JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D23, 8665, doi:10.1029/2002JD003363, 2003
Modeled size-segregated wet and dry deposition budgets of soil dust
aerosol during ACE-Asia 2001: Implications for trans-Pacific
transport
T. L. Zhao and S. L. Gong
Air Quality Research Branch, Meteorological Service of Canada, Toronto, Ontario, Canada
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences,
XiAn, China
X. Y. Zhang
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences,
XiAn, China
I. G. McKendry
Atmospheric Science Programme/Geography, University of British Columbia, Vancouver, British Columbia, Canada
Received 27 December 2002; revised 11 March 2003; accepted 11 April 2003; published 26 August 2003.
[1] Size-segregated budgets of soil dust aerosols in Asia for spring 2001 during ACE-
Asia were investigated using the NARCM model [Gong et al., 2003b]. Simulated mass
size distributions of dust deposition showed a similar size distribution to the dust emission
fluxes over the source regions and a decreased peak corresponding to a 1–3 mm diameter
range over downwind regions. The simulations suggest that dry deposition was a
dominant dust removal process near the source areas and the removal of dust particles by
precipitation was the major process over the trans-Pacific transport pathway, where wet
deposition exceeded dry deposition by up to a factor of 10. The Asian dust deposition
from the atmosphere to the North Pacific Ocean was correlated not only with precipitation
over the North Pacific but also with the dust transport patterns. Variations of monthly
Asian dust outflow were identified with the latitudinal center of transport at 38N in
March, 42N in April, and 47N in May. The monthly trans-Pacific transport patterns of
Asian dust in spring were characterized. The transport axis extended around 30N and
40N from the east Asian subcontinent to the North Pacific in March. A zonal transport
pathway around 40N was well developed in April over the North Pacific and reached
North America. However, the transport in May was separated into two pathways: an
eastward zonal path over the North Pacific and a meridional path from the source regions
to the northeast Asian continent. On the basis of the averaged dust budgets during spring
2001, it was found that the major sources of Asian dust were located in the desert regions
in China and Mongolia with an estimated dust emission of 21.5 tons km2, and the
regions from the Loess Plateau to the North Pacific were sinks of soil dust aerosols with
INDEX TERMS: 0305 Atmospheric
the Loess Plateau as the main sink for Asian dust.
Composition and Structure: Aerosols and particles (0345, 4801); 0322 Atmospheric Composition and
Structure: Constituent sources and sinks; 0368 Atmospheric Composition and Structure: Troposphere—
constituent transport and chemistry; 3210 Mathematical Geophysics: Modeling; KEYWORDS: Asian soil dust,
budgets, deposition, transport patterns, simulation
Citation: Zhao, T. L., S. L. Gong, X. Y. Zhang, and I. G. McKendry, Modeled size-segregated wet and dry deposition budgets of soil
dust aerosol during ACE-Asia 2001: Implications for trans-Pacific transport, J. Geophys. Res., 108(D23), 8665,
doi:10.1029/2002JD003363, 2003.
1. Introduction
[2] Soil dust, produced by wind erosion over arid or
semiarid areas, is a major component of atmospheric
Copyright 2003 by the American Geophysical Union.
0148-0227/03/2002JD003363$09.00
ACE
aerosol. Asian dust storms originate from the high elevation
desert regions in China and Mongolia, where prevailing
monsoon winds with intense frontal activity, mostly during
spring, provide a mechanism for the injection of surficial
material into the lower and middle troposphere [Merrill et
al., 1989; Zhang et al., 1998]. This dust is then transported
thousands of kilometers downwind by westerlies over the
33 - 1
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ZHAO ET AL.: ASIAN DUST DEPOSITIONS AND TRANSPORTS
Pacific Ocean, and on occasion reaches North America
[Duce et al., 1980; Husar et al., 1997, 2001; Jaffe et al.,
1999; Uematsu et al., 1983; Uno et al., 2001]. Long-range
transport of soil dust from natural and anthropogenic
sources has been the subject of intense investigation because it has a considerable impact on climate, air-quality
and biogeochemical processes on a global scale. Soil dust
can affect climate directly by changing the global radiation
budget [Sokolik et al., 2001; Sokolik and Toon, 1996; Tegen
and Fung, 1994] and indirectly by modifying cloud properties and precipitation development [Levin and Gladstein,
1996]. The dust storms not only disrupt human activities but
also link the biogeochemical cycles of land, atmosphere and
ocean [Bergametti, 1998; Zhang et al., 1993]. A geochemically significant quantity of Asian dust, estimated by WMO
[Group of Experts on Scientific Aspects of Marine Pollution
(GESAMP), 1989] to be 400 – 500 Tg, is deposited in the
North Pacific each year.
[3] Because of the atmospheric and geochemical importance of Asian dust storms, an intensive field study was
phased with Aerosol Characterization Experiment (ACE)Asia during spring 2001. This included measurements of
many types of aerosol particles of widely varying composition emitted by human activities and industrial sources, as
well as wind-blown dust at a network of ground stations
along the coast of China, Japan and Korea. These measurements were used to quantify the chemical, physical and
radiative properties of aerosols in the ACE-Asia study area
and assess their spatial and temporal (seasonal and interannual) variability. Surface measurements of soil dust were
made to characterize aerosol properties in Chinese source
regions as a part of ACE-Asia. These also provided size
distributions of Asian dust emission to the numerical
models [Zhang et al., 2003]. To understand the transport
mechanism of Asian dust storms, a regional climate model
with a size-distributed active aerosol algorithm (northern
aerosol regional climate model (NARCM)) was used to
simulate the production and transport of soil dust in east
Asia and over the Northern Pacific Ocean [Gong et al.,
2003b]. The model was driven by NCEP reanalyzed
meteorological fields and included all relevant atmospheric
aerosol processes (i.e., production, transport, growth, coagulation, dry and wet deposition and an explicit microphysical cloud module to treat aerosol-cloud interactions).
A detailed soil texture data set and up-to-date desert
distribution in China was introduced to drive the sizedistributed dust emission module. Comparisons of
NARCM-simulations with both ground based measurements in east Asia and North America, and satellite
observations showed that the model captured most of the
dust mobilization episodes during this period in China. It
also produced reasonable simulations of the dust concentrations in source regions and downwind areas from eastern
China to western North America. The vertical dust loading
above 700 hPa correlated reasonably well with TOMS
aerosol index (AI) observations [Gong et al., 2003b].
[4] NARCM simulation of ACE-Asia soil dust storms for
spring 2001 yielded reasonable spatial and temporal distributions compared with observations. On the basis of the
success of previous NARCM simulations [Gong et al.,
2003b], we extend the focus here to the size distributed
dust budgets including emission fluxes, and dry and wet
deposition. The major objectives of this study are to
(1) characterize the dust emissions over the source regions,
(2) quantify dust deposition from east Asia, over the North
Pacific to western North America, (3) to better quantify the
budgets of the trans-Pacific dust transport, and (4) to present
the meteorological transport pathways of dust outflow from
east Asia to North America.
2. ACE-Asia Simulation
[5] In NARCM a size-segregated multicomponent aerosol mass conservation equation is expressed as follows
[Gong et al., 2003a]:
@cip @cip @cip @cip @cip þ
þ
þ
¼
@t
@t TRANSPORT @t SOURCES @t CLEAR AIR @t DRY
þ
@cip @cip þ
@t IN -CLOUD @t BELOW -CLOUDS
ð1Þ
In equation (1), the rate of change of mixing ratio of dry
particle mass p in a size range i is divided into factor terms
(or tendencies) for transport, sources, clear air, dry
deposition, in-cloud and below cloud processes. The
transport includes resolved motion as well as sub-grid
turbulent diffusion and convection. The sources include
(1) surface emission rate of both natural and anthropogeic
aerosols and (2) production of secondary aerosols (i.e.,
airborne aerosol mass-produced by chemical transformation
of their precursors). The latter together with partical
nucleation, condensation and coagulation contribute to the
clear-air process. Dry deposition of gases and particles
affects the ‘‘dry’’ tendency. Scavenging in in-cloud and
below-cloud processes is regarded as wet deposition of
gases and particles.
[6] NARCM is composed of the Canadian regional
climate model (RCM), a transport model, coupled with
the Canadian aerosol module (CAM) [Gong et al.,
2003a]. RCM uses the physics package from the Canadian
global climate model (GCM) and a semi-Lagrangian and
semi-implicit transport scheme for dynamics and passive
tracers [Robert et al., 1985]. The meteorological boundary
and initial conditions for RCM are driven with the NCEP
reanalyzed meteorological data for spring 2001. NARCM
runs on a stereographic projection with a horizontal resolution of 100 km at 60N and 22 vertical levels on a Gal-Chen
terrain following coordinate system from ground to about
30 km. The integration time step was 20 minutes. Twelve
diameter classes from 0.01 to 40.96mm were used to
represent the size distribution of soil dust (Table 1). All
atmospheric aerosol processes including dust emission
fluxes, concentrations and deposition were calculated for
each size bin. A size distributed soil dust scheme [Alfaro
and Gomes, 2001; Marticorena and Bergametti, 1995;
Marticorena et al., 1997] in NARCM was modified and
driven with a Chinese soil texture scheme that infers the size
distribution with 12 categories and up-to-date desert distribution in China [Gong et al., 2003b]. Combined data sets
for the desert disttribution/texture; satellite land-use/roughness length and observed soil moisture provide a coherent
input parameter set for the soil dust emission scheme for
deserts in east Asia. The model domain covered east Asia,
ZHAO ET AL.: ASIAN DUST DEPOSITIONS AND TRANSPORTS
Table 1. All 12 Size Bins and the Corresponding Aerosol Size in
NARCM
Size Bin Number
Diameter Range, mm
1
2
3
4
5
6
7
8
9
10
11
12
0.01 – 0.02
0.01 – 0.02
0.04 – 0.08
0.08 – 0.16
0.16 – 0.32
0.32 – 0.64
0.64 – 1.28
1.28 – 2.56
2.56 – 5.12
5.12 – 10.24
10.24 – 20.48
20.48 – 40.96
the North Pacific and western North America (Figure 1).
Five regions (A, B, C, D and E) were chosen in the
domain to represent the source region and receptor regions
in China, east Asia, North Pacific and western North
Pacific, respectively. The southernmost edge of the Chinese receptor region was set at 28N, beyond which no
historical records of soil dust deposition were found
[Zhang, 1984]. Region B was further divided into B1
and B2 representing the Loess Plateau and other parts in
China. The NARCM-simulations with four mixed aerosols
of soil dust, sulphate, sea-salt and black carbon were
conducted for four months from 1 February to 31 May
2001. The detailed comparisons of NARCM-simulations
with the surface observations and Total Ozone Mapping
Spectrometer- Aerosol Index (TOMS-AI) are presented by
Gong et al. [2003b]. They showed that the NARCM
provided satisfactory simulations of spatial and temporal
distributions of dust storms in source regions and longrange transport of Asian dust to the North Pacific and
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North America for spring 2001. Here simulations of
March, April, and May are used to investigate Asian dust
budgets including the size-distributed dust emission fluxes,
dry and wet deposition and trans-Pacific transport.
3. Size-Segregated Soil Dust Emission Fluxes
[7] Gong et al. [2003b] identified four major dust source
regions in east Asia: (1) the Taklimakana desert in Xinjiang
Province in west China, (2) Desert groups in west and
middle Inner Mongolia of China, (3) the Onqin Daga
and Horqin deserts in northeast Inner Mongolia of China
and (4) the Gobi desert in Mongolia. Figure 2 shows the
predicted distribution of total dust emission during spring
2001. This was calculated as the sum of emissions from all
12 size bins of soil dust. In addition to major Asian desert
dust sources, there was also dust emissions included from
coastal desert regions around the Pacific Rim, other arid
areas on the Asian Continent and the desert areas of western
North America. Major sources of Asian dust were located in
the desert regions of China and Mongolia with an estimated
dust emission of 21.5 tons km2.
[8] A reasonable size distribution of the vertical dust flux
is required to successfully simulate dust loading, transport
and optical properties [Balkanski et al., 1996]. Ground
based size-segregated aerosol observations (1994 – 2001)
in the vicinity of the Chinese source regions were conducted
using Battle type cascade impactors in the size ranges
<0.25, 0.25 to 0.5, 0.5 to 1, 1 to 2,2 to 4, 4 to8, 8 to 16
and >16 mm in aerodynamic equivalent diameters. The
impactors have a cutoff size of <0.25 mm for the background
mode and >16 mm for the coarse mode. Between 0.25 and
16 mm, the mass size distributions were approximated by a
lognormal fitting of two dust elements (Al and Si) from
Figure 1. Model simulation domain (area with dots) with desert distributions in China (gray scale) and
outside China expressed as fractions of deserts in a grid and shown as contours.
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ZHAO ET AL.: ASIAN DUST DEPOSITIONS AND TRANSPORTS
Figure 2. Total soil dust emission flux distributions during March, April, and May 2001 (ton km2).
desert-sample data in China [Zhang et al., 2003]. Figure 3
shows the average size distributions of simulated vertical
dust fluxes over Chinese deserts at three wind speeds. In
this study, we have assumed that the size distributions of the
vertical soil dust flux are the same as size distributions for
surface soil dust measurements in the source regions.
Therefore, the measured size distributions of surface dust
emission are used as model input.
4. Dry and Wet Deposition
[9] Deposition is the major removal process for aerosol.
In NARCM, deposition includes gas and particle dry and
wet deposition with below-cloud and in-cloud scavenging
[Gong et al., 2003a]. Figure 4 shows the averaged size
distributions of dust deposition modeled over region A, B1,
B2, C, D and E (Figure 1) for spring 2001. The dust
deposition is size dependent (Figure 4). The resultant mass
Figure 3. Size distributions of dust emission fluxes in
Chinese desert regions with surface wind speeds.
size distributions of dust deposition in source region A were
similar to the size distribution of dust emission fluxes with a
peak concentration around 5 mm in diameter. Over the dust
transport pathway away from source region (region B, C, D
and E) the size distributions of deposition showed decreased
peaks corresponding to a 1 – 3 mm diameter. This agrees well
with observations for locations remote from dust sources in
Africa [Dulac et al., 1992], which might be expected to be
reasonably representative of the global mean value.
[10] Figure 5 shows the total dust deposition and ratio of
wet to dry deposition of dust for 1 March to 31 May 2001
for all 12 size bins. The total dust mass deposition ranges
between 0.05 and 500 tons km2 over the NARCM domain.
This range is of the same order of magnitude as that
modeled by Tegen and Fung [1994]. Maximum deposition
was over the dust source regions with most of the emitted
dust redeposited in close proximity to the source. Over
Figure 4. Averaged size distributions of total depositions
in region A, B1, B2, C, D, and E during spring 2001.
ZHAO ET AL.: ASIAN DUST DEPOSITIONS AND TRANSPORTS
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33 - 5
Figure 5. Total depositions (ton km2) and ratio of wet and dry depositions for spring 2001. The
contour lines are for ratio between wet and dry depositions.
Asian source regions, which are arid with low precipitation
(Figure 6), dry deposition is the dominant removal process. On the entire model domain total dry deposition was
also greater than wet deposition with respect to dust mass
deposition because a major part of dust deposition occurred over source areas (Table 1). Nevertheless, on the
pathway of trans-Pacific dust transport, wet deposition
exceeded dry deposition by a factor of 10 (Figure 5).
Wet deposition as a function of precipitation is the major
process of soil dust removal from the atmosphere to ocean
in the North Pacific (Figure 5). Climatologically, precipitation increases from March to May in spring in the North
Pacific. Because of this, wet deposition showed an increasing contribution to the total deposition from March to
May. The modeled averaged fractions of wet deposition to
total deposition over the North Pacific in the model
domain (Figure 1) during spring 2001 rose from 74% in
March, to 77% in April and to 81% in May. The
geographic distribution of dust deposition (Figure 5) is
similar to the pattern of precipitation, especially over the
regions remote from dust sources (Figure 6). These results
indicate that dry deposition is a dominant dust removal
process near the source areas whereas the removal of dust
particles by precipitation is the major process of dust
deposition during the trans-Pacific transport of Asian dust.
[11] Dust storms in China are most frequent in April
when approximately one third to one half of dust storms
occur [Liu et al., 1985]. Similarly, the NARCM-simulation
indicated that the monthly averaged dust emission over
region A (Figure 1) was 5.36 tons km2, 12.71 tons km2
Figure 6. Simulated precipitation (mm) during spring 2001.
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ZHAO ET AL.: ASIAN DUST DEPOSITIONS AND TRANSPORTS
Table 2. Dust Emission and Removal by Dry and Wet Deposition
in Spring 2001
Region
Emission
Dry Deposition,
ton/km2
Wet Deposition,
ton/km2
Balance
A
B1
B2
C
D
E
21.50
2.81
0.31
1.17
1.13
0.45
11.72
5.75
1.79
1.10
0.66
0.27
1.35
2.90
1.81
1.96
0.53
0.11
8.42
5.84
3.29
1.89
0.06
0.07
the regionally averaged positive dust balance between
emission and deposition in region E.
[13] As the prevailing winds over the model domain in
the mid-latitude free troposphere are westerly, most dust
transport from east Asia is expected to be zonal. Therefore
the product of dust concentration and zonal wind component U (i.e., zonal dust transport flux) can be used to
estimate the amount and direction of atmospheric dust
transport. Positive (negative) dust transport fluxes indicate
eastward (westward) transport of dust aerosol. Figure 7
illustrates the monthly averaged dust exports from east
and 3.43 tons km2 in March, April, and May 2001,
respectively. However, the monthly averaged dust deposition in the North Pacific Ocean was 64.19 kg km2 in
March, 61.66 kg km2 in April and 48.92 kg km2 in May
2001. This difference between dust emission from the
source regions and dust deposition in the North Pacific is
caused by changes of dust transport patterns. These are
governed by seasonal changes in the atmospheric general
circulation, especially emergence of a trough in the midlatitude westerlies extending from the Asian continent to the
North Pacific [Gong et al., 2003b]. Asian dust deposition
from the atmosphere into the North Pacific Ocean is
therefore related not only to precipitation over the North
Pacific, but also to the dust transport patterns. The transPacific transport pattern of Asian dust will be discussed in
the next section.
5. Asian Dust Budget and Trans-Pacific
Transport
[12] Table 2 presents modeled dust budgets (balance of
emission and deposition) over regions A, B1, B2, C, D
and E. During the months of March, April, and May 2001
a regionally averaged total of 21.5 tons km2 of dust from
region A was emitted into the model domain. Although
more than half of the emitted dust particles were redeposited onto Region A (dry deposition of 11.72 tons km2
and wet deposition of 1.35 tons km2) Region A was the
major Asian dust source. It had the largest contribution of
dust loading to the atmosphere with a net dust export of
8.42 tons km2. The regionally averaged dust emissions
over region B1, B2, C and D were produced only from the
local arid, semiarid or coast desert areas there. From
averaged dust budgets, however, it is apparent that there
were negative dust balances between emission and deposition over region B1, B2, C and D (from the Loess Plateau
to the North Pacific). This indicates that these areas are net
sinks for Asian soil dust. Region B1 (Loess Plateau) is the
principal sink for Asian dust (largest negative dust balance). Asian dust storms originating mainly from region A
(western and northern China and Mongolia), are widely
considered to be the major sources for Asian dust contributing to loess matter deposited on the Loess Plateau and
marine sediments in the North Pacific [Blank et al., 1985;
Liu et al., 1985; Merrill et al., 1994; Merrill et al., 1989;
Prospero, 1981; Zhang et al., 1996]. They also play an
important role in trans-Pacific dust transport and biogeochemical links between land, atmosphere and ocean in the
Northern Hemisphere. The desert areas in western North
America (Figure 1), another major dust source in the North
Hemisphere [Orgill and Sehmel, 1976], are responsible for
Figure 7. Monthly averaged zonal dust transport flux
(mg m2 s1) through 130E in (a) March, (b) April, and
(c) May.
ZHAO ET AL.: ASIAN DUST DEPOSITIONS AND TRANSPORTS
Figure 8. Averaged zonal dust transport flux (mg m2 s1)
through 140W in spring from east Asia. The dotted lines
indicate a flux flowing from west to east.
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33 - 7
(Figure 9b). Climatologically, stronger mid-latitude winds
prevailed in the middle troposphere between 40N and
45N, and zonal circulation dominated between east Asia
and the west Pacific. This is an ideal situation for transPacific transport of Asian dust [Husar et al., 2001]. In May,
the dust transport was separated into two pathways: an
eastward zonal path over the North Pacific and a meridional
path from China to the Northeast Asian continent (Figure 9c).
The larger dust transport was on the meridional path. This
transport pattern in May weakened the strength of dust
transport and deposition over the North Pacific. It should
be noted in Figure 9, that only Asian dust was engaged in this
high level long-range transport across the Pacific; dust from
the other emission sources in the model domain (Figure 2)
only influenced the surface-level.
6. Conclusions
Asia through 130E from March to May. Most of the dust
export occurred in the lower troposphere between 1 km
and 3 km with the center of dust export moving from
about 38N in March (Figure 7a), to 42N in April (Figure
7b) to 47N in May (Figure 7c). This northward movement of maximum dust export corresponds with the
northward motion of the westerly jet in the North Hemisphere from March to May. Figure 8 shows the altitudelatitude dependence for the averaged zonal dust transport
fluxes in spring at 140W entering North America. Simulated Asian dust transport peaks at around 6 km between
40N and 45N over the eastern North Pacific. Observations over North America during a particularly intense dust
transport event in April 1998 indicate that the dust layer
was concentrated between 5 and 10 km [Husar et al.,
2001; Tratt et al., 2001]. The NARCM simulation for
spring 2001 is therefore in broad agreement with previous
observations of the vertical distribution of Asian dust over
North America.
[14] Regional-scale transport of Asian desert is dominated
by surface-level winds of the Asian winter monsoon [An et
al., 1990]. The Asian winter monsoon is characterized by
the invasion of dry cold air with strong surface winds over
east Asia [Ding, 1994]. Before dust from Asian source
regions reaches the Pacific Ocean or south China under the
influence of northwesterly winter monsoon winds, it is lifted
to the free troposphere and carried by the westerly winds
that are typical of the northern mid-latitudes in the springtime (Figure 7 and 8). Trans-Pacific transport patterns are
closely associated with the global-scale variations of atmospheric circulation, especially of westerlies in the midlatitudes. Most trans-Pacific dust transport occurs in the
middle troposphere, where the zonal dust transport fluxes
are at a maximum. Figure 9 shows the modeled distributions
of monthly averaged zonal dust concentration fluxes at
6000 m in the middle troposphere in March, April, and
May. In March, the main axis of dust transport extended
from around 30N and 40N from the east Asian subcontinent to the mid-Pacific (Figure 9a). Asian dust was
transported eastward across the North Pacific, but not
sufficiently far to reach North America, and deposited into
the Pacific Ocean. This explains the high rate of deposition
in the North Pacific in March. In April, zonal transport
around 40N was well developed over North Pacific
[15] Size segregated Asian dust emission, deposition and
budgets associated with trans-Pacific transport during ACEAsia 2001 were investigated with the NARCM transport
model. The analyses lead to the following conclusions.
[16] 1. The modeled average distribution of dust emission
during 2001 ACE-Asia was in agreement with observations
when the input size distribution of dust emission flux was
derived from the observed size distribution of surface dust
in Chinese deserts. Simulated mass size distributions of
deposition in the source region were similar to the size
distribution of dust emission fluxes. Over the dust transport
pathway far from the source region, the size distributions of
dust deposition showed a decreased peak corresponding to a
diameter of 1 – 3 mm.
[17] 2. Dry deposition is the dominant removal process
over the source regions that are arid with low precipitation.
On the pathway for trans-Pacific transport where precipitation is greater (far from the source regions and in the North
Pacific), wet deposition exceeded dry deposition by up to a
factor of 10. The geographical distribution of dust deposition is similar to the pattern of precipitation, especially over
the regions downwind from the dust sources. The monthly
averaged fractions of wet deposition in total deposition over
the North Pacific during spring rose from about 74% in
March to 81% in May. Wet deposition is the major process
of soil dust removal from the atmosphere over the North
Pacific.
[18] 3. The monthly averaged Asian dust outflow from the
east Asian subcontinent showed peak transport from 38N in
March, 42N in April and 47N in May, respectively. Dust
was lifted from below 3 km in the lower troposphere in east
Asia to around 6 km in the middle troposphere over the North
Pacific and western North America. In March, the transport
axis extended around 30N and 40N from east Asia to the
North Pacific while in April a zonal transport pathway around
40N was well developed over the North Pacific and reached
North America. In May, the transport was separated into two
pathways: an eastward zonal path over North Pacific and a
meridional path from the source regions to the Northeast
Asian continent.
[19] 4. Budget-wise, the desert areas in western and
northern China and Mongolia, where the regionally averaged dust emission was 21.5 tons km2 with a net export of
8.42 tons km2 were found to be the largest contributor to
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ZHAO ET AL.: ASIAN DUST DEPOSITIONS AND TRANSPORTS
Figure 9. Monthly averaged distributions of zonal dust transport flux (mg m2 s1) at 6000 m in
(a) March, (b) April, and (c) May.
the dust transport. The regions from the Loess Plateau to the
North Pacific are shown to be dust sinks with the Loess
Plateau being the principal sink of Asian dust with a net
dust receipt of 5.84 tons km2.
[20] In view of the current state of numerical modeling
studies on Asian dust transport [Kotamarthi and Carmicheal,
1993; Wang et al., 2000; Xiao et al., 1997], especially with
respect to trans-Pacific transport, the NARCM modeling
study described herein represents a first attempt to fully
characterize Asian dust budgets in order to better understand
trans-Pacific transport mechanisms. The success shown for
the ACE-Asia period implies that NARCM could be used to
simulate Asian dust transport, not only in operational mode,
but also for past climatic conditions.
ZHAO ET AL.: ASIAN DUST DEPOSITIONS AND TRANSPORTS
[21] Acknowledgments. The authors wish to thank the Canadian
Foundation for Climate and Atmospheric Sciences (CFCAS) for their
financial support for this research. This research was also supported by
grants from Chinese Academy of Sciences (KZCX2-305), the National Key
Project of Basic Research (G2000048703) and Nature Science Foundation
of China (49825105, 40121303).
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S. L. Gong and T. L. Zhao, Air Quality Research Branch, Meteorological
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5T4. ([email protected])
I. G. McKendry, Atmospheric Science Programme/Geography, University of British Columbia, 251-1984 West Mall, Vancouver, British
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X. Y. Zhang, State Key Laboratory of Loess and Quaternary Geology,
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