Richard C. Flagan

Dual Affiliation with Division of Enigneering and Applied Sciences

Assistant: Irina Meininger

Suspensions of particles in a gas, called aerosols, play a central role in the atmospheric processes involved in climate change. Some aerosols are emitted directly into the atmosphere; others form there through oxidation of gaseous precursors. Both natural processes and anthropogenic sources contribute to the aerosol burden. Climate change is driven by greenhouse gases that warm the air, and by aerosols and the cloud droplets that form on them. Depending on their compositions, the aerosols cool the planet by scattering incident sunlight back to space, or warm it when soot and other particles absorb solar radiation. While the impacts of greenhouse gases are readily quantified, aerosols remain the greatest source of uncertainty in the global radiation budget. Only by understanding the global distribution of aerosols can their impact be properly assessed. Unfortunately, data of the atmospheric aerosol remain sparse. The Flagan group works to increase the level of understanding through a combination of laboratory and field measurements, and by advancing the state of the art in aerosol measurements.

Fine particulate matter in the air also has profound impacts on human health. These particles are usually characterized in terms of the mass concentration of particles that can penetrate to the lower airways when inhaled, so-called PM_2.5. Epidemiological studies reveal a strong association between PM_2.5 levels and a number of adverse health effects, but PM_2.5 is a blunt instrument to understand fine particle effects. Near-roadway increases in of some of these health effects point to possible contributions of particles in the low nanometer regime, and to heavy-duty diesel traffic as the likely culprit, though, again, the data are too sparse to allow rigorous assessment of the causes.

We seek to advance our understanding of the atmospheric aerosol, at scales ranging from the very localized effects of near roadway exposures, to that of the urban, regional, and global atmosphere. By enabling measurements throughout the particle size range from molecular clusters through supermicron particles, we are working to provide the comprehensive data that are needed to probe the fundamental mechanisms of aerosol formation and growth, and to assess their many impacts. A particular focus of our work is the secondary organic aerosol that dominates the atmospheric particles in many locations, and which accounts for most of the growth even when species such as sulfuric acid are responsible for new particle formation. We further study much more localized effects of aerosols, including workplace exposures in the burgeoning nanotechnology arena. Our research broadly encompasses several strongly overlapping areas:

• Laboratory studies of the formation and evolution of secondary atmospheric aerosols.

• Airborne measurements of atmospheric aerosols and clouds.

• Advancing the state of the art for aerosol measurements.

• Sources of nanoparticle exposures in the nanotechnology laboratory and workplace.

• Applications of aerosol methods to the study of planetary atmospheres, molecular separations, and other research arenas.