This study evaluates the optical and microphysical properties of atmospheric aerosols over Chad using satellite data from the MODIS, MISR, SeaWIFS, and OMI sensors, as well as the MERRA-2 reanalysis, with the aim of identifying the most suitable instrument for their monitoring. A comparison of aerosol optical depth (AOD) values reveals a systematic underestimation by MERRA-2, while MODIS, MISR, SeaWIFS, and OMI tend to overestimate them. Linear correlation analysis shows that MODIS exhibits the strongest correlation with MERRA-2 (R = 0.62), followed by MISR (R = 0.61), SeaWIFS (R = 0.55), and OMI (R = 0.41). The spatio-temporal analysis of monthly variations reveals a high aerosol load during spring and summer, as confirmed by the annual cycles of AOD at 550 nm and the Ångström exponent (412 - 470 nm), indicating the predominance of desert dust. Conversely, the concentrations of other aerosol types remain low during both summer and winter. The aerosol index (AI), measured by OMI and TOMS, also highlights a strong presence of absorbing aerosols, with a maximum observed in May and respective minima in September and November. Analysis of the seasonal variability in the distribution of the Ångström exponent (AE) as a function of AOD shows the predominance of accumulation and coarse modes, mainly associated with mineral dust. These results confirm the reliability of the MODIS sensor for aerosol monitoring over Chad, where accumulation and coarse modes dominate the atmosphere.
KeywordsAerosolsAirborne SensorsMERRA-2Optical and Microphysical Properties
Younous, A.A., Niang, S.A.A., Sarr, A. and Drame, M.S. (2024) Assessment of Wind Energy Resources in Chad, Central Africa, Using 100-M Wind Data from ERA5 Reanalysis. Energy Exploration & Exploitation , 43, 473-491. https://doi.org/10.1177/01445987241302424
Engelstaedter, S., Tegen, I. and Washington, R. (2006) North African Dust Emissions and Transport. Earth - Science Reviews , 79, 73-100. https://doi.org/10.1016/j.earscirev.2006.06.004
Guirado, C., Cuevas, E., Cachorro, V.E., Toledano, C., Alonso-Pérez, S., Bustos, J.J., et al . (2014) Aerosol Characterization at the Saharan AERONET Site Tamanrasset. Atmospheric Chemistry and Physics , 14, 11753-11773. https://doi.org/10.5194/acp-14-11753-2014
Bristow, C.S., Drake, N. and Armitage, S. (2009) Deflation in the Dustiest Place on Earth: The Bodélé Depression, Chad. Geomorphology , 105, 50-58. https://doi.org/10.1016/j.geomorph.2007.12.014
Ben-Ami, Y., Koren, I., Rudich, Y., Artaxo, P., Martin, S.T. and Andreae, M.O. (2010) Transport of North African Dust from the Bodélé Depression to the Amazon Basin: A Case Study. Atmospheric Chemistry and Physics , 10, 7533-7544. https://doi.org/10.5194/acp-10-7533-2010
Ernest, A., Laryea, N., Oluwaseun, O.O., Kofi, A.S., Oduro, N.B., et al . (2022) Dust Sources and Impact: A Review. North American Academic Research , 5, 17-37.
Nébon, B., Dramé, M.S., Sall, S.M., Bruno, K., Niang, D.N., Florent, K.P., et al . (2019) Intra-Seasonal and Annual Variation of Aerosols and Their Radiative Impact in the Sahelian Zone of Burkina Faso. Atmospheric and Climate Sciences , 9, 62-74. https://doi.org/10.4236/acs.2019.91004
Orozi, G., Tchiroue, K. and Halawlaw, Y.I. (2022) Analysis of Natural Aerosols’ Vertical Distribution in Sahelian Zone via the OPEN (Clouds Seeding Operation) Project in Chad. International Journal of Current Research and Academic Review , 10, 7-17.
Liu, Y., Huang, J. and Huang, F. (2023) A Comprehensive Review on Study Methods of Aerosol Optical Properties in Different Dimensions. IEEE Access , 11, 36763-36786. https://doi.org/10.1109/access.2023.3266333
Diarra, C. and Ba, A. (2014) Analyse des paramètres optiques des aérosols atmosphériques, de leur distribution et de leur albédo de diffusion par les mesures photométriques au Mali. Afrique Science , 10, 82-97.
Diarra, C., Coulibaly, A.H. and Sow, M. (2019) Caracterisation de types d’aerosols atmospheriques par l’analyse de donnees photometriques du reseau aeronet en afrique de l’ouest.
(2015) Changements climatiques 2014: Rapport de synthèse: Contribution des Groupes de travail I, II et III au cinquième Rapport d’évaluation du Groupe d’experts intergouvernemental sur l’évolution du climat. GIEC.
Mulago, S.K., Makokha, J.W. and Boiyo, R. (2024) Spatial-Temporal Variation of Aerosol Optical Depth and Ångström Exponent over Selected Towns in Kenya: Environmental Impact and Climate Change. OALib , 11, 1-16. https://doi.org/10.4236/oalib.1111803
Goni, S., Adannou, H.A., Diop, D., Kriga, A., Khayal, A.Y., Nebon, B., et al . (2019) Observation and Simulation of Available Solar Energy at N’djamena, Chad. Smart Grid and Renewable Energy , 10, 165-178. https://doi.org/10.4236/sgre.2019.106011
Marticorena, B., Haywood, J., Coe, H., Formenti, P., Liousse, C., Mallet, M., et al . (2011) Tropospheric Aerosols over West Africa: Highlights from the AMMA International Program. Atmospheric Science Letters , 12, 19-23. https://doi.org/10.1002/asl.322
Schwanghart, W. and Schütt, B. (2008) Meteorological Causes of Harmattan Dust in West Africa. Geomorphology , 95, 412-428. https://doi.org/10.1016/j.geomorph.2007.07.002
Washington, R. and Todd, M.C. (2005) Atmospheric Controls on Mineral Dust Emission from the Bodélé Depression, Chad: The Role of the Low Level Jet. Geophysical Research Letters , 32, e2005GL023597. https://doi.org/10.1029/2005gl023597
Korgo, B. (2014) Caractérisation optique et microphysique des aérosols atmosphériques en zone urbaine ouest africaine: Application aux calculs du forçage radiatif à Ouagadougou. Master’s Thesis, Universite de Ouagadougou.
Yusuf, N., Said S, R., Tilmes, S. and Gbobaniyi, E. (2021) Multi-Year Analysis of Aerosol Optical Properties at Various Timescales Using AERONET Data in Tropical West Africa. Journal of Aerosol Science , 151, Article ID: 105625. https://doi.org/10.1016/j.jaerosci.2020.105625
Pierangelo, C. (2005) Apports du sondage infrarouge à l’étude des aérosols atmosphériques. Master’s Thesis, Université Pierre et Marie Curie—Paris VI.
Bado, N., Bazyomo, S.D., Ouedraogo, G.W.P., Korgo, B., Dramé, M.S., Kieno, F.P., et al . (2024) Contribution of Satellite Observations in the Optical and Microphysical Characterization of Aerosols in Burkina Faso, West Africa. Atmospheric and Climate Sciences , 14, 154-171. https://doi.org/10.4236/acs.2024.141010
Bedoum, A., Biona, C.B. and Adoum, I. (2014) Impact de la variabilité pluviométrique et de la sécheresse au sud du tchad: Effets du changement climatique. Revue Ivoirienne des Sciences et Technologie , 23, 13-30.
Remini, B. (2018) Tibesti-Ennedi-Chad Lake: The Triangle of Dust Impact on the Fertilization of the Amazonian Forest. Larhyss Journal , No. 34, 147-182.
Senghor, H., Machu, É., Hourdin, F. and Gaye, A.T. (2017) Seasonal Cycle of Desert Aerosols in Western Africa: Analysis of the Coastal Transition with Passive and Active Sensors. Atmospheric Chemistry and Physics , 17, 8395-8410. https://doi.org/10.5194/acp-17-8395-2017
Bado, N., Ouédraogo, A., Guengané, H., Maurice Ky, T.S., Bazyomo, S.D., Korgo, B., et al . (2019) Climatological Analysis of Aerosols Optical Properties by Airborne Sensors and in Situ Measurements in West Africa: Case of the Sahelian Zone. Open Journal of Air Pollution , 8, 118-135. https://doi.org/10.4236/ojap.2019.84007
Filonchyk, M. and Hurynovich, V. (2020) Validation of MODIS Aerosol Products with AERONET Measurements of Different Land Cover Types in Areas over Eastern Europe and China. Journal of Geovisualization and Spatial Analysis , 4, Article No. 10. https://doi.org/10.1007/s41651-020-00052-9
Mhawish, A., Banerjee, T., Sorek-Hamer, M., Lyapustin, A., Broday, D.M. and Chatfield, R. (2019) Comparison and Evaluation of MODIS Multi-Angle Implementation of Atmospheric Correction (MAIAC) Aerosol Product over South Asia. Remote Sensin g of Environment , 224, 12-28. https://doi.org/10.1016/j.rse.2019.01.033
Peyridieu, S., et al . (2010) Saharan Dust Infrared Optical Depth and Altitude Retrieved from AIRS: A Focus over North Atlantic—Comparison to MODIS and CALIPSO. Atmospheric Chemistry and Physics , 10, 1953-1967.
Bibi, H., Alam, K., Chishtie, F., Bibi, S., Shahid, I. and Blaschke, T. (2015) Intercomparison of MODIS, MISR, OMI, and CALIPSO Aerosol Optical Depth Retrievals for Four Locations on the Indo-Gangetic Plains and Validation against AERONET Data. Atmospheric Environment , 111, 113-126. https://doi.org/10.1016/j.atmosenv.2015.04.013
Cuevas, E., Camino, C., Benedetti, A., Basart, S., Terradellas, E., Baldasano, J.M., et al . (2015) The MACC-II 2007-2008 Reanalysis: Atmospheric Dust Evaluation and Characterization over Northern Africa and the Middle East. Atmospheric Chemistry and Physics , 15, 3991-4024. https://doi.org/10.5194/acp-15-3991-2015
Prospero, J.M., Ginoux, P., Torres, O., Nicholson, S.E. and Gill, T.E. (2002) Environmental Characterization of Global Sources of Atmospheric Soil Dust Identified with the Nimbus 7 Total Ozone Mapping Spectrometer (TOMs) Absorbing Aerosol Product. Reviews of Geophysics , 40, 2-1-2-31. https://doi.org/10.1029/2000rg000095
Washington, R., Todd, M., Middleton, N.J. and Goudie, A.S. (2003) Dust-Storm Source Areas Determined by the Total Ozone Monitoring Spectrometer and Surface Observations. Annals of the Association of American Geographers , 93, 297-313. https://doi.org/10.1111/1467-8306.9302003
Bounhir, A., Benkhaldoun, Z. and Sarazin, M. (2007) Aerosol Characterization of Morocco with AERONET and Intercomparison with Satellite Data: TOMS, MODIS and Misr. SPIE Proceedings , 6745, Article ID: 674506. https://doi.org/10.1117/12.730818
Krueger, A.J., Walter, L.S., Bhartia, P.K., Schnetzler, C.C., Krotkov, N.A., Sprod, I., et al . (1995) Volcanic Sulfur Dioxide Measurements from the Total Ozone Mapping Spectrometer Instruments. Journal of Geophysical Research : Atmospheres , 100, 14057-14076. https://doi.org/10.1029/95jd01222
Al-Salihi, A.M. (2018) Characterization of Aerosol Type Based on Aerosol Optical Properties over Baghdad, Iraq. Arabian Journal of Geosciences , 11, Article No. 633. https://doi.org/10.1007/s12517-018-3944-1
Raptis, I., Kazadzis, S., Amiridis, V., Gkikas, A., Gerasopoulos, E. and Mihalopoulos, N. (2020) A Decade of Aerosol Optical Properties Measurements over Athens, Greece. Atmosphere , 11, Article 154. https://doi.org/10.3390/atmos11020154
Chaabane, M., Elleuch, F., Masmoudi, M. and Medhioub, K. (2007) Caractérisation d’un photomètre solaire conçu pour l’étude des propriétés optiques des aérosols atmosphériques. 18 è Congrès Français de Mécanique , Grenoble, 27-31 August 2007, 1-6.
Korgo, B., Roger, J.-C. and Bathiebo, J. (2013) Climatology of Air Mass Trajectories and Aerosol Optical Thickness over Ouagadougou. Global Journal of Pure and Applied Sciences , 19, 169-181.
Basart, S., Perez, C., Cuevas, E., Baldasano, J.M. and Gobbi, G.P. (2009) Aerosol Characterization in Northern Africa, Northeastern Atlantic, Mediterranean Basin and Middle East from Direct-Sun AERONET Observations. Atmospheric Chemistry and Physics , 9, 8265-8282.
Filonchyk, M., Hurynovich, V., Yan, H., Zhou, L. and Gusev, A. (2019) Climatology of Aerosol Optical Depth over Eastern Europe Based on 19 Years (2000-2018) MODIS TERRA Data. International Journal of Climatology , 40, 3531-3549. https://doi.org/10.1002/joc.6412
Ichoku, C., Chu, D.A., Mattoo, S., Kaufman, Y.J., Remer, L.A., Tanré, D., et al . (2002) A Spatio-Temporal Approach for Global Validation and Analysis of MODIS Aerosol Products. Geophysical Research Letters , 29, MOD1-1-MOD1-4. https://doi.org/10.1029/2001gl013206
Tripathi, S.N., Dey, S., Chandel, A., Srivastava, S., Singh, R.P. and Holben, B.N. (2005) Comparison of MODIS and AERONET Derived Aerosol Optical Depth over the Ganga Basin, India. Annales Geophysicae , 23, 1093-1101. https://doi.org/10.5194/angeo-23-1093-2005
Hyer, E.J., Reid, J.S. and Zhang, J. (2011) An Over-Land Aerosol Optical Depth Data Set for Data Assimilation by Filtering, Correction, and Aggregation of MODIS Collection 5 Optical Depth Retrievals. Atmospheric Measurement Techniques , 4, 379-408. https://doi.org/10.5194/amt-4-379-2011
Misra, A., Tripathi, S.N., Kaul, D.S. and Welton, E.J. (2012) Study of MPLNET-Derived Aerosol Climatology over Kanpur, India, and Validation of CALIPSO Level 2 Version 3 Backscatter and Extinction Products. Journal of Atmospheric and Oceanic Technology , 29, 1285-1294. https://doi.org/10.1175/jtech-d-11-00162.1
Awoleye, P.O., Ogunjobi, K.O. and Balogun, I.A. (2024) Climatology and Dynamics of Aerosol Optical Properties from Selected AERONET Sites over West Africa. Discover Atmosphere , 3, Article No. 11.
Chiapello, I. and Moulin, C. (2002) TOMS and METEOSAT Satellite Records of the Variability of Saharan Dust Transport over the Atlantic during the Last Two Decades (1979-1997). Geophysical Research Letters , 29, 17-1-17-4. https://doi.org/10.1029/2001gl013767
Formenti, P., Schütz, L., Balkanski, Y., Desboeufs, K., Ebert, M., Kandler, K., et al . (2011) Recent Progress in Understanding Physical and Chemical Properties of African and Asian Mineral Dust. Atmospheric Chemistry and Physics , 11, 8231-8256. https://doi.org/10.5194/acp-11-8231-2011
Andreae, M.O. (2019) Emission of Trace Gases and Aerosols from Biomass Burning—An Updated Assessment. Atmospheric Chemistry and Physics , 19, 8523-8546. https://doi.org/10.5194/acp-19-8523-2019
Bond, T.C., Doherty, S.J., Fahey, D.W., Forster, P.M., Berntsen, T., DeAngelo, B.J., et al . (2013) Bounding the Role of Black Carbon in the Climate System: A Scientific Assessment. Journal of Geophysical Research : Atmospheres , 118, 5380-5552. https://doi.org/10.1002/jgrd.50171
Liousse, C., Guillaume, B., Grégoire, J.M., Mallet, M., Galy, C., Pont, V., et al . (2010) Updated African Biomass Burning Emission Inventories in the Framework of the AMMA-IDAF Program, with an Evaluation of Combustion Aerosols. Atmospheric Chemistry and Physics , 10, 9631-9646. https://doi.org/10.5194/acp-10-9631-2010
Tobias, C. and Megie, C. (1980) Les lithométéores au Tchad: Premiers résultats concernant la nature, la composition et l’importance des aérosols transportés par voie atmosphérique dans la région de N’Djamena (Tchad). Cahiers ORSTOM Série Pédologie , 18, 71-81.
Carmona, I. and Alpert, P. (2009) Synoptic Classification of Moderate Resolution Imaging Spectroradiometer Aerosols over Israel. Journal of Geophysical Research : Atmospheres , 114, e2008JD010160. https://doi.org/10.1029/2008jd010160