An aerosol is a collection of tiny (typically smaller than a few microns) particles that remain lofted in the Earth's atmosphere for extended periods of time (days to weeks). Aerosol particles range from desert dust to black and organic carbon from wildfires to nitrate aerosol from pollution. They have significant impacts on climate, visibility and human health. Research on aerosols in the department spans from experimental measurements (Murphy and Caulton) of their chemical, optical, physical, and cloud-particle-nucleation properties to modeling studies (McCoy) of their radiative properties and life cycles (including emission, transport, dry deposition, and wet scavenging by clouds and precipitation). Field studies are conducted from both ground-based and airborne platforms using advanced instrumentation, some of which was developed at UW. Modeling studies are based on the simulations from the global Community Earth System Model (CESM) and regional Weather Research and Forecasting Model with chemistry (WRF-Chem). Modeling of aerosols and their radiative forcings are constrained by validating model results with in-situ surface and aircraft observations and remote sensing observations from satellites and lidar.