Particulate Matter Data Proposed Exceptional Event Flag Demonstrations
Exceptional events are unusual or naturally occurring events that affect air quality and are not reasonably controllable or preventable. Under Section 319 of the Federal Clean Air Act, states are responsible for identifying air quality monitoring data affected by an exceptional event and requesting that the United States Environmental Protection Agency (EPA) exclude the data from consideration when determining whether an area is in attainment or nonattainment of a National Ambient Air Quality Standard (NAAQS). The EPA has promulgated an exceptional event rule, 40 Code of Federal Regulations § 50.14, and guidance to implement the requirements of the Federal Clean Air Act regarding exceptional events.
The Texas Commission on Environmental Quality (TCEQ) has identified exceptional events that led to high concentrations of particulate matter 2.5 micrometers or less in diameter (PM2.5) at the Houston Clinton Drive site on days in 2010, 2011, and 2012. The proposed exceptional event flags are for June 9, 10, and July 13, 2010; May 20, 2011; and July 2, 27, and 28, 2012. All six of the proposed flags in 2010 and 2012 are for African dust events and the proposed flag in 2011 is for a Mexican and Central American smoke event. These events are described in more detail in the Houston Clinton demonstration documents provided below.
The TCEQ has also identified exceptional events that led to high concentrations of PM2.5 and particulate matter 10 micrometers or less in diameter (PM10) in El Paso on days in 2010, 2011, and 2012. There are three PM10 and ten PM2.5 proposed exceptional event flags for data collected at various El Paso monitoring sites on ten separate days from 2010 through 2012. All thirteen of the proposed flags are for high wind regional blowing dust events that are described in more detail in the demonstration document for El Paso provided below.
In accordance with federal regulations, the demonstration documents supporting the TCEQ proposed exceptional event flags for Houston Clinton PM2.5 and El Paso PM10 and PM2.5 data for 2010, 2011, and 2012 were posted for 30-day public review and comment periods. The public review and comment period for the 2010 Houston Clinton PM2.5 Exceptional Events Document closed on June 24, 2013; the public review and comment period for the 2011 and 2012 Houston Clinton PM2.5 Exceptional Events Documents closed on September 30, 2013; and the public review and comment period for the 2010-2012 El Paso Particulate Matter Exceptional Events Document closed on December 2, 2013.
The public comments received by the TCEQ on the proposed flags were forwarded to the EPA for consideration. The EPA will consider information provided in the demonstration documents and public comments when deciding whether to accept or reject each proposed flag. EPA concurrence on a flag will remove the data from consideration for determinations of compliance with the 24-hour PM10, the 24-hour PM2.5, or the newly revised annual PM2.5 NAAQS.