### 1 MEMORANDUM DATE: April 13, 2004 SUBJECT: Development of HAP Emission Factors for Small (< 500 HP) Stationary Reciprocating Internal Combustion Engines (RICE)

FROM: Chuck Zukor Alpha-Gamma Technologies, Inc. TO: Jaime Pagán EPA/OAQPS/ESD/Combustion Group

This memorandum summarizes available hazardous air pollutants (HAP) emissions data for the development of emission factors for small < 500 horsepower (HP) stationary reciprocating internal combustion engines (RICE). Emissions data presented in this memorandum focus on HAP and the subset of 33 HAP covered under EPA’s Urban Air Toxics Strategy which pose the greatest potential health threat in urban areas.

1. Source of Emissions Information During the course of this effort, the following sources of emissions data were identified: 1. EPA’s Office of Air Quality Planning and Standards (OAQPS) RICE Emissions Database used for devel opment of the RICE NESHAP for stationary major sources of HAP. 2. EPA’s OAQPS National Emission Inventory (NEI) version 3 (September 2003). 3. EPA’s Office of Transportation and Ai r Quality (OTAQ) NONROAD engine emission inventory model. 4. California’s Air Resources Board’s draft Reasonably Available Control Technology (RACT) and Best Available Retrofit Control Technology (BARCT) determination for stationar y spark-ignited (SI) internal combustion engines.

### 2 5. EPA’s OAQPS Alternative Control Techniques (ACT) Document – NO X 

### Emissions from Stationary Reciproc ating Internal Combustion Engines, July 1993. Only the first two sources provided informa tion to support HAP emission estimates from RICE. The remaining data sources provi ded information specifically for criteria pollutants: nitrogen oxides (NO X 

### ), carbon monoxide (CO), and volatile organic compounds (VOC). The RICE NESHAP emissions database appears to be the best available source of HAP emissions data for small RICE (< 500 HP), and is described in more detail in the next section of this memorandum. 1.1 EPA/OAQPS National Emission Inventory (NEI) The information provided in EPA’s 2003 NEI is considered marginal for application to this project for several reasons. First, the quality and quantity of data in the NEI is highly dependent upon the resources of each st ate submitting the emissions data. Thus, the majority of data are skewed towards a few states which do not represent the majority of the RICE population. Secondl y, there is no documentation to determine whether the NEI emissions data (kg/yr) are based on site-specific source tests, application of surrogate source test data, AP-42 emission factors, alternate emission factors, or best engineering judgement. Fina lly, the NEI contained little information to distinguish RICE such as HP rating, type of fuel burned, type of engine design (2- or 4- stroke, rich- or lean-burn), and the hours of oper ation of the reported RICE. Thus, it is not possible to effectively estimate the fr action of reported HAP emissions (kg/yr) by different RICE designs. 1.2 EPA/OTAQ NONROAD Inventory EPA’s NONROAD emission inventory model app lies to “non-stationary” RICE with HP ratings generally below 500 HP. Therefore, it was considered a potential source of “surrogate” data. The NONROAD model is very complex. The NONROAD emission inventory is based only on criteria pollutant emission factors derived from a small to moderate amount of source test data. The model applies numerous physical and operational adjustments to a standard engine c ondition referred to as the “zero-mile, steady-state” emission factor for each basic engine design type (2- or 4-stroke, rich- or lean-burn). This reference condition corresponds to when an engine is “new,” thus zero miles of wear and when the engine is operati ng at “even and constant” load. Emission factor adjustments are made to account fo r engine deterioration (age of the engine), annual activity (hours of operation), engine load factors (transient operation), and variability of sulfur content in fuel. M any of these adjustments may not be directly applicable due to the different conditions in which these nonroad RICE operate compared to small stationary RICE.

### 3 1.3 California’s Proposed RACT/BARCT for SI-RICE In Appendix D of California’s proposed reasonabl y available control technology (RACT) and best available retrofit control tec hnology (BARCT) document for SI-RICE, an extensive amount of source test data for NO X 

### , CO, and VOC are available. Four counties (San Joaquin, San Diego, Santa Ba rbara, and Ventura) provided the source test summary data. The data generally included engine design characteristics, HP rating, and type of fuel burned. However, there are no emissions data for speciated HAP, only criteria pollutants.

1.5 EPA’s ACT Document for NO X 

### Emissions from RICE EPA’s Alternative Control Techniques (ACT) document only contained emission factors for criteria pollutants released from the operation of stationary RICE. Since no data were available for HAP emissions, t he document was not further considered.

2. EPA’s RICE NESHAP Emission Database In support of regulatory development for the RICE NESHAP, Alpha-Gamma has compiled extensive HAP source test data and engine design characteristics into a Microsoft Access database. The majority of test reports included in the RICE NESHAP emissions database were obtained from Calif ornia Air Resources Board (CARB) air basins and from the EPA STIRS (Source Test In formation Retrieval System) effort. The database also includes emissions tests conduct ed by the Gas Research Institute (GRI) for natural gas-fired engines. These emissions tests were conducted by GRI in cooperation with GRI member companies. Testing was also conducted at Colorado State University (CSU) by EPA on three engines , and preliminary results of this testing are included in the emissions database. T he emissions tests obtained from state and local air regulatory agencies were conduc ted by source owners and operators in response to air regulatory requirements. No standard protocol was used to conduct the emissions tests included in the RICE em issions database. The pollutants, test methods, detection limits, operating conditions, and reasons for testing vary from test to test. The test reports gathered from Calif ornia air pollution control districts were conducted by source owners and operators to comply with California's AB2588 air toxic regulations. In those cases, test me thods developed and approved by the CARB are generally used to quantify emissions. The target HAP for the California tests vary since the target HAP were negotiated with the local air pollution control district. The information in the RICE NESHAP emissions database was developed from a total of 578 tests, but only 431 tests were conduct ed on RICE that can be classified in one of the subcategories identified by EPA. The H AP concentration data from each test were converted into emission factors of various units, including: lb/hr, lb/MMBTU, and lb/hp-hr. However, some source test dat a were converted only to units of lb/hr and lb/MMBTU. Since the emission factors presented in this analysis are in units of lb/hp-hr,

### 4 available test data in lb/MMBTU were c onverted to lb/hp-hr assuming an average RICE operating efficiency of 34 percent in the following equation: lb/hp-hr = lb/MMBTU * 0.002546 (MMBTU/hp-hr) ÷ 0.34 A summary of the number of emissions test s included in the database, by subcategory, is presented in Table 1. The number of tests on engines with HAP control and small (< 500 HP) engines is also given. Engines test ed range in size from 25 HP to 7,107 HP. Table 1. Number of Emissions Tests Per Subcategory in the RICE NESHAP Emission Database

Subcategory Total Number of Emissions Tests Number of Tests on Engines with HAP

control Number of Tests on

Small Engines ( < 500 HP) 2-Stroke Lean Burn (2SLB) 121 17 41 4-Stroke Lean Burn (4SLB) 94 16 0 4-Stroke Rich Burn (4SRB) 141 55 29 Compression Ignition (CI) 57 10 12 Digester Gas and Landfill Gas 18 0 6 TOTAL: 431 98 88 2.1 Data Availability by Fuel Type

Most of the emissions data are for natural gas-fired engines and diesel engines, which, according to the RICE Population Database, represent over 95 percent of stationary RICE. For fuels other than natural gas and diesel, there are a limited number of HAP emissions tests included in the RICE NESH AP emission database. For digester gasfired RICE, 17 emissions tests are included in the database, and for landfill gas-fired RICE, one emissions test is included in the database. One emissions test is included in the database for propane and three emissions te sts are included for process gas. No emissions tests are included for LPG engines. For compression-ignition (CI) stationary RICE, the majority of the emissions tests included in the database are for diesel fuel; three tests are included for JP-5, and no em issions tests are included for dual fuel, kerosene/naphtha, or heavier fuels, such as residual/crude oil.

### 5 2.2 Data Availability by HAP

### 6 A key advantage in using the RICE NESHAP emissions database is the availability of RICE emission factors for individual HAP. The type of HAP and magnitude released in the exhaust of a RICE depends strongly on the type of fuel burned. For example, a natural gas-fired engine will have a higher conc entration of formaldehyde in the exhaust than a diesel-fired engine. However, t he exhaust of a diesel-fired engine will also include a variety of heavy metal HAP such as cadmium, chromium, lead, and mercury that are not observed in the exhaus t from a natural gas-fired engine. Attachment A provides a summary of the available uncontrolled RICE emission factors for individual HAP (lb HAP/hp-hr) by five types of fuel: diesel, digester gas, landfill gas, natural gas, and propane. For each fuel ty pe, HAP emission factors were determined as the arithmetic mean (aver age) of the available HAP source test data for all small RICE (< 500 HP) and for all RICE regardless of HP rating. Attachment A also lists the number of source test values used in t he HAP emission factor determination (Count) and flags which subset of HAP are cove red under EPA’s Urban Air Toxics Strategy. Table 2 provides a comparison of availabl e HAP emission factors (all RICE regardless of HP rating) by fuel type that are categorized as Urban Air Toxics. Not all HAP were included in the testing program s, so there is some variability in which HAP emission factors are available for each f uel type. For example, formaldehyde is a common HAP released in the exhaust of a RI CE. Formaldehyde emission factors are available for all of the fuel types, except l andfill gas. The one source test available for a landfill gas-fired engine did not include formal dehyde in the testing program, thus a formaldehyde emission factor is not av ailable for landfill gas-fired RICE. In 2000, CARB issued an advisory on the use of CARB test method 430 which has been used to quantify acrolein, formaldehyde, and acetaldehyde. The advisory states that CARB 430 should not be used to quantify acrolein and pollutant interference may occur for formaldehyde and acetaldehyde measurements when NO X 

### concentrations are greater than 50 ppm. In this situation, formaldehyde and acetaldehyde tests should be flagged as “non-quantitative.” All of t he CARB 430 tests in the RICE NESHAP emissions database were without NO X 

### concentration data, thus none of the acrolein, formaldehyde, and acetaldehyde data from CARB 430 tests were used in this analysis. 2.3 Data Availability by Horsepower Rating In earlier analyses of the RICE NESHAP emission database, the available HAP emissions data were categorized into four HP groups:

• 50< to < 100 HP, • 100< to < 250 HP, • 250< to < 350 HP, and • 350< to < 500 HP.

### 7 Table 2. Urban Air Toxics Emission Information by Fuel Type in the RICE NESHAP Emission Database

HAP Emissions in RICE Exhaust RICE Fuel Type

Diesel Digester Gas Landfill Gas Natural Gas Propane ORGANIC COMPOUNDS Formaldehyde TT TT Benzene TTTTT Acetaldehyde TT TT Naphthalene / PAH T T 1,3-Butadiene TT T Acrolein TT TT Methylene chloride T TT Vinyl chloride TTT Tetrachloroethylene T T Chloroform TTT Trichloroethylene T T Carbon tetrachloride TTT Ethylene dichloride T T 1,1,2,2-Tetrachloroethane T 1,3-Dichloroethane T HEAVY METALS Cadmium T Magnesium T Lead T Nickel T Chromium T Selenium T Mercury T Beryllium T

### 8 The data were analyzed to determine if H AP emissions from stationary RICE were disproportional to HP rating. For ex ample, the NONROAD engine emissions model claims that (criteria pollutant) emissions are higher from small nonroad RICE (HP rating between 50 to 100 HP), than larger nonroad RI CE (HP rating greater than 100 HP). However, based on the limited data avail able in the NONROAD engines emission model, this observed trend could possibly be accounted by natural variability in the engines used for testing, the testing prot ocols, and sample recovery. Once the available RICE NESHAP emissions data were separated into the four HP categories, a number of data gaps appeared for many of the HAP in several HP categories. Some HAP data were available in up to three of the HP categories, yet there was no observed trend (across all fuel types) that smaller stationary RICE produced a disproportionate amount of HAP emissions. Due to insuffici ent data, HAP emission factors were not developed for multiple HP categories < 500 HP. Next, the available HAP emissions data were categorized only into two groups:

• “Small” RICE < 500 HP, and • All RICE regardless of HP rating. As observed in the earlier analyses, dividing the available HAP emission data decreases the amount of information that c an be used to develop an emission factor for any category. Since only one-fifth of the av ailable HAP emissions tests are from RICE with a HP rating < 500 HP, any potentially observed trends may be accounted by natural variability. These two sets of emission factor values are included in Attachment A for comparison purposes. These data are shown to document the number of source tests that are included in the derivation of each HAP emission factor. Since the HAP emissions data did not reflect any significant changes across a range of HP ratings, it is recommended that all emissi ons data from all RICE regardless of rating be used to develop HAP emission factors by fuel type. 3. Further Emission Characterization by Fuel Type Data are available to characterize up to 27 different HAP in the exhaust of stationary RICE, of which 14 are covered by the Urban Air Toxics Strategy. However, on a massbasis, only a small number of HAP comprise the bulk of the HAP emissions. For example, formaldehyde is one of the most predominate HAP in the exhaust of RICE regardless of fuel type. Formaldehyde repr esents 25 percent of the total reported HAP emissions from diesel-fired RICE. Fo rmaldehyde represents up to 52 percent and 72 percent of the total reported HAP emissi ons from digester gas- and natural gas-fired RICE, respectively. For natural gas-fired RICE, six HAP (forma ldehyde, acetaldehyde, acrolein, methanol, benzene, and toluene) comprise approximately 95 percent of the total reported HAP emissions. For digester gas-fired RICE, the same six HAP comprise more than

### 9 88 percent of the total report ed HAP emissions. The same six HAP comprise almost 60 percent of the total HAP for diesel-fired RICE.

Listed next to each HAP emission factor in Attachment A is the corresponding percentage of total HAP reported for the f uel type and a running cumulative percentage of the listed HAP emission factors. At t he bottom of each page in Attachment A is the sum of all reported HAP emission fact ors (lb HAP/hp-hr) for each fuel type: • Natural gas 6.68E-04 lb total HAP/hp-hr, • Diesel 1.07E-04 lb total HAP/hp-hr, • Digester gas 3.08E-05 lb total HAP/hp-hr, • Propane 2.34E-04 lb total HAP/hp-hr ( * ), and • Landfill gas 3.09E-06 lb total HAP/hp-hr ( * ).

These total HAP emission factor values co rrespond to using all RICE regardless of HP rating. As one can observe, total HAP emissions from RICE appears to span two orders of magnitude depending on fuel type. Na tural gas-fired RICE result with the largest total HAP emission factor at 6.88E -04 lb total HAP/hp-hr. While, landfill gasfired RICE result in the smallest total H AP emission factor at 3.09E-06 lb total HAP/hphr. Note that the total HAP emission factors for landfill gas and propane do not include any contribution from formaldehyde, ac etaldehyde, and acrolein which typically contributes a significant portion of the total HAP emissions from RICE. In addition, the emission factor for each HAP listed for landfill gas and propane is based on only one source test. Thus, the total HAP em ission factors for landfill gas and propane are considered NOT REPRESENTATIVE ( * ). For the remaining fuel types, the HAP most likely to be released in RICE exhaust are represented in the available emissions data and corresponding emission factors. Therefore, the total HAP emission factors fo r diesel, natural gas, and digester gas are considered representative.

4. Relative Risk Contribut ion by RICE Emissions A key objective of EPA’s Urban Air Toxics Stra tegy is a 75 percent reduction in chronic cancer risk and a “significant” reduction in ch ronic non-cancer effects. Table 3 presents the 10 most predominate HAP in the exhaust gases of RICE. Half of these HAP already have a chronic cancer unit risk estimate ( URE) established for the chemical. However, all ten HAP are already established with a ch ronic, non-cancer Reference Concentration (RfC). As shown in Table 3, these 10 HAP comprise 94 to 98 percent of the cumulative mass percentage of the known total HAP emission factor for diesel, digester gas, and natural gas. When the mass percentage of the total HAP emission factor is considered as a weighting factor for the five HAP asso ciated with a cancer risk, it becomes evident that the exposure to a cancer risk is much greater. The five HAP with a cancer risk represent approximately 50 to 85 percent of the total HAP emissions. Formaldehyde is also the HAP contributing the predomi nate share of the cancer risk.10Table 3. Relative Distribution of Chronic Cancer and Noncancer Based on HAP Emission FactorsDerived from the RICE NESHAP Emission DatabaseMost Predominate HAP inthe Exhaust of RICE Urban Air Toxic?Chronic CancerUnit RiskEstimate(μg/m3)-1ChronicNoncancerReferenceConcentration(mg/m3)RICE Fuel Type andMass Percentage of Total HAPEmission FactorDieselDigesterGasNaturalGasFormaldehyde Yes 1.30E-05 9.80E-03 25.3 52.8 72.3Benzene Yes 7.80E-06 6.00E-02 2.8 23.2 3.1Acetaldehyde Yes 2.20E-06 9.00E-03 18.9 1.4 8.1Naphthalene (PAH) Yes ----- 3.00E-03 27.0a---- 0.5a1,3-Butadiene Yes 3.00E-05 2.00E-02 4.4 ---- 1.2Acrolein Yes ----- 2.00E-05 9.0 ---- 6.7Methylene chloride Yes 7.80E-07 1.00E+00 ---- 2.3 0.1Methanol No ----- 4.00E+00 ---- ---- 3.4Toluene No ----- 4.00E-01 3.8 10.1 1.6Xylene No ----- 4.30E-01 2.7 4.1 0.5Cumulative Mass Percentage of Total HAP Emission Factor: 93.9 93.9 97.5aThe emission factors for naphthalene and PAH are listed as a combined value.

# ATTACHMENT A Summary of Uncontrolled HAP Emissions Factors Derived from EPA’s RICE NESHAP Emission Database

# Attachment A: Uncontro lled HAP Emission Factors (lb HAP/hp-hr) from the RICE NESHAP Database

HAP Avg EF Test Count Avg EF Test Count RICE <500 Hp All RICE Regardless of Hp from <500 hp EF 

# Diesel

% of Total HAP EF Cum.% % of Total HAP EF Cum.% Urban Air

Toxic? %∆

Formaldehyde NA 0 2.72E-05 10 NA NA 0.0% 25.3% 25.3% Yes Acetaldehyde 4.97E-06 1 2.03E-05 11 76% 21.8% 21.8% 18.9% 44.2% Yes PAH 1.66E-06 5 1.93E-05 25 91% 7.3% 29.0% 18.0% 62.2% Yes Naphthalene 1.02E-06 5 9.63E-06 24 89% 4.5% 33.5% 9.0% 71.2% Yes Acrolein 1.73E-07 1 9.63E-06 11 98% 0.8% 34.3% 9.0% 80.1% Yes * * 1,3-Butadiene 7.54E-06 1 4.68E-06 12 -61% 33.0% 67.3% 4.4% 84.5% Yes * Toluene 1.94E-06 3 4.04E-06 17 52% 8.5% 75.8% 3.8% 88.3% * Styrene NA 0 3.74E-06 10 NA NA 75.8% 3.5% 91.7% * Benzene 3.77E-06 3 2.96E-06 17 -27% 16.5% 92.4% 2.8% 94.5% Yes * Xylene 1.09E-06 3 2.91E-06 7 63% 4.8% 97.1% 2.7% 97.2% * Hexane 4.53E-07 1 1.97E-06 12 77% 2.0% 99.1% 1.8% 99.0% * Cadmium NA 0 2.90E-07 3 NA NA 99.1% 0.3% 99.3% Yes * Ethylbenzene 1.90E-07 1 2.78E-07 13 32% 0.8% 100.0% 0.3% 99.6% * Manganese NA 0 2.51E-07 3 NA NA 100.0% 0.2% 99.8% Yes Lead NA 0 8.04E-08 4 NA NA 100.0% 0.1% 99.9% Yes Nickel NA 0 4.46E-08 3 NA NA 100.0% 0.0% 99.9% Yes * Chromium 1.06E-08 1 3.31E-08 4 68% 0.0% 100.0% 0.0% 100.0% Yes Selenium NA 0 2.20E-08 3 NA NA 100.0% 0.0% 100.0% * Mercury NA 0 1.58E-08 3 NA NA 100.0% 0.0% 100.0% Yes Beryllium NA 0 5.58E-09 3 NA NA 100.0% 0.0% 100.0% Yes * 2.28E-05 1.07E-04 Total HAP:

Thursday, April 15, 2004 Page 1 of 5 * = One or more test run repor ted the pollutant as "not dete cted" so one-half the value of the detection limit was used.HAP Avg EF Test Count Avg EF Test Count RICE <500 Hp All RICE Regardless of Hp from <500 hp EF 

# Di g ester Gas

% of Total HAP EF Cum.% % of Total HAP EF Cum.% Urban Air

Toxic? %∆

Formaldehyde 2.62E-05 9 1.63E-05 17 -61% 55.4% 55.4% 52.8% 52.8% Yes * Benzene 1.07E-05 9 7.13E-06 17 -50% 22.7% 78.0% 23.2% 76.0% Yes * Toluene 4.06E-06 9 3.12E-06 17 -30% 8.6% 86.6% 10.1% 86.1% * Xylene 1.88E-06 9 1.26E-06 17 -49% 4.0% 90.6% 4.1% 90.2% * * Methylene chloride 9.52E-07 9 7.07E-07 17 -35% 2.0% 92.6% 2.3% 92.5% Yes * * Acetaldehyde 7.68E-07 7 4.43E-07 15 -73% 1.6% 94.2% 1.4% 94.0% Yes * * Styrene 4.39E-07 9 3.07E-07 17 -43% 0.9% 95.2% 1.0% 95.0% * * Dichlorobenzene 3.93E-07 9 2.74E-07 17 -43% 0.8% 96.0% 0.9% 95.8% * * 1,3-Butadiene 3.88E-07 9 2.59E-07 17 -50% 0.8% 96.8% 0.8% 96.7% Yes * * Acrolein 3.03E-07 6 1.73E-07 12 -75% 0.6% 97.5% 0.6% 97.3% Yes * * Vinyl chloride 1.97E-07 9 1.30E-07 17 -51% 0.4% 97.9% 0.4% 97.7% Yes * * Tetrachloroethylene 1.43E-07 9 1.02E-07 17 -40% 0.3% 98.2% 0.3% 98.0% Yes * * 1,1,1-Trichloroethane 1.42E-07 9 1.01E-07 17 -40% 0.3% 98.5% 0.3% 98.3% * * Chloroform 1.41E-07 9 1.00E-07 17 -40% 0.3% 98.8% 0.3% 98.7% Yes * * Trichloroethylene 1.40E-07 9 9.94E-08 17 -40% 0.3% 99.1% 0.3% 99.0% Yes * * 1,4-Dioxane 1.39E-07 9 9.90E-08 17 -40% 0.3% 99.4% 0.3% 99.3% * * Carbon tetrachloride 7.92E-08 6 5.56E-08 11 -42% 0.2% 99.5% 0.2% 99.5% Yes * * Vinylidene chloride 6.97E-08 9 5.46E-08 17 -28% 0.1% 99.7% 0.2% 99.7% * * Ethylene dichloride 6.97E-08 9 5.45E-08 17 -28% 0.1% 99.8% 0.2% 99.8% Yes * * Ethylene dibromide 7.75E-08 6 4.91E-08 14 -58% 0.2% 100.0% 0.2% 100.0% * * 4.72E-05 3.08E-05 Total HAP:

Thursday, April 15, 2004 Page 2 of 5 * = One or more test run repor ted the pollutant as "not dete cted" so one-half the value of the detection limit was used.HAP Avg EF Test Count Avg EF Test Count RICE <500 Hp All RICE Regardless of Hp from <500 hp EF 

# Land f

ill Gas

% of Total HAP EF Cum.% % of Total HAP EF Cum.% Urban Air

Toxic? %∆

Xylene NA 0 1.14E-06 1 NA NA 0.0% 36.9% 36.9% Toluene NA 0 1.06E-06 1 NA NA 0.0% 34.3% 71.3% Benzene NA 0 5.09E-07 1 NA NA 0.0% 16.5% 87.7% Yes Vinyl Chloride NA 0 1.27E-07 1 NA NA 0.0% 4.1% 91.9% Yes Perchloroethylene NA 0 8.34E-08 1 NA NA 0.0% 2.7% 94.6% Yes Chloroform NA 0 8.11E-08 1 NA NA 0.0% 2.6% 97.2% Yes 1,1,1-Trichloroethane NA 0 4.68E-08 1 NA NA 0.0% 1.5% 98.7% Trichloroethylene NA 0 3.63E-08 1 NA NA 0.0% 1.2% 99.9% Yes Carbon Tetrachloride NA 0 3.89E-09 1 NA NA 0.0% 0.1% 100.0% Yes 0.00E+00 3.09E-06 Total HAP:

Thursday, April 15, 2004 Page 3 of 5 * = One or more test run repor ted the pollutant as "not dete cted" so one-half the value of the detection limit was used.HAP Avg EF Test Count Avg EF Test Count RICE <500 Hp All RICE Regardless of Hp from <500 hp EF 

# Natural Gas

% of Total HAP EF Cum.% % of Total HAP EF Cum.% Urban Air

Toxic? %∆

Formaldehyde 3.67E-04 15 4.98E-04 92 26% 76.9% 76.9% 72.3% 72.3% Yes * Acetaldehyde 1.93E-05 15 5.55E-05 91 65% 4.0% 80.9% 8.1% 80.4% Yes * * Acrolein 1.14E-05 15 4.59E-05 82 75% 2.4% 83.3% 6.7% 87.0% Yes * * Methanol NA 0 2.32E-05 60 NA NA 83.3% 3.4% 90.4% * Benzene 3.74E-05 29 2.16E-05 67 -73% 7.8% 91.1% 3.1% 93.6% Yes * Toluene 1.79E-05 29 1.11E-05 64 -61% 3.7% 94.9% 1.6% 95.2% 1,3-Butadiene 9.11E-06 15 8.03E-06 19 -13% 1.9% 96.8% 1.2% 96.3% Yes * * 2,2,4-Trimethylpentane NA 0 6.46E-06 13 NA NA 96.8% 0.9% 97.3% Hexane 4.19E-06 15 5.10E-06 29 18% 0.9% 97.7% 0.7% 98.0% * * Xylene 7.46E-06 14 3.54E-06 48 -111% 1.6% 99.2% 0.5% 98.5% * * Naphthalene 2.31E-06 12 1.77E-06 19 -30% 0.5% 99.7% 0.3% 98.8% Yes * * PAH NA 0 1.17E-06 5 NA NA 99.7% 0.2% 99.0% Yes Methylene Chloride NA 0 7.46E-07 15 NA NA 99.7% 0.1% 99.1% Yes * Ethylbenzene 6.83E-07 17 7.07E-07 48 3% 0.1% 99.9% 0.1% 99.2% * * Ethylene Dibromide NA 0 6.98E-07 15 NA NA 99.9% 0.1% 99.3% * 1,1,2,2-Tetrachloroethan NA 0 6.79E-07 15 NA NA 99.9% 0.1% 99.4% Yes * Carbon Tetrachloride NA 0 5.77E-07 15 NA NA 99.9% 0.1% 99.5% Yes * Styrene 7.02E-07 15 5.23E-07 34 -34% 0.1% 100.0% 0.1% 99.5% * * 1,1,2-Trichloroethane NA 0 5.01E-07 15 NA NA 100.0% 0.1% 99.6% * Chloroform NA 0 4.48E-07 15 NA NA 100.0% 0.1% 99.7% Yes * 1,2-Dichloropropane NA 0 4.24E-07 15 NA NA 100.0% 0.1% 99.7% * Chlorobenzene NA 0 4.22E-07 16 NA NA 100.0% 0.1% 99.8% * 1,3-Dichloropropene NA 0 4.16E-07 15 NA NA 100.0% 0.1% 99.9% Yes * 1,2-Dichloroethane NA 0 3.73E-07 14 NA NA 100.0% 0.1% 99.9% Yes * 1,1-Dichloroethane NA 0 3.71E-07 15 NA NA 100.0% 0.1% 100.0% * Vinyl Chloride NA 0 2.35E-07 15 NA NA 100.0% 0.0% 100.0% Yes * Tetrachloroethane NA 0 1.63E-08 1 NA NA 100.0% 0.0% 100.0% Yes Chloroethane NA 0 1.24E-08 1 NA NA 100.0% 0.0% 100.0% 4.78E-04 6.88E-04 Total HAP:

Thursday, April 15, 2004 Page 4 of 5 * = One or more test run repor ted the pollutant as "not dete cted" so one-half the value of the detection limit was used.HAP Avg EF Test Count Avg EF Test Count RICE <500 Hp All RICE Regardless of Hp from <500 hp EF 

# Pro p ane

% of Total HAP EF Cum.% % of Total HAP EF Cum.% Urban Air

Toxic? %∆

Benzene 1.78E-04 1 1.78E-04 1 0% 76.2% 76.2% 76.2% 76.2% Yes Toluene 4.31E-05 1 4.31E-05 1 0% 18.5% 94.6% 18.5% 94.6% Xylene 1.12E-05 1 1.12E-05 1 0% 4.8% 99.4% 4.8% 99.4% Naphthalene 1.30E-06 1 1.30E-06 1 0% 0.6% 100.0% 0.6% 100.0% Yes * * 2.34E-04 2.34E-04 Total HAP:

Thursday, April 15, 2004 Page 5 of 5 * = One or more test run repor ted the pollutant as "not dete cted" so one-half the value of the detection limit was used.