Date of Award

Winter 2010

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

Howard Mayne

Abstract

Proton Transfer Reaction Mass Spectrometry (PTR-MS) is an increasingly popular technique for monitoring volatile organic compounds with high sensitivity and time resolution. This dissertation encompasses three different projects, sharing the common theme of expanding the knowledge and utility of the technique.

The first project focuses on elucidating the ion chemistry that occurs within the PTR-MS drift tube reaction chamber. The PTR-MS uses a differentially pumped skimmer to prevent excess water from the ion source from entering the drift tube reaction chamber. By placing a metering valve in between the skimmer region and the pump, it was possible to control the amount of water entering the drift tube. The valve made it possible to parameterize the impact of the pumping speed of the skimmer on ion source performance, cluster formation, and sensitivity. These results are compared with a kinetics model that simulates the protonated cluster distributions in the drift tube.

The second part of this dissertation describes the process for calibrating and deploying the instrument to measure acetic acid. Generating calibrations and measurements of ambient levels acetic acid are challenging because it adsorbs on instrument surfaces and transfer lines. To overcome the challenge of calibrating, a special permeation oven was used to generate a stable flow of acetic acid in the range of 7.0 to 26.5 ppbv, yielding calibration factors of 7.0 +/- 0.3 ncps·ppbv-1 to 10.9 +/- 0.7 ncps·ppbv-1 at 132 Td. At 88 Td, the calibration factor was found to be 30.8 +/- 2.6 ncps·ppbv-1. Measurements made on Appledore Island during ICARTT show that the PTR-MS measurements correlate well with those from the MC/IC technique, with a correlation coefficient of 0.78.

The final project uses the high time resolution of PTR-MS measurements to quantify the impact of storm systems on monoterpene mixing ratios in rural New Hampshire. Analysis of five years of monoterpene measurements at Thompson Farm (in Durham, NH) show storm events with intense precipitation correlate with brief periods of enhanced monoterpene mixing ratios. These events are classified based on duration and intensity, finding that storms can temporarily increase emissions by as much as 4260 g·km-2·hr -1.

Download

Share

COinS