This paper presents a comprehensive analysis of aerosol optical depth (AOD) measurements from the AERONET (Atmospheric Chemistry and Physics Division, NASA/GSFC) network, focusing on monthly means and climatic averages for nine primary sites and 21 additional multiyear sites representing various aerosol regimes. The sites include tropical biomass burning, boreal forests, midlatitude humid and dry climates, oceanic, desert, and background locations. Seasonal trends and climatic averages are discussed for each site. The study highlights the importance of ground-based monitoring systems in assessing global aerosol distribution and its impact on climate and public health. The AERONET program, with over 100 sites worldwide, provides quality-assured aerosol optical properties, which are crucial for satellite remote sensing validation and atmospheric correction. The paper also reviews historical aerosol monitoring efforts, including early systematic studies, the BAPMoN program, and the Global Atmospheric Watch (GAW) network. The instrumentation and methods used in the AERONET program are described, emphasizing the use of CIMEL Sun/sky radiometers and the cloud screening technique. Detailed analyses of aerosol optical depth, Angstrom exponent, and precipitable water at specific sites, such as Mauna Loa, Hawaii, Greenbelt, Maryland, Sevilleta, New Mexico, H.J. Andrews, Oregon, Cape Verde, and Banizoumbou, Niger, are provided, highlighting seasonal variations, frequency distributions, and relationships with other atmospheric parameters. The findings contribute to a better understanding of aerosol behavior and its environmental impacts.This paper presents a comprehensive analysis of aerosol optical depth (AOD) measurements from the AERONET (Atmospheric Chemistry and Physics Division, NASA/GSFC) network, focusing on monthly means and climatic averages for nine primary sites and 21 additional multiyear sites representing various aerosol regimes. The sites include tropical biomass burning, boreal forests, midlatitude humid and dry climates, oceanic, desert, and background locations. Seasonal trends and climatic averages are discussed for each site. The study highlights the importance of ground-based monitoring systems in assessing global aerosol distribution and its impact on climate and public health. The AERONET program, with over 100 sites worldwide, provides quality-assured aerosol optical properties, which are crucial for satellite remote sensing validation and atmospheric correction. The paper also reviews historical aerosol monitoring efforts, including early systematic studies, the BAPMoN program, and the Global Atmospheric Watch (GAW) network. The instrumentation and methods used in the AERONET program are described, emphasizing the use of CIMEL Sun/sky radiometers and the cloud screening technique. Detailed analyses of aerosol optical depth, Angstrom exponent, and precipitable water at specific sites, such as Mauna Loa, Hawaii, Greenbelt, Maryland, Sevilleta, New Mexico, H.J. Andrews, Oregon, Cape Verde, and Banizoumbou, Niger, are provided, highlighting seasonal variations, frequency distributions, and relationships with other atmospheric parameters. The findings contribute to a better understanding of aerosol behavior and its environmental impacts.