Date of Award

Fall 2009

Project Type

Dissertation

Program or Major

Earth and Environmental Science

Degree Name

Doctor of Philosophy

First Advisor

Robert J Griffin

Abstract

Organic aerosols are a ubiquitous component of the troposphere, from heavily polluted cities to the remote Arctic. In Chapters II, III, and V of this dissertation, the formation of organic aerosol through observations of ambient size distributions is addressed. Chapter IV presents a new pathway for the formation of nitrous acid (HONO) in the urban atmosphere.

In Chapter II, the size-resolved chemical composition of sub-micron aerosol was measured at a suburban forested site in North Carolina. Two events were identified in which particle growth, presumably by gas-to-particle conversion, was dominated by accumulation of organic aerosol mass. Growth rates between 1.2 nm hr-1 and 4.9 nm hr-1 were observed. Using a mass-spectral deconvolution method coupled with linear regression analysis, the sub-micron organic aerosol mass observed during the campaign, and during events, was determined to have been influenced by both local and regional secondary processes with only a minor influence from combustion sources.

In Chapter III, the chemical characteristics of sub-10-micron aerosol were explored as a function of ambient particle size at a coastal and inland site in New England. Average organic carbon (OC) concentrations of 4.9 microg C m-3 and 3.4 microg C m-3 were observed at the coastal site at the Isles of Shoals (IOS) and at the slightly inland site at Thompson Farm (TF), respectively. An average of 84 and 72% of OC was found to be water-soluble at IOS and TF, respectively. Size distributions indicate that the formation of dicarboxylic acids, especially oxalic acid, is driven by aqueous-phase reactions. A chemical fingerprint analysis suggests that all water-soluble OC at IOS resembles secondary organic aerosol (SOA), while WSOC at TF appears to result from mixed sources.

In Chapter IV, a newly identified formation pathway for nitrous acid (HONO) is presented. HONO is an important precursor to hydroxyl radicals in the troposphere and thus contributes to the oxidative capacity of the atmosphere. The proposed pathway is shown to depend on the surface chemical characteristics of primary organic aerosol, and concentrations of HONO are shown to exceed those that can be explained by previously identified formation pathways.

In Chapter V, particle growth events were observed at Summit, Greenland, an extremely remote Arctic site. Particle growth was linked indirectly to condensation of organic compounds because measured concentrations of sulfuric acid could not explain the observed growth rates of up to 0.963 nm hr -1. The snowpack may be the source of condensable organic precursors, and thus organic aerosol, based on prior observations at the site. This pathway represents a source of global SOA currently not taken into account that may have implications for climate regulation.

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