12/02/16 - The Guidance on the Development of Modeled Emission Rates for Precursors (MERPs) as a Tier 1 Demonstration Tool for Ozone and PM2.5 under the PSD Permitting Program(79 pp, 1.6 MB, About PDF) is now available for consideration, review, and comment. The EPA will accept comment through Friday, February 3, 2017.

11/17/16 - The PM_2.5 Precursor Demonstration Guidance is now available for consideration, review, and comment. The EPA will accept comment through Tuesday, January 31, 2017.

08/18/16 A webinar regarding the Draft O₃ and PM_2.5 SILs Guidance for PSD Program (Slides from the webinar available on this webpage.) will be conducted on Wednesday, August 24, 2016 from 2:00p to 3:30p EDT.

08/04/16 The draft SO₂ Modeling Technical Assistance Document (PDF) has been updated to clarify receptor placement and the minimum number of years to model.

08/01/16 A Model Clearinghouse concurrence memorandum to Region 6 regarding the use of the beta ARM2 technique as an alternative model has been added to the MCHISRS database.

08/01/16 A Model Clearinghouse concurrence memorandum to Region 8 regarding the use of the ADJ_U* beta option in AERMET as an alternative model has been added to the MCHISRS database.

08/01/16 The Draft Guidance on SILs for Ozone and PM2.5 in PSD has been posted on the NSR Permitting website along with supporting documentation. The EPA will accept public comment on the draft guidance package through Septemebr 30, 2016.

07/26/16 Updated regulatory versions of CALPUFF and CALMET (version 5.8.5, dated 151214) are now available. The links to the updated CALPUFF Modeling System files, the associated Model Change Bulletin (MCB-H) can be found on the CALPUFF webpage.

03/30/16 A coding bug has been discovered with AERSCREEN (v15181) in certain circumstances involving the use of the inversion and/or shoreline fumigation option. A temporary and simple workaround is described in this email message and will be resolved in the next release of AERSCREEN later this spring.

12/10/15 A Clarification on the Approval Process for Regulatory Application of the AERMOD Modeling System Beta Options memorandum is now available. This memo discusses the appropriate process for the approval of the AERMOD Modeling System with the use of various beta options for regulatory applications.

09/14/15 The presentations, transcripts, and audio recordings from the 11th Conference on Air Quality Modeling are now available. Additionally, all of the model code, technical support documentation, draft guidance, IWAQM reports, supporting docket material, etc. related to the proposed Guideline on Air Quality Models rulemaking are accessible through the 11th Conference on Air Quality Modeling informational website.

07/14/15 A proposal to revise the Guideline on Air Quality Models was signed by the Administrator on July 14, 2015. The rulemaking Proposal and Fact Sheet for this proposed rulemaking package are availablce through the 11th Conference on Air Quality Models informational website.

12/04/14 The Draft Modeling Guidance for Demonstrating Attainment of Air Quality Goals for Ozone, PM2s, and Regional Haze is now available for consideration, review, and comment. This document is a revision to the previous modeling guidance which was released in April 2007.

04/08/14 Interim guidance for the treatment of condensable particulate matter test results in the PSD and NSR permitting programs is now available.

01/14/14 The draft SO₂Monitoring and Modeling Technical Assistance Documents have been updated based on public comments and are available on the Sulfur Dioxide Implementation web page.

08/26/13 The NO₂/NO_x In-Stack Ratio (ISR) Database has been updated based on the first database submission from the State of Oklahoma and the second database submission from the State of Alaska.