March 15, 2013

Clean Air Act Section 110(l) Demonstration to Support Amendments to 

10 CSR 10-6.390, Control of NOx Emissions From Large Stationary Internal Combustion 

Engines

Background

The U.S. Environmental Protection Agency (EPA) finalized Phase II of the Nitrogen (NOx) 

State Implementation Plan (SIP) Call on April 21, 2004. Phase II required the Eastern one-third 

of Missouri to participate in the NOx SIP Call and included a provision related to source 

categories of internal combustion (IC) engines. The IC engine provision established a 

requirement to decrease emissions from stationary diesel and dual fuel engines by ninety percent 

(90 %). The NOx SIP Call required each state in the control region to develop and submit a SIP 

that contained adequate provisions prohibiting its sources from emitting air pollutants in amounts 

that would contribute significantly to nonattainment, or interfere with maintenance, in one or 

more downwind states for the 1-hour ozone and 1997 8-hour ozone National Ambient Air 

Quality Standards (NAAQS). The overall amount of emission reductions required by each state 

was based on the sum of the applicable utility, non-utility boiler, cement kiln, and stationary IC 

engine emissions as follows:

(a) 0.15 pounds per million British Thermal Units for electric generating units (EGUs);

(b) 82 percent emission reductions for large natural gas-fired stationary IC engines;

(c) 90 percent emission reductions for diesel and dual fuel stationary IC engines;

(d) 60 percent emission reductions for non-EGU boilers and turbines; and

(e) 30 percent emission reductions for cement manufacturing facilities.

New rule 10 CSR 10-6.390, Control of NOx Emissions From Large Stationary Internal 

Combustion Engines, was developed to address the IC engine provisions of the NOx SIP Call 

and originally became effective October 30, 2005. An amendment to the rule was adopted in 

2010 to include emission rate limitations for both large stationary diesel and dual fuel IC engines 

which were not included in the original rule. At the same time, a NOx twenty-five (25) ton 

exemption was added because meeting the emission limit would be very costly per ton of NOx 

removed, by far exceeding the federal study findings for cost feasibility of two-thousand 

($2,000) per ton.

A total of six (6) facilities with twenty-eight (28) units were originally affected by the 

amendments to 10 CSR 10-6.390. They are as follows: City of Campbell with one (1) engine; 

City of Farmington with fourteen (14) engines; City of Jackson with three (3) engines; City of 

Kahoka with three (3) engines; City of Owensville with four (4) engines; and Poplar Bluff with 

three (3) engines. However, IC engine number 8 at Campbell City has since been retired and is 

no longer in service. As described in greater detail below, these facilities all have very low NOx 

emissions and qualify for the twenty-five (25) ton exemption in the rule. The affected facilities 

are located in an area defined by the federal Phase II NOx SIP Call as the Eastern one-third of 

the state of Missouri, see Attachment A. 
EPA Comments and Purpose

During the rule amendment public comment period, EPA commented that based on Section 

110(l) of the Clean Air Act (CAA) any exemption to the rule must be accompanied by an 

analysis which demonstrates that the exemption will not adversely impact air quality. Section 

110(l) of the CAA specifies that state implementation plan revisions must not interfere with any 

applicable requirement concerning attainment and reasonable further progress, or any other 

applicable requirement of this Act. EPA also commented that Missouri would need to show that 

the exemption will not affect the state’s ability to meet the NOx SIP Call budget obligations. 

The purpose of this document is to address EPA’s comments by demonstrating this rulemaking 

does not impact Missouri’s ability to meet NOx budget obligations under the NOx SIP Call and 

does not adversely impact air quality. For the air quality demonstration, this document focuses 

on the ozone and nitrogen dioxide (NO2) NAAQS, which are the two (2) NAAQS potentially

impacted by NOx emissions from large IC engines.

NOx Budget Demonstration

On August 1, 2005 the Missouri SIP for the NOx SIP Call was submitted to EPA, and it was

approved by EPA on August 15, 2006. The approved SIP revision established a NOx emissions 

budget of twenty-thousand nine-hundred eighty-seven (20,987) tons during the ozone season, 

defined as May 1 through September 30. The budget serves as a cap on overall ozone season 

NOx emissions from affected utilities, non-utility boilers, cement kilns, and IC engines 

beginning in 2007. Please note IC engines were not included in the original Missouri budget for 

the NOx SIP Call.

Table 1 below is a summary of each segment’s budget and ozone season NOx emissions from 

2007-2011. The table shows that Missouri has been below the ozone season budget each year 

based on total ozone season NOx emissions from the utility, non-utility boiler, and cement kiln 

budget segments of the NOx SIP Call.

Table 1. Missouri NOx SIP Call Budget and 2007-2011 Ozone Season NOx Emissions by 

Source Type

Ozone Season (tons NOx)

Emission 

Reduction 

Category

1Yearly 

Ozone 

Season

Budget

2011

Actual

Emissions

2010 

Actual 

Emissions

2009 

Actual 

Emissions

2008 

Actual 

Emissions

2007 

Actual 

Emissions

2Utility 13,400 14,804 13,380 12,336 12,854 12,961

2Non-Utility 

boiler 104 0 0 0 0 2.2

3Cement Kiln 7,483 2,266 2,015 1,092 4,797 5,339

Total 20,987 17,070 15,395 13,430 17,651 18,300

1 NOx SIP Call Budget Demonstration for Missouri.

2

2011, 2010, 2009, 2008, 2007 Ozone Season CAMD reported emissions.

3

2011, 2010, 2009, 2008, 2007 reported annual MoEIS emissions multiplied by ozone season 

days per year over 365 days.
As shown in Table 1, the projected 2007 utility ozone season NOx emissions budget of thirteenthousand four-hundred (13,400) tons was estimated in the NOx SIP Call. Since 2005, two (2) 

selective catalytic reduction with overfire air, one (1) low NOx burner with overfire air and two 

(2) overfire air NOx control units have been installed at utilities located in the Eastern one-third 

of the state of Missouri. Although 2011 utility emissions are over the utility portion of budget

due to additional NOx emission allowances being purchased in the Eastern one-third of the state, 

buying and selling allowances is acceptable under the NOx SIP Call program, and the overall 

emissions from all segments are below the ozone season budget for 2011. Utility boilers 

included in the NOx SIP Call budget are subject to state rule 10 CSR 10-6.360, Control of NOx 

Emissions From Electric Generating Units and Non-Electric Generating Boilers.

The 2007 budgeted ozone season emissions for non-utility boilers were one-hundred four (104) 

tons NOx, and as shown in Table 1, the non-utility boilers 2008 and after ozone season emissions 

were zero (0) tons. The three (3) non-utility units that were included in the NOx SIP Call budget 

were Anheuser-Busch, Inc., unit 6, and Ashley Street Station units 5 and 6. In EPA’s Clean Air 

Markets Division (CAMD) database Anheuser-Busch, Inc. unit 6 (utility identification number

10430) was retired October 10, 2009, and the Ashley Street Station (utility identification number 

880094) units 5 and 6 (EU0060 and EU0070 in CAMD) retired October 29, 2008. Non-utility

boilers included in the NOx SIP Call budget are subject to state rule 10 CSR 10-6.360, Control 

of NOx Emissions From Electric Generating Units and Non-Electric Generating Boilers.

As shown in Table 1, cement kiln emissions have substantially decreased and are well below the 

budget for this sector. In March of 2010 the Holcim-Clarksville facility signed an Idle Status 

Settlement Agreement and will not operate in the future. One new cement kiln, Holcim-Lee 

Island commenced operation in 2009 and is located in the Eastern one-third of Missouri. This 

plant must meet Best Available Control Technology (BACT) NOx requirements for cement 

kilns. The cement kilns included in the NOx SIP Call budget are all subject to 10 CSR 10-6.380, 

Control of NOx Emissions From Portland Cement Plants and are all meeting the requirements of 

the rule.

Table 2 shows the actual annual emissions of IC engines that are subject to 10 CSR 10-6.390, 

Control of NOx Emissions From Large Stationary Internal Combustion Engines for 2011, 2010, 

2009, 2008, and 2007. The table shows that these facilities are consistently very low NOx 

emitters. The total annual potential to emit for these units combined is six-hundred seventy-five 

(675) tons of NOx. If the total IC engine potential to emit six-hundred seventy-five (675) tons 

NOx were added to the total emissions from all source categories in Table 1, Missouri would still 

be below its NOx SIP Call Budget. This is a very conservative assessment of the IC engines’ 

impacts on the NOx SIP Call Budget because the potential to emit is significantly higher than 

emissions reflecting actual operations and this annual value, not just ozone season.

Table 2. Actual Annual NOx Emissions from 2007-2011 for IC Engines Exempted from 10 

CSR 10-6.390

Yearly Actual NOx Emissions (tons)
 Plant Name Number of Units 

Affected 2011 2010 2009 2008 2007

Campbell City 1 N/A N/A 0.0 0.2 0.4

Farmington 14 1.2 1.0 2.1 0.7 2.1

Jackson 3 0.0 0.0 0.0 0.0 0.0

Kahoka 3 0.1 0.1 0.1 2.9 0.0

Owensville 4 0.0 2.5 0.0 0.0 0.0

Poplar Bluff 3 0.9 1.1 1.1 2.2 9.5

Total 2.2 4.9 3.4 6.1 12.1

Air Quality Demonstration

This portion of the technical support document addresses potential impacts of the affected IC

engines on the ozone and NO2 NAAQS.

1. Ozone Season NAAQS

In March 2008, EPA established the current ozone NAAQS of seventy-five (75) parts per billion 

(ppb) measured over an 8-hour time period. Attachment B shows the locations of the ozone 

monitors in the Eastern one-third of the state. Six (6) of the monitors are located in the St. Louis 

area, currently the only ozone nonattainment area in the state (nonattainment for both the 1997 

and 2008 ozone NAAQS), and two (2) ozone monitors are located in Ste. Genevieve and Perry

Counties. 

As discussed in detail in the technical support document for the department’s original 2008 

ozone NAAQS boundary recommendation (submitted to EPA in March 2009), extensive 

meteorological analysis was conducted to determine emission source regions with the highest 

probability of impacting these ozone monitors. A summary of the results is as follows:

 The highest ozone concentrations in the St. Louis area occur when there is a high 

pressure center over the eastern United States (southerly components to flow direction are 

predominant) with reduced wind speeds or stagnant conditions. 

 Emissions from within the metropolitan St. Louis area have the strongest likelihood of 

contribution to the vast majority of the sites in the ozone network.

 Contributions to elevated ozone concentrations at the Farrar ozone monitor in Perry

County are due to transport primarily from areas east and south of the monitor. 

 The Bonne Terre ozone monitor in Ste. Genevieve County has the highest concentrations 

when the winds have a northerly or easterly component, i.e., it tends to be impacted the 

most by emissions from the St. Louis area.

 St. Francois County emission sources do not have a frequent impact on the Bonne Terre 

monitor.

Also in the department’s boundary recommendation for the 2008 ozone NAAQS, it was 

determined that emission sources in St. Francois County were not significant contributors to 

ozone in the St. Louis area and therefore was not recommended as part of the nonattainment 

area. EPA approved the department’s recommendation for the St. Louis nonattainment area 

boundary without modification on May 21, 2012 (77 FR 30088). 
This demonstration centers on the Farmington power plant in St. Francois County. Of the five 

(5) small sources affected by the 10 CSR 10-6.390 NOx exemption (excluding Campbell City

which is retired), the Farmington plant has the greatest potential for impacting the ozone 

monitors. This is because it has the highest overall NOx emissions and greatest number of 

affected IC engine units (14 units) as shown in Table 2. It is also located south and adjacent to 

the St. Louis nonattainment area, which is generally in the path of the predominant wind 

direction on typical high ozone days, and it is near the Bonne Terre monitor in Ste. Genevieve 

County. 

As detailed in the emissions inventory for point, area, and mobile sources in Attachment C, 2008 

NOx emissions from all sources in St. Francois County were 8.76 tons per ozone season day. 

The Farmington power plant’s 2008 NOx emissions were 0.0018 tons per ozone season day, or

0.021% of the county’s total daily ozone season NOx, which is negligible compared to the 

overall county daily emissions. Because total St. Francois County emissions do not have a 

meaningful impact on St. Louis ozone monitors as established in the boundary designation 

process and NOx emissions from the Farmington power plant are a small fraction of the total 

county emissions, it can be concluded that the Farmington power plant has an insignificant 

impact on the St. Louis area ozone monitors.

The Farmington power plant is expected to have minimal contribution to the Farrar and Bonne 

Terre ozone monitors as well. As determined in the boundary designation process, St. Francois 

County emissions do not have a frequent impact on the Bonne Terre ozone monitor. Since 

Farmington power plant is such a small percentage of the total county’s NOx emissions, it likely

does not have a significant impact on the Bonne Terre monitor. Furthermore, with the Farrar 

monitor’s impacts primarily resulting from transported pollutants from the east and south, the 

Farmington power plant is unlikely to contribute to elevated ozone levels measured at that 

monitor. 

If the Farmington plant doesn’t have an impact on the St. Louis and surrounding ozone monitors, 

it is highly unlikely that the other small sources exempted by this rule would have any impacts. 

The Owensville power plant in Gasconade County has very low NOx emissions as shown in 

Table 2 and is located west of the St. Louis nonattainment area, which is not a predominant wind 

direction on high ozone days. The Jackson, Kahoka and Poplar Bluff power plants in Cape 

Girardeau, Clark and Butler Counties, respectively, are all very small NOx sources and are 

located too far away from any of the ozone monitors to have any measurable impact.

 2. NO2 NAAQS

In February 2010, EPA set a new NO2 NAAQS of one hundred (100) ppb measured over one (1) 

hour, while retaining the annual NO2 NAAQS of fifty-three (53) ppb. Attachment B shows the 

location of the only NO2 monitor in the Eastern one-third of the state. It is in St. Louis City. 

Missouri does not have any nonattainment areas for the 1-hour NO2 NAAQS. 

In the preamble to the final 2010 NO2 NAAQS, EPA acknowledges that the highest 

concentrations of NO2 drop off quickly with distance and the impacts of NOx emissions tend to 

be localized:
Research suggests that the concentrations of on-road mobile source pollutants such as

NOX, carbon monoxide (CO), directly emitted air toxics, and certain size distributions of

particulate matter (PM), such as ultrafine PM, typically display peak concentrations on

or immediately adjacent to roads. This situation typically produces a gradient in

pollutant concentrations, with concentrations decreasing with increasing distance from

the road, and concentrations generally decreasing to near area-wide ambient levels, or

typical upwind urban background levels, within a few hundred meters downwind. (75 FR

6479, February 9, 2010).

In addition, a scientific paper titled “Modeling the chemical evolution of nitrogen oxides near 

roadways” (Wang, Yan Jason, Denbleyker, Allison, McDonald-Buller, Elena, Allen, David, and 

Zhang, K. Max) provides further evidence supporting NO2 dissipation rates from roadways.

Based on this assessment that NO2 concentrations dissipate quickly with distance from the 

source, often returning to area background levels within a few hundred meters, the two (2) 

sources closest to the St. Louis NO2 monitor are likely too far away to have a significant impact. 

The Farmington and Owensville power plants are located about sixty (60) and seventy (70) miles 

from the only current NO2 monitor in the St. Louis area. All other sources exempted by 10 CSR 

10-6.390 are located even farther away and are much less likely to have any measurable impact.

Historical data from an NO2 monitor located at Bonne Terre that was shut down in September 

2010 provides evidence of the Farmington power plant’s minimal impact on an NO2 monitor 

located much closer. The Bonne Terre NO2 monitor was approximately eight (8) miles due north 

of the Farmington plant. As shown in the data summaries for this monitor from 1996 through the 

third quarter of 2010 on the department’s website (http://dnr.mo.gov/env/esp/aqm/bonneterre.htm), the annual averages and annual 1-hour daily maximum values are well below both the 

annual and 1-hour NO2 NAAQS. It should be noted that the annual 1-hour daily maximum 

values are not directly comparable to the current 1-hour NO2 NAAQS, which is based on a 3-

year average of the 98th percentile (or 8th highest) of the yearly distribution of 1-hour daily 

maximum concentrations. However, since the 1st high 1-hour daily maximum value is greater 

than the 8th high value, this is a conservative assessment. This historical data from a much closer 

monitor confirms that the Farmington power plant likely has a minimal contribution to the St. 

Louis NO2 monitor that is sixty (60) miles away.

Another consideration in determining the impacts of a particular source on the NO2 NAAQS is 

how it would be modeled to show compliance with the 1-hour standard. A March 1, 2011 

memorandum from Tyler Fox, EPA, titled “Additional Clarification Regarding Application of 

Appendix W Modeling Guidance for the 1-hour NO2 National Ambient Air Quality Standard” 

describes the treatment of intermittent emissions and their sources in conducting modeling 

determinations for the 2010 NO2 NAAQS. This guidance exempts intermittent sources from 

modeling analyses and indicates that modeling analyses should focus on emission sources that 

are continuous over a period of time or frequent enough to significantly contribute to the annual 

distribution of daily 1-hour NO2 contributions. Campbell City (utility identification number 

2903), Farmington (utility identification number 6205), Jackson (utility identification number 

9603), Kahoka (utility identification number 9973), Owensville (utility identification 
number14272), and Poplar Bluff (utility identification number 15229) IC engines are classified 

through the Energy Information Administration’s (EIA’s) 860 report as standby/backup engines 

or operating engines. Each of these engines is connected to the electric grid in order to be 

dispatched for power. These engines are dispatched mainly during times of high demand which 

can fluctuate as summer temperatures may vary on a week to week or day by day basis. The 

Department of Energy (DOE) definition of a standby generator “involves use of generators 

during times of high demand on utilities to avoid extra peak-demand charges,” and the definition 

of an operating generator means “in service (commercial operation) and producing some 

electricity.” The standby generator definition also “Includes peaking units that are run on an as 

needed (intermittent or seasonal) basis.” From this classification, the standby/backup engines 

would be considered intermittent and excluded from any modeling analysis of a source’s impacts 

on the NO2 NAAQS.

Because of their low average daily NOx emissions, distance, and intermittent use, the 

Farmington and Owensville power plants are not expected to have a significant impact on the

St. Louis NO2 monitor and the other power plants exempted from 10 CSR 10-6.390 would have 

even less of an impact.

Conclusion

This document demonstrates that the recent revision of 10 CSR 10-6.390 to exempt five (5) 

small NOx sources will not impact Missouri’s ability to meet NOx budget obligations under the 

NOx SIP Call and does not adversely impact air quality. Even considering the maximum 

potential to emit from these small sources, an extremely conservative level of emissions, overall 

emissions are still well below Missouri’s NOx SIP Call budget. Based on the magnitude of NOx 

emissions, distance to the ozone and NO2 monitors, predominant weather conditions on high 

ozone days, and intermittent use of these engines, the small NOx sources exempted from this 

rule are likely to have an insignificant impact on the ozone and NO2 NAAQS.