I'm nearing the end of the second year of my Ph.D in analytical chemistry here at UCSD under the supervision of Prof. Kim Prather. I moved to San Diego from Toronto in Sept. 2003 to begin my graduate work. My research interests centre around the chemical reactions and mixing that particles undergo as they are transported through the atmosphere. I came to UCSD to work with Kim Prather and use the ATOFMS to investigate these heterogeneous reactions at the single-particle level using this state-of-the-art instrument. I'm focused on investigating the rates and products of these heterogeneous reactions for a wide variety of organic, inorganic, and mixed (realistic) particle types and then looking at how these particles impact the atmosphere's chemical composition and the Earth's climate. Currently my research is focused on the chemistry of mineral dust particles in the troposphere.
2003 - present Pursuing Doctorate in Analytical Chemistry, Department of Chemistry & Biochemistry, University of California at San Diego
Thesis: Single-particle measurements of the heterogeneous aging of aerosols in ambient and laboratory studies and their
climatic effects (Advisor: Kimberly Prather)
1998- 2003 Honours Bachelor of Science in Environmental Chemistry with High Distinction, Department of Chemistry, University of Toronto
Thesis: Oxidation kinetics of bromide on surfaces: A source of active bromine in the troposphere (Advisor: Jonathan Abbatt)
1993 - 1998 High School Diploma, Jarvis Collegiate Institute, Toronto, Ontario.
My main research project involves investigating the interactions between reactive gases and particles in the atmosphere. As particles are transported through the atmosphere they become "aged" by reacting with trace gases such as ozone, nitrogen and sulphur oxides, various acids and organic species, as well as coagulating with different particle types. This aging changes the physical and chemical properties of the particles which dictate their effects on the chemistry of the atmosphere, the Earth's climate, and their toxicity and health effects.
Field measurements made with ATOFMS have provided a great deal of insight into the heterogeneous aging of aerosols in the troposphere at the single-particle level. My particular focus at present is the chemistry of mineral dust particles in the atmosphere. Mineral dust is the largest component of global particulate matter by mass, can be transported for weeks across transcontinental distances and has as of yet undetermined impacts on the chemical composition of the atmosphere (by scavenging and possibly releasing reactive gases from/to the atmosphere) and the earth's climate by absorbing and scattering light and influencing cloud and ice formation.
In 2001 the Prather Group participated in ACE-Asia, an intensive international field campaign occurring on various sampling platforms in the Pacific Ocean and east Asia. An ATOFMS was sampling aboard the NOAA research vessel Ronald Brown when a major dust storm arising from China hit the ship while it was sampling in the Sea of Japan. By looking at the accumulation of reactive gases such as nitric, sulphuric, and hydrochloric acid on these mineral dust particles we have learned a great deal of interesting information about the chemistry of mineral dust particles. Before the dust event most of the particulate nitrate was found in aged sea salt particles. During the dust storm, however, the majority of nitrate was found in reacted mineral dust particles. There is also strong evidence for the uptake of HCl(g) onto the mineral dust particles. Finally, by looking at the ion signals produced when these acids react with dust particles, there are also strong indications that nitrate and chloride do not accumulate on the same dust particles that have accumulated sulphate. Dust with large amounts of sulphate is segregated from dust with large amounts of chloride and/or nitrate. A single dust particle may contain large amounts of both nitrate and chloride, however. This behaviour is displayed in the figures below.
The ternary plot shows the peak areas for nitrate, sulphate and chloride in reacted dust particles that have not mixed with sea-salt. Each point is an individual dust particle's relative amounts of the heterogeneous reaction products. The large group of particles at the top vertex indicates that sulphate does not co-exist with nitrate or chloride in the same dust particle. The surrounding scatter plots show the absolute peak areas for the same heterogeneous reaction products for the same dust particles. Again, it can be seen that nitrate and chloride are strongly mixed in the same dust particles while sulphate-dust is segregated from dust containing nitrate and/or chloride.
These intriguing and unique results have raised many interesting and important questions regarding the behaviour of mineral dust as it is transported through the atmosphere. To investigate the kinetics and products of the reactions of mineral dust particles with these acid gases and better understand our field observations of dust chemistry I will simulate the reaction of mineral dust with various reactive gases in a flow tube reactor. This allows us to perform the reactions under atmospheric pressures and relative humidities, unlike some other commonly used techniques. The entrained aerosol flow tube technique involves flowing an aerosol stream through a long tube to which the reactant gas(es) are added with a moveable injector. By varying the position of the injector the time that the particles are allowed to react with the gases can be altered and thus the kinetics of the reaction determined.
Above is a schematic of the flow tube system I have constructed. It allows us to control many important variables for the heterogeneous reactions such as the particle concentration, relative humidity, reactant gas concentration, and reaction time. The reacted particles are sampled on-line by the ATOFMS to monitor changes in their chemical composition. The gas-phase composition is determined on-line by Chemical Ionization Mass Spectrometry (CIMS) generously provided by Prof. Mario Molina. We are collaborating with Prof. Vicki Grassian and Prof. Greg Carmichael at the University of Iowa for these mineral dust studies and their impacts on atmospheric chemistry and global climate. Collecting a fraction of the reacted particles on a filter membrane will allow us to measure the soluble ions in the reacted dust by ion chromatography which can then be used to calibrate the signal intensities measured by ATOFMS. We will also confirm the single-particle ATOFMS results by analyzing the filter samples using ESEM and EDX at UCSD's electron microscope facility.
Arimoto, R., Kim, Y.J., Kim, Y.P., Quinn, P.K., Bates, T.S., Anderson, T., Gong, S., Uno, I., Chin, M., Huebert, B.J., Clarke, A.D., Shinozuka, Y., Weber, R., Anderson, J., Guazzotti, S.A., Sullivan, R.C., Sodeman, D.A., Prather, K.A., Sokolik, I. Characterization of Asian Dust during ACE-Asia, Global and Planetary Change, Submitted.
Sullivan, R.C., Guazzotti, S., Sodeman, D., and Prather, K.A. Direct Observations of Heterogeneous Processing of Mineral Dust in the Atmosphere. American Physical Society March Meeting, Los Angeles, CA, March 2005. (Oral)
Sullivan, R.C., Guazzotti, S., Sodeman, D., and Prather, K.A. Heterogeneous Uptake of Secondary Acids by Mineral Dust. American Chemical Society National Meeting, San Diego, CA, February 2005.
Sullivan, R.C., Guazzotti, S., Sodeman, D., Coffee, K., Holecek, J., Spencer, M., and Prather, K.A. Direct Observations of Heterogeneous Dust Processing in the Troposphere: Source & Ambient Measurements Using ATOFMS. American Geophysical Union Fall Meeting, San Francisco, CA, December 2004.
Many of the major current uncertainties in models of global chemistry, climate change and radiative balance result from assumptions regarding the distribution of aerosol chemical components in an aerosol population. Filter-based measurements that only determine the bulk concentrations of various species such as nitrate, sulphate, organics, elemental carbon (soot), and dust cannot determine to what degree these species are mixed in the same particles or exist in separate, distinct particles. Knowing this "mixing state" is critical for predicting the physics and chemistry a particle will undergo in the atmosphere, particularly its ability to absorb and/or scatter radiation and its ability to make new cloud or ice nuceli and thus influence the Earth's cloud cover and lifetimes. The best example of how critical this knowledge is involves the mixing of elemental carbon (soot) particles with sulphate. Soot particles are highly absorbing and hydrophobic while sulphate particles are highly reflective and excellent cloud condensation nuclei. When soot is coated by sulphate however, the mixed particle actually becomes more absorbing than a pure soot particle because the sulphate coating refracts light into the absorbing soot core. This can dramatically change the sign of the forcing of soot and sulphate particles on the earth's radiative balance and knowledge of the mixing state of soot and sulphate is critical.
The single-particle measurements of particle composition obtained by ATOFMS allows us to directly answer this critical question. We are currently in the process of summarizing our results from numerous field measurements conducted in a wide variety of locations and environments. With this data we will provide the modeling community with a typical size-resolved mixing state for aerosol populations in urban, rural, polluted marine, and pristine marine environments. Our goal is to provide more accurate inputs to models of global climate and thus to reduce the uncertainty in these models' estimations of the effects of human activities on global climate change. We will also work with Prof. Ramanathan's research group to investigate how our mixing state data change the results of their previous climate models.
My interest in mineral dust heterogeneous chemistry began during my research with Prof. Jon Abbatt in the Department of Chemistry at the University of Toronto. I constructed a static reaction chamber that allowed us to monitor the loss of ozone as it interacted with an alumina powder film using UV absorption to quantify the O3 concentration in real-time. This static chamber allowed the first determination of the kinetics of ozone loss on a mineral surface at atmospheric relative humidities. Interestingly, no difference was found in the reaction probability for ozone with the alumina surface at 25, 50, and 75% RH under our experimental conditions. We also found evidence for partial regeneration of the mineral film's reactivity when placed in a purged atmosphere for several days. Rachel Chang, an undergraduate student, took this project over for me when I left for UCSD and found very analogous results when she repeated the experiments using authentic Saharan Dust films.
Sullivan, R.C.
, Thornberry, T., and Abbatt, J.P.D. Ozone decomposition kinetics on alumina: effects of ozone partial pressure, relative humidity and repeated oxidation cycles. Atmospheric Chemistry & Physics, 4: 1301-1311, 2004. PDFSullivan, R.C., Thornberry, T.D. and Abbatt, J.P.D. Ozone Decomposition Kinetics on Aluminum Oxide: Effects of Relative Humidity, Ozone Partial Pressure and the State of Film Oxidation. American Geophysical Union’s Fall Meeting, San Francisco, CA, Dec. 10, 2003.
My first research project in atmospheric heterogeneous chemistry came about during my honours thesis project in Environmental Chemistry under the supervision of Prof. Jon Abbatt at the University of Toronto. The project involved investigating the mechanism by which active bromine species are released from sea salt particles and the snow packs in the arctic. These bromine species play a major role in the destruction of ozone in the marine boundary layer at polar spring but the exact mechanism by which they are released is still under investigation. It is believed that reactions with oxidants such as ozone as the sea salt-air interface are responsible. I measured the kinetics of ozone destruction on NaCl, NaBr, NaI, synthetic sea salt, and acidified versions of these systems. Our findings of significant ozone destruction on the "inert" NaCl surface motivated my later research into the destruction of ozone on mineral dust (see above).
During an NSERC summer research scholarship with Prof. Scott Mabury at the University of Toronto I was a part of his group's first investigations of the chemistry and environmental fate of an emerging class of pollutants known as fluorinated surfactants. These chemicals are widely used in consumer products such as Scotch GuardTM (until 3M removed them from their formulation in 2001), surface treatments, cleansers and also in industrial formulations such as fire-fighting foams. Due to their prefluorinated carbon chain these surfactants are incredibly persistent and as of yet no environmental or biological degradation mechanism has been found. These chemicals have been found in worldwide blood samples and also in arctic wildlife. My contribution involved the measurement of the sorption of these perfluorinated carboxylates and sulphonates to soil so that we could better predict their environmental transport and fate. I found that the sorption of these compounds was largely determined by their perfluorocarbon chain length and by the fraction of organic matter in the soil being tested. This is expected for a hydrophobic compound but was surprising given that these surfactants exist as dissociated anions under aqueous conditions and would not be expected to exhibit such strong hydrophobicity.
Sullivan, R.C. and Mabury, S.A. Sorption of Perfluorinated Carboxylates and Sulphonates to Soil. Society of Environmental Toxicology and Chemistry Annual Meeting, Baltimore, MA, 12 November 2002.
In the second year of my Bachelor's I completed an undergraduate research opportunity course under the supervision of Prof. Kim Strong in the Department of Physics at the University of Toronto. As part of a larger concept study for the measurement of OH from space I developed a box model to predict [OH] in the troposphere and stratosphere and compared its predictions with measurements previously made at Mace Head, Ireland. This provided the overall project with greater insight into the chemistry that determines atmospheric OH mixing levels.
Arimoto, R., Kim, Y.J., Kim, Y.P., Quinn, P.K., Bates, T.S., Anderson, T., Gong, S., Uno, I., Chin, M., Huebert, B.J., Clarke, A.D., Shinozuka, Y., Weber, R., Anderson, J., Guazzotti, S.A., Sullivan, R.C., Sodeman, D.A., Prather, K.A., Sokolik, I. Characterization of Asian Dust during ACE-Asia, Global and Planetary Change, Submitted.
Sullivan, R.C., and K.A. Prather, Recent Advances in Our Understanding of Atmospheric Chemistry and Climate Made Possible by On-Line Aerosol Analysis Instrumentation, Analytical Chemistry, 77 (12), 3861 - 3886, 2005. PDF
Sullivan, R.C.
, Thornberry, T., and Abbatt, J.P.D. Ozone decomposition kinetics on alumina: effects of ozone partial pressure, relative humidity and repeated oxidation cycles. Atmospheric Chemistry & Physics, 4: 1301-1311, 2004. PDF
Sullivan, R.C., Guazzotti, S., Sodeman, D., and Prather, K.A. Direct Observations of Heterogeneous Processing of Mineral Dust in the Atmosphere. American Physical Society March Meeting, Los Angeles, CA, March 2005. (Oral)
Sullivan, R.C., Guazzotti, S., Sodeman, D., and Prather, K.A. Heterogeneous Uptake of Secondary Acids by Mineral Dust. American Chemical Society National Meeting, San Diego, CA, February 2005.
Sullivan, R.C., Guazzotti, S., Sodeman, D., Coffee, K., Holecek, J., Spencer, M., and Prather, K.A. Direct Observations of Heterogeneous Dust Processing in the Troposphere: Source & Ambient Measurements Using ATOFMS. American Geophysical Union Fall Meeting, San Francisco, CA, December 2004.
Sullivan, R.C., Thornberry, T.D. and Abbatt, J.P.D. Ozone Decomposition Kinetics on Aluminum Oxide: Effects of Relative Humidity, Ozone Partial Pressure and the State of Film Oxidation. American Geophysical Union’s Fall Meeting, San Francisco, CA, Dec. 10, 2003.
Sullivan, R.C. and Mabury, S.A. Sorption of Perfluorinated Carboxylates and Sulphonates to Soil. Society of Environmental Toxicology and Chemistry Annual Meeting, Baltimore, MA, 12 November 2001.
2003 & 2004 NSERC Postgraduate Scholarship
2001 ACS Analytical Chemistry Award for Undergraduate Research
2001 Sidney and Lucille Silver Scholarship for Environmental Science, University of Toronto
2000 NSERC Undergraduate Summer Research Award
2000 AstraZeneca Award for Undergraduate Poster Presentation, University of Toronto
Ultimate Disc (Ultimate Games in San Diego)
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Last Updated: 05 July 2005