A Global Climatology of Dust Aerosols Based on Satellite Data: Spatial, Seasonal and Inter-Annual Patterns over the Period 2005–2019

A satellite-based algorithm is developed and used to determine the presence of dust aerosols on a global scale. The algorithm uses as input aerosol optical properties from the MOderate Resolution Imaging Spectroradiometer (MODIS)-Aqua Collection 6.1 and Ozone Monitoring Instrument (OMI)-Aura version v003 (OMAER-UV) datasets and identifies the existence of dust aerosols in the atmosphere by applying specific thresholds, which ensure the coarse size and the absorptivity of dust aerosols, on the input optical properties. The utilized aerosol optical properties are the multiwavelength aerosol optical depth (AOD), the Aerosol Absorption Index (AI) and the Ångström Exponent (a). The algorithm operates on a daily basis and at 1° × 1° latitude-longitude spatial resolution for the period 2005–2019 and computes the absolute and relative frequency of the occurrence of dust. The monthly and annual mean frequencies are calculated on a pixel level for each year of the study period, enabling the study of the seasonal as well as the inter-annual variation of dust aerosols’ occurrence all over the globe. Temporal averaging is also applied to the annual values in order to estimate the 15-year climatological mean values. Apart from temporal, a spatial averaging is also applied for the entire globe as well as for specific regions of interest, namely great global deserts and areas of desert dust export. According to the algorithm results, the highest frequencies of dust occurrence (up to 160 days/year) are primarily observed over the western part of North Africa (Sahara), and over the broader area of Bodélé, and secondarily over the Asian Taklamakan desert (140 days/year). For most of the study regions, the maximum frequencies appear in boreal spring and/or summer and the minimum ones in winter or autumn. A clear seasonality of global dust is revealed, with the lowest frequencies in November–December and the highest ones in June. Finally, an increasing trend of global dust frequency of occurrence from 2005 to 2019, equal to 56.2%, is also found. Such an increasing trend is observed over all study regions except for North Middle East, where a slight decreasing trend (−2.4%) is found.

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Inter-comparison between the Aerosol Optical Properties Retrieved by Different Inversion Methods from SKYNET Sky Radiometer Observations over Qionghai and Yucheng in China

10.5194/amt-2019-39 ◽

2019 ◽

Author(s):

Zhe Jiang ◽

Minzheng Duan ◽

Huizheng Che ◽

Wenxing Zhang ◽

Teruyuki Nakajima ◽

...

Keyword(s):

Refractive Index ◽

Optical Properties ◽

Complex Refractive Index ◽

Single Scattering ◽

Inversion Method ◽

Aerosol Optical Properties ◽

Validation Data ◽

Mean Values ◽

And Inversion ◽

Volume Size

Abstract. This study analyzed the aerosol optical properties derived by SKYRAD.pack versions 5.0 and 4.2 using the radiometer measurements over Qionghai and Yucheng in China, two new sites of the sky radiometer network (SKYNET). The volume size distribution retrieved by V5.0 presented bimodal patterns with a 0.1–0.2 μm fine particle mode and a 5–6 μm coarse particle mode both over Qionghai and Yucheng. The differences of the volume size distributions between the two versions were very large for the coarse mode with a radius of over 5 μm. The mean values of single scattering albedo (SSA) at 500 nm retrieved from V5.0 were approximately 0.02 lower, but 0.03 higher than those from V4.2 in Qionghai and Yucheng, respectively. The average imaginary part of the complex refractive index (mi) retrieved from V5.0 at all wavelengths was systemically higher than those by V4.2 over Qionghai. Moreover, the differences between the real parts of the complex refractive index (mr) obtained using the two versions were within 4.25 % both at Yucheng and Qionghai. The seasonal variability of the aerosol properties over Qionghai and Yucheng were investigated based on SKYRAD.pack V5.0. The seasonal average SSA during the winter was larger than those in other seasons in Yucheng, while the lowest SSA values occurred in winter over Qionghai. Meanwhile, the mr showed a minimum in winter over both sites. The results can provide validation data in China for SKYNET to continue improving the data-processing and inversion method. The results provide valuable references for continued improvement of the retrieval algorithms of SKYNET and other aerosol observational networks.

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Closure on the single scattering albedo in the WRF-Chem framework using data from the MILAGRO campaign

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-5009-2009 ◽

2009 ◽

Vol 9 (1) ◽

pp. 5009-5054

Author(s):

J. C. Barnard ◽

J. D. Fast ◽

G. Paredes-Miranda ◽

W. P. Arnott

Keyword(s):

Optical Properties ◽

Black Carbon ◽

Chemical Properties ◽

Single Scattering ◽

Single Scattering Albedo ◽

Aerosol Optical Properties ◽

Mean Values ◽

Coarse Mode ◽

Fine Mode ◽

Using Data

Abstract. Data from the MILAGRO field campaign, which took place in the Mexico City Metropolitan Area (MCMA) during March 2006, is used to perform a closure experiment between aerosol chemical properties and aerosol optical properties. Measured aerosol chemical properties, obtained from the MILAGRO T1 site, are fed to two different "chemical to optical properties" modules. One module uses a sectional approach and is identical to that used in the WRF-Chem model, while the other is based on a modal approach. This modal code is employed as an independent check on the WRF-Chem module. Both modules compute aerosol optical properties and, in particular, the single-scattering albedo, ϖ0, as a function of time. The single-scattering albedos are compared to independent measurements obtained from a photoacoustic spectrometer (PAS). Because chemical measurements of the aerosol coarse mode were not available, and the inlet of the PAS could not ingest aerosols larger than about 2 to 3 μm, we focus here on the fine-mode ϖ0. At 870 nm, the wavelength of the PAS measurements, the agreement between the computed (modal and WRF-Chem) and observed fine-mode ϖ0, averaged over the course of the campaign, is reasonably good. The observed ϖ0 value is 0.77, while for both modules, the calculated value was 0.75 resulting in a difference of 0.02 between observations and both computational approaches. This difference is less than the uncertainty of the observed ϖ0 values (6%, or 0.05), and therefore "closure" is achieved, at least for mean values. After adjusting some properties of black carbon absorption and mass concentration within plausible uncertainty limits, the two modules simulate well the diurnal variation of ϖ0, and the absorption coefficient, Babs, but are less successful in calculating the variation of the scattering coefficient, Bscat. This difficulty is probably caused by the presence of larger particles during the day when windblown dust is ubiquitous; this dust likely increases the proportion of large particles introduced into the PAS. The dust also contributes to a very large aerosol mass loading in the coarse mode, and neglect of the coarse mode may cause significant errors, estimated to be as large as 0.07, in the calculation and measurement of ambient ϖ0. Finally, the observed ϖ0 is compared to the ϖ0 computed by the full WRF-Chem model, which includes prognostic aerosol chemistry. Unlike the results discussed above, a comparison between observed and simulated ϖ0 values reveals major differences. This large discrepancy is probably due, in part, to poor characterization of emissions near the T1 site, particularly black carbon emissions.

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Aerosol optical properties in the North China Plain during HaChi campaign: an in-situ optical closure study

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-5959-2011 ◽

2011 ◽

Vol 11 (12) ◽

pp. 5959-5973 ◽

Cited By ~ 106

Author(s):

N. Ma ◽

C. S. Zhao ◽

A. Nowak ◽

T. Müller ◽

S. Pfeifer ◽

...

Keyword(s):

Optical Properties ◽

North China Plain ◽

North China ◽

Scattering Coefficient ◽

Aerosol Optical Properties ◽

Mean Values ◽

The North ◽

The North China Plain ◽

The Mean

Abstract. The largest uncertainty in the estimation of climate forcing stems from atmospheric aerosols. In early spring and summer of 2009, two periods of in-situ measurements on aerosol physical and chemical properties were conducted within the HaChi (Haze in China) project at Wuqing, a town between Beijing and Tianjin in the North China Plain (NCP). Aerosol optical properties, including the scattering coefficient (σsp), the hemispheric back scattering coefficient (σbsp), the absorption coefficient (σap), as well as the single scattering albedo (ω), are presented. The diurnal and seasonal variations are analyzed together with meteorology and satellite data. The mean values of σsp, 550 nm of the dry aerosol in spring and summer are 280±253 and 379±251 Mm−1, respectively. The average σap for the two periods is respectively 47±38 and 43±27 Mm−1. The mean values of ω at the wavelength of 637 nm are 0.82±0.05 and 0.86±0.05 for spring and summer, respectively. The relative high levels of σsp and σbsp are representative of the regional aerosol pollution in the NCP. Pronounced diurnal cycle of $σsp, σap and ω are found, mainly influenced by the evolution of boundary layer and the accumulation of local emissions during nighttime. The pollutants transported from the southwest of the NCP are more significant than that from the two megacities, Beijing and Tianjin, in both spring and summer. An optical closure experiment is conducted to better understand the uncertainties of the measurements. Good correlations (R>0.98) are found between the values measured by the nephelometer and the values calculated with a modified Mie model. The Monte Carlo simulation shows an uncertainty of about 30 % for the calculations. Considering all possible uncertainties of measurements, calculated σsp and σbsp agree well with the measured values, indicating a stable performance of instruments and thus reliable aerosol optical data.

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Spatial distribution of dust's optical properties over the Sahara and Asia inferred from Moderate Resolution Imaging Spectroradiometer

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-10827-2013 ◽

2013 ◽

Vol 13 (21) ◽

pp. 10827-10845 ◽

Cited By ~ 6

Author(s):

M. Yoshida ◽

J. M. Haywood ◽

T. Yokohata ◽

H. Murakami ◽

T. Nakajima

Keyword(s):

Optical Properties ◽

Spatial Distribution ◽

Single Scattering ◽

Surface Reflectance ◽

Carbonaceous Aerosols ◽

Dust Aerosols ◽

Moderate Resolution ◽

Resolution Imaging ◽

Moderate Resolution Imaging Spectroradiometer ◽

Earth’S Climate

Abstract. There is great uncertainty regarding the role of mineral dust aerosols in Earth's climate system. One reason for this uncertainty is that the optical properties of mineral dust, such as its single scattering albedo (the ratio of scattering to total extinction), are poorly constrained because ground observations are limited to a few locations and satellite standard products are not available due to the excessively bright surface of the desert in the visible wavelength, which makes robust retrievals difficult. Here, we develop a method to estimate the spatial distributions of the aerosol single scattering albedo (ω0) and optical depth (τa), with daily 1°×1° spatial resolution using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) as well as model simulations of radiative transfer. This approach is based on the "critical surface reflectance" method developed in the literature, which estimates ω0 from the top of the atmospheric radiance. We estimate the uncertainties in ω0 over the Sahara (Asia) to be approximately 0.020 and 0.010 (0.023 and 0.017) for bands 9 and 1, respectively, while the uncertainty in τa is approximately 0.235 and 0.228 (0.464 and 0.370) for bands 9 and 1, respectively. The 5–95% range of the spatial distribution of ω0 over the Sahara (Asia) is approximately 0.90–0.94 and 0.96–0.99 (0.87–0.94 and 0.89–0.97) for bands 9 and 1, respectively, and that of τa over the Sahara (Asia) is approximately 0.8–1.4 and 0.8–1.7 (0.7–2.0 and 0.7–1.9) for bands 9 and 1, respectively. The results for the Sahara indicate a good correlation between ω0 and the surface reflectance, and between ω0 and τa. However, the relationships between ω0, τa, and surface reflectance are less clear in Asia than in the Sahara, and the ω0 values are smaller than those in the Sahara. The regions with small ω0 values are consistent with the regions where coal-burning smoke and carbonaceous aerosols are reported to be transported in previous studies. Because the coal-burning and carbonaceous aerosols are known to be more absorptive and have smaller ω0 values than dust aerosols, our results indicate that the dust aerosols in Asia are contaminated by these anthropogenic aerosols. The spatial distribution of dust optical properties obtained in our work could be useful in understanding the role of dust aerosols in Earth's climate system, most likely through future collaboration with regional and global modelling studies.

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Aerosol optical properties in the North China Plain during HaChi campaign: an in-situ optical closure study

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-9567-2011 ◽

2011 ◽

Vol 11 (3) ◽

pp. 9567-9605 ◽

Cited By ~ 4

Author(s):

N. Ma ◽

C. S. Zhao ◽

A. Nowak ◽

T. Müller ◽

S. Pfeifer ◽

...

Keyword(s):

Optical Properties ◽

North China Plain ◽

North China ◽

Aerosol Optical Properties ◽

Mean Values ◽

The North ◽

The North China Plain ◽

The Mean ◽

Local Emissions

Abstract. The largest uncertainty in the estimation of radiative forcings on climate stems from atmospheric aerosols. In winter and summer of 2009, two periods of in-situ measurements on aerosol physical and chemical properties were conducted within the HaChi project at Wuqing, a town between Beijing and Tianjin in the North China Plain (NCP). Aerosol optical properties including scattering coefficient (σsp), hemispheric back scattering coefficient (σbsp), absorption coefficient (σap, as well as single scattering albedo (ω) are presented. The characteristics of diurnal and seasonal variations are analyzed together with the meteorological and satellite data. The mean values of σsp, 550 nm of the dry aerosol in winter and summer are 280 ± 253 and 379 ± 251 Mm−1, respectively. The average σap for the two periods are respectively 47 ± 38 and 43 ± 27 Mm−1. The mean values of ω are 0.83 ± 0.05 and 0.87 ± 0.05 for winter and summer, respectively. The relative high levels of σsp and σbsp are representative of the regional polluted aerosol of the North China Plain. Pronounced diurnal cycle of σsp, σap and ω are found, mainly influenced by the evolution of boundary layer and accumulation of local emissions during night-time. Regional transport of pollutants from southwest in the NCP is significant both in winter and summer, while high values of σsp and σap correlate with calm winds in winter, which indicating the significant contribution of local emissions. An optical closure experiment is conducted to better understand uncertainties of the measurements. Good correlations (R>0.98) are found between values measured by nephelometer and values calculated with a modified Mie model. Monte Carlo simulations show an uncertainty of about 30% for the calculations. Considering all possible uncertainties of measurements, calculated σsp and σbsp agree well with measured values, indicating a stable performance of instruments and thus a reliable aerosol optical data.

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Spatial distribution of dust's optical properties over the Sahara and Asia inferred from Moderate Resolution Imaging Spectroradiometer

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-31107-2012 ◽

2012 ◽

Vol 12 (12) ◽

pp. 31107-31151

Author(s):

M. Yoshida ◽

J. M. Haywood ◽

B. T. Johnson ◽

H. Murakami ◽

T. Nakajima

Keyword(s):

Optical Properties ◽

Single Scattering ◽

Spatial Distributions ◽

Surface Reflectance ◽

Carbonaceous Aerosols ◽

Dust Aerosols ◽

Moderate Resolution ◽

Resolution Imaging ◽

Moderate Resolution Imaging Spectroradiometer ◽

Earth’S Climate

Abstract. There is a great deal of uncertainty surrounding the role of mineral dust aerosols in the earth's climate system. One reason for this uncertainty is that the optical properties of mineral dust, such as its single scattering albedo (the ratio of scattering to total extinction), are poorly understood because ground observations are limited to several locations and the satellite standard products are not available due to the excessively bright surface of the desert in the visible wavelength. We develop a method in this paper to estimate the spatial distributions of the aerosol single scattering albedo (ω0) and optical depth (τa), with daily 1 degree latitude and 1 degree longitude resolution, using data from Moderate Resolution Imaging Spectroradiometer (MODIS), as well as model simulations of radiative transfer. This approach is based on the "critical surface reflectance" method developed in the literature, which estimates ω0 from the top of the atmospheric radiance. We confirm that the uncertainties in our estimation of ω0 and τa are suitably minor and that the characteristic spatial distributions estimated over the Sahara and Asia are significant. The results for the Sahara indicate good correlation between ω0 and the surface reflectance and between ω0 and τa. Therefore, ω0 is determined mainly by the mineral composition of surface dust and/or the optical depth of airborne dust in the Sahara. On the other hand, the relationships between ω0, τa, and the surface reflectance are less clear in Asia than in the Sahara, and the values of ω0 are smaller than those in the Sahara. The regions with small ω0 values are consistent with the regions where coal-burning smoke and carbonaceous aerosols are thought to be transported, as reported in previous studies. Because the coal-burning and carbonaceous aerosols are known to be more absorptive and have smaller ω0 values than dust aerosols, our results indicate that the dust aerosols in Asia are contaminated by these anthropogenic aerosols. The spatial distribution of dust optical properties obtained in our work could be useful in understanding the roles of dust aerosols in the earth's climate system, most likely through future collaboration with regional and global modelling studies.

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Seventeen-year systematic measurements of dust aerosol optical properties using the eole ntua lidar system (2000-2016)

EPJ Web of Conferences ◽

10.1051/epjconf/201817605029 ◽

2018 ◽

Vol 176 ◽

pp. 05029

Author(s):

Ourania Soupiona ◽

Maria Mylonaki ◽

Alexandros Papayannis ◽

Athina Argyrouli ◽

Panayotis Kokkalis ◽

...

Keyword(s):

Optical Properties ◽

Mean Value ◽

Saharan Dust ◽

Aerosol Optical Properties ◽

Mean Values ◽

Time Period ◽

Lidar Measurements ◽

Multi Wavelength ◽

Lidar Ratio ◽

Dust Events

A comprehensive analysis of the seasonal variability of the optical properties of Saharan dust aerosols over Athens, Greece, is presented for a 17-year time period (2000-2016), as derived from multi-wavelength Raman lidar measurements (57 dust events with more than 80 hours of measurements). The profiles of the derived aerosol optical properties (aerosol backscatter and extinction coefficients, lidar ratio and aerosol Ångström exponent) at 355 nm are presented. For these dust events we found a mean value of the lidar ratio of ~52±13 sr at 355 nm and of ~58±8 sr (not shown) at 532 nm (2-4 km a.s.l. height). For our statistical analysis, presented here, we used monthly-mean values and time periods under cloud-free conditions. The number of dust events was greatest in late spring, summer, and early autumn periods. In this paper we also present a selected case study (04 April 2016) of desert dust long-range transport from the Saharan desert.

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Over a ten-year record of aerosol optical properties at SMEAR II

10.5194/acp-2018-981 ◽

2018 ◽

Author(s):

Krista Luoma ◽

Aki Virkkula ◽

Pasi Aalto ◽

Tuukka Petäjä ◽

Markku Kulmala

Keyword(s):

Optical Properties ◽

Volume Concentration ◽

Single Scattering ◽

Single Scattering Albedo ◽

Aerosol Optical Properties ◽

Absorption Coefficients ◽

Mean Values ◽

Aerosol Forcing ◽

Seasonal And Diurnal Variations ◽

The Mean

Abstract. The aerosol optical properties (AOPs) of particles smaller than 10 μm (PM10) and 1 μm (PM1) have been measured at SMEAR II since 2006 and 2010, respectively. For the PM10 particles the mean values of the scattering and absorption coefficients, single-scattering albedo, and backscatter fraction at δ = 550 nm, and scattering and absorption Ångström exponents at the wavelength ranges 450–700 nm and 370–950 nm were 15.2 Mm−1, 2.1 Mm−1, 0.86, 0.15, 1.80 and 0.94 respectively. The time series were used to examine the trends and variation in the AOPs. Statistically significant trends were found for example for the PM10 scattering and absorption coefficients, single-scattering albedo, and backscatter fraction, and the slopes of these trends were −0.342 Mm−1, −0.0952 Mm−1, 3.4 ‧ 10−3, and 1.3 ‧ 10−3 per year. The tendency for the extensive AOPs to decrease correlated well with the decrease in aerosol number and volume concentration. The tendency for the singlescattering albedo and backscattering fraction to increase affected to the effective aerosol forcing efficiency, indicating that the dry aerosols were scattering the radiation more effectively back into space. In addition to these trends, we also observed seasonal and diurnal variations and variations between the AOPs of the PM1 and PM10 particles.

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Space-based retrieval of NO<sub>2</sub> over biomass burning regions: quantifying and reducing uncertainties

Atmospheric Measurement Techniques ◽

10.5194/amt-7-3431-2014 ◽

2014 ◽

Vol 7 (10) ◽

pp. 3431-3444 ◽

Cited By ~ 9

Author(s):

N. Bousserez

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Shape Factor ◽

Transport Model ◽

Sensitivity Analyses ◽

The Arctic ◽

Ozone Monitoring Instrument ◽

Aerosol Optical Properties ◽

Atmospheric Scattering ◽

The Impact

Abstract. The accuracy of space-based nitrogen dioxide (NO2) retrievals from solar backscatter radiances critically depends on a priori knowledge of the vertical profiles of NO2 and aerosol optical properties. This information is used to calculate an air mass factor (AMF), which accounts for atmospheric scattering and is used to convert the measured line-of-sight "slant" columns into vertical columns. In this study we investigate the impact of biomass burning emissions on the AMF in order to quantify NO2 retrieval errors in the Ozone Monitoring Instrument (OMI) products over these sources. Sensitivity analyses are conducted using the Linearized Discrete Ordinate Radiative Transfer (LIDORT) model. The NO2 and aerosol profiles are obtained from a 3-D chemistry-transport model (GEOS-Chem), which uses the Fire Locating and Monitoring of Burning Emissions (FLAMBE) daily biomass burning emission inventory. Aircraft in situ data collected during two field campaigns, the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) and the Dust and Biomass-burning Experiment (DABEX), are used to evaluate the modeled aerosol optical properties and NO2 profiles over Canadian boreal fires and West African savanna fires, respectively. Over both domains, the effect of biomass burning emissions on the AMF through the modified NO2 shape factor can be as high as −60%. A sensitivity analysis also revealed that the effect of aerosol and shape factor perturbations on the AMF is very sensitive to surface reflectance and clouds. As an illustration, the aerosol correction can range from −20 to +100% for different surface reflectances, while the shape factor correction varies from −70 to −20%. Although previous studies have shown that in clear-sky conditions the effect of aerosols on the AMF was in part implicitly accounted for by the modified cloud parameters, here it is suggested that when clouds are present above a surface layer of scattering aerosols, an explicit aerosol correction would be beneficial to the NO2 retrieval. Finally, a new method that uses slant column information to correct for shape-factor-related AMF error over NOx emission sources is proposed, with possible application to near-real-time OMI retrievals.

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