On May 13, the Environmental Protection Agency (EPA) issued proposed options for states and local air agencies to use air quality monitoring or modeling to determine whether areas meet the 2010 air quality standards for sulfur dioxide (SO2). Below is a discussion of the proposed rule.
Background of 2010 Revised SO2 NAAQS
In June 2010, the EPA promulgated a revised primary SO2 National Ambient Air Quality Standards (NAAQS). The 2010 rule provided a 1-hour standard at a level of 75 parts per billion based on the 3-year average of the annual 99th percentile of 1-hour daily maximum concentrations.
In 2011, the EPA issued draft guidance for state agencies to implement these standards. Based on feedback, the EPA developed a “comprehensive implementation strategy” for the 2010 SO2 standard in February 2013.
The EPA originally designated 29 areas in 16 states as “nonattainment.” (Rhinelander in Oneida County was the only area designed as non-attainment in Wisconsin). According to the EPA, these nonattainment designations were based on the most recent set of certified air quality monitoring data as well as an assessment of nearby emission sources and weather patterns that contribute to the monitored levels. These areas are now required to develop and implement plans to reduce pollution to meet the SO2 standard.
Proposed Rule: Data Requirements Rule for the 1-Hour SO2 Primary NAAQS
On May 13, 2014, the EPA issued the proposed rule directing state and tribal air agencies to “provide data to characterize current air quality in areas with large sources of sulfur dioxide (SO2) emissions if such areas do not have sufficient air quality monitoring in place to identify maximum 1-hour SO2 concentrations.”
The proposed rule “describes criteria for identifying the sources around which air agencies would need to characterize SO2 air quality.” In addition, the proposed rule describes the process and timetables by which state agencies must characterize air quality around sources through ambient monitoring and/or air quality modeling techniques and submit the data to the EPA.
The rule also includes three options for emissions thresholds which would be used to identify future air quality characterization and the factors that the EPA considered in developing them.
Option 1: Requires ambient air quality characterization around sources with emissions greater than 1,000 tons per year (tpy) of SO2 in metro areas with population greater than 1 million or more persons, and sources greater than 2,000 tpy everywhere else.
Option 2: Requires ambient air quality characterization around sources with emissions greater than 2,000 typ of SO2 in metro areas with population greater than 1 million or more persons, and round sources greater than 5,000 tpy everywhere else.
Option 3: Requires ambient air quality characterization around sources with emissions greater than 3,000 typ of SO2 in metro areas with population greater than 1 million or more persons, and round sources greater than 10,000 tpy everywhere else.
Most notable in the EPA’s proposed rule is the fact that the original proposed rule set the threshold at 100 tons per year. The current proposed rule sets it at 1,000 tpy. The public has 60 days to submit comments with the EPA.
The EPA, in separate non-binding draft technical assistance documents, explains how air agencies can conduct such monitoring or modeling. The air quality data developed by the states in accordance with the draft rule will then be used by the EPA in the future rounds of area designations for the 1-hour SO2 NAAQS.