![]() ![]() As with any Tier 3 NO 2 modeling, the use of any single or collection of NO 2 ratios can only be used in permit modeling with the approval of the appropriate reviewing authority, whether an EPA Regional Office, State, or local permitting organization. Inclusion of data in this database does not imply any pre-approval for usage and no single or collection of datum contained in the database have been reviewed or determined to be complete, correct, or acceptable by OAQPS for modeling applications. ![]() If submissions indicate that more than 80 entries are typical, the template will be updated as appropriate. If more than 80 entries are necessary, it is requested that the extra data be entered in a new template. The template has been prepared to accept a maximum of 80 entries. The entry fields for the template are discussed in detail in the accompanying Read Me file (PDF) (3 pp, 100 K, 09-10-2015. NO 2_ISR_database_template.xlsx (XLSX) (410 K, 09-10-2015) – This file contains the template for submissions of ISR values. NO 2_ISR_database.xlsx (XLSX) (2 MB, 10-29-2020) – This file contains the NO 2 ISR data that has been provided to EPA from various sources, including data collected by various Regional, State, and Local air permitting offices prior to the formal collection initiated by OAQPS, data submitted via the formal collection initiated by OAQPS that meets specific data requirements, and data collected by industry trade groups. However, the recommended default ISR may still be too conservative for many applications such that there remains a significant need for a widely available and well-documented database of ISRs, which is the impetus for the current data collection effort. Additional guidance, Additional Clarification Regarding Applicability of Appendix W Modeling Guidance for the 1-hour NO 2 NAAQS (PDF) (27 pp, 453 K, 03-01-2011), issued on Maallowed for a default ISR of 0.5 in the absence of more appropriate source-specific information. ![]() The Jguidance emphasized the importance of these in-stack ratios for the 1-hour NO 2 NAAQS, recommending that in-stack ratios used with either the OLM or PVMRM options be justified based on the specific application (i.e., there is no “default” in-stack NO 2/NO x ratio for either OLM or PVMRM). The use of the Tier 3 PVMRM and OLM options in AERMOD requires the specification of an in-stack ratio (ISR) of NO 2/NO x for each source (using the CO NO2STACK and/or SO NO2RATIO keywords). EPA issued guidance, Applicability of Appendix W Modeling Guidance for the 1-hour NO 2 NAAQS (PDF) (16 pp, 285 K, 06-28-2010), on June 28, 2010, indicating that the three-tiered approach in Section 4.2.3.4 is generally applicable for the 1-hour NO 2 NAAQS, and also clarified that the Ozone-Limiting Method (OLM) and Plume Volume Molar Ratio Method (PVMRM), included as non-default options in the AERMOD dispersion model, are currently considered to be detailed screening methods under Tier 3. However, with the additional stringency of the new 1-hour NO 2 NAAQS, the need for facilities to use a Tier 3 approach has increased. Prior to the April 2010 revision of the NO 2 NAAQS, most facilities were able to demonstrate compliance with the NAAQS using the Tier 1 and 2 screening methods.
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