Title

Demystifying the atmosphere with a model aerosol system : the photo-enhanced ozonolysis of surface adsorbed organics.

Date of Award

5-1-2014

Document Type

Thesis

School

College of Liberal Arts

Degree Name

Bachelor in Arts

Abstract

The chemical behavior of atmospheric aerosols is an area of great uncertainty due to their diverse chemical composition, unknown reactivity with tropospheric pollutants, and influences of solar radiation. In this study we focus on understanding the influences of simulated solar radiation on biomass burning aerosols by using a laboratory model. We used potassium chloride, a biomass burning tracer, as our solid substrate coated via gas phase adsorption with either eugenol or vanillin as our model semi-volatile lignin pyrolysis products. We used DRIFTS to analyze the reaction kinetics with ozone of these adsorbed organics under light and dark conditions. We identified vanillic acid as the major product of vanillin ozonolysis and homovanillic acid as the major product of eugenol ozonolysis. Ring cleavage products were not directly observed but are inferred by kinetic analysis. Ozonolysis of adsorbed vanillin follows the Langmuir-Hinshelwood mechanism in which ozone partitions to the adsorbed phase and subsequently reacts with vanillin. The maximal rate constant, kmax, for this reaction in dark and light were determined to be 0.013 min -1 and 0.029 min -1 with an ozone equilibrium constant KO3 of 1.81x10-14 cm3. The atmospheric lifetime of vanillin for the dark and light are 8.5 hours and 3.8 hours, respectively. Eugenol ozonolysis occurs at two sites that are affected differently by simulated solar radiation; the alkene side chain ozonolysis is unaffected by simulated solar radiation while the cleavage of the aromatic ring is photoenhanced. Rate constants were used to calculate atmospheric lifetimes of eugenol 18.8 hours and 20.4 hours in the light and dark, respectively. The reaction kinetics and mechanism provides us with valuable information to reduce uncertainty associated with the chemistry of biomass burning aerosols.