Date of Award

Spring 2010

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

Howard R Mayne

Abstract

Atmospheric measurements made at Appledore Island, Maine were used to investigate nighttime nitrate radical (NO3) chemistry and its significance for the nitrogen oxides (NOx = NO + NO2) budget in the Gulf of Maine region during the summer of 2004 International Consortium for Atmospheric Research on Transport and Transformation field campaign. Removal of NOx was strongly dependent on reactions of NO3 with biogenic volatile organic compounds and the fate of dinitrogen pentoxide (N 2O5). For three case studies, temporal profiles of NO 3 were calculated from measured parameters. Comparisons between measured and calculated NO3 mixing ratios highlighted significant uncertainties in the kinetic parameters governing gas-phase and heterogeneous N2O 5 hydrolysis. Removal of NOx was estimated to be ∼11 ppbv day-1, with nighttime chemical pathways contributing ∼50%.

Atmospheric measurements made at the AIRMAP atmospheric monitoring station Thompson Farm (THF) during summer, 2004 were used to test the specificity of a proton transfer reaction-mass spectrometer (PTA-MS) for atmospheric toluene measurements under conditions often dominated by biogenic emissions. Quantitative estimates were made of potential interferences in the PTR-MS toluene measurements related to sampling and analysis of monoterpenes, including fragmentation of the monoterpenes and some of their primary carbonyl oxidation products in the PTR-MS drift tube. The analysis supported only minor interferences from the investigated fragmentation sources, suggesting that toluene can be reliably quantified by PTR-MS with the operating parameters used, under the ambient compositions probed. This work extends the range of field conditions under which PTR-MS validation studies have been conducted.

A GC instrument was developed for measurement of hydrogen cyanide (HCN) in the lower atmosphere. Its major features include a cold temperature analyte enrichment system, a robust porous polymer stationary phase capillary column and a flame thermionic detector. The instrument was deployed for a I week period in April, 2009 at THF. Measured HCN mixing ratios ranged between 0.07(3) and 0.33(3) ppbv, with significant temporal variability, and appeared to agree well with previous tropospheric measurements. Long term, in-situ atmospheric measurement of HCN is necessary to characterize the regional HCN budget and reduce uncertainty in the global budget. Few such measurements have been demonstrated at present.

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