Date of Award

8-2004

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Advisor

Brian G. Frederick

Second Committee Member

MaryAnn McGarry

Third Committee Member

Robert J. Lad

Abstract

Air is present in every layer of Earth's atmosphere from the troposphere to the thermosphere. As inhabitants of Earth, we are constantly affecting and are affected by the quality of the air. For both reasons, it is important to monitor the concentrations of pollutant gases, such as nitric oxide (NO) and ground level ozone (O3) in the atmosphere. The presence of NO in the troposphere, mostly attributed to fossil fuel combustion, leads to stratospheric ozone depletion and to the formation of acid precipitation and ground level ozone. O3 is easily absorbed through the respiratory tract and therefore, adversely affects the lungs in concentrations exceeding 80 ppb. In addition, elevated levels of NO in exhaled human breath have been linked to a respiratory tract inflammation as well as liver and kidney damage. Detection of NO with a portable sensor system is therefore important for both environmental and biomedical applications. In this study, a nitric oxide gas sensor was developed using tungsten trioxide (WO3) sensors modified with 10 or 0.5 Å of a gold (Au) or silver (Ag) catalyst. These sensors demonstrated a direct response to NO, at concentrations ranging from 150 to 1420 ppb, with a decrease in WO3 film conductivity. This decrease in conductivity, we propose, is attributed to the metal catalyst providing a reaction site for the oxidation of NO in air to NO2, which diffuses onto and across the WO3 film until reacting with an oxygen vacancy site. Au modified sensors demonstrated greater stability than Ag modified sensors. Sensor test data and scanning electron microscopy images of 0.5 Å Au modified WO3 sensors was achieved for a mean particle area of 70 nm2 and a projected metal surface coverage of about 0.02%. Through a National Science Foundation GK-12 grant, sensor research and air quality testing was extended into a local hich school's chemistry curriculum and impacted 57 students. An ultraviolet photometer for detecting ground level ozone was acquired for the chemistry students and sparked the development of six air quality projects implemented in the 2003-2004 school year. These projects targeted a variety of student learning styles as well as addressed Maine, national (American Association for the Advancement of Science), and international (North American Association for Environmental Education) education standards. The effectiveness of these projects in improving students' understanding of 1) atmospheric chemistry, 2) the environmental and health risks associated with different types of air pollution, and 3) the analytical methods for detecting various gases in the atmosphere was evaluated based on individual project analysis, student comments, pre/post test scores, education standards, and personal observations. The results revealed a dramatic improvement in students' understanding of the precursors of ground level ozone and the factors, which influence the detected ground level ozone concentrations. A project based curriculum allowed the students to take ownership of the work through independent, critical, and creative thinking while analyzing "in their backyard" data.

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