Events Calendar

Astani Dept. of Civil and Environmental Engineering Seminar

Speaker: Lea Hildebrandt, Carnegie Mellon University, Department of Chemical Engineering

Talk Title: Atmospheric Organic Nanoparticles:Importance, Challenges and Progress

Abstract: Atmospheric nanoparticles (aerosols) affect society in multiple ways. For example, they affect human health by damaging the respiratory and cardiovascular systems, they degrade visibility, and they perturb Earth’s climate by reducing the penetration of solar radiation and by influencing cloud formation and lifetime.

Organic aerosol globally comprises a significant fraction (20-90%) of the submicron particle mass. It is composed of thousands of species, many of them unidentified, and has a myriad of sources – both anthropogenic and biogenic, particle phase and gas phase. Furthermore, organic aerosol is dynamic: most of its components are semi-volatile and can evaporate, can be transported and further processed in the atmosphere, and can repartition to the particle phase, making it very challenging to trace the organic aerosol sources. Three-dimensional chemical transport models often significantly under-predict the concentration, oxidation state and diurnal cycle of organic aerosol, suggesting that our understanding of organic aerosol and, more generally, atmospheric nanoparticles is incomplete. We need to better understand atmospheric nanoparticles and update our models which will then allow us to develop effective policy actions to mitigate atmospheric particles and their adverse effects.

I will present recent results from our laboratory experiments and ambient measurements which shed light on organic aerosol formation, the interaction of different organic aerosol types, and their chemical transformation (aging). Firstly, aerosol production experiments using a state-of-the-art environmental chamber showed that aerosol mass yields from anthropogenic organic aerosol precursors such as toluene (methylbenzene) are much higher than previously reported. Secondly, in order to understand the interaction of organic aerosol from different sources, we developed a new experimental method using isotopically labeled compounds (13C or D) and a High Resolution Time-of-Flight Aerosol Mass Spectrometer. Our results are consistent with pseudo-ideal mixing of anthropogenic and biogenic organic aerosol components at equilibrium. This confirms that the presence of anthropogenic organic aerosol enhances the concentration of biogenic organic aerosol. Finally, our measurements at a remote coastal site on the island of Crete suggest that the variability between different organic aerosol types decreases significantly with chemical transformation (aging). The photochemical age of organic aerosol may be just as important as the aerosol source in understanding its concentrations and characteristics.

All of these findings have been used to more accurately represent organic aerosol in chemical transport models. The updated models agree well with observations of organic aerosol concentrations, approximate oxidative states and diurnal cycles in highly polluted (Mexico City) as well as pristine environments (Crete).

Location: Kaprielian Hall (KAP) - 209

Audiences: Everyone Is Invited

Contact: Evangeline Reyes