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Windblown Dust Contributes to High PM25
Concentrations
Candis S. Claiborn a , Dennis Finn a , Timothy V. Larson b & Jane Q. Koenig c
a Department of Civil & Environmental Engineering , Laboratory for Atmospheric
Research , Washington State University , Pullman , USA
b Department of Civil & Environmental Engineering , University of Washington ,
Seattle , USA
c Department of Environmental Health , University of Washington , Seattle , USA
Published online: 27 Dec 2011.
To cite this article: Candis S. Claiborn , Dennis Finn , Timothy V. Larson & Jane Q. Koenig (2000) Windblown Dust
Contributes to High PM25 Concentrations, Journal of the Air & Waste Management Association, 50:8, 1440-1445, DOI:
10.1080/10473289.2000.10464179
To link to this article: http://dx.doi.org/10.1080/10473289.2000.10464179
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Claiborn, Finn, Larson, and Koenig
TECHNICAL PAPER
ISSN 1047-3289 J. Air & Waste Manage. Assoc. 50:1440-1445
Copyright 2000 Air & Waste Management Association
Windblown Dust Contributes to High PM2.5 Concentrations
Candis S. Claiborn and Dennis Finn
Laboratory for Atmospheric Research, Department of Civil & Environmental Engineering, Washington State
University, Pullman
Timothy V. Larson
Department of Civil & Environmental Engineering, University of Washington, Seattle
Jane Q. Koenig
Department of Environmental Health, University of Washington, Seattle
ABSTRACT
have distinctly different sources, transformations, removal
pathways, chemical compositions, optical properties, and
deposition mechanisms in the human respiratory tract.1
Fine-mode PM is primarily anthropogenic in origin. Typi-
cally, it results either from condensation of hot combus-
tion vapors (nuclei mode, 0.005–0.1 µm, not accounting
for much mass), or from the coagulation of nuclei par-
ticles and condensation of vapors onto existing particles
(accumulation mode, from 0.1 to ~3 µm, accounting for
most of the fine particulate mass). Coarse-mode PM, typi-
cally > ~1 µm, tends to result from mechanical processes
and contains a significant portion of geological material.
There is some overlap between fine-mode and coarse-
mode PM in the particle size range of approximately
1–3 µm aerodynamic diameter. In this paper, we distin-
guish between fine-mode PM and PM2.5 in that the PM2.5
cut point allows for capture of most of the fine-mode PM
but also includes coarse-mode PM in the fine size fraction.
The recent attempt by the U.S. Environmental Pro-
tection Agency to revise the National Ambient Air Qual-
ity Standards for PM to include a fine PM standard targets
fine-mode particles.2 The measure of fine particles, for
regulatory purposes, is based upon gravimetric measure-
ment of PM collected in a device with a 50% cut point at
an aerodynamic diameter of 2.5 µm (PM2.5). Given the
overlap between fine- and coarse-mode PM between 1 and
3 µm, such a device, intended to collect fine-mode par-
ticles, can potentially collect some coarse-mode particles
as well, thus introducing a positive error in the fine-mode
particle mass measurement. This may be particularly true
in arid and semi-arid areas that are subjected to relatively
high fugitive dust emissions.
The revised National Ambient Air Quality Standards for
PM include fine particulate standards based upon mass mea-
surements of PM2.5. It is possible in arid and semi-arid re-
gions to observe significant coarse mode intrusion in the
PM2.5 measurement. In this work, continuous PM10, PM2.5,
and PM1.0 were measured during several windblown dust
events in Spokane, WA. PM2.5 constituted ~30% of the PM10
during the dust event days, compared with ~48% on the
non-dusty days preceding the dust events. Both PM10 and
PM2.5 were enhanced during the dust events. However, PM1.0
was not enhanced during dust storms that originated within
the state of Washington. During a dust storm that origi-
nated in Asia and impacted Spokane, PM1.0 was also en-
hanced, although the Asian dust reached Washington
during a period of stagnation and poor dispersion, so that
local sources were also contributing to high particulate lev-
els. The “intermodal” region of PM, defined as particles
ranging in aerodynamic size from 1.0 to 2.5 µm, was found
to represent a significant fraction of PM2.5 (~51%) during
windblown dust events, compared with 28% during the
non-dusty days before the dust events.
INTRODUCTION
Atmospheric PM is commonly thought of as containing
fine-mode and coarse-mode particles. These two modes
IMPLICATIONS
If the objective of implementing a new PM standard is to
regulate fine-mode rather than coarse-mode particles,
then the use of a PM2.5 inlet may positively bias the mea-
surement during dust storms, due to the inclusion of
coarse-mode PM. The use of a 1.0-µm cut point diam-
eter should reduce this error for arid and semi-arid re-
gions that are prone to windblown dust.
In Spokane, WA, a semi-arid, western city with
nonattainment status for PM10, high particulate
concentrations occur as a result of a number of sources,
1440 Journal of the Air & Waste Management Association
Volume 50 August 2000

Claiborn, Finn, Larson, and Koenig
including combustion processes such as residential wood
combustion, vehicular exhaust, and industrial point
sources, and also fugitive dusts from paved and unpaved
roads and parking lots. Moreover, the expansive area up-
wind of Spokane, in the central and eastern portions of
Washington, is primarily dryland farmland. Due to the
specific farming practices in this area, it is not uncom-
mon for the central and eastern portions of Washington
to experience particulate air pollution from windblown
dust from these areas.3 It has been observed that these
dust storms lead to high concentrations not only of PM10,
but also of PM2.5.4
coarse mode concentration, the coarse-mode PM was cal-
culated for each hour, and the resulting hours were aver-
aged. Similarly, “intermodal” PM (IM) was calculated from
the difference between the PM2.5 and PM1.0 concentrations
on an hourly basis, and the event average was obtained
by averaging the hourly values.
RESULTS
Since 1990, several windblown dust events have impacted
Spokane air quality (Table 1). In the early 1990s, several
dust storms occurred per year. There were no major wind-
blown dust events in 1995 and a brief dust storm in 1994.
In 1998, moderately high PM10 levels were related to long-
range transport of dust from a major windblown dust
storm that originated in Asia. The transport of the Asian
dust storm in late April of 1998 was detected by GOES9
satellite imagery6 and followed by a community of scien-
tists in both Asia and North America.7 The dust plume
was observed to impact southwestern British Columbia
and western Washington State in late April 1998,8 lead-
ing to enhanced PM10 levels over the usual local sources.
A significant regional dust storm occurring on September
25, 1999, led not only to very high concentrations of PM10
in Spokane (Figure 1), but also to a major traffic accident
involving numerous vehicles in north central Oregon.
Real-time PM2.5 and PM10 were measured beginning
January 1994. After this time, it was observed that during
dust events, both PM2.5 and PM10 were enhanced (Figure
The objective of this study is to examine real-time
concentrations of PM10, PM2.5, and PM1.0, in order to evalu-
ate PM2.5 compared with PM1.0 as an appropriate indicator
of fine-mode PM during dust storms occurring in a semi-
arid city.
METHODS
Real-time mass concentrations were made in Spokane for
PM10 and PM2.5, using tapered element oscillating mi-
crobalances (TEOMs) (Rupprecht and Patashnik) equipped
with PM10 and PM2.5 inlets. TEOMs with PM2.5 inlets were
deployed at two locations in Spokane in 1994 and have
been operating since. The two sites include a residential
site (RW) and an industrial site (CZ). In January 1995, a
TEOM equipped with a PM1.0 inlet (designed by A.
McFarland) was deployed at the residential site, which is
the most extensively instrumented of these two sites. In
addition to real-time PM10, PM2.5, and PM1.0 sampling at
this site, daily, 24-hr samples of both fine- (PM2.5) and
coarse-mode PM (between 2.5 and 8 µm) have been col-
lected since January 1995 and have been analyzed for
chemical species, including elements, via energy-disper-
sive x-ray fluorescence (EDXRF). Additional information
regarding the entire sampling and analysis program is
provided by Finn et al.5
PM data were extracted from the TEOMs as hourly
averages. Data screening was conducted by verifying that,
for collocated instruments, PM1.0 < PM2.5 < PM10. Data were
further screened to remove any negative values. The preci-
sion of the TEOM PM10 measurements was determined by
periodically collocating a second TEOM instrument at each
site. The TEOM PM10 measurement was also compared with
that obtained from a size-selective inlet instrument located
at each site. The TEOM PM2.5 measurement was compared
with that obtained from a versatile air pollutant sampling
system (URG, Inc.) also located at the RW site. Further in-
formation on the performance of these instruments is pro-
vided in Haller et al.4 and Finn et al.5
Table 1. History of dust storms and PM10 since 1990 in Spokane. All PM data were
obtained from TEOM measurements.
Date
24-hr Average
Wind Speed
(m/sec) at CZ
24-hr Average
PM10 (µg/m3)
at CZ
24-hr Average
PM10 (µg/m3)
at RW
9/8/90
1.6
217
342
268
N/A
351
321
803
126
252
185
300
207
167
214
98
160
268
166
251
267
N/A
N/A
132
N/A
N/A
255
100
102
128
80
10/4/90
11/9/90
11/23/90
10/21/91
9/4/92
6.2
8.3
8.6
5.6
5.9
9/12/92
9/13/92
9/26/92
10/8/92
9/11/93
11/3/93
7/24/94
8/30/96
4/29/98
9/23/99
9/25/99
5.3
3.6
4.9
3.3
5.1
3.1 (at airport)
2.7
4.5
<1.0
3.8
For the purpose of this work, coarse-mode PM was
calculated from the difference between the PM10 and PM2.5
concentrations. To obtain the event average value of the
141
401
125
256
5.4
Volume 50 August 2000
Journal of the Air & Waste Management Association 1441

Claiborn, Finn, Larson, and Koenig
1). This was first seen during a brief dust event that oc-
curred in July 1994 (Table 2). During the event, peak
hourly PM10 reached nearly 1200 µg/m3, and peak hourly
PM2.5 approached 150 µg/m3.
Since the deployment of a TEOM equipped with a
PM1.0 inlet at the RW site, four additional windblown dust
events have been observed in Spokane (August 30, 1996;
April 29, 1998; September 23, 1999; and September 25,
1999). During the two September 1999 events, both PM10
and PM2.5 were enhanced; however, PM1.0 remained low
at the RW site (maximum PM1.0 concentration was ap-
proximately 10 µg/m3). Similarly, on August 30, 1996,
both PM10 and PM2.5 increased, but PM1.0 did not (Figure
2). As mentioned earlier, the April 1998 event was a
multiple-day dust episode that was attributed to long-
range transport of dust from Asia. The peak of the event
occurred in Spokane on April 29, 1998. In that case, the
ratio of PM2.5 to PM10 was somewhat higher (0.37) than
RW PM10
CZ PM10
RW PM2.5
CZ PM2.5
Date, Time
Figure 1. Hourly PM in Spokane for a windblown dust event, September 23–25, 1999. CZ denotes the industrial site and RW the residential/light
commercial site.
Table 2. PM10 and PM2.5 concentrations measured in Spokane using TEOMs during recent windblown dust events.
Date
24-hr PM10
Maximum 1-hr
PM10 (µg/m3)
24-hr PM2.5
Maximum 1-hr
PM2.5 (µg/m3)
24-hr PM1.0
Maximum 1-hr
PM1.0 (µg/m3)
(µg/m3)
(µg/m3)
(µg/m3)
7/24/94
RW/CZ
8/30/96
RW/CZ
4/29/98
RW/CZ
9/23/99
RW/CZ
9/25/99
RW/CZ
102/167
128/214
80/98
1105/1879
415/717
113/
21/22
25/29
29/
123/127
52/72
44/
NAa/NAb
13/NA
14/NA
8/NA
NA/NA
49/NA
22/NA
8/NA
125/141
256/401
450/425
922/1483
16/NA
22/27
29/NA
65/91
6/NA
10/NA
Notes: aPM1.0 was not available at the RW site until January 1995; bThere was no PM1.0 device at the CZ site.
1442 Journal of the Air & Waste Management Association
Volume 50 August 2000

Claiborn, Finn, Larson, and Koenig
PM10
PM2.5
PM1.0
Hour
Figure 2. Hourly PM for an August 30, 1996, dust storm, at the residential site (RW) in Spokane.
that for the other events (ranging from 0.20 to 0.37)
(Table 3), which is consistent with the longer lifetime of
PM2.5 compared with PM10. This period was also a time
of poor dispersion, so it is likely that the higher PM2.5
was affected by local sources as well. In general, the ra-
tio of PM2.5 to PM10 was quite variable, ranging for the
non-dust days from 0.33 (September 22, 1999) to 0.75
(August 29, 1999). Haller et al.4 reported that, from July
1994 through November 1995, the average
day before each windblown dust event, but for the dust
event days (including the Asian dust event), it com-
prised 51% of the PM2.5 on average.
DISCUSSION
The IM often represents a small fraction of PM2.5; how-
ever, during arid conditions in regions susceptible to
fugitive dusts and windblown dust storms, this fraction
ratio of PM2.5 to PM10 in Spokane, obtained
Table 3. Comparison of coarse-mode PM (PM10 – PM2.5), IM (PM2.5 – PM1.0), and fine PM (PM1.0), for five
windblown dust events and the non-dusty day before the event. All PM data were taken from TEOM measure-
ments. All values for the individual events and the non-dusty day before the event were calculated from hourly
values and averaged for the day.
from TEOM measurements, was approxi-
mately 50%. The ratio of PM2.5 to PM10 on
the dust episode day was significantly
smaller than the ratio on the non-dust day
before.
Date
Coarse Mode
IM
PM1.0
IM/PM2.5
PM2.5/PM10
The IM was enhanced during the dust
storms of September 23 and 26, 1999 (Fig-
ure 3), and August 30, 1996 (Figure 4), while
the fine-mode PM, as determined from
PM1.0, was not. For the dust event of April
29, 1998, the fine mode (PM1.0) was also
high, and possibly enhanced, as well (Table
3). The Asia dust event reached Washing-
ton during a stagnant period of poor dis-
persion conditions,8 and it is speculated that
the higher values of PM1.0 during the April
1998 event in Spokane were due at least in
part to local sources. The IM comprised, on
average, 28% of the PM2.5 for the non-dusty
7/23/94 (non-dust)
7/24/94 (dust)
22
94
NAa
NA
6
NA
NA
21
13
11
8
NA
NA
0.41
0.28
0.75
0.37
0.33
0.20
8/29/96 (non-dust)
8/30/96 (dust)
11
0.25
0.48
0.29
0.48
104
31
13
5
9/22/99 (non-dust)
9/23/99 (dust)
109
8
9/25/99 (dust)
4/27/98 (non-dust)
4/29/98 (dust)
Average non-dust
Average dust
234
25
19
4
6
0.55
0.29
0.51
0.28
0.51
0.29
0.39
0.37
0.47
0.30
10
14
14
10
51
15
5
22
118
14
Note: aThe PM1.0 instrument was not available for the 1994 event as it was deployed in January 1995.
Volume 50 August 2000
Journal of the Air & Waste Management Association 1443

Claiborn, Finn, Larson, and Koenig
PMCF
PM1.0
IM
Date, Time
Figure 3. Hourly PM at the residential site (RW) in Spokane for September 22–26, 1999. PMCF is the coarse fraction PM (PM10 – PM2.5). IM is the
intermodal fraction (PM2.5 – PM1.0).
PMCF
PM1.0
IM
Local Time
Figure 4. Hourly PM1.0, intermodal (IM), and coarse fraction PM (PMCF) in Spokane for August 30, 1996.
1444 Journal of the Air & Waste Management Association
Volume 50 August 2000

Claiborn, Finn, Larson, and Koenig
can comprise a significant contribution of coarse-mode
PM. Observations consistent with this have been made
previously in Spokane and in Phoenix, AZ, another arid
city. An analysis of chemical speciation data from Phoe-
nix (March–December 1995) showed that the intermodal
fraction was correlated to the PM2.5 soil fraction as calcu-
lated from a mass attribution model based upon EDXRF
analysis.4 Haller et al.4 noted that, in Spokane, the IM was
statistically correlated to the coarse-mode fraction (at the
95% confidence level) during the summer (June–August)
which, in Spokane, is hot and dry (the correlation coeffi-
cient was 0.62 for summer). However, the IM was not cor-
related to either the fine or coarse fraction for other seasons
(during which the correlation coefficient ranged from 0.02
to 0.21).
This work has not been reviewed by either EPA or
WADOE and does not necessarily reflect the views of ei-
ther agency. The mention of trade names does not con-
stitute an endorsement of the instruments mentioned.
REFERENCES
1. Seinfeld, J.; Pandis, S. Atmospheric Chemistry and Physics; John Wiley
and Sons: New York, 1998.
2. National Ambient Air Quality Standards for Particulate Matter: Pro-
posed Decision; 40 CFR 50 61 (241); Fed. Regist. 1996, 61 (241).
3. Claiborn, C.; Lamb, B.; Miller, A.; Beseda, J.; Clode, B.; Vaughan, J.;
Kang, L.; Newvine, C. Regional Measurements and Modeling of Wind-
blown Agricultural Dust: The Columbia Plateau PM10 Program; J.
Geophys. Res. 1998, 103, 19,753-19,767.
4. Haller, L.; Claiborn, C.; Larson, T.; Koenig, J.; Norris, G.; Edgar, R.
Airborne Particulate Matter Size Distributions in an Arid Urban Area;
J. Air & Waste Manage. Assoc. 1991, 49, 161-168.
5. Finn, D.; Rumburg, B.; Claiborn, C.; Larson, T.; Koenig, J. Chemical
Characterization of Fine Particulate Air Pollution in Spokane, Wash-
ington. Presented at PM2000: Particulate Matter and Health, Charles-
ton, SC, January 2000.
6. Bachmeier, S. Asian Dust over the Pacific Ocean, 22-24 April, 1998.
http://cimss.ssec.wisc.edu/goes/misc/980424.html, accessed August
2000.
CONCLUSION
7. Husar, R.B.; Tratt, D.M.; Schichtel, B.A.; Falke, S.R.; Li, F.; Jaffe, D.;
Gasso, S.; Gill, T.; Laulainen, N.S.; et al. The Asian Dust Events of
April 1998; J. Geophys. Res., in press.
8. McKendry, I.G.; Hacker, J.P.; Sakiyama, S.; Mignacca, D.; Reid, K. Long-
Range Transport of Asian Dust to the Lower Fraser Valley, British
Columbia, Canada: A Case Study; J. Geophys. Res., in press.
These results show that windblown dust events enhance
both PM10 and PM2.5 in a semi-arid airshed. This work has
also shown that PM1.0 is not necessarily enhanced during
dust storms. The results are consistent with a previous
study in Spokane that showed that the intermodal PM
(between 1.0 and 2.5 µm in aerodynamic diameter) is sig-
nificantly correlated to the coarse mode during the hot,
dry season. Results from Phoenix4 are also consistent with
these findings in that the fine particulate soil fraction in
that arid city is correlated to the intermodal fraction.
True fine-mode PM would not be expected to be af-
fected by windblown dust. If the objective of the recently
proposed PM standards is to regulate fine-mode rather
than coarse-mode PM, then the use of PM2.5 inlets may
introduce a positive bias during windblown dust storms
due to the inclusion of coarse-mode PM. The use of a
1.0-µm cut point inlet should reduce this error in arid or
semi-arid regions.
About the Authors
Candis S. Claiborn, Ph.D., is an associate professor in the
Laboratory for Atmospheric Research, Department of Civil
& Environmental Engineering, at Washington State Univer-
sity, Pullman, WA. Dennis Finn, Ph.D., is a postdoctoral fel-
low in the Laboratory for Atmospheric Research at Wash-
ington State University in Pullman. Timothy V. Larson, Ph.D.,
is a professor of environmental engineering in the Depart-
ment of Civil & Environmental Engineering at the University
of Washington, Seattle, WA. Jane Q. Koenig, Ph.D., is a
professor in the Department of Environmental Health and
the program director for the UW/EPA Northwest Research
Center for Particulate Air Pollution and Health at the Uni-
versity of Washington in Seattle.
ACKNOWLEDGMENTS
The authors wish to acknowledge funding for this project
from the U.S. Environmental Protection Agency (EPA) and
the Washington State Department of Ecology (WADOE).
We are grateful to the Spokane County Air Pollution Con-
trol Authority for assistance with obtaining air quality and
meteorological data, and for access to the Rockwood
monitoring site for locating additional sampling equip-
ment. We also appreciate the work of Matt Cosselman at
Washington State University for his assistance.
Volume 50 August 2000
Journal of the Air & Waste Management Association 1445