TECHNICAL SUPPORT DOCUMENT

Montana Initial Designations 

2012 Revised Annual PM2.5 National Ambient Air Quality Standards 

I. EXECUTIVE SUMMARY

On December 14, 2012, EPA revised the national ambient air quality standards (NAAQS) for 

Particulate Matter smaller than 2.5 microns (PM2.5), revising the annual primary (healthbased) standard from 15 micrograms per cubic meter (μg/m3

) to 12 μg/m3 expressed as the 

3-year average of the annual mean concentrations. The primary 24-hour PM2.5 NAAQS has

been retained and not revised; therefore, Montana’s initial statewide designations address 

only the revised annual PM2.5 NAAQS. The revision was published in the Federal Register 

(FR) on January 15, 2013 at 78 FR 3086.

According to 42 USC §7407, et seq., Montana must submit to EPA an initial list of 

geographic areas that attain the standard or that do not attain the standard or that are 

otherwise unclassifiable based on available information. Montana herby designates all 

areas (Counties) within the state as “attainment” or “unclassifiable” for the 2012 revised 

primary annual PM2.5 NAAQS. The following evaluation substantiates Montana’s area 

designations.

Designations for Counties 

Based on available information, Montana determined that an initial designation of 

“attainment” is appropriate for 6 Montana counties with active PM2.5 State or Local Air 

Monitoring Stations (SLAMS) located within their respective boundaries for the design value 

period of 2010 through 2012. Available monitoring data collected at the SLAMS supports a

conclusion that ambient concentrations of PM2.5 in those counties is in compliance and 

therefore attains the 2012 revised annual PM2.5 NAAQS. 

Those counties to be designated “attainment” include: Silver-Bow, Missoula, Lewis and 

Clark, Lincoln, Powder River and Ravalli.

The remaining 50 counties in Montana should be designated as “attainment” or 

“unclassifiable” due to a lack of appropriate and/or adequate monitoring data to determine 

NAAQS compliance.

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II. MONITORING DATA

Statewide, Montana operates 13 SLAMS and 5 Special Purpose Monitors (SPM). Figure 1 

below shows the location of all PM2.5 monitors in the state. State or Local Air Monitoring 

Stations use only Federal Reference Methods (FRM) or Federal Equivalent Methods (FEM) 

and therefore provide data suitable for NAAQS compliance comparisons. Special Purpose 

Monitors do not necessarily use FRM or FEM monitoring methods and are primarily used for 

research purposes and therefore produce non-regulatory data unsuitable for NAAQS 

compliance comparisons.

Figure 1, Location of all PM2.5 Monitors within Montana

Table 1 below provides monitoring site designations (SLAMS, SPM) and monitor locations

within their respective county for all PM2.5 monitors within the state. Table 1 includes

SLAMS meeting data completeness requirements for the design value period of 2010-2012, 

SLAMS not meeting data completeness requirements for the design value period of 2010-

2012 and SPMs. 

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Table 1, Montana’s PM2.5 Monitoring Network 

Montana is regularly impacted by smoke from wildfires both within and outside of the state. 

When ambient air monitoring data is impacted by wildfires, states flag these data as 

“exceptional events” thereby removing the subject data from consideration in design value 

calculations to be used for NAAQS compliance comparisons. Flagged data may be 

excluded from the design value calculation assuming the event is “not reasonably 

controllable or preventable, is an event caused by human activity that is unlikely to recur at a 

particular location or a natural event, and is determined by the EPA in accordance with 40

CFR 50.14 to be an exceptional event.” In some cases, the data represented in this 

document, and used to calculate design values, includes “exceptional events” that have 

been flagged as wildfire impacted data. 

Figure 2 below shows the calculated design values for all 18 monitors in the state for the 

design value period of 2010-2012, excluding only flagged SLAMS data with EPA 

concurrence. 

Site Location Site Location Site Location

30-063-0024 Missoula-Boyd Park (Missoula Co.) 30-029-0049 Flathead Valley (Flathead Co.)* 30-063-0038 Seeley Lake (Missoula Co.) (SPM)

30-063-0037 Frenchtown (Missoula Co.) 30-083-0001 Sidney (Richland Co.)* 30-111-0085 Billings (Yellowstone Co.) (SPM)

30-093-0005 Butte (Silver-bow Co.) 30-049-0004 Sieben's Flat (Ncore) (Lewis & Clark Co.)* 30-031-0019 Bozeman (Gallatin Co.) (SPM)

30-081-0007 Hamilton (Ravali Co.) 30-071-0010 Malta (Phillips Co.)* 30-013-0001 Great Falls (Cascade Co.) (SPM)

30-053-0018 Libby (Lincoln Co.) 30-087-0001 Birney (Rosebud Co.)* 30-031-0017 W. Yellowstone (Gallatin Co.) (SPM)

30-075-0001 Broadus (Powder River Co.) 30-027-0006 Lewistown (Fergus Co.)*

30-049-0026 Helena (Lewis and Clark Co.)

State & Local Air Monitoring Stations

Montana PM2.5 Monitoring Network

State Special Purpose Monitors (SPM)

Meeting Data Completeness Requirments Not Meeting Data Completeness Requirments Data not flagged for Exceptional Events

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Figure 2, Annual PM2.5 3-Year Average of Annual Mean at All Monitors

Based on the values represented in Figure 2 above, it should be noted that DEQ operates a 

non-FEM SPM at Seeley Lake Elementary School. This SPM was initially sited, installed 

and operated as part of Montana’s “Today’s Air” PM2.5 network which is designed to provide 

the citizens of Montana with near-real-time PM2.5 concentrations in geographically strategic 

locations state-wide. In response to the high PM2.5 values monitored at this SPM site the 

state of Montana, in cooperation with the Missoula City-County Health Department 

(MCCHD), conducted a wintertime study of the area using E-BAMs to determine the 

geographic extent of the problem. Based on the results of this study it has been determined 

that PM2.5 concentrations measured at the Seeley Lake Elementary School SPM site are 

representative of neighborhood scale impacts, and not the overall Seeley Lake airshed. 

In response to this neighborhood scale issue, the MCCHD has initiated an episodic control 

program (PM2.5 Alerts) as well as a substantial and on-going subsidized process to replace 

aging and inefficient wood-burning devices in the Seeley Lake area. The effectiveness of 

this ongoing effort will continue to be monitored at the Seeley Lake Elementary School SPM 

site. 

Figure 3 below removes all non-regulatory data obtained from SPMs and shows data from 

all SLAMS in the state. All data from SLAMS monitors shown in Figure 3 demonstrates

compliance with the 2012 revised annual PM2.5 NAAQS. However, as discussed previously, 

several of Montana’s SLAMS did not meet data completeness requirements for the design 

value period of 2010-2012. Due to a lack of data completeness for the design value period 

of 2010-2012, these SLAMS should not be used to designate the areas as attainment; 

however, they do support a designation of unclassifiable.

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Figure 3, Annual PM2.5 Design Values for All SLAMS 

Figure 4 below removes all data from SLAMS which did not meet data completeness 

requirements during one or more years during the design value period of 2010-2012. The 

data shown in Figure 4 demonstrates compliance with the 2012 revised annual PM2.5 

NAAQS. 

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Figure 4, Annual PM2.5 Design Values for All SLAMS Meeting Data Completeness 

Requirements

Figure 5 below represents the available complete SLAMS ambient monitoring data set for 

the design value period of 2010-2012 excluding all flagged data. As shown in the figure all 

SLAMS meeting data completeness requirements for the 2010-2012 design value period 

demonstrate compliance with the 2012 revised annual PM2.5 NAAQS of 12 ug/m3

.

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Figure 5 – Annual PM2.5 Design Values Excluding Flagged Data

Montana has appropriately flagged all monitoring data impacted by qualifying “exceptional 

events” through calendar year 2012. However, Montana only recently submitted a 

demonstration package providing justification for calendar year 2010 flagged data and to 

date has not submitted a demonstration for flagged data in calendar years 2011 and 2012. 

Therefore, EPA has not had an opportunity to concur with all of the affected data for the 

design value period of 2010-2012. 

Figure 6 below represents a comparison of the data presented in Figure 5 (design values 

excluding all flagged events) with data including all exceptional events without EPA 

concurrence. Figure 6 demonstrates that inclusion of all flagged data (non-concurred)

increases design values but not to a level exceeding the 2012 revised annual PM2.5 NAAQS. 

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Figure 6 – Annual PM2.5 Design Value comparison with and without flagged data.

III. Conclusion

According to 42 USC §7407, Montana is required to submit to EPA a list of all areas (or 

portions thereof) in the state, designating as “nonattainment”, “attainment”, or otherwise 

“unclassifiable” based on available information. Through implementation of a robust PM2.5 

ambient air quality monitoring network the state of Montana has presented a strong case 

supporting the initial designations listed below. 

Based on available information, as presented throughout this document, Montana 

determined that an initial designation of “attainment” is appropriate for the following 

counties: Silver-Bow, Missoula, Lewis and Clark, Lincoln, Powder River and Ravalli. The 

remaining 50 Montana counties should initially be designated as “attainment” or 

“unclassifiable” for the 2012 revised annual PM2.5 NAAQS. 

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