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Draft Guidance on Significant Impact Levels (SIL) for O3 and PM2.5 under the PSD Program

On August 1st, 2016 (revised August 18th, 2016) EPA released a draft guidance memo on Significant Impact Levels (SIL) for Ozone (O3) and particulate matter less than 2.5 microns in aerodynamic diameter (PM2.5).

The salient points from the draft memo are listed below:

The following NAAQS SIL concentrations are recommended:
Ozone 8-hour:  1.0 ppb
PM2.5 24-hour:  1.2 ug/m3
PM2.5 Annual:  0.2 ug/m3
Source: EPA Webinar held on August 24, 2016.

PSD Increments
Currently, there is no PSD increment for 8-hr O3 NAAQS. Therefore, an O3 increment SIL is not recommended in this guidance.

PM2.5 increment SIL recommendations are also provided.

General points
EPA has left the adoption of these SILs to the discretion of permitting authorities.
Final guidance memo is expected by end of 2016.
EPA is accepting informal comments until September 30, 2016.

EPA Website:

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