Combustion aerosols, emitted directly from wildland fires, residential burning, industrial activities, and vehicular emissions, and formed secondarily through atmospheric aging of combustion-derived organic gases, are major contributors to atmospheric aerosols. They influence Earth’s energy balance through radiative effects and aerosol–cloud interactions, affect ecosystem nutrient cycling, and pose risks to human and wildlife health. Yet their impacts on the Earth system remain poorly constrained due to key uncertainties, including, but not limited to, their formation and source contributions, physical and chemical properties, atmospheric transformation and transport, quantification of the spatial and temporal distribution of combustion aerosols, and their representation in models. To address these knowledge gaps, we invite laboratory, field, remote-sensing, and modeling studies on (1) combustion aerosol sources, formation, aging, and transport; (2) quantification of combustion aerosols’ distribution, composition, mixing state, toxicity, and optical, chemical, and microphysical properties; and (3) parameterizations or representations of combustion aerosols in models.