Aerosols Emitted in Underground Mine Air by Diesel Engine

Fueled with Biodiesel

Aleksandar D. Bugarski, Emanuele G. Cauda, Samuel J. Janisko, Jon A. Hummer, and

Larry D. Patts

U.S. Department of Health and Human Services, Public Health Service, Centers for Disease

Control and Prevention, National Institute for Occupational Safety and Health, Pittsburgh Research

Laboratory, Pittsburgh, PA

IMPLICATIONS

Changing fuel supply from petroleum diesel to biodiesel

fuels has been adopted by several underground mines as a

method of choice for controlling the exposure to diesel

aerosols. The results of this study provide more insight into

potential advantages and disadvantages of using biodiesel

fuels for controlling emissions of aerosols and gases. The

role of diesel oxidation catalysts in controlling biodiesel

emissions has also been re-examined. Substantial changes

in physical and chemical properties of aerosols, observed

when diesel was replaced with biodiesel, warrant further

research on establishing the potential health risks associated with exposure to those aerosols.

ABSTRACT

Using biodiesel in place of petroleum diesel is considered

by several underground metal and nonmetal mine operators to be a viable strategy for reducing the exposure of

miners to diesel particulate matter. This study was conducted in an underground experimental mine to evaluate

the effects of soy methyl ester biodiesel on the concentrations and size distributions of diesel aerosols and nitric

oxides in mine air. The objective was to compare the

effects of neat and blended biodiesel fuels with those of

ultralow sulfur petroleum diesel. The evaluation was performed using a mechanically controlled, naturally aspirated diesel engine equipped with a muffler and a diesel

oxidation catalyst. The effects of biodiesel fuels on size

distributions and number and total aerosol mass concentrations were found to be strongly dependent on engine

operating conditions. When fueled with biodiesel fuels,

the engine contributed less to elemental carbon concentrations for all engine operating modes and exhaust configurations. The substantial increases in number concentrations and fraction of organic carbon (OC) in total

carbon over the baseline were observed when the engine

was fueled with biodiesel fuels and operated at light-load

operating conditions. Size distributions for all test conditions were found to be single modal and strongly affected

by engine operating conditions, fuel type, and exhaust

configuration. The peak and total number concentrations

as well as median diameter decreased with an increase in

the fraction of biodiesel in the fuels, particularly for highload operating conditions. The effects of the diesel oxidation catalyst, commonly deployed to counteract the potential increase in OC emissions due to use of biodiesel,

were found to vary depending upon fuel formulation and

engine operating conditions. The catalyst was relatively

effective in reducing aerosol number and mass concentrations, particularly at light-load conditions, but also

showed the potential for an increase in nitrogen dioxide

concentrations at high-load modes.

INTRODUCTION

As of May 20, 2008, the U.S. Mine Safety and Health

Administration (MSHA) regulation1 limits exposures of

underground metal and nonmetal miners to diesel particulate matter (DPM) to 160 fg/m3 of total carbon (TC).

Improvements in mine ventilation and the curtailment of

DPM and toxic gaseous emissions from existing and new

diesel-powered equipment are commonly perceived as

the most promising tools to meet MSHA technology forcing regulations. Although diesel particulate filter (DPF)

systems are gradually becoming more utilized for controlling DPM emissions from underground mining vehicles,2,3 their acceptance has been hindered by their relative complexity, implementation issues, and expense.

Changing fuel supply from petroleum diesel to higherconcentration biodiesel blends is considered by several

underground mine operators to be a viable alternative for

controlling DPM emissions. The major advantages of

biodiesel over petroleum-based diesel fuels with respect to

DPM emissions are due to greater cetane number, absence

of aromatics, and high oxygen content. In addition,

biodiesel was shown to lower the balance point temperature of passively regenerated DPFs and therefore could

potentially facilitate regeneration and the implementation of DPF systems in underground mines.4,5

The effects of biodiesel and biodiesel blends on regulated and nonregulated emissions were compared with

those of petroleum diesel for various on- and off-road

diesel-powered applications. Biodiesel blends were found

to reduce emissions of nonvolatile fractions of DPM4,6

and to increase the particle-bound volatile organic fraction of DPM.6,7 Additionally, biodiesel was found to reduce total polycyclic aromatic hydrocarbons and benzo­

(a)pyrene equivalent emissions8 and to increase carbonyl

emissions.9 The effects of biodiesel on emissions were
found to vary widely with usage conditions, engine type,

and age.10–12 Mine studies showed the potential of neat

biodiesel13 and biodiesel blends2,3,14 to reduce exposure of

underground miners to elemental carbon (EC) and DPM.

The biodiesels were shown to increase oxides of nitrogen

(NOx) emissions.11,15

Several researchers have studied the impact of rapeseed and soy methyl ester (SME) biodiesel on size distribution of aerosols emitted by diesel engines in laboratory

conditions.15–17 An increase in concentrations of smaller

particles15 and nucleation aerosols16,17 and a reduction in

concentrations of accumulation-mode aerosols16,17 were

reported. Research on the impact of biodiesel on particle

size has not produced consistent results18 and additional

research in this area is needed. Swanson and coauthors19

concluded that the speculative nature of a reduction in

health effects based on chemical composition of biodiesel

exhaust needs to be followed up with investigation in

biologic systems.

EXPERIMENTAL METHODOLOGY

The objective of this study was to evaluate the effects of

SME biodiesel fuels on the concentrations, size distribution, and carbon composition of nano- and ultrafine aerosols in mine air downwind of the exhaust discharge. The

effects of neat biodiesel (B100) and a 50/50% blend (B50)

of biodiesel and ultralow sulfur diesel (ULSD) were compared with those established for ULSD. The effects were

evaluated for the cases when a test engine was fitted with

a muffler (Muffler) only or with a diesel oxidation catalyst

(DOC) and muffler combination (DOC + Muffler).

The goal was to study the aforementioned effects

directly in an occupational setting by using the National

Institute for Occupational Safety and Health (NIOSH) Diesel Laboratory. This laboratory, developed in the D-drift

of the NIOSH Lake Lynn Experimental Mine (LLEM), is

designed to allow evaluation of control technologies in an

underground environment.20 The major components of

the laboratory (Figure 1) are an engine/dynamometer system, three sampling and measurement stations, and a

ventilation measurement and control system.

Figure 1. NIOSH Diesel Laboratory in D-drift of LLEM.

The fuels were evaluated using a mechanically controlled, naturally aspirated, directly injected Isuzu C240

engine rated at 41 kW (56 hp). The engine was not altered

to accommodate for differences in fuels.7 To eliminate the

contribution of crankcase emissions, the engine was retrofitted with a closed-loop crankcase filtration system. A

DOC with Cordierite substrate and a proprietary catalyst

formulation (Engine Control Systems Ltd., model A16­

0130) was used in this study.

The engine was operated over four steady-state modes

(Table 1) using the water-cooled eddy current dynamometer.

Table 1. Engine operating conditions. 

Engine Speed Torque Power

Mode (rpm) (Nm) (kW)

M1 2950 63.7 17.2 

M2 2950 108.4 34.3 

M3 2100 73.2 14.9 

M4 2100 138.3 30.6 

The power levels were selected by mapping the engine using all three fuels. One of the selected modes at

each of the engine speeds represented full engine load,

whereas the other was more representative of intermediate engine load. In the case of M1 and M2 modes, the tests

were done for two exhaust configurations: Muffler and

DOC + Muffler. In the case of M3 and M4 modes, the tests

were done for the Muffler configuration.

Fresh unconditioned and unfiltered air was supplied

to the underground facility via a ventilation shaft located

in E-drift (Figure 1). An auxiliary fan and a subsonic Venturi meter were used to maintain and measure the constant flow of fresh air through the drift throughout the

tests. The measurements showed an average volumetric

flow rate of 5.81 ± 0.05 m3

/sec (12,319 ± 106 ft3/min).

The very low test-to-test variability in flow rate eliminated

the need for normalization of the data with respect to it.

The average exhaust dilution ratios for M1, M2, M3, and

M4 engine operating modes were calculated to be 141,

139, 174, and 176, respectively. The average ambient temperatures upstream of the engine were between 7.5 and

17.6 °C. The corresponding average ambient temperatures at the downstream measurement station ranged between 10 and 18.3 °C.
Because quality has been an ongoing issue with

biodiesel fuels,21 special care was taken to secure SME

biodiesel fuel that met all of the specifications for ASTM

D6751. B100, produced by the transesterification of soybean oil,22 was supplied by Stepan Company as Stepansol

SB-W. The ULSD supplied by Guttman Oil was used as a

baseline fuel. The results of the analysis performed on

B100 and ULSD fuels by Core Laboratories, Houston, TX,

are given in Table 2.

Table 2. Properties of the B100 and ULSD fuels. 

Test Method Unit B100 ULSD

Energy, net ASTM D-240 kJ/kg (BTU/lb) 39,975 (17,198) 46,486 (19,999) 

Density ASTM D-4052 g/mL 0.8835 0.8050 

Oxygen content ASTM D-5291M wt % 10.54 0.51 

Flash point, PMCC ASTM D-93A °C (F) 138 (280) 61 (142) 

Sulfur content ASTM D-5453 mg/kg 5.1 10.0 

Notes: PMCC = Pensky–Martens Closed Cup test. 

The B50 blend was prepared at the site. The fractions

of biodiesel and ULSD were determined volumetrically.

Measurements

The effects of biodiesel fuels were determined from the

results of measurements of aerosol size distributions and

concentration at the downstream and upstream measurement stations. The downstream ambient monitoring station was located approximately 60 m (197 ft) downwind

of the dynamometer, and the upstream ambient monitoring station was located approximately 60 m (197 ft) upwind of the dynamometer. The measurements were taken

for each fuel for the aforementioned four steady-state

engine speed and load conditions. The tests were between

4 and 9 hr long. The initial hour of each test was dedicated to achieving concentration equilibrium. The measurements were initiated at the beginning of the second

hour. The background corrections were made by subtracting the results of measurements performed at the upstream station from the corresponding results obtained at

the downstream station.

A custom sampling method was used to collect integrated DPM samples for carbon analysis. Three samples

were collected at the downstream and two samples were

collected at the upstream sampling stations. Each DPM

sample was collected on a stacked primary and secondary

filter by merging flows from five inlets distributed on the

three levels at a sampling grid. A 10-mm Dorr-Oliver

cyclone followed by a single-stage diesel impactor, with

removed filters, was used at each inlet as preclassifiers. A

flow rate of approximately 2 L/min was maintained

through each cyclone and impactor pair. At this sampling

flow rate, only particles with geometric mean diameter

(50Dae) smaller than 0.78 fm were deposited on the filters.

All five preclassifiers were attached to a symmetrical plenum, which uniformly distributed a total flow rate of

approximately 10 L/min among the five streams. Each of

the preclassifier assemblies was connected to the plenum

chamber by a 3-ft long section of conductive tubing. The

outlet of the plenum was directly connected to a cassette

containing two stacked 37-mm tissue quartz fiber filters

(Tissuequartz 2500QAT, Pall Corporation). The total sampling mass flow rates were maintained using an orifice in

each of the three sampling lines from the 37-mm cassettes. The total volumetric flow rates through each of the

sampling streams were verified periodically by inserting a

Gilibrator II bubble flow meter inline, between cassettes

and orifices. The volumetric flow rates measured during

this study were all corrected to ambient conditions. A

model SV25 rotary vane pump from Oerlikon Leybold

Vacuum was used to draw the sample through the sampling system. The samples were analyzed for EC and organic carbon (OC) content using the NIOSH analytical

method 5040.23

The aerosol mass and number concentrations and

size distributions were measured at a single point at the

sampling grids located 60 m downstream and 60 m upstream of the exhaust discharge. A tapered element oscillating microbalance (TEOM) series 1400a ambient particulate monitor from Thermo Scientific was used at the

downstream station to measure total particulate matter

mass concentrations of particles with mean aerodynamic

diameter (50dae) less than 0.82 fm. A second identical

instrument was used at the upstream station for the same

purpose. Two scanning mobility particle sizers (SMPS;

model 3936, TSI)24 were used to measure size distribution

and number concentrations of aerosols. One was located

at the upstream station and the other at the downstream

station. A model CLD 700 AL chemiluminescence analyzer (Eco Physics) was used to measure concentrations of

nitric oxide (NO) and nitrogen dioxide (NO2) at the

downstream station.

The exhaust temperatures at the inlet to the muffler

or DOC averaged over the measurement periods are summarized in Table 3. The temperatures were affected primarily by engine operating conditions, but also by fuel

type. The slightly lower temperatures observed for B100

are consistent with lower energy content of biodiesel.7

The higher exhaust temperatures observed during B50

tests were probably an aberration and they can be potentially explained by higher temperature ( 5–7 °C warmer)

and higher relative humidity ( 20%) of the intake air

(mine air) observed for B50 tests than for corresponding

ULSD and B100 tests.

RESULTS AND DISCUSSION

Carbon Concentrations

The results of the carbon analysis performed on the samples collected at the downstream sampling station are

summarized in Figure 2. The presented EC values are

average concentrations for the sampling periods at the
prevailing ventilation. The analysis of the upstream samples showed an undetectable level of EC in the background air and therefore background correction of EC

data was not necessary. The results of carbon analysis

performed on the primary filters were used to examine the

relation between OC and TC.

The analysis showed that the use of biodiesel fuels

substantially reduced concentrations of EC for all test

modes (Figure 2a). The highest reductions ( 60%) were

observed for B100 when the engine was operated at M2

and M4 modes. The observations on reductions in EC

concentrations are corroborated with observations on the

decrease in median diameter of accumulation-mode aerosols discussed in the section on size distribution.

The effects of the DOC on concentrations of EC varied depending upon engine operating conditions and fuel

type. When the engine was operated at M1, the DOC

reduced the EC mass concentrations by 31.6, 20.8, and

16% for ULSD, B50, and B100, respectively. A DOC associated reduction of 26.1% in concentrations of EC was

also found for ULSD when the engine was operated at M2.

The DOC was found to increase concentrations of EC by

23.8% when the engine was operated at M2 using B50.

The change in EC concentrations for B100 when the

engine was operated at M2 was not significant.

The carbon analysis of the primary filters showed a

positive correlation between the fraction of OC in TC and

the fraction of biodiesel in the fuel (Figure 2b). These

results are in agreement with previous findings6,7 on increase in the particle-bound volatile organic fraction of

Table 3. Average exhaust gas temperatures (°C). 

Exhaust

Configuration Mode ULSD B50 B100

Muffler	 M1 304.4 ± 0.8 318.1 ± 0.9 307.3 ± 0.5 

M2 461.1 ± 2.0 481.6 ± 1.0 454.1 ± 0.9 

M3 237.2 ± 0.8 253.3 ± 0.9 234.8 ± 0.5 

M4 470.5 ± 3.5 485.3 ± 1.4 452.7 ± 1.3 

DOC + Muffler	 M1 317.0 ± 0.7 NA 304.3 ± 0.8 

M2 476.1 ± 4.0 NA 453.6 ± 2.0 

Notes: NA = not applicable. 

Figure 2. Carbon analysis: (a) EC concentrations and (b) percentage of OC in TC for the primary filters.

DPM with the use of biodiesel blends. When the DOC was

incorporated in the exhaust, the fractions of OC in TC on

the primary filter were substantially lower for all tested

fuels and for both modes (M1 and M2).

Mass and Number Concentrations

Table 4 summarizes the results of measurements made

with the TEOM and SMPS for ULSD, B50, and B100. All

concentrations are reported as the averages of values measured during the second hour of measurement at prevailing ventilation conditions. The corresponding standard

deviations were reported next to the averages. The concentrations were not corrected for the differences in dilutions between test modes.

The upstream aerosol mass and number concentrations in unfiltered dilution air were found to be less then

16 and 1.7%, respectively, of the corresponding downstream concentrations. The changes in mass and number

concentrations resulting from the use of B50 and B100 in

place of ULSD are reported in Figure 3. The reduction was

regarded as a positive change.

Biodiesel fuels reduced total mass concentrations for

all modes and both exhaust configurations. With a few

exceptions, reductions in total mass concentrations rose

with an increase in the biodiesel fraction. When the engine was operated at M1, the DOC reduced total mass

concentrations by 33.3, 49.5, and 31.4% for ULSD, B50,

and B100, respectively. For M2, the effects of the DOC on

mass concentrations were found to be dependent on fuel

formulation: the DOC reduced concentrations by 26.3%
in the case of ULSD, increased concentrations by 41.2%

for B50, and did not change concentrations for B100.

These results corroborate with the results of carbon

analysis.

Biodiesel fuels increased total number concentrations

of aerosols between 15 and 39% for M1 and M3, but total

number concentrations of aerosols remained virtually unchanged for M2 and decreased 6 –11% for M4. Increases in

total number concentrations for M1 and M3 rose with an

increase in fraction of biodiesel in the fuels. Reductions in

total number concentrations for M4 increased with a

greater fraction of biodiesel in the fuels. For all tested fuels

the effects of the DOC on number concentrations were

more pronounced for M1 mode than for the M2 mode.

The most significant reductions of 39% in number concentrations were attributed to the DOC when the engine

was operated at light-load M1 using B50 fuel.

Table 4. Total aerosol mass (TEOM) and number concentrations (SMPS) at downstream and upstream stations. 

Number Background

Exhaust Mass Mass Background Number (SMPS; particles/ (SMPS; particles/cm3

Fuel Configuration Mode (TEOM; g/m3

) (TEOM; g/m3) 3 cm [104]) [104])

ULSD Muffler M1 136.2 ± 5.9 3.6 ± 1.2 87.28 ± 1.91 32.0 ± 3.7 

M2 154.1 ± 2.6 0.0 ± 2.0 64.96 ± 1.83 88.0 ± 1.9 

M3 84.7 ± 4.1 0.0 ± 1.4 34.75 ± 1.25 35.0 ± 1.0 

M4 220.2 ± 10.3 3.8 ± 1.9 67.73 ± 2.50 37.0 ± 9.3 

DOC + M1 90.9 ± 7.3 9.6 ± 1.2 66.43 ± 1.77 110.0 ± 22.0 

Muffler M2 113.5 ± 6.0 0.0 ± 1.5 57.15 ± 1.54 28.0 ± 6.4 

B50 Muffler M1 123.9 ± 2.2 3.9 ± 1.4 100.80 ± 2.66 170.0 ± 12.0 

M2 65.3 ± 2.6 5.4 ± 1.5 65.91 ± 1.55 100.0 ± 6.4 

M3 69.3 ± 7.8 6.5 ± 1.3 45.05 ± 1.48 51.0 ± 9.1 

M4 144.2 ± 4.3 12.7 ± 1.7 63.20 ± 1.55 94.0 ± 13.0 

DOC + M1 62.5 ± 1.2 1.5 ± 1.6 61.01 ± 1.77 45.0 ± 6.4 

Muffler M2 92.3 ± 2.8 4.5 ± 2.5 59.90 ± 1.37 34.0 ± 1.9 

B100 Muffler M1 112.9 ± 4.1 0.0 ± 2.5 114.40 ± 4.60 13.0 ± 5.1 

M2 74.8 ± 10.7 2.7 ± 2.4 64.72 ± 4.38 33.0 ± 1.9 

M3 63.6 ± 2.0 0.0 ± 2.0 48.35 ± 1.84 67.0 ± 6.5 

M4 101.0 ± 2.8 1.2 ± 1.6 60.21 ± 1.40 53.0 ± 11.0 

DOC + M1 77.4 ± 2.1 1.9 ± 2.1 79.41 ± 2.27 18.0 ± 7.1 

Muffler M2 74.0 ± 3.1 11.9 ± 21.9 57.41 ± 1.81 45.0 ± 24.0 

Figure 3. Change in mass (TEOM) and number (SMPS) concentrations with use of B50 and B100 (reduction is positive).

Size Distributions

The average number size distributions of aerosols measured

by the SMPS at the downstream sampling station are shown

for each of the four modes in Figure 4. The scales on the xand y-axes were kept equal on all four graphs to allow for

easier comparison. In the case of M1 and M2 modes, the

aerosol distributions were measured for two exhaust configurations: Muffler and DOC + Muffler. In the case of M3 and

M4 modes, the effects on aerosol distributions were examined only for the cases when the engine was fitted with the

muffler. The markers show the average values measured

during the third hour of each test, whereas the corresponding error bars represent single positive and negative standard

deviations. The presented distributions were not corrected

for background concentrations and/or adjusted for prevailing dilution ratios. The average distributions were fitted

with lognormal curves using DistFit software from Chimera

Technologies. The count median electrical mobility diameters (50dem), standard deviation of means (SDOM), and total

number concentrations for the lognormal distributions are

summarized in Table 5. The total concentrations for fitted

and average measured distributions were given for comparison purposes.

In general, aerosol size distributions were strongly affected by engine operating conditions, fuel type, and exhaust configuration. The size distributions (Figure 4 and

Table 5) were found to have a single accumulation mode for

all studied conditions. The peak and total concentrations

were highest when the engine was outfitted with a muffler

and was operated at M1 (Figure 4a and Table 5). For the

same conditions, peak concentrations increased (Figure 4a)

and the median diameter(50dem) slightly decreased (Table 5)

with an increase in the fraction of biodiesel in the fuel.

These changes in aerosol concentrations and properties can

be related to observed increases in total number and decreases in total mass of aerosols (Figure 3) with the use of
biodiesel. At the exhaust temperatures observed for M1 (Table 3), the DOC was found to be effective in oxidizing the

organic aerosols. Consequently, the peak (Figure 4a) and

total number concentrations (Table 5) were substantially

lower than those observed for the muffler only. The median

diameters of the aerosols recorded in the mine air during M1

tests for the engine equipped with a DOC and muffler were

slightly lowerthan those observed during the corresponding

tests when the engine was only fitted with a muffler.

In the case of M2, B50 and B100 did not substantially change the peak (Figure 4b) and total number

(Table 5) concentrations. The median diameter was

found to slightly decrease with a greater fraction

of biodiesel in the fuel (Figure 4b and Table 5). Despite

higher exhaust temperatures (Table 3), the DOC

had less pronounced effects on peak (Figure 4b) and

total number concentrations (Table 5) for M2 than

for M1.

Figure 4. Size distributions measured with SMPS for (a) M1 (Muffler and DOC + Muffler), (b) M2 (Muffler and DOC + Muffler), (c) M3 (Muffler),

and (d) M4 (Muffler) tests.

Table 5. Statistical parameters for lognormal size distributions. 

Accumulation-Mode Parameters Measured

Exhaust Total Concentration Total Concentration

Fuel Configuration Test Mode 50dem (nm) SDOM (nm) (particles/cm3 [104

]) (particles/cm3 [104])

ULSD Muffler M1 48.3 1.62 86.75 87.28 

M2 53.5 1.72 64.32 64.96 

M3 48.5 1.74 34.76 34.75 

M4 60.1 1.76 67.55 67.73 

DOC M1 44.8 1.71 65.77 66.43 

M2 49.9 1.75 60.23 57.15 

B50 Muffler M1 45.0 1.60 97.97 100.80 

M2 41.0 1.77 65.98 65.91 

M3 43.8 1.73 44.44 45.05 

M4 55.3 1.78 63.03 63.20 

DOC M1 39.5 1.70 60.72 61.01 

M2 44.2 1.76 59.67 59.90 

B100 Muffler M1 42.8 1.61 112.60 114.40 

M2 39.3 1.79 65.04 64.72 

M3 42.0 1.72 47.90 48.35 

M4 43.8 1.85 60.45 60.21 

DOC M1 39.1 1.68 79.29 79.41 

M2 39.7 1.81 57.58 57.41 
In the case of M3, peak (Figure 4c) and total concentrations (Table 5) increased whereas median diameters

decreased (Table 5) with a greater fraction of biodiesel in

the fuels. The peak (Figure 4d) and total concentrations

(Table 5) as well as median diameter (Table 5) decreased

with an increase in the fraction of biodiesel in the fuels for

M4.

It is important to note that the pronounced nucleation mode previously observed during some laboratory

studies involving biodiesel16,17 was not observed in this

study. It appears that, under prevailing conditions and in

the presence of high concentrations of accumulationmode aerosols, most semivolatile aerosols condensed and

adsorbed on accumulation-mode aerosols.

NOx

The effects of all fuels on concentrations of NOx were

dependent on the engine operating condition (Figure 5).

Figure 5. Effects of fuels and DOC on (a) concentrations of NO and NO2 and (b) NO2/NOx ratio.

The biodiesel fuels produced minor effects on NO concentrations for all operating conditions. B50 increased

NO2 concentrations by 24, 14, 32, and 46% for M1, M2,

M3, and M4, respectively. The effects of B100 for all of the

modes were found to be minor and within measurement

accuracy. The NO2/NOx ratio was found to be 2–3 times

higher for light than for heavy engine loads (Figure 5b).

The effects of the DOC on concentrations of NOx

were strongly affected by engine operating conditions

(Figure 6).

Figure 6. Effects of DOC on NO and NO2 concentrations.

When the engine was operated at M1, the DOC

increased concentrations of NO and reduced the concentrations of NO2. For M2 conditions, the DOC increased

approximately 3-fold the concentrations of NO2, but the

changes in NO concentrations were found to be within

measurement accuracy. It is important to note that despite those 3-fold increases, the absolute NO2 concentrations did not exceed NO2 concentrations observed during

the corresponding tests conducted at M1 with the engine

fitted only with the muffler (Figure 5a).

These results corroborate the findings of Katare and

coauthors,25 who found that aged DOCs are net consumers of NO2 when exhaust temperature is relatively low and

high concentrations of hydrocarbons and carbon monoxide are present in the exhaust, conditions similar to those

observed for mode M1. The NO2 was formed in DOCs at

the higher exhaust temperatures under conditions similar

to those observed for M2, at which hydrocarbons and

carbon monoxide are oxidized.

CONCLUSIONS

The evaluated SME biodiesel fuels demonstrated the potential to substantially reduce the mine air concentrations

of EC and total DPM mass generated by a naturally aspirated, mechanically controlled engine. The rate of reductions varied depending on engine operating conditions,

but, in general, they were higher for B100 than for the

B50 blend. The downside of using biodiesel fuels was an

increase in the fraction of particle-bound volatile organics

and number concentrations of aerosols, particularly for

light-load engine operating conditions.

These results showed that a DOC (which is similar to

those that are commonly used on underground mining

engines to control carbon monoxide and hydrocarbon

emissions) can be used to control the potential increase in

emissions of OC aerosols resulting from the use of biodiesel. The effects of the DOC on the concentrations of EC

were found to be dependent on fuel type and engine

operation conditions. Generally, these were less pronounced than the effects on the concentrations of OC.

The biggest downside of using this type of DOC was a

substantial increase in NO2 concentrations observed
when the engine was operated at high-load modes. Therefore, DOCs for underground mining applications should

be optimized to provide substantial reductions in concentrations of hydrocarbons and OC without increasing NO2

concentrations.

Although the findings of this study should contribute

to a better understanding of the effects that biodiesel has

on diesel aerosols, additional work is needed to establish

a relationship between substantial changes in physical

and chemical properties of diesel and biodiesel aerosols

and the potential health risks associated with worker exposure to these aerosols.

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About the Authors

Aleksandar Bugarski, Emanuele Cauda, Samuel Janisko,

Jon Hummer, and Larry Patts are research engineers at the

U.S. Department of Health and Human Services, National

Institute for Occupational Safety and Health, Pittsburgh

Research Laboratory. Please address correspondence to:

Dr. Aleksandar Bugarski, 626 Cochrans Mill Road, P.O. Box

18070, Pittsburgh, PA 15236; phone: +1-412-386-5912;

fax: +1-412-386-4917; e-mail: abugarski@cdc.gov.