Tiny solid and liquid particles suspended in the atmosphere are called aerosols. Examples of aerosols include windblown dust, sea salts, volcanic ash, smoke from fires, and pollution from factories. These particles are important to scientists because they can affect climate, weather, and people's health.
Atmospheric aerosols play a major role in Earth's radiative budget. Yet aerosols are one of the greatest sources of uncertainty in climate modeling. Radiative forcing by aerosols may explain the difference between observed and modeled trends in average global temperature. In fact, the interaction with solar and terrestrial radiation by aerosols perturbs the radiative budget via scattering and absorption of sunlight.
By acting as Cloud Condensation Nuclei or Ice Nuclei, aerosol particles also modify cloud microphysics and therefore may change cloud radiative properties. The direct effect of aerosols on Earth's radiation budget and the indirect effect of aerosols on cloud albedo may have a cooling effect that could counter balance the warming due to the increase in carbon dioxide concentration. Present estimates of the aerosols' forcing on global climate range from minus 0.6 watts per square meter to minus 4.0 watts per square meter, when combining both the direct and indirect effects of sulfate aerosols and biomass burning aerosols. Dust originating from local area change is also suspected to be a major climate forcing. The direct aerosol effect is due to direct reflection of sunlight to space by aerosol particles and the indirect effect is by the modification of cloud properties, which in turn modifies the radiative budget.
Many recent studies show the importance of including aerosols in climate models to observe and measure human influence on atmospheric chemistry and climate change. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Terra and Aqua satellites is used to monitor aerosol optical thickness (proportional to the aerosol total loading) and size distribution (integrated on the vertical column) of the ambient (undisturbed) aerosol, over most of the globe (oceans and the moist parts of the continents) on a daily basis. MODIS is used to monitor aerosols' mass concentration, optical properties, and radiative forcing. Over land, aerosol optical thickness is derived using the dark target approach, and the method is limited to moist (and some semi-arid) parts of the continents, excluding snow and ice cover. The aerosol data product algorithms take advantage of MODIS' wide spectral range and high spatial resolution with daily global coverage. These unique MODIS characteristics allow excellent cloud rejection while maintaining high statistics of cloud-free pixels. The instrument's wide spectral range allows sophisticated derivation of aerosol size distribution over the ocean and efficient identification of pixels with dark surface cover over the land. MODIS' aerosol information is used to study aerosol climatology, to monitor the sources and sinks of specific aerosol types (such as sulfates and other industrial/urban aerosol and biomass burning aerosol), to serve as inputs for climate modeling and detection of the finger prints of anthropogenic climate change, and to perform atmospheric corrections of remotely-sensed surface reflectance over the land.
These images are produced using the SDS AOD_550_Dark_Target_Deep_Blue_Combined.