Special Issue Preface pubs.acs.org/JPCA
Autobiography of A. R. Ravishankara
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theory in terms of a physical picture of an ion surrounded by molecules. I thought about his lectures many years later when I was dealing with multiphase atmospheric chemistry. I graduated with a first class M.Sc. in April 1970 and decided to pursue a doctoral degree. I was accepted for a Ph.D. course at another IIT, but I was expected to work on positron annihilation spectroscopy because of my radiochemistry background. I found this boring and moved to the Indian Institute of Science (IISc) in Bangalore. This revered institute was old and beautiful. I really enjoyed a level of independence in research on studying properties of transition metal complexes. The course work was excellent. In particular, I really understood for the first time some stuff about statistical mechanics from A. K. N. Reddy, who was a superb teacher. I also learned glass blowing, machining, and some German. The German teacher from Bavaria gave us free beer at his home, which was great! I met a young assistant professor (S. R. Jain) that had just completed his postdoctoral work at the University of Florida in Gainesville. His description of independence in the U.S. to pursue research was exhilarating. I was not getting along with my thesis advisor and I decided on graduate studies in the U.S. Even though my application was sent in April of 1971, the University of Florida (UF) offered me admission and a teaching assistantship for that Fall. America and My Scientific Research Training. I landed in Gainesville two weeks after the semester had started. I was told to take three intermediate level coursesone each in physical chemistry, inorganic chemistry, and organic chemistry. I thoroughly enjoyed these courses and the way they were taught. The UF Chemistry Department was good to me because I was exempted from taking the comprehensive exams (based on my grades), did not have to take a foreign language (because they made me take TOEFL, a test in English as a foreign language, and I successfully argued that I had done a foreign language), and exempted me from the “library course” and above all the general chemistry lab course that all entering graduate students had to take! I met Robert J. Hanrahan (R.J.H.) when I arrived in Gainesville, because he was in charge of graduate student admissions. I decided to work with R.J.H., which turned out to be a great decision for me. R.J.H. was the ideal professor. He allowed me to pick the topics for my work, helped when needed, was available when needed, and was always willing to help with instruments and with thinking through problems. R.J.H. expected us to build everything; I built my gas chromatograph using a biscuit oven and a thermal conductivity detector with homemade electronics. I improved my machining, glass blowing, and electronics skills. Mike Bowers and Keith Jennings had proposed that the reaction of C2H2F2+ with C2H2F2 proceeded through a cyclic intermediate. R.J.H. enthusiastically agreed with my suggestion
am told that I was born in Shimoga, in the state of Karnataka, in India in my grandfather’s home on the bank of a river. I was brought up until I was about 10 in Akkihebbal, a medium-sized “village”, where my father was trying to be a farmer. He had moved there from Bangalore after India’s independence to make an “honest living” by being a farmer and to help people in the village. I have memories of playing in sugar cane fields, almost drowning in a well (I swore that I would learn to swim and did teach myself to swim years later), teaching myself to ride a bike, building kites, having many encounters with snakes, breaking my patella, and doing many other interesting things. When my father passed away, we moved to a midsized city called Mysore. One of the best things that happened to me a few years later was to attend a very good high school called Sharada Vilas High School where I befriended three classmates. Two of them, Prasad (A. Ramaprasad) and Viji (T. R. Vijayakumar), also ended up in the U.S. and have remained my best and lifelong friends. The third friend, Muralidhar, sadly passed away at a young age. Education in India. In high school, I worked hard on subjects that interested me and badly neglected others. We had a very good science teacher (S.K.we referred to all the teachers by their initials!) and he did try to make science fun. I vividly remember watching a small falling coconut sinking slower and slower down in a tank of water and coming up with an idea to measure the viscosity of liquids. I talked to S.K. about it and he gently told me that somebody else had figured this out a long time ago and that it was good that I thought about it! It was expected that I would go to a university, and I majored in Physics and Chemistry with a minor in Mathematics at the University of Mysore. I graduated with a first class B.Sc. degree when I was around 19. Most of the courses at the university were boring, with no discussions or problem solving. Grades (“marks” in India) were determined by the final exams, which required memorization and regurgitation. What I remember most are riding bicycles with my three friends, discussing topics from politics to science, reading books, and playing cricket (badly), all of which I love to this day. One of the key turning points was coming across Feynman’s lectures on physics, reading it, and solving some of the “undefined” problems. I went to one of the Indian Institutes of Technology (IITs), which were considered the pinnacle of universities in those days, for a M.Sc. course in Physics, stayed there for one week, did not like it, and went back to the University of Mysore. I did a M.Sc. course in Physical Chemistry with an elective in Radiochemistry. One day I plotted the number of neutrons versus protons for all the stable elements and found that my plot extrapolated to infinite neutrons around 120 protons. My conclusion was that we could not have stable isotopes beyond element 120. Again, as with the viscosity measurements idea, this was known for a long time! I had one great lecturer, H. M. K. Naidu, who later became a professor. He actually answered questions, even said “I don’t know” on occasion, always came back with answers later, and really challenged us to think. I particularly remember his explanations of the Debye−Hückel © 2012 A. R. Ravishankara
Special Issue: A. R. Ravishankara Festschrift Published: June 21, 2012 5735
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to study C4H4F4+ itself and bought me 1,1,2,2-tetrafluorocyclobutane (TFCB) from Columbia Chemicals at what seemed to me to be a princely sum. (In those days I used to constantly convert U.S. dollars into Indian Rupees to buy anything. With the Rupee being much weaker than the dollar, everything in the U.S. was exorbitantly expensive in my eyes!) Thus, I started my work on TFCB and my long association with fluorinated chemicals! I set up the time-of-flight (TOF) mass spectrometer to measure appearance potentials and published my first paper in 1975 on this work. R.J.H. told me that I should decide on my “last name”. So, I used my given name as my last name and thus started a new “clan” of Ravishankaras! I knew that I had to study the γ-radiolysis of TFCB because it was R.J.H.’s interest. So, I did it whenever (including nights) I had access to the cobalt-60 source. I wanted to explore the behavior of this molecule when it is dissociated by other means. I built a radio gas chromatograph using surplus equipment to study hot-atom reactions of 18F by irradiating TFCB with neutrons from the reactor next door. Unfortunately, by the time my container was radioactively cold enough to handle, I had lost most of my 18F activity. So, I gave up on hot-atom chemistry. I then studied ion−molecule reactions involving TFCB dissociation products using a “high pressure” ion source and the TOF mass spectrometer. However, the pathways for these reactions were unclear. At that time John Eyler had just arrived at University of Florida as an assistant professor. One of R.J.H.’s students (Tacheng Hsieh) was helping John set up his ion cyclotron resonance mass spectrometer, ICR. I used that ICR to do double resonance experiments and identified the specific reactant and product ions in the reactions I had studied. Then I did mercury-sensitized decomposition of TFCB, and we came up with a way to do micro titrations using a fluoride ion selective electrode. During my last year of graduate school I met my future wife (Rochelle Davidson) and this event completely changed my life, and especially my plans for a postdoc in Germany and returning to India. I had heard Sherry Rowland talk about CFCs and ozone layer depletion and it occurred to me that I could actually work in this area and utilize my gas-phase kinetics background. R.J.H. suggested that I consider working with Doug Davis (who was one of R.J.H.’s earliest graduate students) at the University of Maryland. Doug offered me a postdoc starting in January 1976. Rochelle was accepted at a couple of medical schools in the DC area. We thought that we were all set! Rochelle and I got married in Miami on December 21, 1975, and drove to College Park, MD, on New Year’s Day of 1976. Doug “assigned” me to work with Robert Watson (now Sir Robert!), who was the senior postdoctoral fellow in his group doing kinetics. Doug also told me that he was leaving Maryland later that year! It was quite an eventful year trying to do research and plan for our future. I measured the rate constants for the reactions of OH with HCl (to quantify the rate of conversion of the HCl reservoir in the stratosphere back to active chlorine), reactions of chlorine nitrate (which had just been proposed to be important by Rowland and Molina) to establish its lifetime, and a host of other reaction rate constants. I also started playing with measurements of rate constants at high temperatures. I learned a great deal from Bob Watson and Doug Davis, especially about focusing on important issues. First CareerGeorgia Tech. I was offered a permanent position at the Engineering Experiment Station (EES) at Georgia Tech (now called Georgia Tech Research Institute
(GTRI)) in the research activities that Doug had started, including kinetics, photochemistry, etc. After about two years, Doug moved to the School of Geophysical Sciences (now Earth and Atmospheric Sciences) and a small group of us continued with atmospheric and combustion kinetics. Frank Tully (who later moved to Sandia National Lab in Livermore, CA) and I worked on high temperature reactions. Paul Wine (who is still at Georgia Tech) and I worked on atmospheric reactions. I cannot remember exactly when, but I became the group leader and our group grew to four permanent staff and many students. Frank and I had an Air Force grant that allowed us to directly measure the rate constants for OH reactions with CH4 and H2 between 400 and 1200 K using flash photolysis to produce, and resonance fluorescence to detect, OH. This allowed us to “connect” the disparate shock tube data with the lower temperature data. To our surprise, there was a smooth connection by a curved Arrhenius plot! Paul Wine and I started using pulsed lasers to cleanly create radicals and also to detect them. We studied a host of atmospheric and combustion reactions. In particular, our studies on the reaction of OH with HNO3 turned out to be a great success. We showed that the reaction had a negative temperature dependence, contrary to the accepted “wisdom” in those days, and noted its importance in the stratosphere. A discussion with Ralph Cicerone, the Editor of the Journal of Geophysical Research (JGR) at that time, led to the publication of our kinetics results in that journal (one of the first kinetics papers to be published in JGR). We also started accurate rate constant measurements (as well as product yields) by following the temporal profiles of the product. Notable examples include studies of reactions O(1D) with atmospheric gases and of CH3O2 with NO. We also made a significant foray into measuring rate coefficients for radical− radical reactions at atmospheric pressures by creating “known” concentrations of free radicals via pulsed laser photolysis. The nine years at Georgia Tech, with a host of talented colleagues (in particular Paul Wine and Mike Nicovich) and extraordinary undergraduates, were very productive, fun, and satisfying. I went on a sabbatical in Jürgen Troe’s lab in Göttingen in 1983 to learn more about association reactions and “to do theory”. Rochelle had finished her residency at Emory medical school. I found very quickly that Jürgen did all of his own calculations! I did some calculations on the OH + CO reaction using his statistical adiabatic channel model but made little progress (I think Jürgen wrote a bunch of elegant papers on it years later). I measured rate constants for the CH3 + O2 reaction and the CH3O2 self-reaction with Horst Hippler’s help. During this visit to Germany, I decided that it might be better for me to move from Georgia Tech. This visit also cemented my friendship with John Burrows, who was at Mainz. Second CareerBoulder. Carleton Howard at the National Oceanic and Atmospheric Administration (NOAA) Aeronomy Laboratory in Boulder, CO, had encouraged me to move there. Almost solely on the basis of his initiative, I was offered a position at NOAA, which I joined in 1984. Rochelle and I physically moved to Boulder on a cold February day in 1985 with our 4-week-old son, Isaac. The year 1985 was a very momentous one for me. First, Isaac Hari was born. Second, we moved to Boulder, and third the Antarctic ozone hole was discovered. Each of these events had a profound effect on my life and career. At NOAA, I was unencumbered from writing proposals, was able to hire superb postdocs, and could pursue issues that I knew (or guessed) were emerging. A short walk down the hall got me answers to 5736
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higher pressures. Steve Brown, who had just joined my group as a postdoc, worked on this reaction with Ranajit Talukdar and established its pressure dependence at low temperatures and some unusual kinetic isotope effects. These findings had a big impact on our ability to model stratospheric nitrogen oxides. Tomasz Gierczak and Ranajit studied the reaction of OH with acetone and established its negative temperature dependence as well as unusual kinetic isotope effects. Further, Ranajit studied the reactions of OH with CH3ONO2, its deuterated analogs, etc. These unusual results led to our strong feeling that some OH reactions proceed through hydrogen-bonded complexes in the entrance channel. Many discussions with Casey Hynes of CU were extremely helpful to me. Further discussions with Ian Smith (who was visiting Boulder) led to a paper summarizing our thoughts on hydrogen-bonded complexes in OH reactions. Working with Ian was a delight (a masterful paper magically appeared!) and led to our collaborative studies of vibrational quenching of OH by various molecules that were carried out by David McCabe as a part of his Ph.D. thesis. I have spent a lot of time on OH reactions over the years and I feel that I finally understand at least the reaction of OH with HNO3! I learned two lessons from these studies: (a) atmospheric chemistry demanded studies under conditions that were not normally utilized and could lead to fundamental discoveries about chemical reactions; (b) atmospheric chemistry belongs, in my opinion, in what is referred to as “Pasteur’s quadrant”,2 that is, “use-inspired research”, and should not be thought of as “applied chemistry”. University of Colorado. I want to note that my association with the Chemistry Department at CU has been amazingly rewarding. First, I got a chance to work with many graduate students (listed elsewhere in this issue) who were great. Second, I got to talk to many nonatmospheric chemists whose work impacted how we think about atmospheric chemistry. Third, the chemistry faculty always treated me as a full-fledged faculty member on campus (even including committee work and teaching duties!!) even though I was an Adjoint Professor. Fourth, I got to teach undergraduate and graduate classes, which made me really learn my chemistry! I am grateful to CU for this association. Field Measurements. When I came to Boulder, I was very interested in diode array spectrometers as a way to study reaction kinetics. Andreas Wahner (who was one of my first postdocs in Boulder) put together a modern version of Porter and Norrish’s experiment with a diode array spectrometer in place of photographic plates! Discussions with Art Schmeltekopf, my NOAA Aeronomy Lab colleague, were very helpful. Even though the experiment worked, we never published anything because we were distracted (mostly by Art Schmeltekopf) to put together a zenith sky spectrometer on board a NASA DC-8 aircraft to go to Antarctica. Andreas Wahner took this on (with Roger Jakoubek and George Mount) and we went to Chile for 8 weeks to measure OClO, BrO, NO2, and O3 over Antarctica. We had configured this spectrometer to look directly at the full moon to measure OClO, in particular, at night. We had one opportunity to do it on September 8, 1988, and we almost could not do it because of decisions beyond our control. Also, our inability to repeat atmospheric measurements, unlike in the laboratory, was unsatisfying to a lab scientist like me. I swore that I would not do field measurements unless I had complete control (obviously, I changed my mind on this later)! But, the view of a full moon over the dry Antarctic air and ice-covered mountains
any atmospheric question and a short visit to the University of Colorado (CU) campus enabled chemistry discussions. I was just interested in having a small group and doing some “hands on” science. The many discussions and friendship with Carl Howard during the first few years in Boulder were invaluable. In addition to continuing studies of some gas phase reactions related to the degradation of hydrocarbons, CS2, COS, and CH3SCH3 (DMS), I was eager to get into tropospheric heterogeneous chemistry. But, as usual, extraneous events shaped what I did! In particular, it kept me attached to the stratosphere and started me in stratospheric heterogeneous chemistry. I will just recount a few themes in my work and life in Boulder because it is still an ongoing journey. Focus on Atmospheric Chemistry and Not Just Chemistry. An important turning point was my discussion with Susan Solomon. In her characteristically incisive way, Susan told me that I could measure the best lab data, but they would go “unnoticed” without including atmospheric calculations. So, I asked her if we could collaborate to put this to practice. We had a very fruitful and long collaboration, so much so that I was once referred to as “Solomon’s bench scientist” or something to that effect. I took this comment as a badge of honor! Needless to say, my collaborations with Susan led to many major papers; I give two examples below. (1) Studies of long-lived greenhouse gases: Our work showed1 that perfluorochemicals were very long-lived in the atmosphere (almost “eternal gases”!) and had large global warming potentials. This work started because of my interest in fluorinated chemicals since graduate school days. We looked at every possible way to destroy these moleculesfrom the ground to the top of the atmosphereand found destruction in combustors or way up in the mesosphere to be the likely rate-limiting processes. (2) How to deal with stratospheric heterogeneous reactions: Stephen Schwartz (Brookhaven National Laboratories) had written a seminal paper on how to deal with reactions in tropospheric cloud drops. But, in the stratosphere, it is easier to deal in terms of surface area as opposed to volume (as Steve Schwartz had done). A hallway conversation with David Hanson, an incredibly talented scientist who was working with me at that time, led to the development of the methodology that became the standard for stratospheric calculations. Susan did a host of calculations using this methodology to show how to use it and what the result would mean. It was very satisfying to describe heterogeneous reactions in terms of independently measurable physicochemical parameters. Another venture was my attempt to very accurately measure rate coefficients for moderately slow radical−molecule reactions that determine the atmospheric lifetimes of the closed-shell reactants. Studies on the OH + CH4 reaction by Gammy Vaghjiani (a postdoc at that time) were followed by studies of a large number of reactions involving substitutes for ozonedepleting chemicals and greenhouse gases. A host of people worked on the CFC substitutes in my lab. In particular, Jim Burkholder, a long-time colleague, did a lot of work on the photolysis of these molecules. He continues such studies in his group even today. These studies were very important in evaluating the environmental acceptability of CFC substitutes, and they also changed our bar for accuracy of rate constants for radical-molecule reactions and photochemical parameters. There was a lot of speculation in the 1990s about the photolysis rate of HNO3 being incorrect. It occurred to me that the HNO3 lifetime would be shorter if the rate coefficient for the OH + HNO3 reaction was faster at lower temperatures and 5737
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daughter Amelia have made my life worth living and rounded out my life a great deal. Their weekends in the lab, wandering the halls or playing with dry ice, are indelibly imprinted in my mind. Lastly, the support, love, and encouragement of Rochelle have been key for my career. She has never complained about my long hours and weekends in the lab, has supported and adjusted to our moves from College Park to Atlanta and from Atlanta to Boulder, and has remained supportive. For that, I am grateful! I am deeply honored by all of you who have contributed to this special issue and other aspects of this Festschrift. Thank you. I am especially grateful to James Burkholder, Yinon Rudich, and Paul Wine for making this Festschrift possible.
below was a reward! This was the year when Rochelle and I knew that our daughter Amelia Sita would enter our lives in 1988; when she did, it really changed our lives! I had been interested in measuring NO3 in situ in the atmosphere ever since I worked on its kinetics and spectroscopy at Georgia Tech. We collaborated with National Institute of Standards and Technology (NIST) scientists in Boulder and built a diode laser-based long-path system to measure NO3. Ranajit Talukdar and Yinon Rudich used it to do many lab studies. However, the instrument was not rugged and stable enough to take to the field. While listening to a talk on cavity ring down spectroscopy (CRDS) at a Gas Kinetics meeting in Bilbao, Spain, I was intrigued by the possibility of measuring NO3 using CRDS. A calculation during the talk convinced me that we could indeed do it. I suggested to Steve Brown that he could build a CRDS using existing parts and an old YAG laser. Amazingly, it was working within a week and this started our work on CRDS at NOAA in Boulder. It also was clear to me that we could not avoid measuring N2O5 because it would decompose. The power of chemical titration in these systems, which I had used in measuring NO3 absorption cross sections many years back, proved to be very useful. So started my second venture into field measurements. Ned Lovejoy, Tahllee Baynard, and Anders Petterson turned the major “noise” in CRDS due to aerosols into a signal for aerosol extinction measurements. Steve Brown has really taken the CRDS and optical measurement of atmospheric constituents to new heights over the past decade in Boulder. Others in our lab have really advanced the aerosols measurements. Science Administration. Since 2005, I have moved more and more into administration of a laboratory here. Since becoming the director more than six years back, it has become more difficult to be involved in “day-to-day” science. I have been involved in taking scientific information to policy makers via assessments and NOAA outreach. I have also been able to formulate research priorities, getting NOAA and our lab to do advanced atmospheric chemistry studies, etc. Fortunately, my collaborations with some of the modeling folks in the Chemical Sciences Division have allowed me to continue the exploration of ideas by calculations. The most recent notable work, with John Daniel and Bob Portmann, was to show that N2O is the most important ozone-depleting gas emission today. Many people have immensely helped in doing my administrative and assessment duties, and in particular I am grateful to James Meagher, Chris Ennis, LeAnn Droppleman, and Jeanne Waters. My scientific career has indeed been very rewarding to me. I really look forward to spending more time doing science and maybe even going back into the lab to do experiments one of these days. Thanks. There have been many people who have shaped my life and helped me achieve whatever I have. The influence of my family as I was growing up was enormous. In particular, my mother, my sister Srimathi, and my oldest brother Krishnamurthy influenced me profoundly. My younger sister, Vijayalakshmi Basavaraj, who passed away prematurely, was also a dear friend. My life-long friendships with Prasad and Viji have been a source of support. Robert Hanrahan and Doug Davis helped me grow as a scientist. I am particularly grateful to Daniel Albritton for his confidence in me and his support. Susan Solomon’s influence has been noted earlier. My science colleagues at Georgia Tech and Boulder, listed in this issue, have been instrumental in our scientific accomplishments and making me get to work eagerly each day. My son Isaac and
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REFERENCES
(1) Ravishankara, A. R.; Solomon, S.; Turnipseed, A. A.; Warren, R. F. Atmospheric lifetimes of long-lived halogenated species. Science 1993, 259, 194−199. (2) Stokes, D. E.. Pasteur’s Quadrant − Basic Science and Technological Innovation; Brookings Institution Press: Washington, DC, 1997.
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