The methodology used to develop the annual SERs did not take into account hourly variations in emissions or hourly meteorological conditions. These two factors, varying emissions coupled with varying meteorology, become important considerations when modeling sources with high intermittent emissions at 1-hour averaging times.
Facility emissions that are below the SERs may still cause short-term NAAQS exceedances. In-house analyses at DEQ have demonstrated, through the modeling of hypothetical facilities, that a 1-hour standard can be exceeded while annual average emissions are below the SER.
Both the basis of the SERs and the in-house modeling demonstrations lead DEQ to conclude the current practice of using the SERs to screen out sources from NAAQS compliance modeling may not sufficiently demonstrate that the NO2 and SO2 1-hour NAAQS, and the 24-hour PM2.5 NAAQS are protected.