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Fact Sheet

Proposed Data Requirements Rule for the 1-Hour Sulfur Dioxide

Primary National Ambient Air Quality Standard (NAAQS) 

ACTION

 On April 17, 2014, the U.S. Environmental Protection Agency (EPA) proposed 

requirements for air agencies to characterize sulfur dioxide (SO2) air quality more 

extensively across the country for purposes of implementing the 1-hour SO2 National Air 

Ambient Quality Standards (NAAQS). This approach would focus on characterizing air 

quality in areas with large sources of SO2 emissions, and include smaller sources in areas 

with higher population. This action proposes a reasonable schedule for state and tribal air 

agencies to characterize air quality and provide that air quality data to the EPA.

 Air agencies would have the flexibility to characterize air quality using either modeling 

of actual source emissions or using appropriately sited ambient air quality monitors. The 

EPA intends to use these data in two future rounds of area designations in 2017 and 2020. 

Air quality modeling for SO2 has been demonstrated to be an effective way to assess 

local air quality and may be a cost effective alternative to air quality monitoring in many 

circumstances. 

 The proposed rule includes options for emissions thresholds which would identify the 

sources around which air agencies would need to characterize SO2 air quality. To 

increase public health protection in more highly populated areas, each option includes a 

lower annual emissions threshold for sources located in metropolitan areas greater than 1 

million in population, and a higher threshold for sources outside these areas. 

o Option 1 would cover sources greater than 1000 tons of SO2 in metro areas with 

population greater than 1 million; and sources greater than 2000 tons everywhere 

else.

o Option 2 would cover sources greater than 2000 tons of SO2 in metro areas with 

population greater than 1 million; and sources greater than 5000 tons everywhere 

else.

o Option 3 would cover sources greater than 3000 tons of SO2 in metro areas with

population greater than 1 million; and sources greater than 10,000 tons everywhere 

else.

 Air agencies can avoid a nonattainment designation for an area by working with sources 

to establish permanent and enforceable emission limitations that show attainment with 

the SO2 standards through modeling prior to the next round of designations in 2017. 

Compliance with other emission reduction programs, such as the Mercury and Air Toxics 

Standards for power plants and emission standards for boilers, may help these areas 

improve ambient SO2 air quality earlier. 

 In July 2013, the EPA identified or “designated” as nonattainment, 29 areas in 16 states 

where monitored air quality showed violations of the 2010 1-hour standard. The EPA 

based these nonattainment designations on certified air quality monitoring data provided
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by the states as well as an assessment of other factors (such as nearby emission sources 

and weather patterns) that contribute to the monitored levels. These areas are now taking 

steps to reduce SO2 emissions and improve air quality.

PROPOSED IMPLEMENTATION APPROACH

 The EPA’s Comprehensive Implementation Strategy for the 2010 SO2 standard lays out a 

commonsense approach that focuses resources on identifying and addressing unhealthy 

levels of SO2. In developing the strategy, the EPA carefully considered stakeholder 

feedback obtained during an extensive outreach process. 

 By January 15, 2016, air agencies would be required to submit to the relevant EPA 

Regional Administrator a final list identifying the specific sources in the state around 

which SO2 air quality is to be characterized, and indicating the air agency’s approach to 

characterizing air quality around the source either through monitoring, modeling or a 

combination. 

 For source areas that the air agency identifies would be evaluated through air quality 

modeling, the EPA proposes that the air agency must also provide a modeling protocol to 

the EPA Regional Administrator by January 15, 2016.

 The EPA intends to conduct a second phase of designations during 2017, relying on 

modeling analyses and other related information and to notify the states of intended 

designations by August 2017. The EPA therefore encourages states to submit modeling 

analyses and updated designation recommendations by January 13, 2017. By December 

2017, the EPA intends to issue final designations for areas with modeled violations.

 Air agencies may elect to characterize air quality around some or all sources through 

ambient SO2 monitoring, using existing and new monitoring sites. The EPA proposes that 

air agencies be required to submit relevant information about these monitoring sites to the 

EPA Regional Administrator by July 1, 2016, as part of their annual monitoring network 

plan, in accordance with the EPA’s monitoring requirements specified in 40 CFR part 58. 

States electing to monitor to satisfy this rule will need to take specific actions to identify, 

relocate and/or install new ambient SO2 monitors that would characterize peak 1-hour 

SO2 concentrations in areas around or impacted by identified SO2 sources.

 The EPA proposes that air agencies that have chosen to characterize air quality for certain 

SO2 sources through ambient monitoring must have any relocated and/or new monitors 

operational by January 1, 2017. Air agencies will quality assure data from these monitors 

and submit it to the EPA Air Quality System in the same manner as is currently done for 

existing SO2 monitors. Under this approach, it is anticipated that the first 3 years of data 

would be collected for calendar years 2017 through 2019; and using these data, the 

intended designations process for these areas would be completed in 2020. 
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 Recent Clean Air Act (CAA) rules will help states meet the revised SO2 standard by 

reducing pollution both regionally and across the country. The schedule for designations 

and planning requirements in this rule aligns with the implementation schedules for 

national rules that will reduce SO2 emissions – including the Mercury and Air Toxics 

Standards for power plants, and rules to control emissions from industrial boilers. 

BACKGROUND

 The CAA requires the EPA to issue designations after the agency sets a new NAAQS or 

revises an existing standard. Areas not meeting the standard are designated 

“nonattainment.” 

 On June 2, 2010, the EPA strengthened the primary SO2 air quality standard. The revised 

standard will improve public health protection, especially for people with asthma, 

children and the elderly. In the final SO2 standard rulemaking, the EPA provided initial 

thinking on how states and emission sources should implement the new 1-hour SO2

standard.

On September 21, 2011, the EPA asked for public comment on draft guidance to states 

about how to implement the primary standard for SO2. 

 In May-June 2012, the EPA held a series of stakeholder discussions with states, tribes 

and other interested parties to refine the agency’s approach for implementing the SO2

standard. To facilitate the discussion, the EPA developed a White Paper that identified 

important monitoring, modeling and implementation issues. The White Paper and 

summaries of the stakeholder discussions can be found on the EPA’s website at: 

http://www.epa.gov/airquality/sulfurdioxide/implement.html.

 Based on the input on the White Paper received from a diverse group of stakeholders, the 

EPA developed a comprehensive implementation strategy for the 2010 SO2 standard in 

February 2013. The strategy included the development of a regulation that would require 

states to further characterize air quality near large sources of emissions so that the air 

quality data could be the basis of future SO2 designations. The strategy, “Next Steps for 

Area Designations and Implementation of the Sulfur Dioxide National Ambient Air 

Quality Standards,” is available at: 

http://www.epa.gov/airquality/sulfurdioxide/implement.html.

 On August 5, 2013, the EPA published a rule which identified or “designated” 29 areas in

16 states as “nonattainment.” (No areas in Indian Country were designated nonattainment 

as part of these designations.) The EPA based these nonattainment designations 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 now need to develop and implement plans to reduce pollution to meet the SO2

standard. 
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 After evaluating and responding to stakeholder comments on a May 2013 draft, in 

January 2014, the EPA made available two updated draft documents that provide 

technical assistance for states implementing the 2010 health-based, SO2 standard. These 

documents provide technical advice on the use of air quality modeling (based on actual 

emissions data) and on properly siting ambient monitors to characterize peak 1-hour SO2 

air quality in order to determine if an area meets the 2010 SO2 air quality standard. 

These technical assistance documents are available at: 

http://www.epa.gov/airquality/sulfurdioxide/implement.html.

HOW TO COMMENT

 The EPA will accept comments on this proposed rule for 60 days following publication 

in the Federal Register. 

 Comments on the proposed federal plan requirements, identified by Docket ID No. 

EPA-HQ-OAR-2013--0711, can be submitted by one of the following methods:

o www.regulations.gov: Follow the on-line instructions for submitting comments.

o Email: Send your comments via electronic mail to a-and-r-Docket@epa.gov, 

Attention Docket ID No. EPA-HQ-OAR-2013-0711.

o Facsimile: Fax your comments to (202) 566-9744, Attention Docket ID No. EPAHQ-OAR-2013-0711.

o Mail: Send your comments to: EPA Docket Center (EPA/DC), Environmental 

Protection Agency, Mailcode 6102T, 1200 Pennsylvania Ave., NW, Washington, DC 

20460, Attention Docket ID No. EPA-HQ-OAR-2013-0711. Please include a total of 

two copies. 

o Hand Delivery: Deliver your comments to: EPA Docket Center (EPA/DC), William 

Jefferson Clinton Building, Room 3334, 1301 Constitution Ave., NW, Washington, 

DC, 20004, Attention Docket ID No. EPA-HQ-OAR-2013-0711. Such deliveries are 

accepted only during the normal hours of operation (8:30 a.m. to 4:30 p.m., Monday 

through Friday, excluding legal holidays), and special arrangements should be made 

for deliveries of boxed information.

FOR MORE INFORMATION

 To download a copy of this proposed rule, go to the EPA’s website at: 

http://www.epa.gov/airquality/sulfurdioxide/implement.html.

 Today’s Rule and other associated information are available either electronically at 

http://www.regulations.gov, the EPA’s electronic public docket and comment system, or 
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in hardcopy at the EPA Docket Center’s Public Reading Room. (Docket ID No. EPAHQ-OAR-2013-0711)

 The Public Reading Room is located in the EPA Headquarters, Room Number 3334 in 

the William Jefferson Clinton West Building, located at 1301 Constitution Avenue, NW, 

Washington, DC. Hours of operation are 8:30 a.m. to 4:30 p.m. eastern standard time, 

Monday through Friday, excluding Federal holidays.

 Visitors are required to show photographic identification, pass through a metal detector, 

and sign the EPA visitor log. All visitor materials will be processed through an X-ray 

machine as well. Visitors will be provided a badge that must be visible at all times.