Submicrometer elemental carbon as a selective measure of diesel

particulate matter in coal mines

M. Eileen Birch*a and James D. Nollb

a US Department of Health and Human Services, Public Health Service, Centers for Disease

Control and Prevention, National Institute for Occupational Safety and Health, Division

of Applied Research and Technology, 4676 Columbia Parkway, Cincinnati, OH 45226, USA

b US 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, 626 Cochrans Mill Road, Pittsburgh, PA 15236, USA

Received 18th May 2004, Accepted 2nd July 2004

First published as an Advance Article on the web 16th September

A monitoring method for diesel particulate matter was published as Method 5040 by the National Institute

for Occupational Safety and Health (NIOSH). Organic and elemental carbon are determined by the method,

but elemental carbon (EC) is a better exposure measure. The US Mine Safety and Health Administration

(MSHA) proposed use of NIOSH 5040 for compliance determinations in metal and nonmetal mines. MSHA

also published a rulemaking for coal mines, but no exposure standard was provided. A standard based on

particulate carbon is not considered practical because of coal dust interference. Interference may not be

a problem if an appropriate size-selective sampler and EC exposure standard are employed. Submicrometer

dust concentrations found in previous surveys of nondieselized, underground coal mines were relatively low.

If a large fraction of the submicrometer dust is organic and mineral matter, submicrometer EC

concentrations would be much lower than submicrometer mass concentrations. Laboratory and field results

reported herein indicate the amount of EC contributed by submicrometer coal dust is minor. In a laboratory

test, a submicrometer EC concentration of 31 mg m3 was found when sampling a respirable coal dust

concentration over three times the US compliance limit (2 mg m3

). Laboratory results are consistent with

surveys of nondieselized coal mines, where EC results ranged from below the method limit of detection to

18 mg m3 when size-selective samplers were used to collect dust fractions having particle diameters below

1.5 mm—submicrometer EC concentrations were E7 mg m3

. In dieselized mines, submicrometer EC

concentrations are much higher.

1. Introduction

1.1 Background

In the United States alone, over a million workers (e.g.,

trucking, mining, railroad, agriculture workers) are occupationally exposed to diesel exhaust.1 The widespread and growing use of diesel-powered equipment has raised concern

because workers exposed to diesel exhaust show an elevated

(20–50%) risk of lung cancer.2 While environmental exposure

is a concern, occupational exposure is a greater one because

workplace exposures are generally much higher—especially

among miners. In underground mines, diesel particulate concentrations3–5 are usually more than 100 times higher compared with a typical environmental level (e.g., 2 mg m3

) and

sometimes exceed 2 mg m3

, which is one thousand times

higher. The National Institute for Occupational Safety and

Health (NIOSH) considers diesel exhaust a potential occupational carcinogen and recommends that employers reduce

workers0 exposures.1 Other organizations, including the International Agency for Research on Cancer (IARC),6 the World

Health Organization (WHO),7 the California Environmental

Protection Agency,8 the US Environmental Protection Agency

(US EPA),9 and the National Toxicology Program10 have

reviewed the animal and human evidence, and each has

classified diesel exhaust as a probable human carcinogen or

similar designation. Non-cancer health effects also have been

associated with diesel exhaust exposure. These include immunologic, respiratory, and cardiovascular effects.11–15 Reviews

on the health effects of diesel exhaust have been published

previously.1,2,6–10

Assessment of exposure and the associated health risk is

challenging because diesel exhaust is a highly complex and

variable mixture of gases, vapors, and fine particles. Thus, a

surrogate measure of exposure must be selected. NIOSH

published Method 5040,16,17 which targets the particulate

carbon portion of diesel exhaust. In the analysis, the total

carbon (TC) in a filter sample is quantified as organic and

elemental carbon (TC 1⁄4 OC þ EC). In the absence of interferences, TC is a logical surrogate for diesel particulate matter

(DPM) because DPM is mostly (480%) carbon,18–20 but other

OC sources make TC measurements interference prone. In

contrast, EC (carbon in the soot particle core) is a selective

measure of occupational exposure to DPM17,21 and is therefore

a better exposure surrogate. Fine EC particles are derived

primarily from the combustion of fossil fuels, and diesel

engines are major sources of these particles. Carbonaceous

aerosols such as cigarette and wood smokes contain little, if

any, EC.17,21,22 Gasoline engines emit far less EC than diesels,

so their relative contribution is usually small. In environmental

settings, other sources can contribute to the EC background

levels, which are typically 1–3 mg m3

,

21 but diesel engines are

the primary emitters23,24 of EC air pollution. In occupational

settings, where diesel equipment is used in relatively close

proximity to workers, the contribution of remote sources is

negligible, especially when EC concentrations are elevated. EC

concentrations in occupational settings25–32 are ordinarily

above background—in mines, they are well above it.3–5,30

In addition to selectivity, potential health effects were considered when an EC surrogate was proposed. Diesel particles

and other insoluble fine particles are inhaled deeply into the

lungs, where they can induce an inflammatory response.

PAPER

www.rsc.org/jem

DOI: 10.1039/b407507b

This journal is & The Royal Society of Chemistry 2004 J. Environ. Monit., 2004, 6 , 799–806 799
Further, EC particles increase the long-term retention33,34 of

adsorbed genotoxins and other chemical toxins because the

particles have a high affinity for them.35 In combination with

an inflammatory response induced by the particles, genotoxic

agents may promote tumorigenesis. Ultrafine (o0.10 mm)

particles may pose an even greater health risk. Results of

toxicological studies on solid particles having aerodynamic

diameters in this size range indicate ultrafine particles are

especially toxic.36 This is significant because by mass the

majority of diesel particles are in the fine particle range, and

most are in the ultrafine range by number.20

A review on NIOSH 5040, including detailed rationale for

selection of an EC marker, is provided in a recent chapter of

the NIOSH Manual of Analytical Methods (NMAM).17 The

method has been used in numerous industrial hygiene surveys,25–32 and it was recently applied to an ongoing epidemiological study (NIOSH/National Cancer Institute [NCI]) of

miners. Given the physical and chemical nature of EC particles

emitted by diesel engines, monitoring and controlling exposures to these particles is prudent, especially in mines because

DPM levels are high and EC is a large fraction of the DPM.

1.2 Mines

The Mine Safety and Health Administration (MSHA) proposed use of NIOSH 5040 for compliance determinations in

metal and nonmetal mines. In its Final Rule,3 an interim

standard of 400 mg of TC per m3 air was proposed. A standard

of 160 mg TC per m3 was to apply five years after publication of

the Final Rule, but MSHA initiated limited new rulemaking37,38 to revise specific provisions of the Final Rule. Among

other amendments, MSHA proposed a change of the exposure

standard from TC to EC. A change to EC was proposed

because of potential OC interferences.

For sampling DPM in metal and nonmetal mines, MSHA

recommends3 a specialized impactor with a submicrometer

cutpoint (diameter of particle collected with 50% collection

efficiency, D50) to minimize collection of carbonates and other

carbonaceous dusts. The cutpoint (about 0.8 mm) of the

impactor is based on particle size distributions found in coal

mines. Impactors effect separation of particles according to

their aerodynamic diameter through inertial impaction. Because diesel exhaust particles are mainly submicrometer,20,39–46

their separation by size from larger, mechanically generated

dust is possible. Given the recently proposed change to an EC

exposure standard, an impactor having a submicrometer cutpoint would not be necessary for selective measurement of

DPM EC in many metal and nonmetal mines because DPM is

the only source of EC. Nonetheless, conditions in some metal

and nonmetal mines may dictate its use (e.g., to prevent filter

overloading by inorganic and carbonaceous dusts, and potential interference of graphitic [EC] components in some ores).

MSHA’s recommendation regarding an impactor for metal

and nonmetal mines considers these possibilities.

MSHA also published a rulemaking47 on diesel equipment

usage in underground coal mines, but an exposure standard

was not provided. MSHA did not consider a standard based on

particulate carbon feasible because of coal dust interference,

but coal dust interference may not be an issue if an appropriate

size-selective sampler and EC exposure standard are employed.

Impactors with optimized cutpoints have been used for gravimetric measurements of DPM in coal mines.48–51 Previous

surveys in underground coal mines where no diesel-powered

equipment was used indicated submicrometer dust concentrations were relatively low.49,52,53

Representative, submicrometer coal mine dust concentrations found in previous surveys of underground coal mines are

plotted in Fig. 1. Three results54 (Mutmanski and Consol Coal)

were obtained by a commercial impactor (Marple 298); others

were obtained by a prototype impactor.51,52 Submicrometer

coal mine dust concentrations ranged from 20 to 130 mg m3

. If

a large fraction of the submicrometer dust is organic, the

corresponding EC concentrations would constitute a relatively

small fraction of the submicrometer mass concentrations.

Among other properties, coals are ranked according to their

relative percentages of fixed carbon, which is the residual

carbon remaining after volatile matter is removed thermally

(fixed carbon 1⁄4 100  percentage of volatile matter).55 Lower

rank coals (e.g., lignite) contain less fixed carbon than higher

ranks (e.g., anthracite). Presuming some fraction of the fixed

carbon is quantified as EC, the OC–EC content of coals is

expected to be rank dependent. In addition to its OC content,

some of the submicrometer coal mine dust is mineral matter

(e.g., carbonates, sulfates, silicates, iron pyrites). Thus, the

extent to which the submicrometer dust in coal mines interferes

in the determination of DPM EC will depend on the coal type,

dust concentration, particle size distribution, and the mineral

content of the dust. In this paper, laboratory and field data on

the potential EC contribution of submicrometer coal dust are

reported. Our results indicate the amount of EC contributed by

submicrometer coal mine dust is minor.

2. Methods and materials

2.1 Thermal-optical analysis

NIOSH 5040 is based on a thermal–optical technique for

carbon. The thermal–optical analyzer (Sunset Laboratories,

Inc., Forest Grove, OR) used for the NIOSH 5040 analysis has

been described previously.16,17,21 For the analysis, a filter

portion (punch) of known area (normally 1.5 cm2) was placed

in the sample oven and the oven was tightly sealed. Highpurity, quartz-fiber filters (Pallflex 2500QAT-UP, Pallflex Inc.,

Putnam, CN) were used. Quartz filters are required because

temperatures in excess of 850 1C are employed in the analysis.

Prior to use, all filters were cleaned in a muffle furnace or lowtemperature asher.

The analysis proceeds in inert (helium) and oxidizing (oxygen–helium mix) atmospheres. OC (and carbonate, if present)

is first removed under a constant flow of helium as the

temperature is increased to a preset maximum. The thermally

evolved carbon enters a heated catalyst bed, where it is

oxidized to carbon dioxide (CO2). The CO2 then flows through

a heated reduction catalyst that reduces it to methane (CH4),

and the CH4 is quantified by a flame ionization detector (FID).

After OC is removed, the gas is switched to an oxygen–helium

(O2–He) mix. The temperature is again stepped to a preset

maximum, which effects combustion of the residual sample

carbon. As with OC, the residual carbon is completely

oxidized, reduced, and quantified as CH4.

Fig. 1 Submicrometer dust concentrations in different locations of

nondieselized mines (CM denotes continuous miner).

800 J. Environ. Monit., 2004, 6 , 799–806
The thermal–optical analyzer is equipped with a pulsed

diode laser and photodetector that permit continuous monitoring of the filter transmittance. This optical feature corrects

for the char that is formed during the analysis of some

materials. Char is formed through pyrolysis, which is a thermal

decomposition process. When some organic substances are

heated to elevated temperatures in an inert (non-oxidizing)

atmosphere, carbonization (conversion to carbon) occurs.

Both volatile products and char (thermal decomposition product containing mostly carbon) are formed in the process. As

with EC initially present in the sample, char strongly absorbs

the diode laser light. Thus, if charring occurs, the filter

transmittance decreases as the temperature is stepped to the

maximum in helium. After the gas is then switched to an

O2–He mix, the temperature is again stepped to the maximum.

As the temperature increases, char and original EC are oxidized from the filter, which causes a concurrent increase in

filter transmittance. The split between OC and EC is assigned

when the initial (baseline) value of the filter transmittance is

reached. All carbon removed before the OC–EC split is

considered organic, and that removed after the split is considered elemental.

OC and EC results are reported in micrograms per square

centimeter (mg cm2

) of the sample deposit. The total OC and

EC on the filter are calculated by multiplying the reported

values by the deposit area. In this approach, a homogeneous

deposit is assumed. The TC in the sample is the sum of OC and

EC. (Note: if carbonate is present, the carbon in it is quantified

as OC. Carbonate carbon can be estimated separately, if

desired.16,17)

2.2 Sample bank coals

Cans containing bags of 20 mesh (850 mm) coal (225–450 g)

were purchased from the Penn State Coal Sample Bank at the

Energy and Fuels Research Center, The Pennsylvania State

University. At the Bank, the coals had been stored under argon

in sealed polyethylene bags, and the bags were sealed in no. 2

cans. The coals originated from major coalfields of the United

States. They were selected for inclusion in the Bank to achieve

a representative distribution of seams (by rank, geologic

province, maceral composition, sulfur content, ash yield, and

composition, etc.). After receipt, the cans were stored at room

temperature and remained unopened until ready for use.

The EC fractions and carbon (TC) contents (% carbon) of

seven different coal ranks were determined by thermal–optical

analysis (NIOSH 5040). Prior to analysis, the 20 mesh coals

were sieved to less than 50 mm. Air samples of the sieved dusts

were then collected in an in-house, dust generation system (see

Section 2.5, Dust generation system). Quartz-fiber filters

loaded into 37 mm, three-piece plastic cassettes were used for

dust collection. Nylon cyclones (Dorr-Oliver) were attached to

the inlets of the cassettes to select the respirable fraction. The

filter samples of respirable coal dust were then analyzed to

determine their EC content (an even filter deposit is required

for the OC–EC split). The TC contents (% carbon) of the

sieved dusts were determined by thermal–optical analysis of a

known weight of the dust applied directly to a punch (1.5 cm2

)

from the quartz filter media. Air samples were not used for this

purpose because the dust mass on a punch from the loaded

filter could not be determined with sufficient accuracy.

2.3 Impactors

Commercial, eight-stage, personal cascade impactors (Marple

298, Andersen Instruments, Inc., Smyrna, GA) and four prototype impactors were used to examine the potential EC

contribution of submicrometer coal dust. All impactors were

operated at 2 L min1

. The four prototype impactors included:

an in-house (NIOSH) design,48 a MSHA design,50 one designed jointly by the University of Minnesota (UMN) and the

US Bureau of Mines (BOM),53 and a BOM design.51 As

mentioned previously (Section 1.2), these impactors were developed for determination of DPM concentrations (as submicrometer mass) in underground coal mines. In mines, a nylon

cyclone is used with the impactors to preselect the respirable

dust fraction.

The in-house design48 is a single-stage, single-jet impactor

made from a three-piece, 37 mm cassette. The impaction

substrate is held between the top and spacer ring portions of

the cassette, and the cassette’s inlet diameter is modified

(reduced). The impactor was designed to provide an approximate cutpoint of 1 mm. The MSHA impactor50 is based on a

modified MSA (Mine Safety Appliances Company, PO Box

426, Pittsburgh, PA) cassette. It is similar to the in-house

design (single stage and jet), but the filter cassette and jet-toplate distance (i.e., distance from inlet to impaction surface)

differ. The impactor53 designed jointly by researchers at UMN

and BOM is a single-stage, four-jet design, as is the BOM

impactor.51 With the UMN/BOM device, the sample filter is

located inside the impactor—with the BOM device, it is contained in a MSA cassette inserted into the outlet of the

impactor. For the work reported in this paper, the BOM

sampling train (i.e., cyclone/impactor/cassette) and the MSHA

impactor were modified slightly to better accommodate the

quartz filter collection medium, which does not fit into the

MSA cassette well. Specifically, a 37 mm cassette was used with

the BOM impactor, and the bottom portion of the MSHA

impactor was replaced with the base of a 37 mm cassette. To

accommodate the base, the top portion (inlet piece and impactor substrate) of the MSHA impactor was glued to a 37 mm

cassette spacer ring, and this piece was used with the cassette

(37 mm) base.

2.4 Field samples

Field samples were collected in dieselized and nondieselized

(electric-powered) coal mines. Personal sampling pumps were

used to pull air (2 L min1

) through the impactors. The

sampling time varied from mine to mine (3–8 h). Two of each

of the cascade impactors were assembled to include eight,

seven, and six stages, which provided impactor cutpoints at

0.52 mm, 0.93 mm, and 1.5 mm, respectively. Different size cuts

were examined to determine the impact of cutpoint on the EC

results. Greased, stainless steel impaction substrates were used

inside the impactors to prevent particle bounce to subsequent

stages. A 37 mm cassette containing a quartz-fiber filter was

attached to the outlet of each cascade impactor to collect the

dust fractions. A short length (about 3 cm) of Tygons tubing

was used to attach the cassette. The quartz filter was not used

inside the impactor, where a PVC (polyvinyl chloride) final

filter is normally used, because an uneven deposit often

formed. An even deposit is required for thermal–optical

analysis.

Two additional cascade impactors were collocated with the

others to determine the total, respirable, and submicrometer

dust concentrations and particle size distribution. Pre-weighed,

greased, stainless steel impaction substrates were used on the

impactor stages, and a PVC filter was used inside the impactor

as the final filter as usual. The dust masses on all impaction

substrates and the final filter were used to calculate the total

dust concentration and determine the particle size distribution.

The dust masses for stages four through to the final filter were

used to calculate the respirable dust (British Medical Research

Council [BMRC] convention) concentration, while the dust

masses for stages seven, eight, and the final filter were summed

to calculate the submicrometer dust concentration. For comparison with the cascade impactors, an in-house impactor48

previously used in preliminary field studies also was included.

J. Environ. Monit., 2004, 6 , 799–806 801
2.5 Dust generation system

Laboratory samples were collected inside the dust chamber of

an in-house, dust generation system. Details on the operation

and design of the generation system have been described

previously.56 Briefly, coal dust (20 mesh sieved to o50 mm)

was introduced to the chamber through a fluidized bed

generator (Model 3400, Fluidized Bed Generator, TSI, Inc.,

St. Paul, MN) located outside the chamber. A stainless steel

cyclone supplied with the generator was used for further size

classification of the sieved dust. Air flow through the cyclone

was adjusted to 9 L min1

. The reported cutpoint (D50 value)

of the cyclone at this flow rate is 3.5 mm. A tapered element

oscillating microbalance (TEOM 1200 Mass Measurement

Systems, Rupprecht and Patashnick Co., Inc., Albany, NY)

was used to monitor the dust concentration, and an aerodynamic particle sizer (APS Model 3310, TSI, Inc., St. Paul, MN)

monitored the particle size distribution.

2.6 Evaluation of prototype impactors

The performance of the four prototype impactors was evaluated at two dust concentrations. A bituminous coal dust

(sieved to o50 mm) and an in-house dust generation system

(see Section 2.5, Dust generation system) were used for dust

generation. Two of each prototype were included (eight total).

Cascade impactors (two each) loaded with eight and seven

stages (0.52 mm and 0.93 mm cutpoints, respectively) also were

included for comparison. As with the field samples, 37 mm

cassettes containing quartz-fiber filters were attached at the

outlets of the cascade impactors to collect the dust size

fractions.

For the evaluation, prototype impactors were positioned in a

circular arrangement in a Plexiglass holder at the base of the

dust chamber. Prototype impactors of a given type (two each)

were diametrically opposed. The two personal cascade impactors were operated in the center of the prototypes. Tygons

tubing was used to connect the impactor (all) outlets to critical

orifices (2 L min1

) mounted in the Plexiglass holder. Air

was pulled through the orifices by a high volume pump. The

flow (2 L min1

) through each orifice was measured to verify

critical flow.

Prior to the evaluation, the homogeneity of the coal dust

concentration within the chamber was confirmed in a separate

experiment. To confirm an even distribution, eight nylon

cyclones each in series with a 37 mm plastic cassette containing

a pre-weighed PVC filter were used for dust collection. Two

cascade impactors containing pre-weighed, stainless steel impaction substrates and a PVC final filter were used to determine

the dust size distribution. The sampling flow rate (2 L min1

),

sampler placement (cyclone/cassettes in circular arrangement

and two cascade impactors in center), and coal dust were

identical to those used in the evaluation of the prototypes.

3. Results and discussion

3.1 EC–TC content of coals

The carbon contents of seven different ranks of coals purchased from the Penn State Coal Sample Bank are listed in

Table 1. Thermal–optical results and the percentages of carbon

and fixed carbon reported in the data sheet provided with each

coal are listed. For comparison with the reported TC contents,

thermal–optical results for three of the coal types (lignite,

subC, and anthracite) were obtained shortly after they were

received. Four others, and again the same three, were analyzed

about one year later. Except for the low volatile bituminous

(lvb) and anthracite ranks, significant volatile OC losses occurred. The TC content (TC mass/dust mass) of a lignite coal

was about 10% lower than the reported value. TC contents of

two subbituminous coals (subC and subB) were about 20%

and 15% lower, and those of two high volatile bituminous

coals (hvCb and hvAb) were 21% and 10% lower.

Char plus EC (Char þ EC) and EC mass fractions are also

reported in Table 1. Char plus EC is the total carbon removed

in the oxidative mode (O2–He atmosphere). It includes char

carbon generated through pyrolysis of the organic matter in

coal and EC initially present in the coal. Except for anthracite,

the amount of EC initially present is lower than the Char þ EC

by up to 40%. Lignite and subC coals had a higher EC content

than expected, but the EC in these coals can be distinguished

from typical, diesel-source EC in mine samples because it is

more readily oxidized (i.e., removed in O2–He at a lower

temperature). In contrast, EC in anthracite cannot be distinguished from diesel-source EC because it is present originally

(i.e., not generated through pyrolysis) and removed over the

same temperature range. Thermal–optical results for lignite

and anthracite are shown in Fig. 2.

Table 1 Carbon content of coals

Reported values (%) Thermal–optical resultsa (%)

Rank Origin TC Fixed C TC (SD)b TCc Char þ ECc ECc (SD)

Lignite ND 62.61 46.75 62 (5) 53 39 19

SubCd WY 64.68 32.65 66 (3) 45 26 13.3 (0.3)

SubBd MT 71.93 52.80 — 57 44 16.2 (0.8)

HvCbd IL 66.23 46.92 — 45 33 1

HvAbd PA 71.88 51.90 — 62 42 2 (2)

Lvbd PA 79.67 71.96 — 76 46 29 (4)

Anthracitee PA 88.85 89.52 78 (10) 80 76 76

a Where standard deviation (SD) is reported, n 1⁄4 3 or 4. b As received. c Carbon content determined one year after opening coal sample. d Classified according to the American Society for Testing and Materials (ASTM) Standard Specification for Classification of Coals by Rank

(ASTM D 388-77). SubC and subB are subbituminous coals; hvCb, hvAb, and lvb are bituminous. e Anthracite does not char.

Fig. 2 Thermal–optical results for filter samples of lignite and

anthracite dusts. Peak beginning at 360 s corresponds to lignite;

vertical line through lignite peak is OC–EC split for lignite. Peak to

immediate right of lignite is anthracite; OC–EC split for anthracite is

vertical line at about 340 s (final peak is calibration peak; stepped

dashed line is temperature).

802 J. Environ. Monit., 2004, 6 , 799–806
Thermal behavior of the other coals was intermediate to that

for lignite (and subC) and anthracite. Briefly, subB produced a

peak in the same region as lignite and another where anthracite

(and diesel-source) EC was oxidized. The magnitude of the two

peaks was similar, and the OC–EC split was assigned slightly

before the apex of the second peak. HvCb also produced two

peaks, but the first was small relative to the second. HvAb’s

thermal behavior was similar to HvCb’s, but the area of the

first peak relative to the second was a bit smaller still.

Depending on the instrument and dust loading, the peak

profiles and percentages of char carbon and EC may differ

somewhat from those reported here, but the conclusion remains unchanged. Namely, optical correction for char and the

different thermal properties (relative to diesel EC in mines) of

most coals provide additional selectivity in the measurement of

diesel-source EC. When the thermal behavior together with the

selectivity provided by size-selective sampling (submicrometer

dust) is considered, only low levels of coal-source EC are

anticipated in coal mines. Results obtained in underground

coal mines are discussed in the following section.

3.2 Underground coal mines

EC and TC concentrations found in nondieselized (electricpowered) underground coal mines are reported in Table 2. As

described earlier (see Section 2.4, Field samples), commercial

cascade impactors were used to collect three different dust size

fractions (o0.52 mm, o0.93 mm, and o1.5 mm) for thermal–

optical analysis, and an in-house impactor (PM1 in Table 2)

was included for comparison. Two additional cascade impactors collocated with the others were used to determine the total,

respirable (BMRC), and submicrometer dust mass concentrations (Table 2) and particle size distributions (Fig. 3 and Fig. 4)

of the dusts.

Relatively low EC concentrations were found in nondieselized coal mines when impactors with submicrometer cutpoints

were used. In five locations of four mines (D, E, G, and H),

submicrometer (o0.93 mm) EC concentrations ranged from

about 2 mg m3 to 7 mg m3

. EC concentrations found by the

cascade impactors having a 1.5 mm cutpoint were higher, but

they were still much lower than those in dieselized mines. EC

concentrations found by an in-house prototype impactor

(PM1, Table 2) were higher than those found by the 1.5 mm

cutpoint impactor (cascade). The in-house device48 was designed to produce a cutpoint near 1 mm. Based on the cascade

impactor results, the apparent cutpoint is more likely to be

closer to 2 mm.

The survey of Mine F was one of the first surveys where

samples were collected for thermal–optical analysis. In this

mine, only the in-house impactor was used. EC results for two

locations (intake and haulage) of the mine were below the limit

of detection (LOD). EC concentrations of about 20 mg m3 and

50 mg m3 were found in a very dusty area (return) of the mine,

but the respirable dust levels there were quite high (6 and 16 mg

m3

) compared to the US compliance limit (2 mg m3).

EC concentrations in three dieselized mines—one limestone

and two coal—also are reported in Table 2 (mines A–C). A

dieselized limestone mine (A) was included to illustrate the

effect of impactor cutpoint when a dust contains no EC. Here,

EC results obtained with the 0.93 mm and 1.5 mm impactors

were identical. Slightly lower results were obtained with the

0.52 mm impactor, which excluded a small fraction of the diesel

DPM, while the in-house impactor48 gave slightly higher

results (possibly due to the presence of larger diesel agglomerates). As expected, EC concentrations in the three dieselized

mines are much higher—about 200–560 mg m3 for dust

fractions o1.5 mm. Comparable EC results for metal and

nonmetal mines have been reported elsewhere.38

3.3 Evaluation of prototype impactors

A test of the dust generation system indicated the coal dust

concentration in the sample collection area of the system

chamber was homogeneous. The RSD (n 1⁄4 8) for the mean

Table 2 Fine particulate carbon (EC and TC) and dust (total, respirable, and submicrometer) mass concentrations in dieselized and nondieselized

underground mines

Mine typea Sampling locationb

EC/mg m3 TC/mg m3 Dust concentratione/mg m3

PM1c o1.5d oo0.93d o0.52d PM1c o1.5d o0.93d o0.52d Total Respirable Sub-mm

Limestone Haulage 235 198 197 168 462 428 443 308 — — —

Dieselized coal Mine A Return 531 427 — 313 706 626 — 564 4.17 1.15 0.51

Intake 459 — — — 565 — — — 0.92 0.81 0.76

Mine B Haulage 651 558 — 356 964 866 — 522 1.82 1.31 1.10

Intake 86 — — — 164 — — — 0.34 0.23 0.20

Mine C Haulage 539 — — — 674 — — — 2.15 1.39 0.93

Nondiesel coal Mine D Beltline 32 18 7 (3)f 125 81 33 24 5.03 0.67 (0.04)f

Mine E Shield 13 6 (4)f — 426 186 104 — 21.51 2.27 (0.04)f

Headgate (2)f — NDg — 58 — 66 — 4.16 0.63 NDg

Mine F Intake NDg Not sampled 50 Not sampled 3.72 1.13 0.41

Haulage NDg 48 4.07 1.42 0.52

Return 50 1011 34.00 16.17 4.33

Haulage NDg 23 2.59 0.87 0.24

Intake NDg 18 1.44 0.44 0.22

Return 20 121 14.38 6.11 0.85

Mine Gh Shield — 14 7 — — 287 309 — 15.60 0.81 NDg

Mine Hi Tailgate — — (5)f — — — 38 — — 2.55 —

Tailgate — — NDg — — — NDg — — 1.27 —

a Mines A and B are located in UT; coals were bituminous with 37% (A) and 42% (B) fixed carbon. Mine C is located in KY (no information on

coal type). Mine D is located in WV, E in PA, and F in OH. Mine D coal was bituminous with 75% fixed carbon, E was high volatile bituminous

with 50–54% fixed carbon, and F was bituminous with 42% fixed carbon. Mine G coal was bituminous (fixed carbon unknown). b Except for mine

G, sample volume ranged from 300–720 L, depending on location. c In-house (NIOSH) design. d Impactor cutpoint/mm. e Determined with

cascade impactors; see text for details. f Parentheses indicate result is at or above limit of detection (LOD) and below limit of quantitation (LOQ).

LOD 1⁄4 3sb,where sb is standard deviation of blank; LOQ 1⁄4 10sb. EC LOD 1⁄4 2 mg m3

; LOQ 1⁄4 5 mg m3. TC LOD 1⁄4 4 mg m3; LOQ 1⁄4 14 mg m3.

Dust concentration LOD 1⁄4 20 mg m3

; LOQ 68 mg m3. g Not detected (ND). h TC results blank corrected because of low sample volume

(160 L). i Mine located in the UK; actual impactor cut was 0.8 mm.

J. Environ. Monit., 2004, 6 , 799–806 803
dust concentration (1.26 mg m3

) found with the cyclone filter

samplers was 4.6%. After verifying that the dust concentration

was homogeneous, the performance of the four prototype

impactors was evaluated at two respirable coal dust concentrations: about 2 mg m3 and 5 mg m3

. A bituminous coal

(hvAb) was used for the evaluation. The particle size distribution of the dust is shown in Fig. 5.

TC and EC results corresponding to the two dust concentrations are listed in Tables 3 and 4. The respirable dust concentrations reported (Tables 3 and 4) for the prototype impactors

are the actual mass concentrations, not MRE (Mining Research Establishment) equivalents (used by MSHA). MRE

equivalent concentrations can be calculated by multiplying

the reported values (for prototypes) by 1.38.

At a respirable dust concentration of 1.75 mg m3 (MRE

equivalent 1⁄4 2.42 mg m3

), the TC concentrations found by

the BOM, UMN/BOM, and MSHA impactors were: 44 mg

m3

, 61 mg m3, and 68 mg m3 (Table 3). The EC concentrations found by these three impactors ranged from about 7 mg

m3 to 17 mg m3

, and EC results for the Marple impactors

were comparable. The TC concentration (304 mg m3

) found

by the in-house design (PM1) was about five times higher than

the mean (58 mg m3

) for the other three prototypes, while the

EC concentration (40 mg m3

) was about four times higher. As

already mentioned, the in-house device was designed to have

a 1 mm cutpoint, but the apparent cut was likely to be about

2 mm.

At a respirable dust concentration of 5 mg m3 (MRE

equivalent 1⁄4 7 mg m3

), only the BOM and UMN/BOM

impactors, which are four-nozzle designs having cutpoints near

0.8 mm, effectively excluded coal dust. The mean TC concentration (Table 4) found with these two impactors was about

129 mg m3

, and the corresponding EC concentration was

about 31 mg m3

. The TC on the final filter of the MSHA

impactor was nearly six times higher than the mean for the

BOM and UMN/BOM impactors, and the loading on the inFig. 5 Particle size distribution for laboratory generated coal dust.

GMD is geometric mean diameter.

Fig. 4 Particle size distributions in nondieselized underground coal mines (D–G). See Table 2 for details on mines. GMD is geometric mean

diameter.

Fig. 3 Particle size distributions in dieselized underground coal mines

(A–C). See Table 2 for details on mines. GMD is geometric mean

diameter.

804 J. Environ. Monit., 2004, 6 , 799–806
house impactor was ten times higher; EC results also

were higher.

4. Summary and conclusions

Our results indicate that the amount of EC contributed by

submicrometer coal dust is relatively small. In a laboratory

test, even when the respirable coal dust concentration was as

high as 5 mg m3 (MRE equivalent 1⁄4 7 mg m3

, which is 3.5

times the US compliance limit), the average EC concentration

found by two impactor designs (UMN/BOM and BOM) was

only 31 mg m3

. Laboratory results are consistent with those

obtained in surveys of nondieselized, underground coal mines,

where low levels (E7 mg m3

) of submicrometer EC were

found by commercial cascade impactors. In some mines, the

EC background (from submicrometer coal dust) may be higher

than a typical background (environmental) level, but it is still

quite low relative to EC concentrations in dieselized mines.

Thus, with an appropriate sampler design, NIOSH 5040 most

likely can be used in many coal mines for DPM exposure

monitoring and evaluation of emission controls. Monitoring

DPM in underground coal mines is important because concentrations are often quite high.

A commercial version of the UMN/BOM and BOM

impactors was recently introduced by SKCs (Catalog no.

225–317, SKCs, 863 Valley View Road, Eighty Four, PA

15330). MSHA recommended this impactor, called the DPM

Cassette, for DPM sampling in metal and nonmetal mines.

Given the intended application (i.e., monitoring DPM mass

concentrations in coal mines) of the original impactors on

which the DPM Cassette design is based, it is likely well suited

for use in underground coal mines. To this end, its efficacy for

DPM EC sampling in the presence of coal dust was recently

investigated. Results of this investigation will appear elsewhere.57

Mention of company name or product does not constitute

endorsement by the Centers for Disease Control and

Prevention.

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