Atmospheric Organic Particulate Matter: Measurements, Models and MItigation

Atmospheric particles (aerosols) damage human health, degrade visibility, and perturb Earth's climate. Organic aerosol (OA) globally comprises a significant fraction (20--90%) of the submicron particle mass. Chemical transport models often significantly under-predict the concentration and oxidation state of OA, suggesting that our understanding of OA is incomplete. We need to better understand OA and update our models if we are to develop effective policy actions aimed at mitigating atmospheric particles and their adverse effects.;This thesis presents results from laboratory experiments and ambient measurements which shed light on OA formation, the interaction of different OA types, and their chemical transformation (aging). First, aerosol production experiments showed that aerosol mass yields from anthropogenic OA precursors such as toluene (methylbenzene) are much higher than previously reported. Second, in order to understand the interaction of OA from different sources, a new experimental method was developed using isotopically labeled compounds (13C or D) and a High Resolution Time-of-Flight Aerosol Mass Spectrometer. Results are consistent with mixing of anthropogenic and biogenic OA components at equilibrium. This confirms that the presence of anthropogenic OA enhances the concentration of biogenic OA. Third, measurements at a remote coastal site on the island of Crete suggest that the variability between different OA types decreases significantly with chemical transformation (aging). The photochemical age of OA 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 OA in chemical transport models. The updated models agree well with observations of OA concentrations, approximate oxidative states and diurnal cycles at different locations and in different seasons. A sensitivity analysis reveals that the predicted OA concentrations and relative importance of different OA types depend greatly on the assumptions made about OA aging and mixing; a more detailed understanding of these processes is therefore essential. Overall, anthropogenic gaseous OA precursors are more important than previously assumed suggesting that future regulatory efforts targeting these compounds are promising.