Scientific Colloquium
February 15, 2017, 3:30 p.m.

"Desert Dust, Wildfire Smoke, Volcanic Ash, Urban and Industrial Pollution – Grasping the Role Particles Play in Global Climate and Regional Air Quality "  

Airborne particles are ubiquitous components of our atmosphere, originating from a variety of natural and anthropogenic sources, exhibiting a wide range of physical properties, and contributing in multiple ways to regional air quality as well as regional-to-global-scale climate. Most remain in the atmosphere for a week or less, but can traverse oceans or continents in that time, carrying nutrients or disease vectors in some cases. Bright aerosols reflect sunlight, and can cool the surface; light-absorbing particles can heat the atmosphere, suppressing cloud formation or mediating larger-scale circulations. In most cases, particles are required to collect water vapor as the initial step in cloud formation, so their presence (or absence) and their hygroscopic or hydrophilic properties can affect cloud occurrence, structure, and ability to precipitate.

Grasping the scope and nature of aerosol environmental impacts requires understanding microphysical-to-global-scale processes, operating on timescales from minutes to days or longer. Satellites are the primary source of observations on kilometer-to-global scales. Spacecraft observations are complemented by suborbital platforms: aircraft in situ measurements and surface-based instrument networks that operate on smaller spatial scales and shorter timescales. Numerical models play a third key role in this work — providing a synthesis of current physical understanding with the aggregate of measurements, and allowing for some predictive capability. This presentation will focus on what we can say about aerosol amount and type from space. Constraining particle “type” is at present the leading challenge for satellite aerosol remote sensing. We will review recent advances and future prospects, including the strengths and limitations of available approaches, and work toward better integrating measurements with models to create a clearer picture of aerosol environmental impacts, globally.

About the Speaker:

Dr. Kahn, a Senior Research Scientist at NASA’s Goddard Space Flight Center, received his PhD in applied physics from Harvard University. He spent 20 years as a Research Scientist and Senior Research Scientist at the Jet Propulsion Laboratory, where he studied climate change on Earth and Mars, and also led the Earth & Planetary Atmospheres Research Element. Kahn is Aerosol Scientist for the NASA Earth Observing System's Multi-Angle Imaging SpectroRadiometer (MISR) instrument, using MISR’s unique observations, combined with other data and numerical models, to learn about wildfire smoke, desert dust, volcano and air pollution particles, and to apply the results to regional and global climate-change questions. Kahn has authored about 200 technical articles, has lectured on Climate Change and atmospheric physics at UCLA and Caltech, has presented numerous invited talks at national and international scientific meetings, and is editor and founder of PUMAS, the on-line journal of science and math examples for pre-college education. He is currently also Adjunct Professor at the University of Maryland.

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