PRSRT STD U . S . POSTAGE PAID AUSTIN , TEXAS PERMIT NO . 1718
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Next , the change in the form of the annual NAAQS requires that , for areas with multiple eligible monitoring sites , the site with the highest design value will determine the attainment status for that area , unlike the process for designating attainment under the 2006 annual PM 2 . 5
NAAQS , which was made based on spatial averaging over multiple monitors in metropolitan areas . The implication of this change is that even more areas could be declared in nonattainment with the
PM 2 . 5 standard .
Also , as difficult as it is to demonstrate modeled compliance with the 24-hour standard and the prior 15-μg / m 3 annual standard in the permitting of major projects , it will be even more difficult in permitting new projects under the tightened annual standard . One aspect of this difficulty is the way that measured concentrations are used to establish background levels in the permitting context . Based on EPA guidance , a representative measured background concentration determined from recent monitoring data is added to the modeled annual concentrations for sources being permitted and other sources not reflected in the background to determine if combined concentrations will exceed the annual NAAQS . However , if the 3-year average of annual concentrations measured at a representative monitor is 12 μg / m 3 or greater , it might be difficult to permit a project unless EPA refines its guidance related to the use of dispersion modeling results and air monitoring data . that coincident PM 2 . 5 reductions associated with implementing other national strategies and regulations , such as the Cross-State Air Pollution Rule and Mercury and Air Toxics Standards , will ease the burden of complying with the new PM 2 . 5 standard . However , since several of these regulations are only in the beginning stages of implementation , their true impact on PM 2 . 5 emissions and ambient PM 2 . 5 concentrations is not knowable at this time . If the number of counties able to attain the new annual PM 2 . 5
NAAQS has been underestimated by EPA , the costs associated with measures required in State Implementation Plans will have also been underestimated .
In conclusion , while the revision of the annual PM 2 . 5 NAAQS does not by itself require that any specific air pollution control measures be taken , it puts emitting sources on a trajectory that could potentially require significant investment in process and emissions controls to limit PM 2 . 5 emissions . The shrinking margin of compliance associated with the lower standard also introduces new implementation challenges to the use of dispersion models to assess compliance and will likely be an obstacle to the future growth of facilities . Therefore , the need for internal reductions to offset increases in PM 2 . 5 emissions and the necessity of compliance planning has never been greater for PM 2 . 5
. Z
Lucy Fraiser Principal
Finally , EPA ’ s estimates of the costs associated with implementing the new PM 2 . 5 annual NAAQS assumed
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