Gathering – In-Stack Ratio Presentation

“… The June 28, 2010 guidance emphasized the importance of these in-stack ratios for the 1-hour NO2 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 NO2/NOx ratio for either OLM or PVMRM). Additional guidance issued on March 1, 2011 allowed for a default ISR of 0.5 in the absence of more appropriate source-specific information. 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.”

– from EPA SCRAM website* NO2/NOx In-Stack Ratio (ISR) Database”


EUEC 2015_Abstract_At the Intersection of NAAQS Modeling

This post is about extending an invite to those interested in contributing information about their perspectives, experiences, reference materials, and resources related to ISRs. Also, if you want to rant or rave, I enjoy great stories!

Please feel free to CONTACT ME to chat up ISRs.

We all want the same thing – fair and representative NO2/NOx In-Stack Ratios. (And yes, based on any conversations and information exchange, I would appropriately and fairly cite information shared.)

2015 February 18 EUEC Conference

I will be presenting at the EUEC 2015 Conference next month on the ISR topic. As part of preparing my 20-minute presentation, I am surveying and talking with agency and industry colleagues regarding their perspectives and experiences. I also am compiling reference materials and resources that may be helpful. My understanding is that there continues to be ISR information not yet part of EPA’s database (discussed over here). How do I know that? I have found myself encouraging people to submit their information.

The Goal of Representative NO2/NOx ISRs

In short, I believe each stakeholder party – affected public, project developer, agency, lawyer, source tester, policy maker, consultants, etc. – would like to assure that representative ISRs are used. Default value (0.50) aside, the ISRs are party-neutral. They are derived from measured values and/or estimated mathematically based on various assumptions.

Having been with EPA Region 9 from 2007-2014 in the Air Permits Office, I was part of a group that was responsible for permit preparation and/or oversight (e.g., PSD, NSR, Title V), as well as supporting other intra-agency groups and inter-agency groups with air quality-related issues. Like all agency personnel, I had the opportunity of not only understanding the agency’s (and partner agencies’) perspectives but also industries’ and public-at-large perspectives. This applied to ISR issues.

1-hour NO2 Standard – Because Region 9’s jurisdiction includes California, air quality modeling of 1-hour NO2 was already being performed for those projects triggering the state requirement; California has had a state ambient air quality standard for 1-hour NO2. Initially at 0.25 ppm, California later adopted in 2007 a 1-hour state standard (0.18 ppm NO2).  With regards to the federal standard, in 2010, EPA adopted (after only have an annual standard) a 1-hour NAAQS of 100 ppb in “[t]he form of the 1-hour standard is the 3-year average of the 98th percentile of the yearly distribution of 1-hour daily maximum NO2 concentrations.” In short, the federal 1-hour NO2 NAAQS is relatively stringent.

Without going into too much nerd-speak, the importance of the ISR is that it can potenitally contribute to a “go” or “no go” decision for a project requiring 1-hour NO2 NAAQS modeling.

Again, feel free to CONTACT ME to chat up ISRs.

* EPA’s website contains updated information and guidance since the database/data collection was initiated; however, with ISRs, the process generally remains the same.


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