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 development 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 Air 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 stationary spark-ignited (SI) internal

combustion engines.
2

5. EPA’s OAQPS Alternative Control Techniques (ACT) Document – NOX

Emissions from Stationary Reciprocating Internal Combustion Engines,

July 1993.

Only the first two sources provided information to support HAP emission estimates from

RICE. The remaining data sources provided information specifically for criteria

pollutants: nitrogen oxides (NOX), 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 state 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. Secondly, 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. Finally, 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 operation of the reported RICE. Thus, it is

not possible to effectively estimate the fraction of reported HAP emissions (kg/yr) by

different RICE designs.

1.2 EPA/OTAQ NONROAD Inventory

EPA’s NONROAD emission inventory model applies 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 condition 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 operating at “even and constant” load. Emission

factor adjustments are made to account for engine deterioration (age of the engine),

annual activity (hours of operation), engine load factors (transient operation), and

variability of sulfur content in fuel. Many 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 reasonably available control technology (RACT) 

and best available retrofit control technology (BARCT) document for SI-RICE, an

extensive amount of source test data for NOX, CO, and VOC are available. Four

counties (San Joaquin, San Diego, Santa Barbara, 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 NOX 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, the 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 California Air Resources Board (CARB) air

basins and from the EPA STIRS (Source Test Information Retrieval System) effort. The

database also includes emissions tests conducted 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. The emissions tests obtained from state and

local air regulatory agencies were conducted 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 emissions database. The pollutants, test

methods, detection limits, operating conditions, and reasons for testing vary from test to

test. The test reports gathered from California air pollution control districts were

conducted by source owners and operators to comply with California's AB2588 air toxic

regulations. In those cases, test methods 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 conducted on RICE that can be classified in one of

the subcategories identified by EPA. The HAP 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 data 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 converted 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 tests 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 tested 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 NESHAP 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 tests 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 emissions 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 concentration of formaldehyde in the exhaust

than a diesel-fired engine. However, the 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 exhaust 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 type, HAP emission factors were determined

as the arithmetic mean (average) 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 the HAP emission factor determination (Count)

and flags which subset of HAP are covered under EPA’s Urban Air Toxics Strategy. 

Table 2 provides a comparison of available 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 programs, so there is some variability in which

HAP emission factors are available for each fuel type. For example, formaldehyde is a

common HAP released in the exhaust of a RICE. Formaldehyde emission factors are

available for all of the fuel types, except landfill gas. The one source test available for a

landfill gas-fired engine did not include formaldehyde in the testing program, thus a

formaldehyde emission factor is not available 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 NOX concentrations are

greater than 50 ppm. In this situation, formaldehyde and acetaldehyde tests should be

flagged as “non-quantitative.” All of the CARB 430 tests in the RICE NESHAP

emissions database were without NOX 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 HAP emissions from stationary RICE were

disproportional to HP rating. For example, 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 RICE (HP rating greater than 100 HP). 

However, based on the limited data available in the NONROAD engines emission

model, this observed trend could possibly be accounted by natural variability in the

engines used for testing, the testing protocols, 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 insufficient 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 can be used to develop an emission factor for

any category. Since only one-fifth of the available 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 emissions 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 represents 25 percent of the total reported HAP

emissions from diesel-fired RICE. Formaldehyde represents up to 52 percent and 72

percent of the total reported HAP emissions from digester gas- and natural gas-fired

RICE, respectively.

For natural gas-fired RICE, six HAP (formaldehyde, 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 reported 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 fuel type and a running cumulative percentage

of the listed HAP emission factors. At the bottom of each page in Attachment A is the

sum of all reported HAP emission factors (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 correspond 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. Natural 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 HAP 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, acetaldehyde, 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 emission 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 for diesel, natural gas, and digester gas are

considered representative. 

4. Relative Risk Contribution by RICE Emissions

A key objective of EPA’s Urban Air Toxics Strategy is a 75 percent reduction in chronic

cancer risk and a “significant” reduction in chronic 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 chronic, 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 associated 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 predominate share of the cancer risk. 
10

Table 3. Relative Distribution of Chronic Cancer and Noncancer Based on HAP Emission 

Derived from the RICE NESHAP Emission Database

Most Predominate HAP inthe Exhaust of RICE Urban Air Toxic?

Chronic Cancer

Unit Risk

Estimate

(μg/m3)-1

Chronic

Noncancer

Reference

Concentration

(mg/m3)

RICE Fue

Mass Percenta

Emissio

Diesel

Dige

G

Formaldehyde Yes 1.30E-05 9.80E-03 25.3 52Benzene Yes 7.80E-06 6.00E-02 2.8 23Acetaldehyde Yes 2.20E-06 9.00E-03 18.9 1Naphthalene (PAH) Yes ----- 3.00E-03 27.0a --

1,3-Butadiene Yes 3.00E-05 2.00E-02 4.4 --Acrolein Yes ----- 2.00E-05 9.0 --Methylene chloride Yes 7.80E-07 1.00E+00 ---- 2Methanol No ----- 4.00E+00 ---- --Toluene No ----- 4.00E-01 3.8 10Xylene No ----- 4.30E-01 2.7 4

Cumulative Mass Percentage of Total HAP Emission Factor: 93.9 93

a The 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: Uncontrolled 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 Yes NA 0.0% 25.3% 25.3%

Acetaldehyde 4.97E-06 1 2.03E-05 11 76% Yes 21.8% 21.8% 18.9% 44.2%

PAH 1.66E-06 5 1.93E-05 25 91% Yes 7.3% 29.0% 18.0% 62.2%

Naphthalene 1.02E-06 5 9.63E-06 24 89% Yes 4.5% 33.5% 9.0% 71.2%

Acrolein 1.73E-07 1 9.63E-06 11 98% Yes * * 0.8% 34.3% 9.0% 80.1%

1,3-Butadiene 7.54E-06 1 4.68E-06 12 -61% Yes * 33.0% 67.3% 4.4% 84.5%

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% Yes * 16.5% 92.4% 2.8% 94.5%

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 Yes * NA 99.1% 0.3% 99.3%

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 Yes NA 100.0% 0.2% 99.8%

Lead NA 0 8.04E-08 4 NA Yes NA 100.0% 0.1% 99.9%

Nickel NA 0 4.46E-08 3 NA Yes * NA 100.0% 0.0% 99.9%

Chromium 1.06E-08 1 3.31E-08 4 68% Yes 0.0% 100.0% 0.0% 100.0%

Selenium NA 0 2.20E-08 3 NA NA 100.0% 0.0% 100.0% *

Mercury NA 0 1.58E-08 3 NA Yes NA 100.0% 0.0% 100.0%

Beryllium NA 0 5.58E-09 3 NA Yes * NA 100.0% 0.0% 100.0%

Total HAP: 2.28E-05 1.07E-04

Thursday, April 15, 2004 Page 1 of 5

* = One or more test run reported the pollutant as "not detected" 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

Digester Gas

% of Total 

HAP EF Cum.%

% of Total 

HAP EF Cum.%

Urban Air 

Toxic?

%∆

Formaldehyde 2.62E-05 9 1.63E-05 17 -61% Yes * 55.4% 55.4% 52.8% 52.8%

Benzene 1.07E-05 9 7.13E-06 17 -50% Yes * 22.7% 78.0% 23.2% 76.0%

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% Yes * * 2.0% 92.6% 2.3% 92.5%

Acetaldehyde 7.68E-07 7 4.43E-07 15 -73% Yes * * 1.6% 94.2% 1.4% 94.0%

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% Yes * * 0.8% 96.8% 0.8% 96.7%

Acrolein 3.03E-07 6 1.73E-07 12 -75% Yes * * 0.6% 97.5% 0.6% 97.3%

Vinyl chloride 1.97E-07 9 1.30E-07 17 -51% Yes * * 0.4% 97.9% 0.4% 97.7%

Tetrachloroethylene 1.43E-07 9 1.02E-07 17 -40% Yes * * 0.3% 98.2% 0.3% 98.0%

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% Yes * * 0.3% 98.8% 0.3% 98.7%

Trichloroethylene 1.40E-07 9 9.94E-08 17 -40% Yes * * 0.3% 99.1% 0.3% 99.0%

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% Yes * * 0.2% 99.5% 0.2% 99.5%

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% Yes * * 0.1% 99.8% 0.2% 99.8%

Ethylene dibromide 7.75E-08 6 4.91E-08 14 -58% * * 0.2% 100.0% 0.2% 100.0%

Total HAP: 4.72E-05 3.08E-05

Thursday, April 15, 2004 Page 2 of 5

* = One or more test run reported the pollutant as "not detected" 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

Landfill 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 Yes NA 0.0% 16.5% 87.7%

Vinyl Chloride NA 0 1.27E-07 1 NA Yes NA 0.0% 4.1% 91.9%

Perchloroethylene NA 0 8.34E-08 1 NA Yes NA 0.0% 2.7% 94.6%

Chloroform NA 0 8.11E-08 1 NA Yes NA 0.0% 2.6% 97.2%

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 Yes NA 0.0% 1.2% 99.9%

Carbon Tetrachloride NA 0 3.89E-09 1 NA Yes NA 0.0% 0.1% 100.0%

Total HAP: 0.00E+00 3.09E-06

Thursday, April 15, 2004 Page 3 of 5

* = One or more test run reported the pollutant as "not detected" 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% Yes * 76.9% 76.9% 72.3% 72.3%

Acetaldehyde 1.93E-05 15 5.55E-05 91 65% Yes * * 4.0% 80.9% 8.1% 80.4%

Acrolein 1.14E-05 15 4.59E-05 82 75% Yes * * 2.4% 83.3% 6.7% 87.0%

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% Yes * 7.8% 91.1% 3.1% 93.6%

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% Yes * * 1.9% 96.8% 1.2% 96.3%

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% Yes * * 0.5% 99.7% 0.3% 98.8%

PAH NA 0 1.17E-06 5 NA Yes NA 99.7% 0.2% 99.0%

Methylene Chloride NA 0 7.46E-07 15 NA Yes * NA 99.7% 0.1% 99.1%

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 Yes * NA 99.9% 0.1% 99.4%

Carbon Tetrachloride NA 0 5.77E-07 15 NA Yes * NA 99.9% 0.1% 99.5%

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 Yes * NA 100.0% 0.1% 99.7%

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 Yes * NA 100.0% 0.1% 99.9%

1,2-Dichloroethane NA 0 3.73E-07 14 NA Yes * NA 100.0% 0.1% 99.9%

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 Yes * NA 100.0% 0.0% 100.0%

Tetrachloroethane NA 0 1.63E-08 1 NA Yes NA 100.0% 0.0% 100.0%

Chloroethane NA 0 1.24E-08 1 NA NA 100.0% 0.0% 100.0%

Total HAP: 4.78E-04 6.88E-04

Thursday, April 15, 2004 Page 4 of 5

* = One or more test run reported the pollutant as "not detected" 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

Propane

% of Total 

HAP EF Cum.%

% of Total 

HAP EF Cum.%

Urban Air 

Toxic?

%∆

Benzene 1.78E-04 1 1.78E-04 1 0% Yes 76.2% 76.2% 76.2% 76.2%

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% Yes * * 0.6% 100.0% 0.6% 100.0%

Total HAP: 2.34E-04 2.34E-04

Thursday, April 15, 2004 Page 5 of 5

* = One or more test run reported the pollutant as "not detected" so one-half the value of the detection limit was used.