This research project seeks better ways to simulate atmospheric aerosols, or tiny particles suspended in air. Aerosols are important for at least three reasons: 1) they include harmful particulate pollution, 2) they include condensation nuclei which are essential for the formation of clouds and precipitation, and 3) they affect Earth's temperature, both directly by reflecting sunlight back to space and indirectly by affecting the reflectivity of clouds. Aerosols are difficult to simulate in weather and climate models because of their large numbers, small size, and the complex ways in which they form, interact with each other, and dissipate. Due to limitations in computing power, aerosols are often represented in very simple ways, and many atmospheric models track aerosol concentration only as a function of the effective radius of the particles. But in reality aerosols of a given size behave quite differently depending on their chemical makeup (e.g. sulfate, nitrate, ammonium, sea salt, black carbon, mineral dust, etc.), so that it would take perhaps 20 separate parameters to properly describe each particle. The coarse-graining technique to be developed in this project provides a framework for developing approximate aerosol simulation techniques, in which aerosol concentrations are simulated by tracking the evolution of a finite number of randomly generated "superparticles". Each superparticle represents a distribution of particles in the 20-dimensional parameter space, and the aerosol simulation is accomplished by tracking the evolution of the superparticles.
The project will have several benefits beyond its contribution to aerosol simulation. For the broader scientific community, improvements in aerosol simulation will lead to better simulations of climate change, since much of the uncertainty in climate simulations comes from uncertainty in aerosols and their interactions with clouds. Better aerosol simulation also means an improved ability to simulate particulate air pollution, which will lead to improvements in air quality assessment and forecasting. In addition, the project will support education through the development of an undergraduate course in which calculus concepts are taught through their application to atmospheric thermodynamics.
