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On February 9, 2010, EPA established a new 1-hour National Ambient Air Quality Standard (NAAQS) for NO2. The new 1-hour standard is 100 parts per billion (ppb), and supplements the existing annual standard which remains in effect. This new standard went into effect on April 12, 2010, 60 days after the publication of the rule in the Federal Register. According to recent verbal guidance provided by the Texas Commission on Environmental Quality (TCEQ), an applicant may be required to perform site-wide air dispersion modeling demonstrating compliance with the new 1-hour NO2 standard before the agency will issue an air quality authorization, including a Permit by Rule (e.g., Permit by Rule 106.512, Stationary Engines and Turbines). However, to date, there is no guidance from the EPA regarding critical values needed for performing an NO2 1-hour air dispersion modeling analysis. More specifically, EPA has not defined a Significance Impact Level, and there are concerns regarding the quality and availability of background NO2 data. According to the TCEQ, they are still in the process of determining the best path forward and will be meeting internally the week of April 19, 2010, to develop additional guidance.

Also expressing concerns regarding the new 1-hour NO2 standard are the American Petroleum Institute (API), the Utility Air Regulatory Group (UARG), and the New Mexico Environment Department (NMED). On April 12, 2010, the API and UARG filed a petition with the EPA to “stay” the standard, challenging the basis for the 100 ppb standard and citing improper implementation of the standard for PSD permitting, including discussion on why API deems the air dispersion modeling to be potentially problematic. EPA has 60 days to respond to their comments. The NMED has stated that they will not pursue 1-hour NO2 modeling until they obtain the necessary guidance from EPA.