1

Enclosure

New Hampshire

Area Designations For the 

2010 SO2 Primary National Ambient Air Quality Standard

Summary

Pursuant to section 107(d) of the Clean Air Act (CAA), EPA must designate areas as either 

“nonattainment,” “attainment,” or “unclassifiable” for the 2010 1-hour sulfur dioxide (SO2) 

primary national ambient air quality standard (NAAQS). The CAA defines a nonattainment area 

as one that does not meet the NAAQS or that contributes to poor air quality in a nearby area that 

does not meet the NAAQS. Table 1 below identifies the portions of counties in New Hampshire

in the Central New Hampshire area EPA is initially designating “nonattainment” based on 

monitored violations. EPA is not yet prepared to designate other areas in New Hampshire.

Table 1. Nonattainment Designation for New Hampshire

Area

New Hampshire

Recommended 

Designation of

Areas/Counties

EPA’s Designation of 

Areas/Counties

Central New Hampshire

Hillsborough County (partial) 

Goffstown

Merrimack County (partial) 

Allenstown 

Bow 

Chichester 

Concord 

Dunbarton 

Epsom 

Hooksett 

Loudon 

Pembroke

Pittsfield

Rockingham County (partial)

 Candia

 Deerfield

 Northwood

Nonattainment

Nonattainment

Nonattainment

Nonattainment

Nonattainment

Nonattainment

Background

On June 2, 2010, EPA revised the primary SO2 NAAQS (75 FR 35520, June 22, 2010) by 

establishing a new 1-hour standard at a level of 75 parts per billion (ppb) which is met at an 
2

ambient air quality monitoring site when the 3-year average of the annual 99th percentile of the 

daily maximum 1-hour average concentrations at is less than or equal to 75 ppb, as determined in 

accordance with Appendix T of 40 CFR part 50. 40 CFR 50.17(a)-(b). EPA has determined this 

is the level necessary to provide protection of public health with an adequate margin of safety, 

especially for children, the elderly and those with asthma. These groups are particularly 

susceptible to the health effects associated with breathing SO2. The Agency is revoking the two 

prior primary standards of 140 ppb evaluated over 24-hours, and 30 ppb evaluated over an entire 

year because the standards will not add additional public health protection given a 1-hour 

standard at 75 ppb. Accordingly, EPA is not designating areas in this process on the basis of 

either of these two prior primary standards. Similarly, the secondary standard for SO2 has not 

been revised, so EPA is not designating areas in this process on the basis of the secondary 

standard.

EPA’s SO2 Designation Approach

Section 107(d) of the CAA requires that not later than 1 year after promulgation of a new or 

revised NAAQS, state Governors may submit their recommendations for designations and 

boundaries to EPA. This deadline was in June, 2011. Section 107(d) also requires EPA to 

provide a notification to states of no less than 120-days prior to promulgating an initial area 

designation that is a modification of a state’s recommendation. EPA has reviewed the State’s 

recommendations and has notified the State Commissioner through a letter signed by the 

Regional Administrator of any intended modifications. While language in section 107 

specifically addresses states, we followed the same process for the tribal governments, pursuant 

to section 301(d) of the CAA and Tribal Authority Rule (40 CFR Part 49). Therefore, we are 

designating tribal areas, in consultation with the tribal governments, on the same schedule as 

state designations. New Hampshire does not have any tribal governments affected by this 

designation. If a state or tribal government does not submit designation recommendations, EPA 

will promulgate the designations that it deems appropriate. If a state or tribal government

disagrees with EPA’s intended area designations, it has an opportunity to demonstrate why any 

proposed modification is inappropriate.

Designations guidance was issued by EPA through a March 24, 2011, memorandum from 

Stephen D. Page, Director, U.S. EPA, Office of Air Quality Planning and Standards, to Air 

Division Directors, U.S. EPA Regions I-X. This memorandum identifies factors EPA intends to 

evaluate in determining boundaries for areas designated nonattainment. These 5 factors include: 

1) air quality data; 2) emissions and emissions-related data (location of sources and potential 

contribution to ambient SO2 concentrations); 3) meteorology (weather/transport patterns); 4) 

geography/topography (mountain ranges or other air basin boundaries); and 5) jurisdictional 

boundaries (e.g., counties, air districts, pre-existing nonattainment areas, reservations, 

metropolitan planning organization), among any other information deemed relevant to 

establishing appropriate area designations and boundaries for the 1-hour SO2 NAAQS.

The March 24, 2011, memo recommended that area boundaries be defaulted to the county 

boundary unless additional provided information justifies a larger or smaller boundary than that 

of the county. EPA believes it is appropriate to evaluate each potential area on a case-by-case 

basis, and to recognize that area-specific analyses conducted by states, tribal governments and/or 

EPA may support a different boundary than a default county boundary.
3

In this TSD, EPA discusses its review and technical analysis of the recommendations submitted 

by the state for designations of the 1-hour SO2 standard and any modifications from these 

recommendations.

Definition of important terms used in this document:

1) Designated “nonattainment” area – an area which EPA has determined, based on a state 

recommendation and/or on the technical analysis included in this document, has violated the 

2010 SO2 NAAQS, based on the most recent three years of air quality monitoring data, or 

contributes to a violation in a nearby area. 

2) Recommended nonattainment area – an area that a state or tribal government has 

recommended to EPA to be designated as nonattainment.

3) Violating monitor – an ambient air monitor meeting all methods, quality assurance and citing 

criteria and requirements whose valid design value exceeds 75 ppb, as described in Appendix T 

of 40 CFR part 50.

4) 2010 SO2 NAAQS - 75 ppb, national ambient air quality standard for SO2 promulgated in 

2010. Based on the 3-year average of the 99th percentile of the annual distribution of daily 

maximum 1-hour average concentrations.

5) Design Value – a statistic that describes the air quality status of a given area relative to the 

level of the NAAQS.

Nonattainment Designations

Technical Analysis for Central New Hampshire Nonattainment Area 

Introduction 

This technical analysis for the Central New Hampshire nonattainment area analyzes the county 

with a monitor that violates the 2010 SO2 NAAQS based on 2009-2011 data, and evaluates the 

risk of nearby cities and towns in different counties being above the standard. EPA has 

evaluated this area based on the weight of evidence of the factors recommended in the March 24, 

2011 issued EPA guidance. 

Figure 2 is a map of New Hampshire showing the locations of air quality monitors in the area, 

and the counties surrounding any violating air quality monitors. Figure 3 shows the cities and 

towns included in the Central New Hampshire nonattainment area. 

Figure 1. Central New Hampshire Nonattainment Area

In July 2011, Governor Lynch recommended that certain partial counties be designated as 

“nonattainment” for the 2010 SO2 NAAQS based on monitored air quality data from 2008-2010

and through an analysis that included air quality data, emissions data, geography and topography, 

meteorology and transport patterns, and jurisdictional boundaries. 
4

Based on EPA's technical analysis described below, EPA is initially designating 14 cities and 

towns in 3 different counties in New Hampshire as nonattainment for the 2010 SO2 NAAQS as 

part of the Central New Hampshire nonattainment area, based upon currently available 

information. These cities and towns are listed above in Table 1. EPA is not yet prepared to 

designate other areas in New Hampshire.

Detailed Assessment

Air Quality Data 

This factor considers the SO2 air quality monitoring data, including the design values (in ppb) 

calculated for all air quality monitors in the Central New Hampshire area and the surrounding 

area based on data for the 2009-2011 period. 

Governor Lynch’s recommendation was based on data from Federal Reference Method monitors 

located in the state. See letter from Governor Lynch to Curt Spalding, EPA Region 1

Administrator, dated July 6, 2011.

The 2011 SO2 NAAQS design values for counties in the Central New Hampshire and 

surrounding area are shown in Table 2.

Table 2. Air Quality Data in New Hampshire

County Monitor 

Name

Monitor Air 

Quality 

System ID

Monitor 

Location

SO2 Design 

Value, 

2009 - 201109

(ppb)

Merrimack Pembroke

Exchange St

330131006 Pembroke 221

Hillsborough Manchester 330110020 Manchester 56

Rockingham Portsmouth 330150014 Portsmouth 41

Monitor in Bold has the highest 2009-2011 design value in the state.

Merrimack County shows a violation of the 2010 SO2 NAAQS. Therefore, some area in this 

county and possibly additional areas in surrounding counties must be designated nonattainment.

The absence of a violating monitor alone is not a sufficient reason to eliminate nearby counties 

as candidates for inclusion in a nonattainment status. Each area has been evaluated based on the 

weight of evidence of the five factors and other relevant information. 

The largest emitter of SO2 emissions in New Hampshire is within a few miles of the Pembroke 

Exchange St monitor. This emitter is identified as Public Service of New Hampshire’s 

Merrimack Station in Bow, New Hampshire. Wind frequency diagrams based on meteorological 

data gathered at Merrimack Station during 1994 and wind frequency data from the years 2000-

2004 obtained at a nearby airport (Concord) shows the prevailing wind direction is from the 

northwest. Merrimack Station is northwest of the Pembroke Exchange St monitor. 

Emissions and Emissions-Related Data
5

Evidence of SO2 emissions sources in the vicinity of a violating monitor is an important factor 

for determining whether a nearby area is contributing to a monitored violation. For this factor, 

EPA evaluated county level emission data for SO2 and any growth in SO2 emitting activities

since the date represented by the emissions data.

Emissions

EPA recognizes that there may be important new information on emissions levels for the period 

after 2008, and would consider more recent information if available. New Hampshire did not 

provide updated emissions information, therefore EPA relied on the 2008 National Emissions 

Inventory (NEI) emissions data (08NEIV3).

Table 3 shows total emissions of SO2 (given in tons per year) for violating and potentially 

contributing counties in and around the Central New Hampshire nonattainment area, including 

sources emitting greater than 100 tons per year of SO2 according to the 2008 NEI. The counties 

that are partially included in the Central New Hampshire nonattainment area for the 2010 SO2

NAAQS are shown in bold. 

Table 3: Sources with SO2 greater than 100 tons in 2008

County City/Town Facility Name SO2

Emissions 

(2008 in tpy)

Total County 

SO2 Emissions 

(tons per year)

Merrimack Bow PSNH - Merrimack Station 31,307.4 99%

Rockingham Portsmouth PSNH - Schiller Station 4,988.4 88%

Rockingham Newington PSNH - Newington Station 590.0 10%

Strafford Rochester

Turnkey Recycling & 

Environmental Enterp 150.2 67%

Hillsborough Bennington

Monadnock Paper Mills, 

Inc 132.9 58%

Emission Controls

The emissions data used by EPA in this technical analysis and provided in Table 3 represent 

emission levels taking into account any control strategies implemented on the listed stationary 

sources up to and including the year 2008. EPA is aware SO2 controls have been installed at 

Merrimack Station. The facility is required by state law to have the wet scrubber operational no 

later than July 1, 2013. Once fully operational, the wet scrubber should significantly reduce SO2

emissions from Merrimack Station.

Meteorology (weather/transport patterns)

Evidence of source-receptor relationships between specific emission sources and high SO2

values at violating monitors is another important factor in determining the appropriate 

contributing areas and the appropriate extent of the nonattainment area boundary. For this factor, 

EPA considered recent hourly or sub-hourly meteorological data from the site nearest to the 

violating monitor to determine which wind vectors were associated with 1-hour SO2

exceedances. For the designated nonattainment area, the meteorological data used in this 
6

analysis is based on data at the Pembroke monitor. The monitor is approximately 0.75 miles 

southeast of PSNH-Merrimack Station.

Figure 1 shows a map of the monitor location with meteorological data and large SO2 sources in 

the area. Figure 4 shows the wind direction associated with exceedances at the Pembroke 

monitor during 2009-2011. Most of the exceedances occur when the wind is from the northwest. 

As shown if Figure 1, a wind from out of the northwest would carry the plume from PSNHMerrimack over the Pembroke monitor.

On July 6, 2011, New Hampshire submitted its analysis of wind patterns depicting SO2

emissions from Merrimack Station having a large effect on the violating monitor. The state 

submitted two wind roses, one using meteorological data gathered at Merrimack Station in 1994 

and five years (2000-2004) worth of meteorological data from a nearby airport (Concord 

Municipal). Both wind roses show the wind is predominantly from the northwest. The 

Pembroke monitor is southeast of Merrimack Station.

EPA compared the wind roses submitted by New Hampshire and meteorological data obtained 

from the Concord, NH Airport for the period from 2006 to 2011. The distribution of wind 

direction is consistent with that shown in the wind rose provided by New Hampshire. 

The wind roses also demonstrate the low probability that emissions from other sources with SO2

emissions above 100 tpy will contribute to the Pembroke monitor’s design value in the Central 

New Hampshire nonattainment area. As shown in Figure 1, three of these sources are east of the 

nonattainment area and at least 10 miles away. The other source is 20 miles west of the 

nonattainment area. Given that the dominant wind direction is from the northwest, the emissions 

from the three facilities east of the nonattainment area will have more effect on the Portsmouth 

monitor than on the Pembroke monitor, and the Portsmouth monitor’s design value is less than 

the standard.

Geography/topography (mountain ranges or other air basin boundaries)

Merrimack Station and the Pembroke monitor are located in a river valley surrounded by rolling 

hills which reach 1000 feet above sea level. These hills are approximately 10 miles from 

Merrimack Station. Coupled with stable plume heights of 800 and 1000 feet from the two coalfired units at Merrimack Station, New Hampshire used the terrain data to determine the 

boundaries for the Central New Hampshire nonattainment area. EPA concurs with the state’s 

findings. 

Jurisdictional boundaries 

As explained above, the Central New Hampshire nonattainment area is based on city and town 

boundaries instead of entire counties and does not limit the nonattainment area to Merrimack 

County where the violating monitor is located. 

Other Relevant Information

EPA did not receive additional information relevant to establishing a nonattainment boundary for 

this area.
7

Conclusion

After considering the factors described above, EPA finds that it is appropriate to include the 

cities and towns in Table 1 in the Central New Hampshire Area as the initial nonattainment area 

for the 2010 SO2 NAAQS. Areas and sources that we are not yet prepared to conclude are 

contributing to the monitored violation at the Pembroke monitor are not included in this initial 

nonattainment area. Such areas and sources will be further addressed in subsequent 

designations.

The air quality monitor in Pembroke in the Central New Hampshire Area shows a violation of 

the 2010 SO2 NAAQS, based on 2009-2011 air quality data. Based on the consideration of all 

the relevant and available information, as described above, EPA is designating the Central New 

Hampshire Area as nonattainment for the 2010 SO2 NAAQS. In a subsequent round of 

designations we will make final designations decisions for areas that are not currently included in 

the nonattainment area designation addressed in this TSD.
8

Figure 1:

Map of the Central New Hampshire nonattainment area including location of sources with 

emissions greater than 100 tpy (based on 2008 data from NEI) and ambient monitors.
9

Figure 2
10

Figure 3
11

Figure 4