Updated NO2/SO2 1-hr modeling guidance

EPA released additional guidance for modeling 1-hour NO2 NAAQS compliance 3/1/2011. It updates OLM and PVMRM policy, addresses significant contribution analyses using the SILs, and discusses how to perform cumulative analyses including the option of incorporating temporally-varying background concentrations.

It also "[r]ecommends that compliance demonstrations for the 1-hour NO2 NAAQS address emission scenarios that can logically be assumed to be relatively continuous or which occur frequently enough to contribute significantly to the annual distribution of daily maximum 1-hour concentrations based on existing modeling guidelines, which provide sufficient discretion for reviewing authorities to not include intermittent emissions from emergency generators or startup/shutdown operations from compliance demonstrations for the 1-hour NO2 standard under appropriate circumstances."

3/1/2011 Policy Memo

See this blog post for access to previous memos.

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See this article for a helpful discussion of the state of SO2 and NO2 1-hr NAAQS modeling guidance, including April updates to AERMOD and AERMET. It also talks about recent EPA guidance to states for 1-hr SO2 NAAQS attainment designation.
(added 5/20/2011, KMM)
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