1 

 

MEMORANDUM

DATE: January 21, 2015 

SUBJECT: Technology Review for Primer and Topcoat Application Operations in the 

Aerospace Source Category

FROM: EC/R Incorporated and Eastern Research Group, Inc. 

TO: Kim Teal, U.S. EPA/OAQPS/SPPD/MMG 

1.0 INTRODUCTION 

Section 112 of the Clean Air Act (CAA) requires the U.S. Environmental Protection Agency 

(EPA) to establish technology-based standards for listed source categories. These technologybased standards are often referred to as maximum achievable control technology (MACT) 

standards. The Aerospace MACT (40 CFR part 63, subpart GG) regulates HAP emissions from 

facilities that are major sources and are engaged, either in part or in whole, in the manufacture or 

rework of commercial, civil, or military aerospace vehicles or components. The rule requires the 

use of MACT to reduce HAP emissions from the following operations: cleaning; primer, topcoat 

and chemical milling maskant application; depainting; and waste storage and handling. 

Section 112 also contains provisions requiring the EPA to periodically revisit these standards. 

Specifically, section 112(d)(6) states: 

(6) REVIEW AND REVISION. – The Administrator shall review, and revise as 

necessary (taking into account developments in practices, processes, and control 

technologies), emissions standards promulgated under this section no less often than 

every 8 years. 

To comply with this CAA requirement, the EPA conducted a technology review for the 

Aerospace MACT standard for major sources. This memorandum addresses the portion of the 

technology review for primer and topcoat application operations. 

For the purposes of reviewing a MACT standard, the EPA considers a “development” in 

practices, processes, and control technologies to be: 

• Any add-on control technology or other equipment that was not identified and considered 

during MACT development; 

• Any improvements in add-on control technology or other equipment (that was identified 

and considered during MACT development) that could result in significant additional 

emission reduction; 
2 

• Any work practice or operational procedure that was not identified and considered during 

MACT development; and 

• Any process change or pollution prevention alternative that could be broadly applied that 

was not identified and considered during MACT development. 

Section 2 of this memorandum presents a summary of the sources of data that were used to 

conduct the technology review and Section 3 presents the technology review for primer and 

topcoat application operations. 

2.0 SOURCES OF AVAILABLE CONTROL TECHNOLOGY INFORMATION

To identify any developments in practices, processes, or control technologies that could be 

applicable to topcoat and primer application operations in the Aerospace industry, we consulted 

the following sources of data: RACT/BACT/LAER Clearinghouse, the California Statewide Best 

Available Control Technology (BACT) Clearinghouse, regulatory actions promulgated 

subsequent to the Aerospace MACT, regional and state regulations, and correspondence with 

state agencies and industry. 

In addition, in order to assess developments in practices, processes and control technologies that 

have occurred in the aerospace manufacturing and rework industry since promulgation of the 

MACT standards, the EPA sent out a comprehensive information collection request (ICR) to all 

known facilities in February 2011. The ICR requested information on material usage and control 

techniques used on all of the regulated and unregulated emission sources. Responses were 

received from 100 major source facilities and 145 synthetic minor facilities with adequate 

information to determine the current level of control of HAP emissions, as well as to calculate 

HAP emissions. 

2.1 RACT/BACT/LAER Clearinghouse Database

Under the EPA's New Source Review (NSR) program, if a company is planning to build a new 

plant or modify an existing plant such that criteria air pollution emissions will increase by a 

certain amount, then the company must obtain an NSR permit. The NSR permit is a construction 

permit which generally requires the company to minimize air pollution emissions by changing 

the process to prevent air pollution and/or installing air pollution control equipment. 

The terms "RACT," "BACT," and "LAER" are acronyms for different program requirements 

relevant to the NSR program. RACT, or Reasonably Available Control Technology, is required 

on sources in areas that are not meeting national ambient air quality standards (non-attainment 

areas). BACT, or Best Available Control Technology, is required on new or modified major 

sources in clean areas (attainment areas). LAER, or Lowest Achievable Emission Rate, is 

required on new or modified major sources in non-attainment areas. 

BACT and LAER (and sometimes RACT) are determined on a case-by-case basis, usually by 

State or local permitting agencies. The EPA established the RACT/BACT/LAER Clearinghouse, 

or RBLC, to provide a central data base of air pollution technology information (including past 

BACT and LAER decisions contained in NSR permits) to promote the sharing of information 
3 

among permitting agencies and to aid in future case-by-case determinations. However, data in 

the RBLC are not limited to sources subject to RACT, BACT, and LAER requirements. 

Noteworthy prevention and control technology decisions and information may be included even 

if they are not related to past RACT, BACT, or LAER decisions. 

The RBLC contains over 5,000 air pollution control permit determinations that can help identify 

appropriate technologies to mitigate most air pollutant emission streams. It was designed to help 

permit applicants and reviewers make pollution prevention and control technology decisions for 

stationary air pollution sources, and includes data submitted by several U.S. territories and all 50 

States on over 200 different air pollutants and 1,000 industrial processes. 

 

The RBLC provides several options for searching the permit database on-line to locate 

applicable control technologies. On October 21, 2013, we conducted a search of the RBLC. Our 

search specified processes in the Aerospace surface coating category, with permits dating back to 

1995. The search results included the following data fields:

 

• RBLC ID; 

• Facility Name, and State; 

• Permit Date; 

• Process name; 

• Throughput; 

• Pollutant; 

• Control technology; and 

• Percent efficiency of control. 

The results of the search are presented in Appendix 1 for the Aerospace source category. 

Finally, a search of Washington State’s records of permits for aerospace facilities identified a 

Final Prevention of Significant Deterioration (PSD) permit dated September 10, 2014 for the 

Boeing Everett facility.1 In this, the PSD permit considers BACT for VOC coating operations as 

complying with all applicable VOC emission standards of the Aerospace NESHAP. The 

accompanying technical support document identified add-on control technologies, including 

RTO, but these were not considered BACT after taking into account energy, environmental, and 

economic impacts.2

2.2 Subsequent Regulatory Actions

 

1

 Department Of Ecology, State Of Washington: Prevention Of Significant Deterioration (PSD) Permit. 

Issued To: The Boeing Company, Boeing Commercial Airplanes, Everett Facility. Facility Location: 3003 West 

Casino Road, Everett, Washington 98203, Permit Number: PSD-14-01, Date of Original Permit Issuance: September 

10, 2014. Effective Date of Permit: September 10, 2014. 

2

 Department Of Ecology, State Of Washington: Technical Support Document For The Boeing Company, Boeing 

Everett 777X Project. Prepared by Air Quality Program, Washington State Department of Ecology, Olympia, 

Washington, September 9, 2014 
4 

Regulatory actions promulgated subsequent to the 1995 Aerospace MACT have been identified 

for sources similar to Aerospace coating operations. These regulatory actions, listed in Table 1, 

were reviewed for developments in practices, processes and control technologies. 

Table 1. Subsequent Regulatory Actions for Sources Similar to 

Aerospace Coating Operations 

MACT Standards Subpart Date Practices, Processes, and Control Technologies 

Evaluated 

Surface Coating of 

Metal Furniture RRRR 5/23/2003 

Emission limit as mass HAP per volume solids used, 

add-on control devices, low-HAP coatings (powder, 

non/low-HAP solvents, UV-curable, autophoretic) 

Surface Coating of 

Wood Building 

Products 

QQQQ 5/28/2003 Emission limit as mass HAP per volume solids used, 

add-on control devices, low-HAP coatings 

Surface Coating of 

Large Appliances NNNN 7/23/2002 

Emission limit as mass HAP per volume solids used, 

add-on control devices, low-HAP coatings (powder, 

non/low-HAP solvents, UV-curable, autophoretic) 

Surface Coating of 

Automobiles and 

Light-Duty Trucks 

IIII 4/26/2004 

Emission limit as mass HAP per volume solids used, 

low-hap coatings (low/ non-HAP solvents), powder 

coatings, improved capture and control systems 

Surface Coating of 

Plastic Parts and 

Products 

PPPP 4/19/2004 

Emission limit as mass HAP per volume solids used, 

add-on control devices, low-HAP coatings 

(waterborne, UV-curable), high solids coatings, 

vacuum metalizing

Surface Coating of 

Miscellaneous 

Metal Parts and 

Products 

MMMM 01/02/2004

Emission limit as mass HAP per volume solids used, 

add-on control devices, low-HAP coatings (UVcurable, electron beam-curable), powder coatings 

Area Source 

Standards Subpart Date Practices, Processes, and Control Technologies Evaluated 

Paint Stripping and 

Miscellaneous 

Surface Coating 

Operations 

HHHHHH 1/9/2008 

Confining all coating operations to a spray booth, 

high transfer efficiency spray guns, training and 

certification of spray equipment operator to optimize 

transfer efficiency, spray booth filters 

Residual Risk 

Standards Subpart Date Practices, Processes, and Control Technologies Identified as Developments 

Magnetic Tape EE 04/07/2006 No developments 

Printing and 

Publishing KK 4/21/2011 Permanent total enclosures installed on controlled presses 

Shipbuilding and 

Ship Repair II 11/21/2011

Concentrator/RTO installed on spray booths to 

achieve 95% control efficiency; lower VOC coating 

limits based on California regional rules 

Wood Furniture 

Manufacturing JJ 11/21/2011

RTO; Lower VOC coating limits based on California 

regional rules, more efficient spray guns, limit 

formaldehyde emission to 400 lb per 12 months 
5 

Developments identified in the regulatory actions listed in Table 1 will be discussed in Section 3 

(Technology Review for Primer and Topcoat Application Operations). 

2.3 State and Regional Regulations

In the original Aerospace MACT proposal3, the EPA considered numerous regional regulations, 

including the following California regional rules: 

• San Diego Air Pollution Control District Rule 67.9 – Aerospace Coating Operations, 

VOC limits; 

• South Coast Air Quality Management District Rule 1124 – Aerospace Assembly and 

Component Manufacturing Operations; 

• Bay Area Air Quality Management District Regulation 8, Organic Compounds, Rule 29 – 

Aerospace Assembly and Component Coating Operations. 

Clean Air Act (CAA) section 172(c)(1) requires that state implementation plans (SIPs) for 

nonattainment areas must provide for the implementation of “reasonably available control 

measures” (RACM), including “reasonably available control technology” (RACT), for sources of 

emissions. The Control Techniques Guidelines (CTG) for Aerospace Manufacturing and Rework 

Operations4 and Miscellaneous Metal and Plastic Parts Coatings5 were developed to provide 

State and local air pollution control authorities information to assist them in determining RACT 

for VOCs from surface coating operations. The CTG includes detailed information on practices, 

processes and control technologies for the reduction of VOC and HAP. 

3.0 TECHNOLOGY REVIEW FOR PRIMER AND TOPCOAT APPLICATION 

OPERATIONS 

As defined in the Aerospace MACT, a coating is a material that is applied to the surface of an 

aerospace vehicle or component to form a decorative or functional solid film, or the solid film 

itself. A primer is the first layer and any subsequent layers of coating prior to the topcoat and is 

typically used for corrosion prevention, protection from the environment, functional fluid 

resistance, and adhesion of subsequent coatings. A topcoat is a coating that is applied over one or 

more layers of a primer for appearance, identification, camouflage, or protection. Specialty 

coatings are not included under the definition of primers or topcoats. 

 

3

59 FR 29216. June 6, 1994. 

4

 Guideline Series: Control of Volatile Organic Compound Emissions from Coating Operations at Aerospace 

Manufacturing and Rework Operations, EPA-453/R-97-004. December 1997. 

5

 Control Techniques Guidelines for Miscellaneous Metal and Plastic Parts Coatings, US EPA/OAR/OAQPS. 

September 2008. 
6 

Most aerospace coatings contain a mixture of organic solvents and/or inorganic HAP. The 

organic HAP emissions from the application of primers and topcoats occurs from the evaporation 

of organic solvents during mixing, application, and drying. Emissions of inorganic HAP from 

coating operations, typically metal compounds (e.g., chromium, cadmium compounds), occur 

when particles do not adhere to the surface being coated (i.e., overspray). The organic and 

inorganic emissions from coating application occur in large open areas, such as hangars, or 

partially or fully enclosed spaces, such as within spray booths. 

3.1 Summary of Existing MACT Level of Control 

The Aerospace MACT standard (subpart GG) promulgated in 1995 requires the following 

organic HAP and VOC content limits for uncontrolled primers and topcoats: 

• Primers: 2.9 lb/gal (less water) as applied; or 4.5 lb/gal (less water) as applied for general 

aviation rework facilities, or 5.4 lb/gal (less water) as applied, to large commercial 

aircraft components (parts or assemblies) or fully assembled, large commercial aircraft; 

• Topcoats: 3.5 lb/gal (less water) as applied; or 4.5 lb/gal (less water) as applied for 

general aviation rework facilities. 

Alternatively, a control system can be used to capture and control emissions from the primer or 

topcoat application operation. The system must achieve an overall control efficiency of 81 

percent. 

In addition, subpart GG requires the use of one of the following coating application techniques: 

• Flow/curtain coat application; 

• Dip coat application; 

• Roll coating; 

• Brush coating; 

• Cotton-tipped swab application; 

• Electrodeposition (dip) coating; 

• High volume low pressure (HVLP) spraying; 

• Electrostatic spray application; or 

• Other coating application methods that achieve emission reductions equivalent to HVLP 

or electrostatic spray application methods. 

Subpart GG also provides operating requirements for the application of primers or topcoats that 

contain inorganic HAP, including control of spray booth exhaust streams with either particulate 

filters or waterwash. 

3.2 Identified Control Measures for Primer and Topcoat Application Operations 

3.2.1 Add-On Control Technology or Other Equipment Not Identified and Considered During 

MACT Development

Add-on control technologies considered during MACT development for the reduction of organic 

HAP include carbon adsorbers, thermal oxidizers, ultraviolet oxidation, and activated carbon 

fiber adsorbents frequently used in conjunction with thermal oxidizers. Equipment considered 
7 

during MACT development includes the use of high transfer efficiency spray guns, enclosed 

spray gun cleaners, and proportional paint mixers. Particulate filters, including HEPA filters, and 

waterwash were considered during MACT development for the control of inorganic HAP. 

The technology review conducted for the Printing and Publishing Industry identified the retrofit 

of permanent total enclosures onto controlled presses as a development. Total enclosures were 

considered during development of the Aerospace MACT and are widely used on paint spray 

booths in the industry – in the 2011 ICR data, sources reported the booth type of permanent total 

enclosure more frequently than any other booth type. 

The Wood Furniture Manufacturing technology review identified the use of a regenerative 

thermal oxidizer (RTO) on a spray booth as a development and the Shipbuilding and Ship Repair 

technology review identified the use of a concentrator/RTO to achieve a 95 percent control 

efficiency for HAP as a development. The use of an RTO was considered during development of 

the Aerospace MACT as a control technology capable of a achieving an efficiency up to 98 

percent. In addition, the Aerospace MACT standard provides for the use of an add-on control 

device in the form of a compliance alternative to the pound HAP/VOC per gallon coating limits. 

No new equipment or control technologies were identified that were not considered during 

MACT development. 

3.2.2 Improvements in Add-On Control Technology or Other Equipment (That Was Identified 

and Considered During MACT Development)

The BACT determinations in the RBLC database that were made subsequent to promulgation of 

the Aerospace MACT specify the use of add-on controls, including zeolite concentrators, thermal 

oxidizers, and zeolite concentrators with thermal oxidizers. All of these control technologies 

were in use during development of the Aerospace MACT. 

The technology review conducted for the Wood Furniture Manufacturing Industry identified the 

use of more efficient spray guns as a development, and adopted regulations preventing the use of 

conventional spray guns. The Wood Furniture Manufacturing MACT identified the use of air 

assisted airless spraying as a more efficient coating application technology. The Surface Coating 

of Plastic Parts and Products identified the use of the vacuum metalizing application process 

which is similar to electrodeposition and involves the evaporation of metals inside a vacuum 

chamber which then bonds to the substrate. Although the Aerospace MACT standard does not 

specifically prohibit the use of conventional spray methods, it does specify that only spray 

application methods that are equivalent to HVLP or electrostatic spray application methods may 

be used. 

High efficiency particulate arrestors (HEPA filters), rated at 99.97 percent efficiency, were 

known and considered in the development of the Aerospace MACT for the control of inorganic 

HAP. No other particulate control technology having a higher control efficiency has been 

identified. 

In addition to the regulatory actions promulgated subsequent to the Aerospace MACT, numerous 

other data sources were considered, including the RBLC, regional and state rules and databases, 
8 

and industry correspondence, and no improvements in add-on control technology or other 

equipment were identified. 

3.2.3 Work Practices and Procedures Not Identified and Considered During MACT 

Development

No additional work practices or procedures were identified that were not already identified and 

considered during MACT development. The current MACT standards require that the handling 

and transfer of primers and topcoats be done in a manner that minimizes spills. 

3.2.4 Any process change or pollution prevention alternative that could be broadly applied that 

was not identified and considered during MACT development.

Pollution prevention measures that are currently used by the industry and were considered during 

MACT development include product reformulations for coatings, including waterborne, higher 

solids, powder, and self-priming topcoats. For the purposes of this analysis, product 

reformulations will be divided into two categories – low-HAP liquid coatings and high solids 

coatings. A review of regulatory actions promulgated subsequent to the Aerospace MACT has 

revealed potential developments in the control of emissions from coating operations, including 

lower VOC content and formaldehyde limits. These potential developments are discussed further 

in the sections below. 

Advancements in the Use of Low-HAP Liquid Primers and Topcoats

The most common type of low HAP liquid coatings are those that have been reformulated with 

solvents that are not organic HAP, such as waterborne coatings. A secondary category of low 

HAP liquid coatings was identified in several subsequent regulatory actions (see Section 2.2) and 

includes coatings that result from alternate technologies, such as Ultraviolet (UV)-curable, 

electron beam (EB)-curable, and autophoretic. Liquid UV and EB curable coatings are converted 

into a solid, cured film using alternate forms of energy that interact with the components of the 

coating as a catalyst.6 As described in the Surface Coating of Large Appliances MACT 

proposal7, autophoretic coatings are applied using a dip application method in which a chemical 

reaction deposits the coating on the surface of the part. However, this process is best suited for 

long runs of relatively small parts, such as in the manufacture of appliances and some automotive 

parts, but is not suitable for the painting of large structures with components and sub-assemblies 

that cannot be submerged in the coating process. 

In the development of the MACT floor, the EPA assumed that facilities would replace their 

conventional primers and topcoats with reduced HAP content, high solids primers and topcoats 

to meet the MACT floor limits rather than controlling emissions through abatement. This was 

verified in the 2011 ICR data where only 5 percent of facilities reported the use of a control 

device for a coating operation. 

 

6

 UV/EB Curing. Fast. Tough. Easy on the environment, PPG Industries. 8/27/2009. Available at: 

http://www.ppg.com/coatings/industrial/technologiesproducts/electrocoat/Pages/default.aspx 

7

 65 FR 81133. December 22, 2000. 
9 

Advancements in the use of primers and topcoats with significantly lower HAP content than the 

current MACT limits could constitute a development as a pollution prevention alternative. To 

determine if advancements have been made in the use of low-HAP primers and topcoats, the 

2011 ICR data were compared with the Aerospace MACT HAP/VOC content limits. The same 

procedure that was used to determine the MACT floor limits, as outlined in the Background 

Information Document (BID) for the Aerospace MACT proposed rule8, was applied to the ICR 

data. This procedure involves finding the volume weighted average HAP content of all primers 

or topcoats used at each facility. For the purposes of this analysis, the weighted average HAP 

content values were then averaged across all facilities for comparison with the MACT limits. 

The average HAP content from the ICR data are presented in Table 2. 

There are three differences between the MACT floor limits and the ICR data that must be 

addressed. 

First, the coating usage volumes in the denominator of the MACT floor limits are “less water,” 

while the coating usage volumes reported in the ICR include water. Table 2 provides a 

theoretical HAP content less water that was calculated from the average HAP content from the 

ICR data, assuming 10 percent water content and a coating density of 10 pounds per gallon. 

The second difference involves the derivation of the MACT floor organic HAP content limit. 

When the MACT floors were originally determined for subpart GG, the EPA could not 

determine an organic HAP content limit due to the limited data that were available at the time of 

proposal. Therefore, the EPA set the organic HAP limits at the same level as the VOC limits. 

Consequently, the ICR data, which include information on all HAP and VOC that are also HAP, 

cannot be directly compared to the VOC based content limits of the MACT floor. 

The third difference is that the ICR only required facilities to report coatings as either primers or 

topcoats. It did not require them to report by the three different types of primers and four 

different types of topcoats that are in the current rule. These different types distinguish among 

military, general aviation, and large commercial aircraft, between original equipment 

manufacturing and rework, and between self priming topcoats and standard topcoats. 

Based on data obtained from the section 114 responses collected as part of the 1995 Aerospace 

rule development, the EPA concluded that approximately 50 percent of the VOC reported were 

also organic HAP, on average, but the EPA did not calculate the ratio by coating type or 

document the variability in the ratio. Therefore, the theoretical VOC content presented in Table 2 

was calculated based on a HAP-to-VOC ratio of 0.5 for all coating types, and is provided only 

for comparison with the current MACT VOC content limits. 

The data collected in 2011 from the industry indicates that most of the aerospace manufacturing 

and rework facilities perform original equipment manufacturing and rework of large commercial 

aircraft, general aviation aircraft, and military aircraft. The only sources that do not perform 

original equipment manufacturing of aerospace vehicles are the military facilities and the 

National Aeronautics and Space Administration (NASA). 

 

8

 National Emission Standard for Hazardous Air Pollutants (NESHAP) for the Aerospace Industry - Background 

Information for Proposed Standards, US EPA/OAR/OAQPS. April 1994. 
10 

Table 2. Comparison of the Average 2011 ICR HAP Content to the MACT Floor 

Coating 

Category 

Average HAP 

Content from 

ICR data (lb/gal) 

Theoretical HAP 

Content (lb/gal 

less water) 

Theoretical VOC 

Content (lb/gal 

less water) 

Current MACT 

HAP/VOC Limit 

(lb/gal less water) 

Primers 1.36 1.55 3.10 2.90 

Topcoats 1.38 1.57 3.14 3.50 

* The procedure used to calculate the theoretical HAP content less water and the theoretical VOC content are

provided in Appendix 2. 

This analysis suggests that significant advancements in the use of low-HAP primers and topcoats 

have not been broadly achieved in the facilities that perform original equipment manufacturing 

of aerospace vehicles. Although the theoretical VOC content of topcoats is below the current 

MACT HAP/VOC limit, the assumptions made for the water content and HAP to VOC ratio are 

likely conservative (e.g., not every coating is going to contain water), resulting in lower 

theoretical VOC content values. The ICR data show a wide variation in the HAP content and a 

difference in HAP content between the best performers (i.e., facilities with the lowest HAP 

content) and the least performers. Because of this variability, it would be difficult for many 

affected sources to comply with an emission limit established lower than the current MACT 

standards. 

While there are a number of facilities that have weighted-average HAP content values in the 

2011 ICR data that are well below the current limits, it is unlikely that all of the affected sources 

in the source category could achieve HAP content values equal to the lower emitting facilities. 

Any emission limit established lower than the MACT floor as part of EPA’s technology review 

process must be achievable throughout the aerospace industry. However, as outlined in the 

Aerospace CTG, the types of coatings used in the aerospace industry will vary significantly as 

each coating must meet individual performance standards particular to a specific design. Many of 

the currently used coatings have already been reformulated to meet the current MACT HAP 

content limits. Manufacturers of aerospace vehicles are constrained to using certain types of 

primers and topcoats based on the market segment for which the coating is intended (i.e., 

military OEM, military rework, commercial OEM, or commercial rework) and the unique 

circumstances and design considerations within each market segment. For example, certain 

aerospace manufactures must consider the corrosive resistance of a primer or topcoat for flights 

overseas, or for various military applications, such as primers and topcoats that are chemical 

agent resistant9. Other considerations that differ between and within market segments include the 

weight of the aircraft, aesthetics, the level of airworthiness and safety of the final product, and 

many others. 

 

9

 The SERDP, the Department of Defense’s environmental science and technology program, highlights numerous 

projects involving the development and demonstration of alternative military coatings that do not require toxic 

materials to provide corrosion protection. Available at: http://www.serdp.org/Program-Areas/Weapons-Systemsand-Platforms/Surface-Engineering-and-Structural-Materials/Coatings. 
11 

In addition to the Aerospace MACT, aerospace vehicle manufacturing is also regulated by the 

Federal Aviation Administration, the Department of Defense, and specific customer 

requirements. As outlined in EPA’s 1998 promulgation of amendments to the Aerospace 

MACT10, affected sources must comply with FAA Airworthiness Directives (AD) that can 

potentially require the use of chemicals containing HAP, and affected sources may have to 

obtain alternative means of compliance for ADs to allow for the substitution of non-HAP 

materials. These multiple regulations can result in lengthy processes of qualifying new paint 

systems. The 1998 amendments also describe concerns from industry representatives that the 

long-term impact of alternative chemical usage on various aircraft structures is not consistent 

across various products and manufacturers. 

 For these reasons, it is unlikely that revised emission limits lower than the current MACT limits 

could adequately represent the full range of variability in the source category. 

Advancements in the Use of High Solids Primers and Topcoats

During MACT development, the EPA identified high solids primers and topcoats as a likely 

product substitution that affected sources would use to comply with the emission limits. To 

determine if significant advancements have been made in the use of high solids primers and 

topcoats, the average solids volume fraction (gallon solids/gallon coating) was determined for 

values reported in the 2011 ICR; calculated as 0.42 for primers and 0.48 for topcoats. These 

values are lower than what was considered “high solids coatings” in the 1994 Aerospace 

proposal, which specifies 50 to 65 percent solids by volume. In addition, the solid volume 

fraction of primers and topcoats remains relatively constant for the lowest and highest average 

HAP content values for each facility in the ICR data; as shown in Chart 1 for primers and Chart 

2 for topcoats. Based on this information, we found no direct evidence of significant 

advancements in the use of high solids primers or topcoats. 

Chart 1. Solid Volume Fraction Plotted as a Function of 

Increasing HAP Content – Primers 

 

10 63 FR 46525, September 1, 1998. 
12 

 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.000.080.110.220.340.410.430.490.640.680.820.850.991.091.341.431.541.611.852.022.483.99

Facility Weighted Average Solid Volume 

Fraction (gal solids/gal coating)

Facility Weighted Average HAP Content (lb HAP/gal Coating)
13 

Chart 2. Solid Volume Fraction Plotted as a Function of 

Increasing HAP Content – Topcoats 

Lower VOC Content Limits 

Both the Shipbuilding and Ship Repair and Wood Furniture Manufacturing technology reviews 

identified more stringent VOC content limits established in California regional rules as a 

development. These regional limits are also lower than the limits established in the Aerospace 

MACT; however, they are unique to their specific industries. The current versions of the three 

California regional rules identified in section 2.3 that specifically regulate aerospace coating 

operations provide VOC content limits for primers and topcoats that are identical to the VOC 

limits for general primers and topcoats in the Aerospace MACT. However, the California air 

district rules include exemptions for certain coating operations that are subject to HAP and VOC 

limits under the Aerospace MACT. One example of an exempt operation is the surface coating of 

assembled aircraft at rework facilities when the original coating formulation is used. Under the 

Aerospace MACT, rework operations are subject to HAP and VOC content limits that are not 

found in the California air district rules. Therefore, these district rules cannot be considered more 

stringent than the current Aerospace MACT when these exemptions are taken into account. In 

addition, any limit established lower than the MACT floor would likely not be achievable 

throughout the aerospace industry for the reasons detailed in the section above (Advancements in 

the Use of Low-HAP Liquid Primers and Topcoats). 

 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.040.130.170.220.280.320.450.520.580.650.690.760.820.860.881.031.131.291.411.581.862.693.293.63

Facility Weighted Average Solid Volume 

Fraction (gal solids/gal coating)

Facility Weighted Average HAP Content (lb HAP/gal Coating)
14 

Appendix 1. Practices, Processes and Control Technologies Identified for Aerospace 

Coating Operations in the October 21, 2013, Query of the RBLC Database 

RBLCID Facility Name State Process Name POLLUTAN

T 

Control Method Emission 

Reduction 

(%) 

CA-0685 T.B.M. INC. CA AIRCRAFT 

REFINISHING 

OPERATION 

VOC LOW-VOC 

COATINGS AND 

HERCULES 

GW/R 

ENCLOSED GUN 

0

CA-0685 T.B.M. INC. CA AIRCRAFT 

REFINISHING 

OPERATION 

PM HVLP SPRAY 

GUN 

0

CA-0771 CA AIR 

NATIONAL 

GUARD, FRESNO 

CA HVLP 

APPLICATOR 

USED TO COAT 

AEROSPACE 

PARTS 

VOC LOWEST 

AVAILABLE 

VOC CONTENT 

WHICH MEETS 

MILITARY 

SPECIFICATIONS 

0

CA-0771 CA AIR 

NATIONAL 

GUARD, FRESNO 

CA HVLP 

APPLICATOR 

USED TO COAT 

AEROSPACE 

PARTS 

PM HVLP GUN 

APPLICATOR, 

DRY FILTERS 

AND 10 BHP 

EXHAUST FAN 

0

CA-0881 HUCK INT.-

DEUTSCH 

OPERATIONS 

CA FOUR SPRAY 

BOOTHS 

VOC TELLKAMP 

SYSTEMS 

REGENERATIVE 

THERMAL 

OXIDIZER WITH 

A 1.6 MMBTU/H 

NAT GAS 

BURNER 

0

CA-0889 KAL-GARD 

COATING & 

MFG., E/M CORP. 

CA SPRAY 

BOOTHS, NINE 

BRINKS, 

DEVILBISS 

& BLEKKER 

VOC BACT 

DETERMINATIO

N IS USE OF 

ZEOLITE 

CONCENTRATO

R AND 

THERMAL 

OXIDIZER. 

PERMIT LIMIT IS 

LB VOC/DAY 

FACILITY LIMIT. 

0

CA-0901 TIME AVIATION 

SERVICES, INC. 

CA SPRAY 

BOOTHS, TWO 

DRY FILTER 

VOC PERMIT LIMIT IS 

USAGE LIMIT 

AND USE OF 

SCAQMD 

REGULATION XI 

COMPLIANT 

MATERIALS. 

0

CA-0977 KAL-GUARD 

COATINGS & 

MANUFACTURIN

G 

CA AEROSPACE 

METAL PART 

COATING 

OPERATION 

VOC ZEOLITE 

CONCENTRATO

R AND 

THERMAL 

97
15 

OXIDIZER

CA-1045 KAL-GARD 

COATING & MFG. 

E/M 

CA SPRAY BOOTH VOC A ZEOLITE 

CONCENTRATO

R AND 

THERMAL 

OXIDIZER 

0

IN-0126 DEAN BALDWIN 

PAINTING LP 

IN REFINISH 

OPERATION 

VOC MANGAMENT 

AND WORK 

PRACTICES 

0

UT-0058 HILL AIR FORCE 

BASE 

UT SURFACE 

COATING, 

MILITARY 

AIRCRAFT 

OPERATIONS 

HAP ZEOLITE 

ADSORPTION 

SYSTEM - M&W 

CONDESORB 

FOB - 26ZEOLITE 

ADSORPTION 

CELLS 

90

UT-0058 HILL AIR FORCE 

BASE 

UT SURFACE 

COATING, 

MILITARY 

AIRCRAFT 

OPERATIONS 

VOC ZEOLITE 

ADSORPTION 

SYSTEM - M&W 

CONDESORB 

FOB - 26 

ZEOLITE 

ADSORPTION 

CELLS 

95

WA0344 RENTON WA PAINT 

BOOTH/HANGA

R 

VOC LOW VOC 

VAPOR 

PRESSURE 

CLEANING 

SOLVENTS AND 

STRIPPERS 

WITH LOW 

PRESSURE 

APPLICATORS 

OR MANUAL 

APPLICATION 

FOR 

DEPAINTING. 

0

*WA0347 BOEING RENTON WA Floor Activities VOC Compliance with 

VOC emission 

standards of 

Aerospace 

NESHAP 

0

*WA0347 BOEING RENTON WA New Vertical 

Wing Booth (PB5) 

VOC Compliance with 

VOC emission 

standards of 

Aerospace 

NESHAP 

0

*WA0347 BOEING RENTON WA New Vertical 

Wing Booth (PB6) 

VOC Compliance with 

VOC emission 

standards of 

Aerospace 

NESHAP 

0

*WA0347 BOEING RENTON WA New Vertical 

Wing Booth (PB7) 

VOC Compliance with 

VOC emission 

0
16 

standards of 

Aerospace 

NESHAP 

*WA0347 BOEING RENTON WA New Corrosion 

Inhibitor 

Compound Booth 

(CB1) 

VOC Compliance with 

VOC emission 

standards of 

Aerospace 

NESHAP 

0

*WA0347 BOEING RENTON WA New Corrosion 

Inhibitor 

Compound Booth 

(CB2) 

VOC Compliance with 

VOC emission 

standards of 

Aerospace 

NESHAP 

0

*WA0347 BOEING RENTON WA New Corrosion 

Inhibitor 

Compound Booth 

(CB3) 

VOC Compliance with 

VOC emission 

standards of 

Aerospace 

NESHAP 

0

*WA0347 BOEING RENTON WA New Paint Hangar 

(P-7/P-8) 

VOC Compliance with 

VOC emission 

standards of 

Aerospace 

NESHAP 

0

*WA0348 BOEING RENTON WA Final exterior 

coating Building 

5-50 

VOC low VOC primers, 

coatings, and 

solvents. 

Application 

requirements. 

composite vapor 

pressure of 45 mm 

Hg @ 20 degree C 

0
17 

Appendix 2 

Calculation of Theoretical HAP Content Less Water

To determine the mass of organic HAP per volume of coating (lb/gal) less water, the volume of 

water in one gallon of coating was first determined using an assumed coating density of 10 

pounds per gallon with the following equation: 

 

= 	

 ∗ 



where: 

VW = volume of water in one gallon of coating (gal); 

DC = density of coating (lb/gal); 

WWC = weight fraction of water in coating; 

DW = density of water (8.33 lb/gal). 

The volume of water was then subtracted from the total coating volume as shown in the 

following equation: 

	 = 	




1 − 

where: 

H = mass of organic HAP emitted per volume of coating (lb/gal) less water as applied; 

MH = mass (lb) of organic HAP in one gal of coating; 

VW = volume (gal) of water in one gal of coating. 

Calculation of Theoretical VOC Content

The theoretical VOC content was calculated by dividing the theoretical HAP content less water 

by an assumed HAP/VOC ratio of 0.5.