimed to have affected the air quality in the area • The event is associated with a measured concentration in excess of normal historical fluctuations, including background; and • There would have been no exceedance or violation “but for” the event. • Provided that all the Exceptional Event Rule requirements are met, EPA shall exclude such data from use in determinations of a NAAQS violation. • Note: The rule has special provisions regarding fireworks and prescribed fires. The preamble discusses other situations of interest.
Definition of “Exceptional Event”40 CFR 50.1(j) • Event affected air quality • Event was either • Natural or • Caused by human activity and unlikely to recur at a particular location • Event was not reasonably controllable or preventable • Event was not related to: • Air mass stagnation • Inversion • High temperature • Lack of precipitation • Source noncompliance • EPA Administrator has determined through the process established in the rule thatit was an exceptional event.
Clear Causal Relationship Between Measurement and the Event • Can be demonstrated using data from a variety of sources • Several online tools are available on Datafed website: http://datafedwiki.wustl.edu/index.php/Data_Views_Catalog • Products by Dr. Rudy Husar, Washington University • Compiles data and generates maps from multiple sources, including EPA, NASA, NOAA, Navy, and others. • Tools available to assist in evaluating several types of events including wildfires, dust, and fireworks
Clear Causal Relationship Between Measurement and the Event (cont.) • Other useful data sources include: • Trajectories • Surface weather maps • Wind profiler data • Windroses • Satellite data • Air Quality Monitors • Newspaper reports • Maps of networks, fires, etc.
Comparison to Historical Data • In order for a measurement to be excluded, it must be “in excess of normal historical fluctuations, including background.” Observed PM2.5 concentration over historical 95th percentile
Comparison to Historical DataEPA Region 4 two-step analysis for PM2.5 • Step 1:Is the flagged measurement greater than the historical 84th percentile for the site for the month? • Step 2:If the flagged value is not an exceedance of the 24-hr PM2.5 NAAQS, is the historical monthly average for the site below the annual PM2.5 NAAQS? • If either of these conditions is not met, then the burden of proof needed in the demonstration is much greater
No Exceedance “But For” the Event • EE Demonstration must quantitatively show that without impact from EE, no exceedance would have occurred. This is the only scenario in which data may be excluded
No Exceedance “But For” the EventHow To Demonstrate Using PM2.5 Speciation Data • For wildfires, calculate an Organic Mass Increment (OMI):OC is Organic CarbonOCaverage is the average OC observed at the site during the month over the past 3 yearsA multiplier of 2.0 is used to estimate total organic mass from smoke (Turpin and Lim 2001)Note: Similar approaches can be taken for other events such as Saharan dust or fireworks.
The orange line approximates what the observed PM2.5 concentration would have been “but for” the event.