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Environmental Protection Agency (EPA) Administrator Gina McCarthy signed the proposed sulfur dioxide (SO2) National Ambient Air Quality Standards (NAAQS) Data Requirements rule on April 17, 2014. When finalized and promulgated, this action will create a new Subpart BB in 40 CFR Part 51 called “Data Requirement for Characterizing Air Quality for the primary SO2 NAAQS.” The draft rule can be found at

The new proposed rule lays out guidance directing state, local, and tribal agencies to provide emissions, modeling, and/or monitoring data to characterize current air quality in areas with large sources of SO2 emissions where sufficient monitoring was not in place to allow designation in July 2013. This guidance is intended to provide tools to allow states, local, and tribal governments to complete the designation process for nonattainment areas. The new rule gives agencies the flexibility to use either monitoring or modeling to characterize SO2 concentrations that are due to a specific set of target sources. The target sources will primarily include the largest sources of SO2 such as coal-fired electric utilities, industrial boilers, refineries, smelters, pulp and paper related facilities, chemical manufacturing, and facilities with industrial boilers for power generation.

EPA proposed three threshold options that would dictate which sources are targeted. The basis for the selection is on SO2 emissions and on population where the source is located, with the goal of increasing public health protection in more highly populated areas. These are lower emission thresholds than previously proposed by EPA. As shown below, EPA is considering three options currently while this draft rule is being considered.

  • Option 1: Sources > 1000 tpy SO2 emissions in population areas of > one million persons and > 2000 tpy everywhere else
  • Option 2: Sources > 2000 tpy SO2 emissions in population areas of > one million persons and > 5000 tpy everywhere else
  • Option 3: Sources > 3000 tpy SO2 emissions in population areas of > one million persons and > 10000 tpy everywhere else

EPA states that its preferred option is Option 1. According to EPA’s proposed implementation schedule, States will have until January 15, 2016 to notify EPA which SO2 sources will be targeted (based on the threshold) and whether they will use monitoring, modeling, or a combination of both.

For facilities selected to be addressed by modeling, States will have to submit a modeling protocol by January 15, 2016 and provide a modeling demonstration by January 13, 2017. EPA would make the second round of SO2 designations based on the modeling results by December 2017.

 EPA New SO2 Data Req Rule

For facilities selected to be addressed by monitoring, monitoring network plans for selected facilities will need to be submitted by States by July 2016 and have monitors operational by January 1, 2017. States will then collect three years of monitoring data over 2017-2019 and provide the results to EPA by May 2020. EPA would make the third round of SO2 designations based on the monitoring data by August 2020.

New SO2 SIP Guidance

On April 23, 2014, EPA Director Stephen Page issued a memorandum to the EPA Regional Directors distributing guidance entitled “Guidance for 1-Hour SO2 Nonattainment Area SIP Submissions.” The document is intended to provide guidance for the development of SIPs under the 1-hour NAAQS for SO2. The letter and guidance can be found at

The new guidance contains recommendations on a wide range of issues in the development of nonattainment area SIPs. Key issues include attainment dates, SIP credit for other Federal measures (e.g., CSAPR), timing of controls, modeling requirements and strategies, scope and criteria for attainment demonstrations, averaging times of emissions limits, a clean data policy, and transition from prior SO2 SIPs and NAAQS. Due dates for the 29 areas initially designated as nonattainment are emphasized (have not changed) and discussion is presented for considering new areas that will be potentially designated under EPA’s proposed data requirements rule (see above). The document describes the use of the SIP process by air agencies as a tool used to discern culpable sources and facilities that contribute to area nonattainment and thereby select emission reduction measures on that basis to achieve attainment. Specific details are provided in the form of modeling guidance and guidance for assessing air quality due to setting longer-term average emission limits that will be protective of short term NAAQS.

Trinity can provide strategic assistance in both discerning this proposed rule and its implications as well as implementing programs to achieve near term and ongoing compliance.