ABSTRACT
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Coordinated, three-dimensional monitoring of the global aerosol distribution and its temporal variability is a basic requirement of climate research. Such four-dimensional observations are needed for an adequate consideration of particles in atmospheric models that are used to simulate the regional and intercontinental aerosol transport and the inŸuence of aerosol particles on short-term weather and the Earth’s radiation budget (direct climate effect), and on cloud processes (indirect climate effect).* However, such a four-dimensional monitoring system is not available. Thus, the uncertainty in estimating the aerosol impact on future climate is unacceptably large for constraining climate simulations and climate change projections.1−3† Quantifying the aerosol impact would require a multiinstrument, global observing system and a capacity for integrating diverse data.4−7 A program for coordinating and integrating these observations, dubbed the Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) initiative, has been proposed by Diner et al.8
