Numerical modeling of light absorption and radiative forcing impacts of biomass burning emission proxies undergoing aqueous chemistry and photolysis
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Civil, Environmental and Geodetic Engineering Honors Theses; 2021
Understanding and predicting climate change is essential to building knowledge for policymaking, engineering, and public health. Recent wildfires in the western United States resulted in biomass burning (BB) emissions that directly impacted regional air quality, and indirectly impacted climate change. However, quantifications of BB radiative forcing are uncertain. BB emits black carbon and various organic compounds ranging from particulate organic carbon to volatile organic compounds (VOC). Water soluble VOCs, including oxygenated aromatic compounds, can enter cloud water, in which they may undergo aqueous chemistry in cloudy atmospheres to form secondary organic aerosols (SOA). SOA contribute to radiative forcing by reflecting light (net cooling) or absorbing light (climate warming) when radiation is released as thermal energy. The objective of this study was to model and predict absorption to quantify the climate warming effects of BB emission chemistry. Three MATLAB scripts were developed and tested for analysis of BB emission proxies using absorption values from another study. The first code fit experimental data to quantify the imaginary refractive indices (related to light absorption and warming) of the compounds and identified the absorbing and warming effects of the colored compounds produced. The second code modeled absorbance changes as chemical processes occurred over time. The third code modeled nonlinear imaginary refractive indices and absorbance changes over time. The codes successfully modeled the imaginary refractive indices with experimental data and predicted absorbance chemistry of some BB SOA. Absorbance experiments were deferred due to technical complications. A procedure to measure absorbance for modeling inputs was created for future experimental work. A solar simulator will be used to irradiate oxygenated aromatic compounds produced in BB (phenol, furfural, and benzaldehyde). The solar simulator imitates natural sunlight and requires calibration using a chemical actinometer such as ferrioxalate, a photosensitive iron oxide solution. A portable darkroom was constructed to prevent photodegradation of ferrioxalate. Calibration and experiments will be performed in the same method to minimize discrepancies. Six cuvettes will be filled with solution and irradiated in the solar simulator. The cuvettes will be removed at specific time points and the spectral absorbances will be measured using a UV-vis spectrometer. Finally, the absorbance and imaginary refractive index results will be implemented into the models to quantify radiative forcing impacts.
Academic Major: Environmental Engineering
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