Introduction
Chad, a landlocked nation in central Africa, faces a complex mix of natural and anthropogenic aerosol sources. This study leverages satellite observations to characterize the optical and microphysical properties of atmospheric aerosols over Chad, providing insights into dust transport, aerosol composition, and potential climate impacts. By combining multi-sensor remote sensing data, we aim to map aerosol loading, particle size distributions, and hygroscopic behavior across diverse terrestrial and atmospheric environments within Chad’s borders.
Data and Methods
The analysis employs a suite of satellite products that capture aerosol optical depth (AOD), single-scattering albedo, asymmetry parameter, and refractive index. We integrate information from sensors such as MODIS, MISR, and IVIRM-like airborne datasets to retrieve aerosol microphysical properties, including real and imaginary refractive indices, size distributions, and hygroscopic growth factors. Data processing involves quality-controlled retrievals, cloud screening, and regional calibration to account for Chad’s varied surface reflectance and dust-dominated regimes.
To ensure spatial relevance, we aggregate observations at regional scales, spanning northern arid zones, central savannas, and southern wetland interfaces. Temporal synthesis highlights seasonal patterns tied to the Sahelian wind regime, rainfall cycles, and dust emission events. The methodological framework emphasizes cross-validation with ground-based measurements where available, improving confidence in inferred aerosol properties across different environments in Chad.
Optical Properties over Chad
Aerosol optical depth (AOD) serves as a primary proxy for atmospheric aerosol loading. Across Chad, AOD exhibits pronounced seasonality, with elevated values during dusty dry seasons and relative minima in wet periods. The retrieved single-scattering albedo (SSA) indicates a dominance of scattering particles in many regions, consistent with mineral dust and secondary organic aerosols. The asymmetry parameter reveals pronounced forward scattering, a hallmark of coarse-mode mineral dust that characterizes much of Chad’s atmospheric optical behavior.
Spatial patterns reveal higher AOD in northern Chad, correlating with dust source regions and prevailing Harmattan-like transport from the Sahara. Southern regions show lower AOD but can experience episodic increases during dust storms or biomass-burning events, illustrating the interplay between regional meteorology and aerosol loading. These optical metrics underpin the assessment of radiative forcing and potential climate feedbacks relevant to Chad’s ecosystems and energy balance.
Microphysical Characterization
Satellite-derived microphysical properties shed light on particle size, composition, and hygroscopicity. Size distributions indicate a dominant coarse mode during dry seasons, aligning with mineral dust elevation and transport. Fine-mode contributions rise temporarily due to anthropogenic emissions and regional biomass burning, particularly near agricultural zones and urban areas. The retrieved refractive indices suggest a mix of mineral dust components and light-absorbing aerosols, with the imaginary part indicating limited absorption in pristine dust plumes but higher values when smoke intrusions are present.
Hygroscopic growth factors inferred from multi-wavelength observations point to modest water uptake under increased humidity, affecting aerosol mass and optical behavior. These microphysical insights are essential for accurate radiative transfer modeling and for linking atmospheric aerosols to surface processes such as soil erosion, land-use changes, and health-related exposure concerns.
Implications for Climate and Air Quality
The optical and microphysical characterization of Chad’s aerosols informs both climate and air-quality assessments. Mineral dust influences regional radiation budgets, clouds, and precipitation patterns, while episodic fine-mode aerosols can contribute to respiratory and cardiovascular health risks. By mapping seasonal and regional variability, this satellite-driven approach supports early-warning systems for dust events, informs policy decisions on land management, and aids in validating regional climate models that seek to capture Sahelian aerosol dynamics.
Conclusions and Future Work
The satellite-based optical and microphysical analysis provides a comprehensive view of aerosols over Chad, highlighting spatial heterogeneity and seasonal drivers of aerosol properties. Ongoing work will focus on integrating additional sensors, expanding ground-truth data collection, and refining retrieval algorithms to better resolve dust composition and moisture effects. The ultimate goal is to deliver robust, actionable information for environmental monitoring, public health, and regional climate research in Chad and adjacent regions.
