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MEMORANDUM

DATE: October 25, 2011

SUBJECT: Emissions Data and Acute Risk Factor Used in Residual Risk Modeling: Pesticide Active 

Ingredients, Polyether Polyols, and Group IV Polymers and Resins

1.0 INTRODUCTION AND BACKGROUND

The purpose of this memorandum is to provide information on the Environmental Protection Agency 

(EPA) Risk and Technology Review (RTR) database used in estimating residual risk for the 

Pesticide Active Ingredients (PAI), Polyether Polyols (PEPOs), and Group IV Polymers and Resins 

(P&RIV) Maximum Achievable Control Technology (MACT) source categories. These MACTs 

cover only major sources.

Section 112 of the Clean Air Act (CAA) establishes a two-stage regulatory process to address 

emissions of hazardous air pollutants (HAPs) from stationary sources. In the first stage, section 

112(d) requires the EPA to develop technology-based standards for categories of industrial sources. 

In the second stage, known as the residual risk stage, section 112(f)(2) requires EPA to assess the 

health and environmental risks that remain after sources come into compliance with MACT. If 

additional risk reductions are necessary to protect public health with an ample margin of safety or to 

prevent adverse environmental effects, EPA must develop standards to address these remaining 

risks. 

2.0 DEVELOPMENT OF THE DATA SET USED IN RESIDUAL RISK MODELING

The 2005 National Air Toxics Assessment (NATA) National Emissions Inventory (NEI) data served 

as the starting point for this assessment. Using the process MACT codes1, a list of facilities in the 

Pesticide Active Ingredients (PAI), Polyether Polyols (PEPOs), and Group IV Polymers and Resins 

(P&RIV) source categories (MACT codes: PAI-0911, PEPOs-1625, P&RIV-1302, 1318, 1331, 

1328, 1338) was developed. This facility list was used to create a subset of the NEI that contained 

facility wide emissions data for each facility in the source categories. Facility information was 

checked against compliance databases and permit information to ensure that the facilities were 

subject to the relevant rules. Specific changes to data within each source category are discussed in 

2.1, 2.2, and 2.3.

Upon the request of industry trade groups such as the American Chemistry Council (ACC) and the 

Society of Chemical Manufacturers & Affiliates (SOCMA), the 2005 NATA NEI data was 

voluntarily reviewed by industry for correctness of facility names, Source Classification Codes 

(SCC), MACT codes, emissions, location (latitude and longitude coordinates) and other modeling 

parameters contained in the NEI. The proposal revisions were reviewed on a case by case basis and 

were accepted where appropriate. For these 3 source categories, revisions were made at 10 facilities.

 

1 Assigning data with MACT codes allows EPA to determine reductions attributable to the MACT 

program. The NEI associates MACT codes corresponding to MACT source categories with stationary 

major and area source data.
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EPA conducted an extensive review of the location coordinates for all facilities in the 3 source 

categories. Locations were visually reviewed using Google Earth. Adjustments were made for 

approximately 40% of the coordinates based on these visual evaluations.

Stack and fugitive parameters that did not meet EPA Quality Assurance (QA) routines and standards 

were corrected. Permit data and input from industry was used to make area/major source 

designations. Finally, a standard QA of the modeling file was conducted.

Risks associated with facilities covered by the PAI, PEPOs, and P&RIV MACT standards were 

modeled using the resulting file. Specific revisions to each data set are discussed below.

2.1 DEVELOPMENT OF PAI DATA SET

The 2005 NATA NEI data had 18 facilities that were documented as having emissions 

sources subject to the PAI MACT. In the review of additional information, one facility, 

NEI11879 was determined to be permanently shut down. Therefore, there were 17 total 

facilities in the PAI source category. Supplemental emissions information within the source 

category was received from and accepted for NEI7211 and NEIMIB4942. Supplemental 

emissions information for sources not in the source category was also accepted for NEI11295 

and NEI11906. Some emissions sources at NEI11906 were reassigned to the source category 

after input from the facility. 

2.2 DEVELOPMENT OF PEPOs DATA SET

The 2005 NATA NEI data had 49 facilities that were documented as having emissions 

sources subject to the PEPOs MACT. In the review of additional information from industry, 

Title V permits, and permitting authorities, this list was reduced to 25 facilities. 

Supplemental emissions information within the source category was received from and 

accepted for NEI11906, NEI6013, and NEI8011. Some emissions sources at NEI11906 were 

reassigned out of the source category after input from the facility. Supplemental emissions 

information for sources not in the source category was also accepted for NEI11295, 

NEI11906, NEI12483, NEI7296, and NEI8011. Additionally, updated stack parameters for 

some emissions not in the source category were received and accepted for NEI56265. 

2.3 DEVELOPMENT OF P&RIV DATA SET

The 2005 NATA NEI data had 48 facilities that were documented as having emissions 

sources subject to the P&RIV MACT. In the review of additional information from industry, 

Title V permits, and permitting authorities, this list was reduced to 32 facilities. Sources 

subject to P&RIV belong to one or more of the following 7 source categories of 

thermoplastics: acrylonitrile-butadiene-styrene resin (ABS), styrene-acrylonitrile resin (SA), 

methyl methacrylate-butadiene-styrene resin (MBS), polystyrene resin (PS), polyethylene 

terephthalate resin (PET), methyl methacrylate acrylonitrile butadiene styrene resin (MABS), 

and nitrile resin (although only the first 5 of the 7 source categories currently have operating 

facilities in the U.S.). Supplemental emissions information was received for: NEI8510 (some 

emissions were reassigned out of the PET source category) and NEI11906 (some emissions 

were reassigned out of ABS and some were reassigned to SA). Emissions information for 

sources not in the source categories was also accepted for NEI11295 and NEI11906.
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3.0 ACUTE RISK

As outlined in Appendix B: Analysis of Data on Short-Term Emission Rates Relative to Long-Term 

Emission Rates (Palma and Smith, 2009), short-term emission rates can be estimated based on 

annual average rates in order to assess risk associated with acute exposure. For RTR rulemakings, 

unless more detailed information is available, it is generally assumed that the 1-hour emission rate 

for each facility exceeds the annual average hourly emission rate by tenfold, and that this tenfold 

emission spike could coincide with worst-case meteorological conditions and the presence of a 

human receptor at the facility boundary. This method was developed as a means of screening for 

potentially significant acute exposures. This factor of ten was applied to all average annual hourly 

emission rates for a source, with two exceptions, described in 3.1 and 3.2. Changes to the data that 

were made after modeling was complete that affect the risk assessment are described in 4.0.

3.1 EMISSIONS FACTOR FOR ACUTE RISK BASED ON LONG-TERM VOC EMISSIONS

Figure 1 describes the relationship of the ratio between the event emission rate to the longterm emission rate and the long-term VOC releases. A conservative value of ten was chosen 

as the factor which to multiply all emissions in order to model acute risk (Palma and Smith, 

2009). However, the relationship in Figure 1 suggests that the highest ratios were produced 

by facilities whose routine VOC emissions were relatively small and therefore facilities that 

have large VOC emissions also have a smaller ratio of event emission rate to long-term 

emission rate. Based on this relationship, a factor of two was used for facilities that have 

long-term VOC releases of greater than 200 lb/hr (or 876 tpy), as calculated from the 2005 

NEI. A list of facilities where we used the factor of two instead of ten is provided in 

Appendix 7 of the risk assessment document.
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Figure 1. Relationship between ratio of event to duration emission rate and total amount emitted during 

the event. (Palma and Smith, 2009)

3.2 EMISSIONS FACTOR FOR ACUTE RISK BASED ON PROCESS KNOWLEDGE

A factor of two for acute risk was chosen for emissions from equipment leaks. However, this 

factor was chosen after most of the risk assessment was already complete and was therefore 

only applied to several facilities showing the highest risk. The factor of two was chosen 

because emissions from equipment leaks are inherently different from other emission sources 

at chemical manufacturing facilities. While we believe that it is possible that worst-case 

short-term emission episodes from sources such as process vents, stacks, or flares may be as 

high as ten times the annual average due to events such as upsets or process flow variability, 

this does not apply to equipment leaks. Equipment leaks are not affected acutely by variable 

flow in a system and thus cannot emit in the same way as aforementioned emission sources 

during a large-scale upset. If an event causing a pressure increase occurred in a process 

stream where a leak was present, we would not expect the toxic vapor analyzer (TVA) used 

as a part of EPA Method 21 to give a higher reading because the concentration read by the 

TVA is only a function of the composition of the process stream. The emissions estimate is 

based on this concentration measurement and has already incorporated variability, as 

discussed below. While releases from emission sources such as pressure relief devices are an 

acute risk issue because they are generally high concentration releases for short durations, 

equipment leaks pose more of a chronic risk issue because they are generally a small 

emission rate over a long period of time. Therefore, we do not believe that emissions from 

equipment leaks pose a large acute risk.

Additionally, a large uncertainty factor has already been incorporated into the emission rate 

estimates from equipment leaks and we have determined that it was not appropriate to add 

another level of uncertainty to this. To calculate emissions from equipment leaks in this 

industry, screening is conducted on a regular basis and when a leak is measured using EPA 
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Method 21, a predetermined emission factor from EPA’s Protocol for Equipment Leak 

Emission Estimates document is applied. When these emission rates for equipment leaks 

were developed, EPA used data from a number of different studies of bagged samples at 

petroleum and synthetic organic chemical manufacturing facilities. In these studies, EPA 

measured for leaks using EPA Method 21 and where leaks were found, the concentration was 

recorded, the leak was bagged, and an estimate of the mass emission rate was calculated from 

the bagged sample. From the results of these studies, mass emission rates were found to vary 

up to five orders of magnitude for a given EPA Method 21 concentration reading. A 

correlation was developed based on these results, which was inherently biased towards 

higher emission rates. A more detailed discussion on how these correlations were developed 

can be found in Appendix B of EPA’s Protocol for Equipment Leak Emission Estimates

document. Based on this information, we do not believe it is appropriate to add yet another 

order of magnitude of uncertainty to emissions from equipment leaks, and that a factor of two 

is more appropriate. A list of facilities where we used the factor of two instead of ten is 

provided in Appendix 7 of the risk assessment document. 

4.0 DATA REVISIONS AFFECTING RISK ANALYSIS

Some revisions to the data set were made post-modeling after receiving additional information from 

other regulatory entities or industry. Part of these changes reflected facilities which were shut down or 

no longer operating. Other information received reflected changes in the source category of certain 

emission points or that a specific process unit had been shut down within a facility. These changes were 

not made directly to the modeling file, as they would cause changes in the modeling itself. Instead, this 

information can be used qualitatively to understand the risk results. This information is detailed below:

NEINC0595 is not in the PEPOs source category

NEI12483 is not in the PEPOs source category

NEI41302 has been shut down

NEI43310 has ceased operations

The hexachlorobenzene emission point at NEI11906 should actually be attributed to the PAI 

source category and not PEPOs

NEI45591 has closed the PET production process and acetaldehyde emissions are almost 

zero

Phosgene emissions in the PAI source category at NEI 8596 are incorrect and should reflect 

one fugitive emission point and one stack emission point, both of 0.01 tpy, totaling 0.02 tpy

The arsenic emission point at NEIWV0390007 is not in the PAI source category

REFERENCES

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003. September 1980.

Development of Fugitive Emission Factors and Emission Profiles for Petroleum Marketing Terminals. 

Volumes I and II, API 4588, Radian Corporation, Prepared for American Petroleum Institute, 

1993.
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DuBose, D.A., J.I. Steinmetz, and G.E. Harris (Radian Corporation). Frequency of Leak Occurrence and 

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Environmental, Prepared for American Petroleum Institute, 1993.

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Letter from Robert Strieter, API, to David Markwordt, U.S. EPA, regarding the submittal of gasoline 

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Palma, Ted and Roy Smith. Appendix B: Analysis of Data on Short-Term Emission Rates Relative to 

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1980.

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No. 93-209-081-02, Radian Corporation, Prepared for Western States Petroleum Association, 

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