Hi all,
I am happy to announce to my 100,000 friends at DailyKos that I will be defending my thesis tomorrow. Hopefully this won't cause a media frenzy! ;-) I invited about 50 people and at the last minute they tried to change it to a room that holds about 15.
I am confident that I will pass, though they may ask me to make lots of changes and additions to the text. Some of you may remember my diary on water dimer. That is about a third of the defense. I am also discussing a new way to measure NO2 and some particle composition studies I did that found large amounts of acyl peroxynitrates (PANs) in the particles in Riverside. (Riverside, CA is a great place to study pollution. It is so easy to measure here.)
Some people have complained that science is not appropriate for a political blog. I think nothing could be further from the truth. To do politics and policy well you need to know the best knowlege about the most important issues. Science is the best way we have found to find that. We also don't help people by studying science in a vacuum. Even a guess as to what is going on is worth discussing. The internet makes this possible in a way that it never has been before.
Disclaimer... My results are mine alone. UCR and everyone else are not responsible for my views. Lots of people helped me with my thesis over the past 4.5 years. Hopefully I will thank them appropriately tomorrow.
Here is my abstract... I will stick around to discuss for a while but I am teaching until 10:00 pm tonight and I still have to get my lecture notes together.
ABSTRACT OF THE DISSERTATION
The Application of Cavity Ring-Down Spectroscopy to
Atmospheric and Physical Chemistry
by
James McChesney Hargrove
Friday August 24, 2007 Kohler lecture room
Doctor of Philosophy, Graduate Program in Chemistry
University of California, Riverside
Dr. Jingsong Zhang, Chairperson
Cavity ring-down spectroscopy (CRDS) is a sensitive form of absorption spectroscopy. Thousands of reflections between two multilayer dielectric mirrors give CRDS an extremely long path-length. The rate of decay of the signal is measured instead of the magnitude of attenuation, so laser intensity fluctuations do not affect the measurement.
At 405.23 nm, NO2 had a detection limit of 150 ppt/10 s (3σ). Particles were removed by a 0.45 μm filter. Water vapor had a 2.8 ppb NO2 equivalent interference for 1% water vapor in air, with a simple quadratic dependence on water monomer concentration that might have been due to water dimer. Removing NO2 with an annular denuder coated with guiacol and sodium hydroxide, or reacting the NO and NO2 with ozone, allows for an interference measurement. An NOy measurement can be obtained after thermal decomposition of higher oxides and ozone. The interference was easier to accommodate than the quenching found in chemiluminescence.
The water dimer hypothesis was supported by temperature studies resulting in thermodynamics consistent with theory. The oscillator strength at 409 nm was roughly three orders of magnitude stronger than the best available calculations, leading to a serious unanswered question of the possible source of the additional enhancement. Measurements at 532 nm found a similar response, and others have measured a response at 440 nm, suggesting the 6th, 7th and 8th overtones of water dimer occur at ~532 nm, ~440 nm and 409 nm with a similar magnitude that is possibly larger than the 3rd and 4th overtones that have not been detectable.
The excellent NO2 detection sensitivity enabled the measurement of NO2 emitted by ambient particles from thermal decomposition. Gas phase interferences were removed with radial aerosol denuders. PANs, ANs, and ammonium nitrate were measured sequentially at 150 °C, 215 °C and 250 °C by the emitted NO2. This technique was applied to ambient air during the Study of Organic Aerosols in Riverside (SOAR) campaign in Riverside during August 2005, and found that PANs were much higher than anticipated. Chamber studies found that PANs were a significant particle phase product from aldehydes.