Title: Composition, Formation and Evolution of Atmospheric Organic Aerosol: Known Knowns and Known  Unknowns

Speaker: Dr. Yong Bin Lim

Time: 10:00--11:30 a.m Sep 5, 2014

Location: Room 301, Old Geoscience Building
Abstract: Atmospheric fine particulate matter (PM2.5) affects global climate directly by scattering or absorbing solar radiation and indirectly by acting as cloud condensation nuclei, and also causes adverse health effects. The major fraction is known as secondary organic aerosol (SOA), but its chemical and physical properties are nearly unknown because SOA formation itself is largely unknown. In the past few decades, laboratory experiments and field studies along with developments of instrumental measurement techniques attempt to reveal atmospheric formation. Smog chamber experiments in labs successfully simulate secondary organic aerosols from reactions of volatile organic compounds (VOCs) with atmospheric oxidants (e.g., OH, NO3 radical and ozone), and this type of formation can be predicted by the partitioning theory, based on the traditional thought that semi-volatile products from oxidation of VOCs forms aerosols through gas-particle partitioning. Field studies measure constituents of organic aerosols, and oxygen-to-carbon ratios (O/C) of organic aerosols provide a key to reveal formation and evolution. SOA with O/C of 0.20.5 (i.e., semi-volatility oxygenated organic aerosol: SV-OOA) indicates the formation via gas-particle partitioning, and SOA with higher O/C of 0.51.1 (i.e., low volatility oxygenated organic aerosol: LV-OOA) suggests the chemical aging of SV-OOA or the formation through aqueous chemistry in/on atmospheric waters (e.g., cloud/fog droplets and wet aerosols). Aqueous chemistry can explain several unknowns: 1) magnitude/distribution discrepancy between measured SOA and model-predicted SOA; 2) LV-OOA formation; 3) water-associated SOA formation, which cannot be explained by the traditional partitioning theory, and 4) SOA formation from biogenic organic precursors with anthropogenic tracers (e.g., NOx). Aqueous chemistry includes both radical and non-radical reactions between organic and inorganic constituents. Sulfates and ammoniums enhance SOA formation by forming organo-sulfates, organo-nitrogens and ammonium catalytic reactions. Acid catalyzation (e.g., hemiacetal formation, aldol condensation) forms an oligomer type of SOA. OH radical reactions and photolysis form multifunctional products mostly in cloud droplets and oligomers through organic radical-radical reactions in wet aerosols.
Resume: Research Associate       2012Present  Rutgers, The State University of New Jersey
                 Postdoctoral Associate  20082012    Rutgers, The State University of New Jersey
                 Ph.D.                                 2008         University of California, Riverside
                 B.S.                                    2002         University of California, Riverside