Will Future NAAQS Violations Be Modeled Rather than Monitored?

The DC Circuit Court has affirmed EPA's adoption of sulfur dioxide and nitrogen oxide National Ambient Air Quality Standards. National Environmental Development Association v. EPA approved the SO2 NAAQS, in which 

EPA mandated that States must meet a new 1-hour SO2 standard using a 99th percentile form, set at 75 ppb maximum SO2  concentration.  75 Fed. Reg. at 35548.   The goal of the new standard is to prevent asthmatics from being exposed to shortterm, five- to ten-minute bursts of SO2 , which EPA found could cause lung function decrements in asthmatics.  Id. 

In American Petroleum Institute v. EPA the Court approved the new  NOx  NAAQS, which mandates that  

 “the three-year  average of the annual 98th percentile of the daily maximum 1-hour average concentration  [be] less than or equal to 100 ppb.”   Primary National Ambient Air Quality Standards for Nitrogen Dioxide, 75 Fed. Reg. 6474, 6531 (Feb. 9, 2010) (codified at 40 C.F.R. § 50.11(f)).  The EPA concluded this standard was needed “to provide protection for asthmatics and other at-risk populations against an array of adverse respiratory health effects related to short-term NO2 exposure.”  Id. at 6502.

Another important issue was also presented in these cases -  the manner in which the NAAQS  may be enforced. In the preamble to the SO2 final decision, EPA had stated that it would rely on air modeling (computer guesses of emissions)  in addition to air monitoring (actual air pollution emission measurements) to determine compliance.

 In the preamble to the final rule, EPA also explained that, based on comments it received,  “we are revising our general anticipated approach toward implementation of the new 1-hour NAAQS.”  75 Fed. Reg. at 35550.  Instead of assessing attainment of the standard primarily by monitoring the ambient air, as it had stated it would in the proposed rule, EPA suggested it would use a “hybrid analytic approach” that would combine monitoring with computer modeling to determine compliance. 75 Fed. Reg. at 35551.

The Sierra Club has already served notice that it will rely on modeling to bring actions against power plants that it believes cannot achieve the standards. See the blog article from Bart Cassidy of  Manko, Gold, Katcher and Fox about the Sierra Club and Earthjustice's citizen suit against a coal-fired plant that they allege is violating the new one-hour SO2 standard based on modeling they have performed.