Atmospheric Chemistry Program Seminar
Optimization of Surface-Initiated Atom Transfer Radical Polymerization for Application to Small Analyte Detection by Nathan Reed, CU Boulder, ANYL 1st year
"The research project I contributed to as an undergraduate student sought to investigate molecular transport as a means of signal enhancement in small analyte detection. Selective transport of analyte molecules to a nanosensor location will lower the limit of detection compared to analyte collection from free diffusion alone. Polymer brushes can be grown off a detector surface directly and can then be used to bring small molecules closer in proximity to the detector. The small molecules will selectively partition into the polymer-brush surface based on attractions caused by hydrophobic effects, hydrogen bonding, or ionic interactions. To foster such controlled and specific interactions on a device surface, uniform polymer thin films needed to be synthesized and the appropriate materials used for transport of target analytes needed to be understood. Additionally, there was a need for the method to be standardized so that non-polymer scientists and engineers could replicate it with ease. Atom transfer radical polymerization (ATRP) presented a polymerization technique able meet these needs. ATRP is a controlled polymerization technique whose parameters may be tuned to meet specific needs such as functionality and length. In addition, ATRP is an approachable technique to scientists unfamiliar with polymerization techniques once synthetic methods are unified and optimized. My undergraduate research has investigated ATRP reaction conditions applicable to a broad range of polymer types, both in solution and surface-tethered, to develop a unified and optimized synthetic approach."
Global simulation of brown carbon and single scattering albedo calculation using a chemical transport model by Duseong Jo, CU Boulder, Postdoc
"Recent observations suggest that a certain fraction of organic carbon (OC) aerosol effectively absorbs solar radiation, which is also known as brown carbon (BrC) aerosol. Despite much observational evidence of its presence, very few global modeling studies have been conducted because of poor understanding of global BrC emissions. I will present an explicit global simulation of BrC in a global 3-D chemical transport model (GEOS-Chem), including global BrC emission estimates from primary (biomass burning and biofuel) and secondary sources. The BrC absorption leads to a general reduction of NO2 photolysis rates, whose maximum decreases occur in Asia up to 9% (19%) on an annual (spring) mean basis. The inclusion of BrC absorption reduces the overestimation of single scattering albedo (SSA) in the model, but still the model overestimates the observed SSA by AERONET. To further reduce the overestimation, the sensitivity calculations of SSA are conducted by focusing on the physical properties of Black Carbon (BC), the inclusion of Brown Carbon (BrC), and the size distribution of dust. Large variations in the calculated SSA may result from slight changes of the geometric mean radius, geometric standard deviation, real and imaginary refractive indices, and density of BC. The inclusion of BrC and observationally-constrained dust size distributions also significantly affect the SSA, and result in a remarkable improvement for the simulated SSA at 440 compared with the AERONET observations."