July 31, 2009: Modeling and Effects Review Applicability (MERA) Guidance Document

Notice regarding updated guide to MERA

The MERA document (commonly referred to as the flowchart) gives Air Permits Division personnel the general guidance they need to evaluate constituents that have effects screening levels—in other words, constituents that do not have a state or federal air quality standard. The ESL for a given constituent is its concentration in ambient air that the Toxicology Division has determined will not be expected to cause adverse effects on health, odor nuisance, or vegetation.

Minor revisions to the MERA document have been made, and a description of the toxicology effects evaluation has been included as Appendix D. A summary of significant changes appears on pages 1–2 and includes changes made since the August 2008 version. TCEQ personnel emphasize that the MERA is a conservative evaluation tool that must ensure protectiveness, and that case-by-case reviews are always available if the tool cannot be used at a particular step.

• Modeling and Review Effects Applicability: How to Determine the Scope of Modeling and Effects Review for Air Permits (PDF file. Help with PDF.)

For further information, please contact Louise Ngo at 512-239-1267 or by e-mail at lngo@tceq.texas.gov and include “MERA” in the subject line.