Coarse-mode aerosol in the atmosphere and its impact across spatial scales

Most of the atmospheric aerosol mass is in the coarse (diameter 2.5-10 μm) and supercoarse modes (diameter > 10 μm). Particles in these size ranges have substantial, but as yet underappreciated, impacts on climate, primarily through their large contributions to aerosol optical properties and cloud condensation nuclei (CCN) and ice nuclei (IN) budgets. These particles are primarily derived from natural sources, such as surface erosion of soil, wave breaking in the ocean, and emissions of bioaerosols from soil and vegetation. Coarse-mode aerosol loading is poorly represented in global models, with most climate models underrepresenting atmospheric concentrations of dust particles with diameters greater than 5 μm by as much as a factor of four because of inadequate model representation of emissions and sinks. The indirect eKects of coarse-mode aerosol on climate are frequently dependent on

chemical and surface properties of single particles, necessitating the use of single-particle characterization techniques to fully understand coarse-mode particle populations. In this talk, I will discuss some recent results in characterization of atmospheric particles with single-particle mass spectrometry (SPMS) and scanning electron microscopy/energy dispersive X-ray (SEM/EDX) focused on coarse-mode dust and bioaerosols. I will also discuss the use of machine learning approaches in unraveling the complexity of coarsemode aerosol and its impacts on clouds and climate.