Title

Acid-catalyzed heterogeneous reaction of limonene with mineral aerosols : a new mechanism for the organic coating of inorganic aerosols.

Date of Award

5-1-2015

Document Type

Thesis

School

College of Liberal Arts

Degree Name

Bachelor in Arts

Abstract

Many uncertainties remain about the reaction of atmospheric volatile organic compounds to form secondary organic matter (SOM) on inorganic aerosols. This thesis describes a previously unstudied reaction between limonene and mineral aerosols involving an acid-catalyzed heterogeneous mechanism by which volatile organics react directly with inorganic aerosols to form condensed phase organic compounds. Kaolinite and [alpha]-alumina were exposed to gaseous limonene at varying concentrations and under conditions of varying relative humidity, HNO3 presence and carrier gases. Product formation was monitored using infrared spectroscopy (DRIFTS), and products were identified using GC-MS. Kaolinite exposed to limonene formed [alpha]-terpineol. Alumina exposed to limonene formed 1-methyl-4-(prop-1-en-2-yl) cyclohex-2-enol (53%), carveol (28%) and limonene glycol (13%). Pre-exposing the mineral surface to gaseous HNO3 increased the rate of product formation and affected the type of product formed. Limonene concentration and the initial rate of product formation varied linearly indicating an Eley-Rideal type reaction, in which gaseous limonene reacted directly with the surface sites and condensed water. Increasing the relative humidity decreased the initial rate of reaction and saturation of products indicating competition of water and product for adsorption sites. This reaction between limonene and mineral aerosols represents an additional mechanism which may work in conjunction with the traditional gas phase oxidation and condensation to adhere organic compounds to mineral aerosols.