Posted on January 8, 2016 by Todd E. Palmer
The Wisconsin Department of Natural Resources (WDNR) is finalizing guidance documents which will simplify how air permit applicants demonstrate that their emissions do not cause or contribute to exceedances of the PM2.5 National Ambient Air Quality Standards (NAAQS). This guidance is based upon a technical analysis showing that direct emissions of PM2.5 from most stationary sources do not meaningfully contribute to ambient concentrations of PM2.5. Building on this conclusion, WDNR will no longer require air dispersion modeling to be performed for PM2.5 when issuing most air permits. This novel state approach to PM2.5 regulation should adopted by other jurisdictions.
As EPA shifts its focus to regulating smaller forms of PM, the chemistry associated with these smaller pollutants has added to the complication of regulation. With respect to PM2.5, it is a pollutant emitted directly by certain emission sources (e.g., combustion processes) and is also formed secondarily in the atmosphere by the chemical interaction of precursor pollutants (NOx, SO2, ammonia). To date, states have generally implemented air permitting policies that simplify these complications. For example, states may assume that a percentage of a source’s PM10emissions consist of PM2.5 or that direct emissions of PM2.5 have the potential to significantly contribute to ambient concentrations of PM2.5. These generalities and assumptions have presented problems for stationary sources, especially when performing the air dispersion modeling attendant to receiving an air permit.
Recognizing these problems, WDNR undertook its own technical analysis which concludes that dispersion modeling of direct PM2.5emissions does not provide information useful for understanding the impact of those emissions on ambient air quality. WDNR found that direct, industrial stationary source PM2.5 emissions do not correlate with the ambient concentrations of PM2.5 in the atmosphere around a stationary source. Rather, PM2.5 exhibits characteristics more like a regional pollutant influenced by the emissions from numerous sources dispersed throughout a broad geographic region. Using this premise, WDNR will be restricting the circumstances when PM2.5 air dispersion modeling will be required when issuing air permits and the instance where sources will be subjected to PM2.5 emission limitations.
In this draft guidance, WDNR proposes to no longer require estimating PM2.5 emissions from fugitive dust sources, mechanical handling systems, grain handling operations or other low temperature PM sources. Rather, PM2.5 emission estimates will only be required for combustion and high temperature industrial processes that directly emit significant amounts of PM2.5. For these high temperature sources, WDNR will use a “weight of evidence” approach to conclude that direct emissions of PM2.5 do not cause or exacerbate a violation of the PM2.5 NAAQS or increments in ambient air. This will greatly simplify the manner in which air permit applicants must calculate PM2.5 emissions from a project, significantly limit the circumstances in which PM2.5 modeling must be performed as part of a permit application and restrict the instances in which PM2.5 emission limitations must be included in air permits.