Update on MERPs Guidance. Tyler Fox/Kirk Baker US EPA/OAQPS/Air Quality Modeling Group June 5, 2018

Transcription

1 Update on MERPs Guidance Tyler Fox/Kirk Baker US EPA/OAQPS/Air Quality Modeling Group June 5, 2018

2 Overview: Chapter 5 of Guideline Totally new chapter in 2017 revisions to Guideline Clear distinction between nonattainment planning for NAAQS (multisource) vs. permit (single source) modeling recommendations Outlines a multi-tiered approach for single source permit assessments that reflects a screening approach with no preferred model Emphasizes the importance to develop modeling protocols and consult with the reviewing authority Emphasis on use of chemical transport models (e.g. photochemical & Lagrangian models) or techniques that reflect state of science atmospheric chemistry for the less-anticipated situations where a refined assessment is necessary Section 5 does not provide a requirement for chemical transport modeling 2

3 Final Action: Single-Source Impacts on Ozone and Secondary PM 2.5 The EPA believes photochemical grid models are generally most appropriate for addressing ozone and secondary PM 2.5, because they provide a spatially and temporally dynamic realistic chemical and physical environment for plume growth and chemical transformation. Lagrangian models (e.g. SCICHEM) applied with a realistic 3-dimensional field of chemical species could also be used for single source O 3 or PM 2.5 assessments. The EPA has finalized a two-tiered demonstration approach for addressing single-source impacts on ozone and secondary PM 2.5. Tier 1 demonstrations involve use of technically credible relationships between emissions and ambient impacts based on existing modeling results or studies deemed sufficient for evaluating a project source s impacts. Tier 2 demonstrations would involve case-specific application of chemical transport modeling (e.g., with an Eulerian grid or Lagrangian model). 3

4 Chemical Transport Models for Permit Related Regulatory Assessments In lieu of an EPA preferred model, EPA recommends chemical transport models for estimating single source O3 and secondary PM2.5 impacts Chemical transport models include Lagrangian puff models and Eulerian grid (e.g. photochemical transport) models Lagrangian puff models need as input a realistic chemical environment Photochemical transport models typically estimate a realistic chemical environment Even though single source emissions are injected into a grid volume, comparisons with in-plume measurements indicate these types of models can capture downwind secondary pollutant impacts when applied appropriately for this purpose Further testing is needed for both types of chemical transport modeling systems (Lagrangian and Eulerian) to best understand the configurations appropriate for permit related assessments 4

5 Tier 1 Assessments For Tier 1 assessments, EPA generally expects that applicants would use existing empirical relationships between precursors and secondary impacts based on modeling systems appropriate for this purpose. The use of existing credible technical information that appropriately characterize the emissions to air quality relationships will need to be determined on a case-by-case basis. Examples of existing relevant technical information that may be used by a permit applicant, in consultation with the appropriate permitting authority, include air quality modeling conducted for the relevant geographic area reflecting emissions changes for similar source types as part of a State Implementation Plan (SIP) demonstration, other permit action, or similar policy assessment as well air quality modeling of hypothetical industrial sources with similar source characteristics and emission rates of precursors that are located in similar atmospheric environments and for time periods that are conducive to the formation of O 3 or secondary PM

6 MERPs as a Tier 1 Demonstration Tool December 2016, EPA provided draft technical guidance that provided a framework for development of Tier 1 demonstration tools under Appendix W for PSD permitting. MERPs can be viewed as a type of Tier 1 demonstration tool under the PSD permitting program that provides a simple way to relate maximum downwind impacts with an applicable SIL value. For PSD, separate MERPs could be developed to relate: volatile organic compounds (VOCs) and/or nitrogen oxides (NO x ) to O 3 sulfur dioxide (SO 2 ) and/or NO X to secondary PM 2.5 Completing updated version for EPA management review that addresses public comments with emphasis on: Added Executive Summary Extended EPA modeling of hypothetical sources More clarity on use of MERPs at national, regional and local level with more detail in the examples provided in the guidance 6

7 Definition of MERP value To derive a MERP value, the model predicted relationship between precursor emissions from hypothetical sources and their downwind maximum impacts can be combined with the applicable SIL value using the following equation: MERP = Applicable SIL value * (Modeled emission rate from hypothetical source / Modeled air quality impact from hypothetical source) MERPs are expressed as an annual emissions rate in tons per year consistent with the modeled emissions rates that are input to the air quality model to predict a change in pollutant concentrations. Based on EPA modeling to inform illustrative MERPs, these values will vary across the nation reflecting different sensitivities of an area s air quality level to precursor emissions, thereby providing an appropriate basis for evaluating the impacts of these precursors to PM 2.5 and ozone formation because they reflect the regional or local atmospheric conditions for particular situations. 7

8 EPA Single Source Impact Model Assessments DRAFT VERSION UPDATED VERSION 8

9 Lowest MERP value for each hypothetical source location 9

10 Distribution of EPA s illustrative MERP Values (tons per year) for 8-hour Ozone NAAQS by precursor and climate zone 8-hr O 3 from NO X 8-hr O 3 from VOC Climate Zone Lowest Median Highest Lowest Median Highest Northeast ,773 2,068 3,887 15,616 Southeast ,817 7,896 42,964 Ohio Valley ,346 1,159 3,388 12,362 Upper Midwest ,775 1,462 2,080 30,857 Rockies/Plaines , ,425 12,788 South ,075 1,885 4,494 30,381 Soutwest ,179 1,097 9, ,744 West ,094 1,681 17,086 Northwest ,031 1,049 2,399 15,929 10

11 Distribution of EPA s illustrative MERP Values (tons per year) for Daily PM2.5 NAAQS by precursor and climate zone Daily PM2.5 from NO X Daily PM2.5 from SO 2 Climate Zone Lowest Median Highest Lowest Median Highest Northeast 2,218 16,165 57, ,137 17,868 Southeast 1,820 8,721 27, ,547 9,012 Ohio Valley 2,499 10,266 63, ,001 32,927 Upper Midwest 2,963 10,651 51, ,821 10,475 Rockies/Plaines 1,925 9,808 60, ,387 34,381 South 1,693 7,417 39, ,310 14,727 Soutwest 6,514 26, ,170 1,508 9,065 45,857 West 1,073 8,570 34, ,236 24,596 Northwest 3,003 11,943 20,716 1,203 3,319 8,418 11

12 Distribution of EPA s illustrative MERP Values (tons per year) for Annual PM2.5 NAAQS by precursor and climate zone Annual PM2.5 from NO X Annual PM2.5 from SO 2 Climate Zone Lowest Median Highest Lowest Median Highest Northeast 10,142 49, ,728 4,014 21,353 78,732 Southeast 3,664 46, , ,906 48,475 Ohio Valley 7,427 31, ,074 3,104 23, ,711 Upper Midwest 7,405 39, ,959 2,409 21,200 85,018 Rockies/Plaines 9,509 43, ,542 2,289 19, ,382 South 6,431 33, ,089 1,290 10,489 96,915 Soutwest 11, , ,099 10,884 39, ,289 West 3,182 29, ,000 2,331 11,977 66,773 Northwest 7,942 21,928 71,569 11,276 15,507 18,263 12

13 Model Input/Output Data Availability The availability of model inputs and outputs of photochemical models (i.e., model platform data) allows for development of area/source MERPs (and, if necessary, streamline a Tier 2 demonstration). EPA and other organizations have made such model platform data freely available to interested users. For instance, modelready inputs for both CAMx and CMAQ for the entire year of 2011 are available at EPA is currently working on a 2016 Modeling Platform (Winter 2019) Further, multi-jurisdictional organizations typically either have existing photochemical grid model inputs or can direct those interested to other groups/organizations in the same region that may have suitable data. 13

14 Multi-Jurisdictional Organizations Organization Region of the country Internet site CENSARA Central U.S. LADCO Upper Midwest MARAMA Mid-Atlantic NESCAUM Northeast U.S. NW-AIRQUEST Northwestern U.S. SESARM Southeast U.S. WRAP Western U.S. 14