A severe dust storm event originated from the Gobi Desert in Central and East
Asia during 2–7 May 2017. Based on Moderate Resolution Imaging
Spectroradiometer (MODIS) satellite products, hourly environmental monitoring
measurements from Chinese cities and East Asian meteorological observation
stations, and numerical simulations, we analysed the spatial and temporal
characteristics of this dust event as well as its associated impact on the
Asia-Pacific region. The maximum observed hourly PM
MODIS Terra images showing dust outbreak across East Asia from 2 to 7 May 2017. Red stars, rectangles, and circles indicate Beijing, Seoul, and Tokyo, respectively.
A major dust storm arose and swept over East Asia on 2–7 May 2017. This dust
storm originated from the deserts of Central and East Asia, namely the
Mongolian Gobi Desert, the Taklimakan Desert, the Hexi Corridor, and the Alxa Desert
(Figs. 1 and 2). Visibility was reduced to
Location of environmental monitoring stations in the Chinese mainland and lidar monitoring stations in East Asia.
Dust aerosols can be transported long distances, even on a global scale from
Africa to the Americas or from Asia to North America (Merrill et al., 1994;
Uno et al., 2009; Shao et al., 2011a). Atmospheric dust has been observed
across continents and oceans, giving rise to its importance in both
terrestrial and marine ecosystems (Huebert et al., 2003; Mahowald et al.,
2009; IPCC, 2013; Kok et al., 2017). Mineral aerosols can influence air
quality by reducing visibility and bolstering concentrations of inhalable
particulate matter (Sharratt and Lauer, 2006; Huneeus et al., 2011; Goudie,
2014). In dust source regions, atmospheric dust concentrations can approach
1–10 mg m
Asian dust has long been an environmental concern to China, which notably has affected the formation of the Loess Plateau and historic Chinese civilization (Tsoar and Pye, 1987; An et al., 1991; Zhang et al., 1996; An, 2000; Husar et al., 2001; Chen et al., 2014; Goudie, 2014; Huang et al., 2014). To quantify and assess the impact of dust cycles on the environment, remote sensing (i.e. satellite) and modelling techniques based on physical processes must be used along with environmental monitoring data and surface observations (Shao et al., 2011a). Few studies, however, have combined the use of these techniques and monitoring data to document the fate of dust in the atmosphere and especially the range of transport of dust from its source in East Asia. Trans-Pacific transport not only has the potential to impact the North Pacific marine environment, but also air quality of communities within and downwind of the source region. The purpose of this study was therefore to determine dust emission, transport, and deposition during the May 2017 Asian dust storm using environmental observations and remote sensing data along with simulation techniques.
Ambient particulate matter concentration related to air pollution levels in China.
Air quality data were collected from China and the United States during the
May 2017 dust storm event. In China, hourly PM
In the United States, hourly ambient PM
Moderate Resolution Imaging Spectroradiometer (MODIS) Terra satellite data were collected from the U.S. National Aeronautics
and Space Administration (
The CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite
Observations) satellite was launched on 28 April 2006 to study the roles of
clouds and aerosols on climate and weather. The satellite carries three
instruments: the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), the Imaging Infrared Radiometer (IIR), and the Wide Field Camera
(WFC). Passive and active remote sensing instruments on the satellite
continuously monitor aerosols and clouds at a temporal and spatial resolution
of 0.74 s and 333 m, respectively. We used CALIPSO AOD data at 532 nm of the Vertical Feature Mask (VFM) level 2 version 4.10 to
analyse mineral dust transport across the North Pacific Ocean. The use of CALIPSO products
(
List of lidar observation stations in this study.
Meteorological data, including synoptic conditions, surface wind speed, and
visibility, for more than 2000 meteorological observation stations in East
Asia were collected from the China Meteorological Administration.
Observations were taken every 3 h. Dust conditions at each station
were defined by visibility and subjective synoptic reports according to World
Meteorological Organization (WMO) protocol. Both “present weather” and
“past weather” conditions were recorded by the meteorological observer with
descriptions in specified format and codes. Codes were used to designate the
intensity and duration of dust periods
(
Lidar data, which were used to examine the vertical distribution of dust in
the atmosphere, were collected from the Asian dust observation network, AD-Net
(
The Weather Research and Forecasting with Chemistry (WRF-Chem) model (version 3.7.1 available at
Observations of PM
We used the FLEXPART model (FLEXible PARTicle model, version 9.0.2, available at
Hourly air quality index as observed for major stations in China
during 2–7 May 2017. The PM
Distribution of mean AOD at 550 nm derived from the MODIS Terra Deep Blue product in East Asia during 2–7 May 2017.
Figure 1 shows an overview of the severe dust storm that developed over East
Asia on 2–7 May 2017 using data from the MODIS Terra sensor. The dust storm
originated in the Mongolian Gobi Desert, the Hexi Corridor, and the Taklimakan Desert
on 2 May 2017. Dense dust clouds formed initially over southern Mongolia and
western Inner Mongolia on 2–3 May 2017, then moved quickly across northern and
northeastern China and migrated pervasively into the southeast China coast, the Korean Peninsula, and Japan. On 4 May, yellow dust clouds masked the North
China Plain and northeastern China as these regions were not visible from space.
The strongest dust plumes were observed over southern Mongolia and western Inner
Mongolia on 3 May 2017. Dust signals were accordingly captured in the Yellow
Sea and the East China Sea on 4–6 May, and in the north of the Sea of Japan and Sea of
Okhotsk on 6–7 May. Figure 3 depicts the movement of dust clouds across
continental China according to the spatio-temporal variation in average hourly
PM
Maximum wind speed across East Asia during 2–7 May 2017. Land cover types in East Asia are derived from global land cover products published by the European Space Agency (ESA).
Airborne dust is one of the chief pollutants influencing air quality in China (Zhang et al., 2010). Thus, the relative contribution of mineral dust to the AQI was analysed to identify the impact of airborne dust on air quality in major cities of China. We examined the relative contribution of dust to AQI at Alxa, Erdos, and Hohhot in the arid region of northern China, Beijing, Tianjing, and Shijiazhuang in the North China Plain, Xi'an, Zhengzhou, and Qingdao in central China, and Wuhan, Nanjing, and Shanghai in southeastern China (Fig. 4). The data suggest that atmospheric dust pollution decreased from north to south and from west to east (inland to coast). Degraded air quality would have affected more than 700 million Chinese people living in the path of the dust storm.
MODIS AOD, with a quality assurance confidence (level 2 single pixel
measurements) of 3 over land and
Lidar profile of dust vertical distribution in Beijing, Seoul, Matsue, Osaka, and Tokyo during 2–10 May 2017. Colours indicate depolarization ratio observed in ground lidar.
Dust storms are typically caused by anticyclone conditions that result in
high winds across northwestern China (Shao, 2000). The magnitude of wind speed
is one of the main factors influencing dust emission, transport and
deposition processes (Pye, 1987; Liu et al., 2005). Dry soil particles were
uplifted from the surface by aerodynamic forces under strong winds,
generating dust emission. The uplift of particles or initiation of wind erosion
generally occurs at wind speeds above 7 m s
The observed temporal and vertical dust layering structures and dust mass
concentration provide information for the validation of dust transport simulation
studies. These dust characteristics were identified by lidars and suggest the
transport and dispersion of dust originating in northwestern China were
influenced by strong atmospheric circulation forcing. Figure 7 illustrates
lidar observations of vertical dust profiles in Beijing, Seoul, Matsue,
Osaka, and Tokyo from 2 to 10 May 2017. Airborne dust appeared to be uplifted to
altitudes of 1.5–3.5 km. Dust was clearly visible in lidar observations
beginning on 2 May in Beijing and Seoul and ending in the Korean Peninsula
and Japan on 9 May. The detection of dust in Beijing and Seoul on 2 May
indicates the rapidity of transport of dust from northwestern China. The
layering structures from lidars were identified as dust using the
depolarization ratio. Unfortunately, lidar observations in Beijing were not
possible on 6 May due to routine maintenance. In the lidar measurement for
this study, the well-mixed boundary layers in East Asia, prior to the obvious
intermingling of subsiding layers from above, show depolarization ratios
150–250 % higher than boundary layers in North America (Cottle et al.,
2013a). This indicates that dust clouds moved across the North China Plain at
altitudes
Dust arising from the surface during wind erosion events may be transported
along different pathways in the atmosphere due to variations in atmospheric
circulation and vertical mixing within the atmosphere across events (Satake
et al., 2004). To provide insight into dust flow trajectories and the impact of
dust from the potential sources (discussed in Sect. 3.2) on regions downwind
of the source, Fig. 8 depicts the 9-day forward trajectories of dust
particles from 2 May 2017 (00:00 UTC) by the FLEXPART model. This numerical
experiment identified the location of dust emissions according to the ground
observations by WMO. Simulations indicated dust particles were released from
source regions with an intensity of 1000 mg m
Forward trajectory analysis of dust transport (units:
Estimation of daily dust emission
The long-range transport of dust is influenced by dry and wet depositional
processes (Shao and Dong, 2006; Tanaka and Chiba, 2006; Zheng et al., 2016).
Atmospheric mineral dust and subsequent deposition in the ocean is an
important source of iron in high-nutrient, low-chlorophyll (HNLC) oceanic
regions (Mahowald et al., 2009). The intensity of dust deposition on land or
ocean can exceed 100 g m
Vertical profiles of atmospheric features derived from
CALIPSO satellite VFM data on 7 May
Estimates of atmospheric dust emission and deposition over the Asian-Pacific region during 2–10 May 2017.
Transport of dust emitted from East Asian desert sources is highly dependent on atmospheric circulation (Zhang et al., 1997). The Eurasian atmospheric circulation greatly influences weather of East Asia and is primarily driven by the strength of the Asian monsoon and the Siberian High (Park et al., 2011; Shao et al., 2013). Strong winds associated with these atmospheric circulations cause large amounts of mineral dust to be emitted into the atmosphere and then redeposited after long-range transport through wet scavenging and dry settling. According the WRF-Chem model, dust emitted from East Asian Gobi Desert sources on 2 May took 3, 3.5, and 7 days to reach the Korean Peninsula, Japan, and the western coast of the United States and Canada, respectively.
The Gobi and sand deserts in East Asia are important sources of global
atmospheric mineral dust (Ginoux et al., 2001; Shao et al., 2013; Chen et
al., 2017a). Atmospheric deposition of mixed Asian dust pollutants can result
in the deposition of many compounds (e.g. sulfate, nitrate, ammonium, base
cations, and heavy metals) in remote areas (Carrico et al., 2003; Li et al.,
2012). Figure 10 displays the vertical profile variations over the North Pacific
Ocean on 7–8 May 2017. The profiles show atmospheric mineral dust at
latitudes of 35–50
Based upon WRF-Chem simulations, dust was emitted from localized sources in
North America during 2–10 May 2017. Tanaka and Chiba (2006) and Wu et
al. (2018) also suggest that dust is emitted from localized sources in North
America. There was 0.7 Tg of dust emitted across Arizona, Nevada, and the
Sonoran Desert during 2–10 May 2017
according to WRF-Chem simulations. Approximately 0.7 Tg of dust was
deposited across the United States. To visualize the influence of the North
American dust sources on atmospheric dust loading, Fig. S3 displays the
hourly PM
The long-range transport of mineral dust aerosols occurs with high temporal and spatial variability (Mahowald et al., 2017). In addition, dust deposition rates are highly variable as deposition during singular dust storms can account for over 3 % of the annual dust deposition flux (Liu et al., 2004; Zhang et al., 2010). For marine ecosystems, long-range transport and subsequent deposition of mineral dust can result in an influx of nutrients and thereby stimulate growth of aquatic organisms. For example, aeolian dust contains Fe, which is essential to the growth of aquatic organisms such as phytoplankton (Zhuang et al., 1992; Luo et al., 2005; Mahowald et al., 2009, 2017; Tagliabue et al., 2017). Zhuang et al. (1992) proposed that Fe contained in dust may couple with anthropogenic S in the atmosphere and ocean, thereby enhancing solubility and subsequent availability to aquatic organisms. Thus, an influx of nutrients to the ocean during the May 2017 dust event would significantly influence aquatic primary productivity.
Cottle et al. (2013a) and Hu et al. (2016) reported that the long-range transport of Asian dust can impact the Pacific region. Indeed, high-altitude dust clouds from the May 2017 event were observed crossing toward North America as evidenced by CALIPSO retrieval signals in Fig. 10. Dust was observed at heights of approximately 2–8 km over North America on 9–10 May (Fig. S4b and e), a week after initiation of the East Asian dust storm. The source of high-altitude dust over North America may not be entirely from Asia, but could also be attributed to dust emissions from the southwestern US and northern Mexico. Indeed, the WRF-Chem model predicted that 0.7 Tg of dust was emitted from these regions of North America during 2–10 May 2017 (Fig. 9a and Table 3). While we are unable to conclusively determine the source of high-altitude dust over North America, we believe the likely source was Asian dust due to the zonal transport of high-altitude dust from Asia as well as seemingly little dust remaining in the atmosphere after deposition was accounted for (dust emissions and deposition were equal as indicated in Table 3) over the southwestern United States and northern Mexico. Strong signals of dust aerosols were also observed at mid-latitudes in the east North Pacific (Fig. S4a and e).
Asian dust can be transported further north to the Arctic at altitudes of
3–7 km as a result of either a blocking high pressure system in the
northwest Pacific Ocean or a trough–ridge configuration between East Asia and
the North Pacific Ocean (Di Pierro et al., 2011). Mineral dust was observed
throughout the vertical profile over high latitudes near the North Pole on
9 May as indicated by CALIPSO satellite data (Fig. S4a). The
zonal transported dust may mix with ice nuclei at high latitudes through
microphysical nucleation processes and result in cloud formation (Liu et al.,
2012; Yu et al., 2012; Sand et al., 2017). Our simulations showed by the time
the dust had been transported across the Pacific Ocean that
During intercontinental transport, particulate matter more likely remained at low altitudes due to less uplift by thermal eddies and precipitation. The long-range transport of dust aerosols in the troposphere has been detected from satellite and lidar observations. Our results suggest a 3-fold increase in dust deposition over the Pacific Ocean during dust events, emphasizing the importance of dust emission sources from East Asian lands to current ambient particulate matter levels in the environment. In general, long-range-transported Asian dust originated from the Gobi Desert or other sources can significantly elevate ambient particulate matter concentration and affect air quality in major cities of China, Mongolia, the Korean Peninsula, Japan, and far beyond (Uno et al., 2006; Huang et al., 2008, 2017; Mahowald et al., 2009, 2017; Chen et al., 2017b).
The atmospheric environment of East Asia is severely affected by dust emitted
from arid and semiarid regions. This study was undertaken to quantify ambient
PM
The data used in this study are available upon request by contacting the first author (zhangxx@ms.xjb.ac.cn).
The supplement related to this article is available online at:
The authors declare that they have no conflict of interest.
The authors would like to thank anonymous reviewers for their useful comments
that contributed to improving the manuscript. We thank the NASA Goddard Space
Flight Center for providing the MODIS satellite data. We gratefully thank
AD-Net (