May 2003 • NREL/SR-540-33793 

Impact of Biodiesel Fuels on Air

Quality and Human Health 

Summary Report

September 16, 1999–January 31, 2003 

R.E. Morris, A. K. Pollack, G. E. Mansell, 

C. Lindhjem, Y. Jia, and G. Wilson 

ENVIRON International Corporation 

Novato, California 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory

Operated by Midwest Research Institute • Battelle • Bechtel 

Contract No. DE-AC36-99-GO10337 
May 2003 • NREL/SR-540-33793 

Impact of Biodiesel Fuels on Air

Quality and Human Health 

Summary Report

September 16, 1999–January 31, 2003

R.E. Morris, A. K. Pollack, G. E. Mansell, 

C. Lindhjem, Y. Jia, and G. Wilson 

ENVIRON International Corporation 

Novato, California 

NREL Technical Monitor: K.S. Tyson and R. McCormick 

Prepared under Subcontract No. AXE-9-29079-01 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory

Operated by Midwest Research Institute • Battelle • Bechtel 

Contract No. DE-AC36-99-GO10337 
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TABLE OF CONTENTS 

EXECUTIVE SUMMARY .......................................................................................................... 2

Acronyms and Abbreviations ...................................................................................................... 4

1. INTRODUCTION.................................................................................................................... 5

BACKGROUND..................................................................................................................... 5 

PURPOSE ............................................................................................................................... 6 

BIODIESEL EMISSION EFFECTS....................................................................................... 6 

OVERALL EFFECTS OF BIODIESEL FUEL USE ON EMISSIONS AND TOXICITY... 8 

2. EFFECTS OF BIODIESEL ON AMBIENT OZONE CONCENTRATIONS .................. 9

MODEL AND DATABASES USED ..................................................................................... 9 

EFFECTS OF BIODIESEL USE .......................................................................................... 10 

EMISSION SUMMARY RESULTS .................................................................................... 10 

OZONE MODELING RESULTS......................................................................................... 12 

CONCLUSIONS ................................................................................................................... 14 

3. BIODIESEL EFFECTS ON AMBIENT CO CONCENTRATIONS ............................... 15

INTRODUCTION................................................................................................................. 15

OVERVIEW OF APPROACH ............................................................................................. 15 

BIODIESEL CO IMPACT ASSESSMENT ......................................................................... 16 

4. BIODIESEL IMPACTS ON PM CONCENTRATIONS................................................... 18

PM MODELING APPROACH............................................................................................. 18 

PM MODELING RESULTS................................................................................................. 18 

5. IMPACTS OF BIODIESEL FUEL ON AIR TOXICS AND RISK.................................. 21

EFFECTS OF BIODIESEL ON DIESEL PM EMISSIONS MASS AND TOXICITY....... 21 

EFFECTS OF BIODIESEL FUEL ON AIR TOXICS RISK ............................................... 22 

1
EXECUTIVE SUMMARY 

Biodiesel is derived from domestic renewable resources and can be used as an extender for 

petroleum based diesel fuels. One reason for the interest in biodiesel is because of its ability to 

reduce emissions from diesel engines for many air pollutant precursors, and the lower toxicity of 

the diesel particulate matter (PM) emissions. There have been numerous studies on the effects of 

biodiesel fuel on diesel engine emissions, however, the effects of biodiesel fuel use on air quality 

have not yet been quantified, although EPA is studying this issue. The National Renewable 

Energy Laboratory (NREL) contracted with ENVIRON International Corporation to conduct the 

“Impact of Biodiesel Fuels on Air Quality and Human Health” study. The study employed 

inventory and air quality modeling to analyze the impacts of biodiesel use in the on-road heavyduty diesel vehicle (HDDV) fleet on: 

• ambient ozone (O3) concentrations in the Northeast Corridor, Lake Michigan, and the 

South Coast (Los Angeles) Air Basin (SoCAB) regions; 

• carbon monoxide (CO) in Las Vegas, Nevada; 

• particulate matter (PM) in the SoCAB; and 

• air toxics, risk, and human health in the SoCAB. 

Biodiesel test data were analyzed to determine the average effect that biodiesel (B100) and a 

20%/80% biodiesel/diesel fuel blend (B20) would have on mass emissions from diesel vehicles. 

Table ES-1 summarizes the estimated average changes in mass emissions from diesel engines 

using biodiesel versus standard diesel that were used in the air quality modeling. The analysis of 

the diesel test data also found that diesel PM emissions from B100 and B20 biodiesel have, 

respectively, 20% and 5% less toxicity than standard diesel fuel. 

Table ES-1. Average change in HDDV mass emissions due to use of a biodiesel fuel relative to 

a standard diesel fuel1

 (Lindhjem and Pollack, 2002). 

Biodiesel Fuel NOx PM CO VOC SO2 

B20 +2.4% -8.9% -13.1% -17.9% -20% 

B100 +13.2% -55.3% -42.7% -63.2% -100% 

1 Standard diesel has sulfur content of < 500 ppm. 

Three emissions scenarios were analyzed: (1) a standard diesel base case; (2) a 100% penetration 

of B20 biodiesel in the HDDV fleet; and (3) a 50% penetration of B20 biodiesel in the HDDV 

fleet. Table ES-2 summarizes the estimated peak pollution concentrations for the standard diesel 

and 100% B20 emission scenarios and the maximum increases and decreases that occurred 

anywhere in the region between the 100% B20 and standard diesel fuel scenarios. The 

difference between the 50% B20 and standard diesel scenarios were half that of the 100% B20 

scenario. The increases or decreases in modeled ozone, CO, PM2.5, and PM10 ambient 

concentrations due to the use of biodiesel are extremely small (<± 1%) for all air pollutants, 

regions, and averaging times studied. The use of biodiesel (100% B20) is estimated to reduce 

risk in the SoCAB associated with air toxics by approximately 5%. The changes in air pollutant 

concentrations are below the resolution of the measurements that are typically reported to the 

State and EPA compliance databases, so that the impacts of biodiesel would not be measurable. 

2
Table ES-2. Change in peak estimated pollutant concentrations and maximum increase and decrease in daily ma

concentrations within the study area, and one in a million risk due to exposure to air toxics due to the use of a 10

B20 biodiesel in the HDDV fleet. 

Location Pollutant 

Avg. 

Time Units 

Federal 

Standard 

Peak Predicted Concentration M

Diesel 100% B20 Diff In

Northeast Corridor Ozone 1-Hour ppb 124 177 177 <1 +Lake Michigan Ozone 1-Hour ppb 124 178 178 <1 +Southern California Ozone 1-Hour ppb 124 176 176 <1 +Northeast Corridor Ozone 8-Hour ppb 84 155 155 <1 +Lake Michigan Ozone 8-Hour ppb 84 158 158 <1 +Southern California Ozone 8-Hour ppb 84 145 144 <1 +Las Vegas CO 1-Hour ppm 35 18.4 18.4 <1 Las Vegas CO 8-Hour ppm 

μg/m3 

9 13.7 13.7 <1 

Southern California PM10 Annual 

μ g/m3 

50 75.8 75.6 <1 +

Southern California PM10 24-Hour 

μ g/m3 

150 187 186 <1 +

Southern California PM2.5 Annual 

μ g/m3 

15 52.7 52.4 <1 +

Southern California PM2.5 24-Hour 65 178 178 <1 +Southern California Risk Annual 1:Million NA 1,257 1,191 -66 

3
Acronyms and Abbreviations 

B100 100% biodiesel 

B20 20% biodiesel, 80% petroleum diesel 

CAAA Clean Air Act Amendments 

CAMx Comprehensive Air Quality Model with Extensions 

CARB California Air Resources Board 

CO carbon monoxide 

DOE U.S. Department of Energy

EC elemental carbon 

EMA Engine Manufacturers Association 

EMS Emission Modeling System 

EPA U.S. Environmental Protection Agency

GEM Gridded Emissions Model 

HC hydrocarbons 

HDDV heavy-duty diesel vehicle 

I/O indoor/outdoor 

LVV Las Vegas Valley

MATES II Multiple Air Toxics and Exposure

NHAQS National Ambient Air Quality Standards 

NOx nitrogen oxide 

NREL National Renewable Energy Laboratory

OC organic carbon 

OTAG Ozone Transport Assessment Group 

PAH polyaromatic hydrocarbons 

PM particulate matter

SCOS Southern California Ozone Study

SIP State Implementation Plan 

SoCAB South Coast Air Basin 

THC total hydrocarbons 

URF unit risk factor 

VOC volatile organic compounds 

4
1. INTRODUCTION 

BACKGROUND 

Biodiesel is derived from domestic renewable resources and can be used as an extender for 

petroleum based diesel fuels. One reason for the interest in biodiesel relates to the potential for a 

more environmentally benign fuel. One potential benefit of biodiesel is that it can biologically 

degrade, making spills and leaks less of a concern. But the potential for exhaust emission 

reductions from diesel vehicles and reductions in the toxicity of diesel particulate matter (PM) 

emissions are of the most interest. Several studies have shown that large reductions in 

hydrocarbon (HC), PM, and carbon monoxide (CO) emissions are expected from its use either as 

a neat fuel or as a blend with petroleum-derived fuels. 

Diesel PM and, to a lesser extent, diesel HC exhaust emissions, have garnered much scrutiny for 

their inherent toxicity. Diesel fuels are typically characterized by heavy hydrocarbons, which 

produce, through partial combustion, a variety of compounds that are believed to be toxic. The 

State of California has listed diesel PM as a toxic substance, and recent U.S. Environmental 

Protection Agency (EPA) reports also discuss the toxicity of diesel PM. The recent Multiple Air 

Toxic Exposure Study (MATES-II) in the South Coast (Los Angeles) Air Basin (SoCAB) 

estimated that 70% of the risk due to air toxics in theSoCAB is due to diesel PM emissions 

(SCAQMD, 2000). Therefore, the potential to reduce overall toxic emissions through fuel 

substitution is of great interest given the reduced toxicity of PM using biodiesel. 

Biodiesel has emission advantages when used in diesel engines because it can improve a number 

of important fuel properties, most importantly cetane, and oxygen content. Generally, these 

properties are thought to be responsible for improving emissions by improving ignition and 

distribution of oxidant. The effect of fuel substitution may be unique by engine type; the Engine 

Manufacturers Association (EMA) has theorized that newer engines may show less benefit 

because of more precise engine management (EMA, 1995). Nonroad diesel engine technology 

lags behind highway engine technology, so emission benefits may be greatest for nonroad 

engines, which also have higher base emissions of HC and PM. 

Most of the potential problems typically cited for the introduction of biodiesel blends are related 

to the lack of a running history for their use. Unforeseen complications arising from materials 

compatibility, consistent fuel quality, gumming, low temperature effects, and various other longterm durability factors not specifically listed are feared with the use of biodiesel blends and may 

affect its penetration into the nonroad market. Most of these concerns do not affect the emission 

testing results in the laboratory; and the lack of cold temperature testing is typical of emission 

testing for diesel, gasoline, or other types of vehicles and engines. 

Cost of an alternative fuel is always a concern, especially when the production facilities have 

neither been optimized nor can take advantage of economies of scale. The Department of 

Energy (DOE) estimates that a fuel blend of 20% biodiesel and 80% diesel (known as B20) 

would cost approximately 30 to 40 cents a gallon more than regular diesel. This cost differential 

is high enough to adversely affect the penetration of biodiesel in the market. For the most part, 

this price differential is due to the price of the base vegetable oil or tallow. In addition, there 

may be a small reduction in fuel economy because biodiesel has lower energy density than 

standard diesel fuels. 

5
There have been several studies regarding the effects of biodiesel on exhaust emissions of 

nitrogen oxide (NOx), volatile organic compounds (VOC), CO, and PM. Almost all of these 

studies have examined emissions from heavy-duty diesel vehicle (HDDV) engines. However, 

the effects of biodiesel use on ambient air quality have not been quantified. Thus, the National 

Renewable Energy Laboratory (NREL) has retained ENVIRON International Corporation to 

estimate the air quality and resultant toxic impacts from the use of biodiesel in several cities in 

the United States. 

PURPOSE 

This document discusses the results of the NREL “Impact of Biodiesel Fuels on Air Quality and 

Human Health” study. This report provides a summary of the key results on the air quality and 

risk impacts from the use of biodiesel in the heavy-duty diesel vehicle (HDDV) fleet. Details on 

the air quality impacts from the use of biodiesel are found in the five Task Reports prepared for 

the NREL biodiesel study: 

Task 1 Report: “Incorporate Biodiesel Data into Vehicle Emission Databases for Modeling” 

(Lindhjem and Pollack, 2002), NREL report number: NREL/SR-540-33794; 

Task 2 Report: “The Impact of Biodiesel Fuels on Ozone Concentrations – Ozone Impacts in 

the Northeast Corridor, Chicago, Other Cities in the Eastern United States, and in the South 

Coast Air Basin Region of Southern California” (Morris, Mansell, Jia, and Wilson, 2002) , 

NREL report number: NREL/SR-540-33795; 

Task 3 Report: “The Impact of Biodiesel Fuels on Ambient Carbon Monoxide Levels in the 

Las Vegas Nonattainment Area” (Mansell, Morris, and Wilson, 2002) , NREL report 

number: NREL/SR-540-33796; 

Task 4 Report: “Effects of Biodiesel Fuel Use on Particulate Matter (PM) Concentrations in 

the South Coast Air Basin Region of Southern California” (Morris and Jia, 2002a) , NREL 

report number: NREL/SR-540-33797; and 

Task 5 Report: “Air Toxics Modeling of the Effects of Biodiesel Fuel use on Human Health 

in the South Coast Air Basin Region of Southern California” (Morris and Jia, 2002b) , NREL 

report number: NREL/SR-540-33798. 

BIODIESEL EMISSION EFFECTS 

The effect on emissions from truck and bus engines using biodiesel or a blend of biodiesel and 

standard diesel have been studied to investigate the effect on total hydrocarbon (THC), NOx, 

CO, and PM emissions. Some studies have also investigated the chemical compositional effects 

such as toxic compounds. The effect of biodiesel on emissions has been measured using both 

engine dynamometer and chassis dynamometer tests. An analysis of the data revealed that the 

engine dynamometer tests were more consistent and robust than the chassis tests so these were 

used to estimate the effects of biodiesel on tailpipe emissions from HDDVs. The engine 

dynamometer tests estimated the effects of biodiesel using both 2-stroke and 4-stroke engines for 

different model years that represent different levels of engine certification standards. These data 

were analyzed to obtain the mean effect of a 100% biodiesel (B100) and a 20%/80% 

6
biodiesel/standard diesel fuel blend (B20) as shown in Table 1-1. The average of the biodiesel 

effect across engine types was used to estimate the overall effect that a B100 and B20 fuel would 

have on the HDDV fleet in the air quality modeling analysis. Details of the data used and the 

analysis are provided in the Task 1 report (Lindhjem and Pollack, 2002). 

EPA’s Office of Transportation and Air Quality has been compiling a biodiesel effects database 

over the last several years. EPA’s work extended over a longer time period than the emissions 

analysis for this study, and their database is therefore more comprehensive. EPA included No. 1 

and No. 2 diesel fuel in their database as well as related blends that can be used in a typical 

heavy-duty diesel engine without engine modifications. EPA’s draft analysis of their data, which 

was released as this report was being finalized, is based on statistical regressions, which can then 

be used to estimate the percent change in exhaust emissions as a function of the concentration of 

biodiesel in conventional diesel fuel (EPA, 2002). Table 1-1 compares the average emissions 

effects used in this study with the EPA estimated biodiesel effects. Although the EPA analysis is 

based on a more comprehensive data base, the estimated emissions effects are very similar to the 

averages estimated for this study. 

Table 1-1. Emission effects by technology type from engine dynamometer testing for biodiesel 

fuels compared against a standard diesel fuel. Recent EPA analysis is provided for comparison. 

Engine Type/ Fuel Pair Engines NOx PM CO THC Model Year 

20% Biodiesel Emission Effects 

2-Stroke < 1991 D-2 / B-20 6 3.2% -1.8% -13.9% -20.9% 

2-Stroke 1991+ D-2 / B-20 2 3.9% -17.8% -12.0% -17.5% 

4-Stroke <1991 D-2 / B-20 3 2.9% -15.7% -13.6% -12.2% 

4-Stroke 1991-3 D-2 / B-20 4 -0.9% -15.7% -12.0% -2.8% 

4-Stroke 1994+ D-2 / B-20 5 2.8% -9.8% -15.2% -24.0% 

Overall Average D-2 / B-20 17 2.4% -8.9% -13.1% -17.9% 

EPA (2002) Average 43 2.0% -10.1% -11.0% -21.1% 

100% Biodiesel Emission Effects 

2-Stroke 1991+ D-2 / B-100 1 19.6% -33.0% -42.4% -72.7% 

4-Stroke 1991-3 D-2 / B-100 2 13.3% -68.3% -41.8% -38.7% 

4-Stroke 1994+ D-2 / B-100 5 9.9% -36.6% -41.5% -76.3% 

Overall Average D-2 / B-100 5 13.2% -55.3% -42.7% -63.2% 

EPA (2002) Average 10.3% -47.2% -48.1% -67.4% 

Diesel PM includes several known toxic compounds that fall into a class known as polyaromatic 

hydrocarbons (PAH) and nitro-PAH compounds. Studies that measured the PAH and nitro-PAH 

compounds in standard diesel and B20 and B100 biodiesel fuel blends were compared to obtain 

an estimate of the reduction in these toxic compounds in the biodiesel as shown in Table 1-2. 

7
Table 1-2a. Relative fraction (x 106

) of selected PAH compounds to PM emissions from Sharp 

(1998) and Durbin (1999). 

Standard Diesel B20 B100 Compounds Sharp Durbin Sharp Durbin Sharp Durbin 

Benzo(a)anthracene 1.59 1.01 1.51 0.43 1.37 1.11 

Chrysene 2.21 1.01 1.32 0.65 1.04 0.89 

Benzo(b)fluoranthene 0.96 0.50 0.97 0.22 0.77 0.22 

Benzo(k)fluoranthene 1.01 * 0.92 * 0.73 * 

Benzo(a)pyrene 1.12 0.25 0.69 1.72 0.49 0.00 

Indeno(1,2,3-cd)pyrene 0.72 0.00 0.56 0.00 0.60 0.00 

Dibenz(a,h)anthracene 0.21 0.00 0.19 0.00 0.13 0.00 

Benzo(g,h,i)perylene 0.94 0.00 0.88 0.00 0.93 0.00 

Total 8.76 2.77 7.04 3.02 6.06 2.22 

* Included in Benzo(b)fluoranthene. 

Table 1-2b. Relative fraction (x 106

) of selected Nitro-PAH compounds to PM emissions. 

Compounds D2 B20 B100 

2-Nitrofluorene 0.14 0.11 0.09 

1-Nitropyrene 0.11 0.11 0.02 

7-Nitrobenz(a)anthracene 0.01 0.00 0.00 

6-Nitrochrysene 0.00 0.00 0.00 

6-Nitrobenz(a)pyrene 0.01 0.00 0.00 

Total 0.27 0.22 0.11 

OVERALL EFFECTS OF BIODIESEL FUEL USE ON EMISSIONS AND TOXICITY 

The overall effects of the use of biodiesel on emissions in the HDDV fleet are assumed to be the 

average effect from the engine dynamometer test data provided in Table 1-1. Based on the data 

in Table 1-2 and the dilution effect of the biodiesel fuel, the toxicity of the PM emissions from 

B100 and B20 fuels were assumed to be 20% and 5% less, respectively, than a standard diesel 

fuel. 

8
9

2. EFFECTS OF BIODIESEL ON AMBIENT OZONE CONCENTRATIONS 

The effect of biodiesel use on ozone air quality was evaluated in the SoCAB, lower Lake 

Michigan (Chicago), Northeast Corridor (New York, Philadelphia, Baltimore, and Washington, 

DC), and other cities in the Eastern United States . The largest impacts on ambient ozone 

concentrations due to the use of biodiesel are expected to be due to changes in NOx emissions 

from diesel vehicles. Studies, such as the Ozone Transport Assessment Group (OTAG), have 

concluded that regional NOx controls are one of the most effective control strategies for reducing 

regional ozone concentrations in the eastern United States. However, in some cases, NOx 

controls result in increased ozone levels, particularly in the urban cores of large cities. The 

assessment of ozone impacts due to biodiesel must therefore include the effects of the fuel on 

regional ozone and ozone transport as well as the effects within urban areas. The ozone air 

quality modeling conducted as part of this study therefore takes into account both urban-scale 

and regional-scale ozone formation through the use of high-resolution (4 - 5-km) urban-scale 

modeling of the cities under study as well as coarser-scale (12-km) regional-scale modeling. 

The 1-hour ozone National Ambient Air Quality Standard (NAAQS) has a threshold of 0.12 ppm 

(124 ppb) that is not to be exceeded more than once per year over three consecutive years (i.e., 

with complete data capture a violation occurs if the fourth highest daily maximum 1-hour ozone 

concentration at a monitor exceeds 0.12 ppm). More recently EPA has promulgated a more 

stringent 8-hour ozone standard that is based on a three-year average of the fourth highest annual 

daily maximum 8-hour ozone concentration with a threshold of 0.08 ppm (84 ppb). EPA is 

currently formulating the implementation policy for the 8-hour ozone NAAQS. 

The assessment of the impacts of biodiesel use on ozone concentration is made with respect to 

both 1-hour and 8-hour ozone concentrations (Morris, Mansell, Jia, and Wilson, 2002). An 

analysis of daily peak ozone concentrations in each urban area is made along with displays of 

spatial distributions of daily maximum ozone concentrations. These results are used to evaluate 

the effects of biodiesel use on the 1-hour and 8-hour ozone concentrations and attainment of the 

NAAQS. As part of the assessment, ozone exposure metrics are also calculated and evaluated as 

a measure of the biodiesel impacts on ozone air quality and human health. 

MODEL AND DATABASES USED 

The Comprehensive Air Quality Model with Extensions (CAMx) was selected to conduct the air 

quality modeling because (a) it is state-of-science, (b) it is publicly available, (c) it uses two-way 

grid nesting so that both urban- and region-scale issues can be addressed, (d) the databases are 

available, and (e) it has been used recently for regulatory decision making (e.g., EPA NOx SIP 

Call Rule and Dallas-Fort Worth and Houston/Galveston SIPs). 

An enhanced July 1995 OTAG database was used to model the eastern United States; the July 

1995 OTAG 36/12-km database was enhanced by adding two 4-km fine grids, one covering the 

lower Lake Michigan region and the other covering the Northeast Corridor, to better simulate 

urban ozone formation. 
10

The EPA 2007 State Implementation Plan (SIP) Call emissions inventory was used for the 

eastern United States and the baseline (standard diesel) scenario with the MOBILE5 mobile 

source emissions was updated to incorporate some of the MOBILE6 emission effects. 

A new SoCAB database for the August 3-7, 1997 Southern California Ozone Study (SCOS) 

episode was used for ozone modeling of Southern California. 

The California Air Resources Board (CARB) latest emissions inventory for 1997 based on the 

EMFAC2000 mobile source emissions model was used for the baseline (standard diesel) 

emissions scenario. 

EFFECTS OF BIODIESEL USE 

The incorporation of biodiesel effects in the emission inventory used in this study was 

accomplished by applying the 1995 version of the Emission Modeling System (EMS95) for the 

eastern US and the ARB’s Gridded Emissions Model (GEM) for the SoCAB. Biodiesel effects 

were accounted for in the HDDV fleet only, and only the effects of B20 were considered. Under 

Task 1 of the NREL study, engine test data were analyzed and the average effects of using 

biodiesel rather than a standard diesel fuel on HDDV tailpipe emissions of ozone precursors 

were estimated as shown in Table 2-1 (Lindhjem and Pollack, 2002). 

Table 2-1. Overall average change in mass emission effects due to 

use of biodiesel fuels in HDDVs over using a standard diesel fuel. 

Biodiesel Fuel NOx CO VOC 

B20 +2.4% -13.1% -17.9% 

B100 +13.2% -42.7% -63.2% 

Three emission scenarios were analyzed for 2007 in the eastern United States and 1997 for the 

SoCAB: 

• Standard diesel baseline scenario; 

• 100% penetration in the HDDV fleet of a B20 biodiesel fuel scenario; and 

• 50% penetration in the HDDV fleet of a B20 biodiesel fuel scenario. 

EMISSION SUMMARY RESULTS 

Table 2-2 summarizes the on-road mobile source NOx, VOC, and CO emission inventory in 

terms of the fractional contribution to the total inventory, the fractional contribution to the 

anthropogenic component, and the fraction of the on-road mobile inventory due to HDDV for the 

Lake Michigan and Northeast Corridor high-resolution (4-km) modeling domains, the 12-km 

eastern United States OTAG domain, and the SoCAB high-resolution (5-km) domain. While the 

on-road mobile component represents a considerable percentage of the overall inventory, the 

HDDV contribution is relatively small, with the exception of the HDDV NOx emissions, which 

account for approximately one third of the on-road mobile inventory. 
11

The resulting changes in the emission inventory for a representative episode weekday are 

presented in Table 2-3 for the two biodiesel emission scenarios and for the Lake Michigan, 

Northeast Corridor, eastern United States, and SoCAB domains. The use of biodiesel fuel with 

the HDDV fleet is estimated to cause a very small change (<1%) in all ozone precursor 

emissions. 

Table 2-2. Summary of on-road mobile and HDDV emission contributions. 

2007 SIP Call Base Case and Eastern US OTAG 12-km Domain 

NOx VOC CO 

Mobile % of Total Inv. 30% 2.2% 49% 

Mobile % of Anthro. 37% 17% 49% 

HDDV % of Mobile Inv. 35% 4.7% 4.5% 

2007 SIP Call Base Case and Lake Michigan 4-km Domain 

NOx VOC CO 

Mobile % of Total Inv. 28% 7.4% 48% 

Mobile % of Anthro. 40% 156% 48% 

HDDV % of Mobile Inv. 32% 4.6% 4.7% 

2007 SIP Call Base Case and Northeast Corridor 4-km Domain 

NOx VOC CO 

Mobile % of Total Inv. 42% 2.6% 42% 

Mobile % of Anthro. 46% 14% 42% 

HDDV % of Mobile Inv. 36% 7.3% 6.3% 

1997 EMFAC2000 Base Case and South Coast Air Basin 5-km Domain 

NOx VOC CO 

Mobile % of Total Inv. 63% 29% 87% 

Mobile % of Anthro. 63% 33% 87% 

HDDV % of Mobile Inv. 41% 6.5% 8.3% 
Table 2-3. Summary of ozone precursor emission effects due to B20 biodiesel fuel use. 

100% B20 Biodiesel 50% B20 Biodiesel 

Emission 

Component 

2007 EUSA OTAG 12-km Domain 2007 EUSA OTAG 12-km Domain 

%Change 

NOx 

%Change 

VOC 

%Chang 

e CO 

%Change 

NOx 

%Change 

VOC 

%Chang 

e CO 

On-Road Mobile 0.84% -0.85% -0.59% 0.42% -0.42% -0.29% 

Total Anthropogenic 0.32% -0.29% 0.16% -0.15% 

Total 0.25% -0.02% -0.29% 0.13% -0.01% -0.15% 

2007 Lake Michigan 4-km 

Domain 

2007 Lake Michigan 4-km 

Domain 

%Change 

NOx 

%Change 

VOC 

%Chang 

e CO 

%Change 

NOx 

%Change 

VOC 

%Chang 

e CO 

On-Road Mobile 0.78% -0.83% -0.60% 0.39% -0.41% -0.30% 

Total Anthropogenic 0.31% -0.29% 0.16% -0.14% 

Total 0.22% -0.06% -0.29% 0.11% -0.03% -0.14% 

2007 Northeast Corridor 4-km 

Domain 

2007 Northeast Corridor 4-km 

Domain 

%Change 

NOx 

%Change 

VOC 

%Chang 

e CO 

%Change 

NOx 

%Change 

VOC 

%Chang 

e CO 

On-Road Mobile 0.86% -1.31% -0.82% 0.43% -0.65% -0.41% 

Total Anthropogenic 0.40% -0.35% 0.20% -0.17% 

Total 0.36% -0.04% -0.35% 0.18% -0.02% -0.17% 

1997 SoCAB 5-km Domain 1997 SoCAB 5-km Domain 

%Change 

NOx 

%Change 

VOC 

%Chang 

e CO 

%Change 

NOx 

%Change 

VOC 

%Chang 

e CO 

On-Road Mobile 0.79% -0.27% -0.075% 0.39% -0.14% -0.04% 

Total Anthropogenic 0.50% -0.07% 0.25% -0.03% 

Total 0.50% -0.08% -0.07% 0.25% -0.04% -0.03% 

-0.14% -0.07% 

-0.13% -0.07% 

-0.19% -0.09% 

-0.09% -0.05% 

OZONE MODELING RESULTS 

The CAMx, version 3.02, air quality model was exercised for the 7-18 July, 1995 episode on the 

enhanced 36/12/4-km OTAG modeling domain for the 2007 SIP Call Base Case and the 100% 

and 50% B20 penetration into the HDDV fleet emission scenarios. Of the 12 episode days 

modeled, the July 11-15, 1995 period was analyzed in detail to evaluate the effects of biodiesel 

fuel use on urban and regional ozone air quality; the July 7-10, 1995 period is used to initialize 

the model and eliminate the influence of the initial concentrations, whereas the July 16-18, 1995 

is a clean out period when ozone is relatively low so is not regulatory relevant. Modeling results 

were evaluated separately in the Lake Michigan and Northeast Corridor 4-km modeling domains 

and for selected urban areas in the eastern United States within the 12-km OTAG modeling 

domain. The August 3-7, 1997 SCOS episode was simulated by CAMx version 3.10 for the 

three 1997 emissions scenarios in the SoCAB. Results for August 3, 1997 were not analyzed as 

it was used as an initialization day. 

Tables 2-4 and 2-5 summarize the maximum increases and decreases in daily maximum 1-hour 

and 8-hour ozone concentrations, respectively, in each of the three regions due to using biodiesel 

12
fuel in HDDVs. In the Lake Michigan region, the maximum increase and decrease in daily 

maximum ozone concentrations anywhere in the modeling domain for the 100% B20 emissions 

scenario are +0.09 and –0.53 ppb, respectively. The maximum increases and decreases in daily 

maximum ozone concentrations in the Northeast Corridor are +0.20 and –0.25 ppb, 

respectively. Similar numbers for the SoCAB are +0.22 and –1.20 ppb. Thus, the maximum 

changes in daily maximum 1-hour and 8-hour ozone concentrations due to the introduction of 

biodiesel fuels in the HDDV fleet in the Lake Michigan, Northeast Corridor, and SoCAB regions 

are very small. 

The use of a 100% or 50% penetration in the HDDV results in very small changes, both 

increases and decreases, in the peak daily maximum 1-hour and 8-hour ozone concentrations in 

the SoCAB and Northeast Corridor, Lake Michigan, and other cities in the eastern United States 

(see Morris, Mansell, Jia, and Wilson, 2002). The changes in 1-hour and 8-hour ozone peaks 

due to use of the biodiesel fuel are always < 1 ppb. 

Table 2-4. Maximum increases and decreases in daily maximum 1-hour ozone concentrations 

(ppb) in the Lake Michigan, Northeast Corridor, and South Coast Air Basin regions. 

50% B20 Biodiesel (ppb) 100% B20 Biodiesel (ppb) 

Date Max Increase Max Decrease Max Increase Max Decrease 

2007 Lake Michigan Domain 

July 11, 1995 +0.03 -0.16 +0.05 -0.33 

July 12, 1995 +0.07 -0.10 +0.09 -0.19 

July 13, 1995 +0.05 -0.12 +0.09 -0.24 

July 14, 1995 +0.07 -0.09 +0.09 -0.18 

July 15, 1995 +0.04 -0.26 +0.08 -0.53 

2007 Northeast Corridor Domain 

July 11, 1995 +0.06 -0.08 +0.11 -0.14 

July 12, 1995 +0.07 -0.12 +0.13 -0.25 

July 13, 1995 +0.12 -0.06 +0.15 -0.07 

July 14, 1995 +0.15 -0.04 +0.20 -0.09 

July 15, 1995 +0.10 -0.10 +0.18 -0.20 

1997 South Coast Air Basin Domain 

August 4, 1997 +0.09 -0.48 +0.17 -0.95 

August 5, 1997 +0.10 -0.56 +0.19 -1.1 

August 6, 1995 +0.11 -0.60 +0.22 -1.2 

August 7, 1995 +0.13 -0.49 +0.26 -0.98 

13
Table 2-5. Maximum increases and decreases in daily maximum 8-hour ozone concentrations 

(ppb) in the Lake Michigan, Northeast Corridor, and South Coast Air Basin regions. 

50% B20 Biodiesel (ppb) 100% B20 Biodiesel (ppb) 

Date Max Increase Max Decrease Max Increase Max Decrease 

2007 Lake Michigan Domain 

July 11, 1995 +0.02 -0.14 +0.04 -0.28 

July 12, 1995 +0.03 -0.09 +0.07 -0.17 

July 13, 1995 +0.04 -0.11 +0.09 -0.21 

July 14, 1995 +0.03 -0.09 +0.07 -0.18 

July 15, 1995 +0.03 -0.20 +0.07 -0.40 

2007 Northeast Corridor Domain 

July 11, 1995 +0.05 -0.07 +0.10 -0.13 

July 12, 1995 +0.05 -0.10 +0.11 -0.20 

July 13, 1995 +0.07 -0.04 +0.12 -0.07 

July 14, 1995 +0.07 -0.04 +0.14 -0.07 

July 15, 1995 +0.06 -0.04 +0.15 -0.08 

1997 South Coast Air Basin Domain 

August 4, 1997 +0.06 -0.34 +0.12 -0.68 

August 5, 1997 +0.07 -0.39 +0.15 -0.77 

August 6, 1995 +0.08 -0.48 +0.15 -0.96 

August 7, 1995 +0.08 -0.42 +0.15 -0.83 

CONCLUSIONS 

Measured ozone is typically reported to EPA’s AIRS ozone compliance database to the nearest 1 

ppb. The maximum estimated increase and decrease in daily maximum 1-hour or 8-hour ozone 

concentrations due to the use of either a 100% or 50% penetration of a B20 fuel in the HDDV 

fleet in any of the areas studied is +0.26 ppb and –1.20 ppb for 1-hour ozone and the 100% B20 

fuel scenario in the SoCAB region. As the maximum ozone increase (+0.26 ppb) is well below 1 

ppb, the use of biodiesel is estimated to have no measurable adverse impact on 1-hour or 8-hour 

ozone attainment in Southern California and the Eastern United States. 

14
3. BIODIESEL EFFECTS ON AMBIENT CO CONCENTRATIONS 

INTRODUCTION 

Carbon monoxide (CO) air pollution is generated by a variety of combustion processes ranging 

from industrial sources, to household heating, to motor vehicles. Due to the sheer number of 

automobiles, the vast majority (typically 90%) of area-wide CO emissions in congested urban 

areas come from on-road motor vehicles. Numerous urban centers in the western United States 

have experienced elevated CO air pollution episodes due to climatic influences, particularly 

during cold, dry, stagnant winter evenings and mornings. During these periods, CO emissions 

are trapped near the ground where they build up in direct response to hourly variations in traffic 

volume during the commute hours. Two NAAQS have been established for CO: a one-hour 

standard of 35 parts-per-million (ppm), and an eight-hour standard of 9 ppm. The 1990 Clean 

Air Act Amendments (CAAA) specify that regions exceeding the CO NAAQS more than three 

times in a three-year period are to be classified as nonattainment areas. The CAAA required CO 

nonattainment areas to develop SIPs which list various control strategies that, by appropriate 

demonstration, are estimated to lead to attainment of the CO NAAQS by the date required in the 

CAAA. 

OVERVIEW OF APPROACH 

CO modeling databases for the Las Vegas Valley (LVV) developed for Clark County, Nevada 

(Emery et al., 1999) were selected for use in assessing the impacts of biodiesel use on ambient 

CO concentrations for the following reasons: 

• Clark County was designated an 8-hour CO nonattainment area in the CAAA; 

• The databases were used in recent (1999) SIP CO modeling; 

• The database year (1996) was more recent than that used for CO SIP modeling in 

other areas; and 

• The databases and models used were publicly available. 

Two LVV CO modeling databases were used in the SIP modeling: December 8-9, 1996 and 

December 19-20, 1996. Because biodiesel would occur in a future-year, the biodiesel CO 

assessment was performed for the year 2001, the only future year for which emissions projection 

data were readily available. 

Based on an analysis of engine dynamometer test data for a standard diesel, B100, and a B20, 

Lindhjem and Pollack (2002) estimated that the mean effect on fleet average HDDV emissions 

of a B20 fuel would be to reduce CO emissions by 13.1 percent. Three different emission 

scenarios were analyzed in 2001 using the two 1996 LVV CO episodes: 

• 2001 Base Case diesel (CARB standard diesel); 

• 100% penetration of a B20 fuel in the HDDV fleet; and 

• 50% penetration of a B20 fuel in the HDDV fleet. 

Table 3-1 summarizes the CO emissions in the LVV for the 1996 and 2001 base case 

simulations. Although on-road mobile sources contribute the most to CO emissions in the LVV 

15
area (> 90%), the HDDV fraction contributes less than one percent (0.7%) to the total on-road 

mobile CO emissions. The percent reduction in CO emissions due to the 100% B20 and 50% 

B20 biodiesel emissions scenarios from the 2001 standard diesel base case for the HDDV, onroad mobile, and total emissions are shown in Table 3-2. Although the biodiesel results in 

substantial reductions in CO emissions from the HDDV fleet (7%-13%), because the HDDV 

contributes such a small fraction of the total CO emissions, the CO reductions from on-road 

mobile sources (0.08%-0.19%) and total emissions in the LVV area (0.09-0.18%) are quite 

small. 

Table 3-1. Base year 1996 and base year 2001 CO emissions by emission component for the 

Las Vegas Valley. 

Emissions (tons/day) 

Emissions Component December 9 December 20 

1996 2001 1996 2001 

Area 12.7 14.3 12.7 14.3 

Surface Points 22.6 22.6 22.6 22.6 

Elevated Points 2.1 2.1 2.1 2.1 

On-Road Mobile 415.2 366.6 511.8 451 

Total 452.6 405.6 549.2 490 

Table 3-2. Reductions from base year 2001 CO emissions by emission component for the Las 

Vegas Valley due to a 100% and 50% penetration of a B20 biodiesel fuel in the HDDV fleet. 

Emissions Reductions (%) 

Emissions Component December 9 December 20 

50% B20 100% B20 50% B20 100% B20 

HDDV 6.55 13.1 6.55 13.1 

On-Road Mobile 0.095 0.190 0.084 0.168 

Total 0.089 0.178 0.082 0.164 

BIODIESEL CO IMPACT ASSESSMENT 

Table 3-3 displays the peak estimated 1-hour and 8-hour CO concentrations in the LVV area for 

the standard diesel base case and the two biodiesel emission scenarios. The use of biodiesel is 

estimated to reduce the peak CO concentrations as well as CO concentrations throughout the 

LVV area (see Mansell, Morris, and Wilson, 2002). However, these reductions are extremely 

small, ranging from 0.01 to 0.03 ppm (< 0.2%). 

16
Table 3-3. Peak estimated 1-hour and 8-hour CO concentrations in the Las Vegas Valley for the 

2001 Base Case, 100% B20, and 50% B20 emission scenarios and the differences in CO 

concentrations between the biodiesel fuel scenarios and standard diesel base case. 

Std. Diesel 50% B20 100% B20

Peak 

(ppm) 

Peak 

(ppm) 

Difference 

(ppm) 

Peak 

(ppm) 

Difference 

Episode (ppm)

1-Hour CO Dec 8-9 17.90 17.89 -0.01 17.87 -0.02 

8-Hour CO Dec 8-9 9.39 9.38 -0.01 9.37 -0.02 

1-Hour CO Dec 19-20 18.38 18.36 -0.02 18.35 -0.03 

8-Hour CO Dec 19-20 13.73 13.72 -0.01 13.71 -0.02 

17
4. BIODIESEL IMPACTS ON PM CONCENTRATIONS 

There are several areas in the United States that are currently in nonattainment for particulate 

matter of 10 μm or less (PM10). The PM10 NAAQS consists of an annual standard of 50 μg/m3 

that is not to be exceeded and a 24-hour average standard of 150 μg/m3 that is not to be exceeded 

more than once per year over three consecutive years (i.e., fourth highest in 3 years). In addition, 

there is a new fine particulate matter (PM2.5) standard that will result in new areas being in 

nonattainment for PM. The form of the PM2.5 standard is similar to the PM10 standard with 

annual and 24-hour average thresholds of 15 and 65 μg/m3

, respectively. The use of biodiesel is 

estimated to reduce several precursors to PM (e.g., PM, SO2, and VOC), but increase others 

(NOx). Thus, the net affect of biodiesel fuel use on ambient PM levels is unclear based on 

analyzing changes in emissions alone, so it was assessed using air quality modeling. 

PM MODELING APPROACH 

The SoCAB region of southern California was selected to assess the effects of biodiesel use 

because: (1) it is currently a PM10 nonattainment area; and (2) ammonium nitrate (for which 

NOx is a precursor) is a major component of the PM. Thus, the SoCAB would provide a 

conservative (i.e., tending toward overstating any adverse effects) assessment of the impacts of 

biodiesel fuel on PM because the one PM precursor that biodiesel fuel increases (NOx) is a 

precursor to ammonium nitrate, which is a major component to PM in the SoCAB. Outside of 

California, ammonium nitrate is usually a minor contributor to ambient PM. The CAMx 

photochemical and PM grid model were applied to the SoCAB for an April 1998 through March 

1999 annual modeling period to estimate the effects a 100% and 50% penetration of B20 in the 

HDDV fleet has on ambient PM levels. The effects of biodiesel were separately assessed for 

particulate sulfate, nitrate, ammonium, elemental carbon (EC), organic carbon (OC), other fine 

particulate, coarse matter, total PM10 mass, total PM2.5 mass, and exposure to PM10 and PM2.5 

(Morris and Jia, 2002). 

PM MODELING RESULTS 

The average effect of using a B20 and B100 biodiesel fuel over a standard diesel fuel was based 

on an analysis of test data and is shown in Table 4-1. This effect was assumed to occur in the 

HDDV fleet in the air quality modeling. 

Table 4-1. Average change in HDDV mass emissions due to use of a biodiesel fuel over use of a 

standard diesel fuel (Lindhjem and Pollack, 2002). 

Biodiesel Fuel NOx PM CO VOC SO2 

B20 +2.4% -8.9% -13.1% -17.9% -20% 

B100 +13.2% -55.3% -42.7% -63.2% -100% 

18
Table 4-2 summarizes the NOx, VOC, SOx, and PM emissions in the SoCAB domain for the 

standard diesel and 100% B20 biodiesel emission scenarios and for the summer and winter 

periods. The difference between the 50% B20 and standard diesel scenario are half that of the 

100% B20 scenario. For the standard diesel base case, on-road diesel vehicles account for 

22.0%, 0.5%, 0.4%, 7%, and 0.7% of the NOx, VOC, CO, SOx, and PM emissions in the 

SoCAB, respectively. The change in total NOx, VOC, CO, SOx, and PM emissions in the 

SoCAB from all sources due to the 100% B20 scenario are, respectively, +0.5%, -0.1%, -0.1%, -

1.3%, and –0.1%. 

Table 4-2. Summary of domain-wide total on-road diesel (Total DSL), area plus point sources, 

and total NOx, VOC, CO, SOx, and PM emissions in the SoCAB (tons per day) for the 1997 

standard diesel Base Case and 1997 100% penetration of B20 biodiesel scenarios. 

1998 Summer Baseline 1998 Summer 100% B20 Biodiesel 

NOx TOG CO SOx PM NOx TOG CO SOx PM 

Total DSL 336.5 13.5 7.7 8.0 11.3 6.2 7.3 

On-Road 932.9 860.5 38.1 23.7 940.9 858.2 36.6 23.1 

Area+Point 571.1 1466.9 73.3 1076.0 571.1 1489.3 1466.9 73.3 1076.0 

Total 1504.0 2349.8 8379.2 111.4 1099.7 1512.0 2347.5 8374.8 110.0 1099.1 

% Change 

Total DSL 2.38 -16.57 -12.55 -19.30 -8.30 

Total 0.53 -0.10 -0.05 -1.33 -0.06 

1999 Winter Baseline 1999 Winter 100% B20 Biodiesel 

Total DSL 364.1 14.8 5.4 7.9 12.4 4.3 7.3 

On-Road 1009.4 944.5 26.7 23.6 1018.0 942.0 25.7 23.0 

Area+Point 503.7 1528.4 72.1 1070.7 503.7 1484.3 1528.4 72.1 1070.7 

Total 1513.1 2428.8 7732.8 98.8 1094.3 1521.7 2426.3 7728.8 97.8 1093.7 

% Change 

Total DSL 2.36 -16.58 -12.53 -19.31 -8.30 

Total 0.57 -0.10 -0.05 -1.05 -0.06 

35.3 344.5 30.9 

6912.3 6907.8 

1489.3 

31.7 372.7 27.7 

6204.4 6200.4 

1484.3 

Table 4-3 summarizes the estimated maximum increases and decreases in total PM10 and PM2.5 

mass and PM components due to a 100% penetration of a B20 fuel in the HDDV fleet. The 

results for the 50% B20 penetration are approximately half those of the 100% B20 penetration 

scenario. The maximum increases and decreases in PM2.5 and PM10 mass concentrations are 

extremely small. The largest effect is for particulate nitrate that exhibits both small increases and 

decreases due to the B20 fuel. The decreases in nitrate occur in the more populated portions of 

the SoCAB, whereas the increases occur east of the SoCAB in the desert (see Morris and Jia, 

2002). The 100% B20 biodiesel fuel scenario is estimated to reduce exposure to annual and 24-

hour exceedances of the PM10 standard by 4% and 7%, respectively, over use of a standard diesel 

fuel. 

19
Table 4-3. Estimated maximum increases and decreases in PM concentrations (μg/m3

) in the 

SoCAB due to a 100% penetration of B20 biodiesel in the HDDV fleet. 

Annual Average Maximum 24-Hour Average 

PM Species 

Maximum 

Increase 

Maximum 

Decrease 

Maximum 

Increase 

Maximum 

Decrease 

Sulfate 0.00 0.00 

Nitrate +0.04 +0.58 

Ammonium +0.01 +0.15 

EC 0.00 0.00 

OC 0.00 0.00 

Other PFIN 0.00 0.00 

Other PCRS 0.00 0.00 

PM10 Mass +0.04 +0.62 

PM2.5 Mass +0.04 +0.62 

-0.03 -0.07 

-0.09 -1.12 

-0.03 -0.34 

-0.06 -0.10 

-0.15 -0.27 

-0.01 -0.01 

-0.01 -0.01 

-0.31 -1.61 

-0.30 -1.61 

20
5. IMPACTS OF BIODIESEL FUEL ON AIR TOXICS AND RISK 

Diesel particulate matter has been declared a toxic substance by the state of California, and 

reports from the EPA have also identified it as a toxic compound. In the recent MATES-II 

study in the SoCAB of Southern California, 70% of the air toxic risk in the SoCAB was 

identified as being associated with diesel PM (SCAQMD, 2000). The use of biodiesel not only 

reduces the level of diesel PM mass emissions, but also reduces their toxicity. The impacts from 

the use of biodiesel in the HDDV fleet on air toxics and risk is discussed below. 

EFFECTS OF BIODIESEL ON DIESEL PM EMISSIONS MASS AND TOXICITY 

An analysis of engine test data has found that B20 fuel reduces tailpipe diesel PM emissions by 

approximately 9% and reduces the toxicity of the diesel PM by approximately 5% (Lindhjem and 

Pollack, 2002). These effects were accounted for in air toxics modeling for the SoCAB region of 

Southern California for three emission scenarios: 

• Standard diesel emissions based on the EMFAC2000 mobile source emissions model; 

• 100% penetration of a B20 biodiesel fuel in the HDDV fleet; and 

• 50% penetration of a B20 biodiesel fuel in the HDDV fleet. 

Table 5-1 summarizes the diesel PM emissions (lb/day) in the SoCAB for the standard diesel 

Base Case and the two B20 biodiesel fuel scenarios. The 100% penetration of a B20 biodiesel 

fuel in the HDDV fleet is estimated to reduce diesel PM emissions from the HDDV fleet by 

approximately 9%. As the HDDV fleet contributes approximately 53% of the total diesel PM 

emissions in the SoCAB, this represents an overall reduction in diesel PM emissions in the 

SoCAB of approximately 5% for the 100% B20 biodiesel fuel scenario. The effects of the 50% 

B20 biodiesel fuel scenario are half that of the 100% B20 scenario. Note that no diesel PM 

emission reductions are assumed for other non-HDDV diesel engines due to the biodiesel fuel. 

This is a conservative assumption (i.e., understating the benefits of biodiesel fuel use) as the 

distribution of biodiesel fuel to the HDDV fleet would certainly result in penetration into some 

other on-road and non-road diesel engines that would produce additional diesel PM emission 

reductions. 

21
22

Table 5-1. Diesel particulate matter emissions in SoCAB modeling domain for the three 

emission scenarios (lb/day). 

Source 100% B20 Biodiesel 50% B20 Biodiesel 

Category 

Standard 

Diesel (lb/day) (lb/day) (%) (lb/day) (%) 

HDDV 23239.6 21171.3 (-8.9) 22205.4 (-4.4) 

Other On-Road 1668.9 1668.9 (0.0) 1668.9 (0.0) 

Other Diesel 19061.1 19061.1 (0.0) 19061.1 (0.0) 

 Total 43969.6 41901.3 (-4.7) 42935.4 (-2.4) 

The air toxics modeling accounted for six air toxics compounds: diesel PM, four organic air 

toxics (benzene, 1, 3-butadiene, formaldehyde, and acetaldehyde) and hexavalent chromium. 

According to the MATES-II study, these six air toxic compounds accounts for over 90 percent of 

the risk associated with exposure to air toxic compounds in the SoCAB (SCAQMD, 2000). 

EFFECTS OF BIODIESEL FUEL ON AIR TOXICS RISK 

As used in the MATES-II study, species-dependent unit risk factors (URFs) were applied to the 

air toxics estimates to estimate the one in a million risk of premature death due to long-term 

exposure to air toxics as follows: 

• Benzene: 2.9 x 10-5 (μg/m3

)

-1

• 1,3-Butadiene: 1.7 x 10-4 (μg/m3)

-1 

• Acetaldehyde: 2.7 x 10-6 (μg/m3)

-1 

• Formaldehyde: 6.0 x 10-6 (μg/m3

)

-1 

• Standard Diesel Particles: 3.0 x 10-4 (μg/m3

)

-1

• B20 Diesel Particles: 2.85 x 10-4 (μg/m3

)

-1

In the MATES-II study, risk was calculated using “front-yard” exposures that assumed no 

indoor/outdoor effects on exposure to the ambient air toxics concentrations. For this analysis, 

risk was estimated using both outdoor “front-yard” exposures as well as two simple 

representation of indoor/outdoor (I/O) effects on diesel PM: (1) using an annual I/O factor 

applied to the annual average diesel PM concentrations; and (2) using an hourly I/O factor by 

time of day for several different conditions (at home, at work, outside, and in a car) that is 

applied to the hourly air toxics concentrations and accumulated for the annual simulation. Table 

5-2 summarizes the estimated average one in a million risk of premature death due to exposure to 

air toxic compounds for the standard diesel base case and 100% and 50% B20 biodiesel fuel 

scenarios. The 100% penetration of a B20 biodiesel fuel in the HDDV fleet is estimated to 

reduce risk of premature death due to exposure to air toxics in the SoCAB by 5%-6%. The 

reduction in risk for the 50% B20 scenario relative to standard diesel is about half that 

(approximately 2%). 
Table 5-2. Average risk (out of a million) of premature death due to exposure to air toxics for 

the standard diesel base case and the 50% and 100% penetration of B20 biodiesel in the HDDV 

fleet emission scenarios calculated with no indoor/outdoor (I/O) effects and accounting for I/O 

effects on an annual average and hourly basis. 

Std Diesel 50% B20 Fuel 100% B20 Fuel 

Scenario Risk Risk (%) Risk (%) 

No I/O Effects 1,950 1,910 (-2.1) 1,835 (-5.9) 

Annual I/O Effects 1,284 1,261 (-1.8) 1,216 (-5.3) 

Hourly I/O Effects 1,257 1,235 (-1.8) 1,191 (-5.3) 

In conclusion, the use of a B20 fuel in the HDDV fleet is estimated to reduce the per million risk 

of premature death due to exposure to air toxics in the SoCAB by approximately 2% and 5% for 

the 50% and 100% HDDV fleet penetration B20 scenarios, respectively. 

23
REPORT DOCUMENTATION PAGE Form Approved 

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 

May 2003 

3. REPORT TYPE AND DATES COVERED 

Subcontract Report 

September 16, 1999–January 31, 2003 

4. TITLE AND SUBTITLE 

Impact of Biodiesel Fuels on Air Quality and Human Health: Summary Report 

5. FUNDING NUMBERS 

AXE-9-29079-01 

6. AUTHOR(S) 

R.E. Morris, A.K. Pollack, G.E. Mansell, C. Lindhjem, Y. Jia, G. Wilson 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

Environ International Corporation 

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National Renewable Energy Laboratory 

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13. ABSTRACT (Maximum 200 words) 

This document discusses the results of the NREL “Impact of Biodiesel Fuels on Air Quality and Human Health” study. This 

report provides a summary of the key results on the air quality and risk impacts from the use of biodiesel in the heavy-duty 

diesel vehicle fleet. 

14. SUBJECT TERMS 

biodiesel; air quality 

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