Exposure to outdoor fine particulate matter (PM2.5) is a leading risk factor for mortality. We develop global estimates of annual PM2.5 concentrations and trends for 1998–2018 using advances in ...satellite observations, chemical transport modeling, and ground-based monitoring. Aerosol optical depths (AODs) from advanced satellite products including finer resolution, increased global coverage, and improved long-term stability are combined and related to surface PM2.5 concentrations using geophysical relationships between surface PM2.5 and AOD simulated by the GEOS-Chem chemical transport model with updated algorithms. The resultant annual mean geophysical PM2.5 estimates are highly consistent with globally distributed ground monitors (R 2 = 0.81; slope = 0.90). Geographically weighted regression is applied to the geophysical PM2.5 estimates to predict and account for the residual bias with PM2.5 monitors, yielding even higher cross validated agreement (R 2 = 0.90–0.92; slope = 0.90–0.97) with ground monitors and improved agreement compared to all earlier global estimates. The consistent long-term satellite AOD and simulation enable trend assessment over a 21 year period, identifying significant trends for eastern North America (−0.28 ± 0.03 μg/m3/yr), Europe (−0.15 ± 0.03 μg/m3/yr), India (1.13 ± 0.15 μg/m3/yr), and globally (0.04 ± 0.02 μg/m3/yr). The positive trend (2.44 ± 0.44 μg/m3/yr) for India over 2005–2013 and the negative trend (−3.37 ± 0.38 μg/m3/yr) for China over 2011–2018 are remarkable, with implications for the health of billions of people.
The Arabian Peninsula has experienced pronounced interannual to decadal variability in dust activity, including an abrupt regime shift around 2006 from an inactive dust period during 1998–2005 to an ...active period during 2007–2013. Corresponding in time to the onset of this regime shift, the climate state transitioned into a combined La Niña and negative phase of the Pacific Decadal Oscillation, which incited a hiatus in global warming in the 2000s. Superimposed upon a long‐term regional drying trend, synergistic interactions between these teleconnection modes triggered the establishment of a devastating and prolonged drought, which engulfed the Fertile Crescent, namely, Iraq and Syria, and led to crop failure and civil unrest. Dried soils and diminished vegetation cover in the Fertile Crescent, as evident through remotely sensed enhanced vegetation indices, supported greater dust generation and transport to the Arabian Peninsula in 2007–2013, as identified both in increased dust days observed at weather stations and enhanced remotely sensed aerosol optical depth. According to backward trajectory analysis of dust days on the Arabian Peninsula, increased dust lifting and atmospheric dust concentration in the Fertile Crescent during this recent, prolonged drought episode supported a greater frequency of dust events across the peninsula with associated northerly trajectories and led to the dust regime shift. These findings are particularly concerning, considering projections of warming and drying for the eastern Mediterranean region and potential collapse of the Fertile Crescent during this century.
Key Points
The Arabian Peninsula underwent a regime shift in dust activity in the mid‐2000s
A shift in PDO/ENSO led to a prolonged Fertile Crescent drought and crop failure
The drought increased dust generation and transport to the Arabian Peninsula
Annual global satellite-based estimates of fine particulate matter (PM2.5) are widely relied upon for air-quality assessment. Here, we develop and apply a methodology for monthly estimates and ...uncertainties during the period 1998–2019, which combines satellite retrievals of aerosol optical depth, chemical transport modeling, and ground-based measurements to allow for the characterization of seasonal and episodic exposure, as well as aid air-quality management. Many densely populated regions have their highest PM2.5 concentrations in winter, exceeding summertime concentrations by factors of 1.5–3.0 over Eastern Europe, Western Europe, South Asia, and East Asia. In South Asia, in January, regional population-weighted monthly mean PM2.5 concentrations exceed 90 μg/m3, with local concentrations of approximately 200 μg/m3 for parts of the Indo-Gangetic Plain. In East Asia, monthly mean PM2.5 concentrations have decreased over the period 2010–2019 by 1.6–2.6 μg/m3/year, with decreases beginning 2–3 years earlier in summer than in winter. We find evidence that global-monitored locations tend to be in cleaner regions than global mean PM2.5 exposure, with large measurement gaps in the Global South. Uncertainty estimates exhibit regional consistency with observed differences between ground-based and satellite-derived PM2.5. The evaluation of uncertainty for agglomerated values indicates that hybrid PM2.5 estimates provide precise regional-scale representation, with residual uncertainty inversely proportional to the sample size.
The Middle Eastern Shamal is a strong north‐northwesterly wind, capable of lifting dust from the Tigris‐Euphrates basin and transporting it to the Persian Gulf and Arabian Peninsula. The present ...study explores the poorly understood spatial and temporal variability of summer Shamal on the diurnal, seasonal, and interannual time scales, along with its influence on dust storm activity and sensitivity to global patterns of sea surface temperature using a comprehensive set of observational data. Statistics of the summer Shamal season are quantified for the first time, including its onset, termination, duration, and the occurrence of distinct break periods. Based on a multistation criteria, the mean onset and termination of the Shamal season occur on 30 May ± 16 days (1 standard deviation) and 16 August ± 22 days, respectively. Anomalously early (late) onset and termination of the Shamal season are typically associated with La Niña (El Niño) conditions, which favor (inhibit) the development of the Iranian heat low in spring and inhibit (favor) its persistence into late summer. Dust source regions in the Tigris‐Euphrates basin and Kuwait, as well as southeastward dust transport during the summer Shamal, which cannot be detected by satellite aerosol products alone, are identified, for the first time, from the Multiangle Imaging Spectroradiometer plume motion vector products and confirmed by surface observations and lidar data. A close interrelationship has been revealed among summertime dust activity across the eastern Arabian Peninsula, frequency of Shamal days, and duration of the Shamal season on the interannual time scales.
Key Points
Middle Eastern summer Shamal causes increased occurrence of dust storms
Summer Shamal behaves like summer monsoon with variability in onset and termination
Early (late) onset and termination are typically supported by La Niña (El Niño)
Since early 2000, the Multi-angle Imaging SpectroRadiometer (MISR) instrument on NASA's Terra satellite has been acquiring data that have been used to produce aerosol optical depth (AOD) and particle ...property retrievals at 17.6 km spatial resolution. Capitalizing on the capabilities provided by multi-angle viewing, the current operational (Version 22) MISR algorithm performs well, with about 75 % of MISR AOD retrievals globally falling within 0.05 or 20 % × AOD of paired validation data from the ground-based Aerosol Robotic Network (AERONET). This paper describes the development and assessment of a prototype version of a higher-spatial-resolution 4.4 km MISR aerosol optical depth product compared against multiple AERONET Distributed Regional Aerosol Gridded Observations Network (DRAGON) deployments around the globe. In comparisons with AERONET-DRAGON AODs, the 4.4 km resolution retrievals show improved correlation (r = 0. 9595), smaller RMSE (0.0768), reduced bias (−0.0208), and a larger fraction within the expected error envelope (80.92 %) relative to the Version 22 MISR retrievals.
Motivated by limitations in current satellite‐based dust source identification techniques, this study examines dust emissions and concentrations over North Africa and the Middle East during 2000–2016 ...by analyzing stereo and optical products from the Multiangle Imaging SpectroRadiometer instrument on the National Aeronautics and Space Administration polar‐orbiting Terra satellite. Based on the occurrence of fast‐moving, near‐surface dust plumes from the Multiangle Imaging SpectroRadiometer cloud motion vector product, dust sources in the study region are identified in geographical depressions, including the Bodélé Depression, which represents the leading source. The West African El Djouf desert generates substantial dust emissions, which are typically underestimated by aerosol loading‐based dust source identifications. In response to local vegetation cover anomalies, dust emissions and concentrations increased at 15% year−1 over the Middle East and decreased at 12% year−1over the central Sahel during 2001–2013 but partly recovered toward their climatological means afterward.
Plain Language Summary
Dust storm activity exerts significant influence on society and the environment in North Africa and the Middle East. However, identifying dust source regions across this region remains a challenge due to the limitations and uncertainties in the current satellite‐based techniques. Here we present a new dust source identification approach based on dust plume motion, as detected by the Multiangle Imaging SpectroRadiometer instrument aboard the polar‐orbiting Terra satellite. Using the new satellite technique, dust sources in the study region are identified in geographical depressions, including the Bodélé Depression in Chad as the leading source. The West African El Djouf desert generates substantial dust emissions, which are typically underestimated by other dust source identifications. Our joint analysis of Multiangle Imaging SpectroRadiometer plume motion and aerosol data reveals that dust emissions and concentrations increased over the Middle East and decreased over the central Sahel during 2001–2013 but partly recovered afterward.
Key Points
The plume motion‐based approach overcomes limitations present in other techniques and provides an independent identification of dust sources
Dust sources are mostly located in geographical depressions in North Africa and Middle East, highlighting the Bodélé Depression and the West African desert
Dust emissions increased (decreased) across the Middle East (central Sahel) during 2001–2013 but recently returned to their climatological means
The Multi-angle Imaging SpectroRadiometer (MISR)
instrument has been operational on the National Aeronautics and Space
Administration (NASA) Earth Observing System (EOS) Terra satellite since
early ...2000, creating an extensive data set of global Earth observations.
Here we introduce the latest version of the MISR aerosol products. The level
2 (swath) product, which is reported on a 4.4 km spatial grid, is designated as version 23 (V23) and contains retrieved aerosol optical depth (AOD) and
aerosol particle property information derived from MISR's multi-angle
observations over both land and water. The changes from the previous version
of the algorithm (V22) have significant impacts on the data product and its
interpretation. The V23 data set is created from two separate retrieval
algorithms that are applied over dark water and land surfaces, respectively.
Besides increasing the horizontal resolution to 4.4 km compared with the
coarser 17.6 m resolution in V22 and streamlining the format and content,
the V23 product has added geolocation information, pixel-level uncertainty
estimates, and improved cloud screening. MISR data can be obtained from the
NASA Langley Research Center Atmospheric Science Data Center at https://eosweb.larc.nasa.gov/project/misr/misr_table (last access: 11 October 2019). The
version number for the V23 level 2 aerosol product is F13_0023. The level 3 (gridded) aerosol product is still reported at
0.5∘×0.5∘ spatial resolution with results aggregated
from the higher-resolution level 2 data. The format and content at level 3
have also been updated to reflect the changes made at level 2. The level 3
product associated with the V23 level 2 product version is designated as
F15_0032. Both the level 2 and level 3 products are now
provided in NetCDF format.
Motivated by the ongoing debates about the relative contribution of specific North African dust sources to the transatlantic dust transport to the Amazon Basin, the current study integrates a suite ...of satellite observations into a novel trajectory analysis framework to investigate dust transport from the leading two North African dust sources, namely, the Bodélé depression and El Djouf. In particular, this approach provides observation‐constrained quantification of the dust's dry and wet deposition along its transport pathways and is validated against multiple satellite observations. The current large ensemble trajectory simulations identify favorable transport pathways from the El Djouf across the Atlantic Ocean with respect to seasonal rain belts. The limited potential for long‐range transport of dust from the Bodélé depression is attributed to the currently identified extensive near‐source dust removal primarily by dry and wet deposition during boreal winter and summer, respectively.
Plain Language Summary
North African deserts have been reported to export ~200 million tons of dust per year to the tropical Atlantic Ocean, degrading air quality over the Caribbean Islands in boreal summer and supplying nutrients to fertilize the Amazon Rainforest in boreal winter and spring through transatlantic dust transport. It has been assumed that the Bodélé depression is the main contributor to this transatlantic dust transport and Amazonian dust fertilization in boreal winter. However, these claims have not been supported by geochemical analysis. Here, we integrate a suite of satellite observations into a novel trajectory analysis framework to investigate dust transport from the leading two North African dust sources, namely, the Bodélé depression and El Djouf, and provide the first ever observation‐constrained quantification of the dust's dry and wet deposition along its transport pathways. The approach yields the novel observational finding that the El Djouf is the preferred source of intercontinental transport across the Atlantic Ocean rather than the Bodélé depression, bridging the geochemical impact of North African minerals on the Amazon Basin to the specific dust origin.
Key Points
The current trajectory simulations quantify observation‐derived dust deposition and capture the observed three‐dimensional dust distribution
El Djouf is the preferred source of the transatlantic dust transport, due to favorable transport pathways with respect to seasonal rain belts
Extensive near‐source dust deposition supports the observed limited potential for long‐range transport of dust from the Bodélé depression
Asian dust, primarily emitted from the Taklamakan and Gobi deserts, has been
reported to reach remote destinations, such as North America. However, the
relative contribution of the Taklamakan and ...Gobi deserts to dust loadings
through long-range transport remains unaddressed in any observational study.
Here, the climatology of Asian dust activation and potential for transport is
investigated using stereo observations of dust sources from the Multi-angle
Imaging SpectroRadiometer (MISR) instrument combined with
observation-initiated trajectory modeling. MISR-derived dust plume top height
and dust plume motion vectors confirm the peak of dust activation and
transport potential in spring over the Gobi Desert and in both spring and
summer over the Taklamakan Desert. The long-range trajectory patterns of
Asian dust, including the influence on North America through trans-Pacific
transport, are assessed using extensive forward trajectories initiated by
MISR dust plume observations. The trajectory analysis reveals
latitude-dependent spread of dust trajectories from the Taklamakan and Gobi
deserts, with Taklamakan dust dominantly affecting to the south of
50∘ N and Gobi dust primarily affecting to the north of
50∘ N in North America. The Asian dust activation and transport
potential exhibit substantial seasonal and interannual variability,
motivating future studies on the potential drivers.
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