Papers by Timothy Raymond
Aerosol Science and Technology, Feb 26, 2014
The Jing Ltd. miniature combustion aerosol standard (Mini-CAST) soot generator is a portable, com... more The Jing Ltd. miniature combustion aerosol standard (Mini-CAST) soot generator is a portable, commercially available burner that is widely used for laboratory measurements of soot processes. While many studies have used the Mini-CAST to generate soot with known size, concentration, and organic carbon fraction under a single or few conditions, there has been no systematic study of the burner operation over a wide range of operating conditions. Here, we present a comprehensive characterization of the microphysical, chemical, morphological, and hygroscopic properties of Mini-CAST soot over the full range of oxidation air and mixing N 2 flow rates. Very fuel-rich and fuel-lean flame conditions are found to produce organic-dominated soot with mode diameters of 10-60 nm, and the highest particle number concentrations are produced under fuel-rich conditions. The lowest organic fraction and largest diameter soot (70-130 nm) occur under slightly fuel-lean conditions. Moving from fuel-rich to fuel-lean conditions also increases the O:C ratio of the soot coatings from ∼0.05 to ∼0.25, which causes a small fraction of the particles to act as cloud condensation nuclei near the Kelvin limit (κ ∼ 0-10 -3 ). Comparison of these property ranges to those reported in the literature for aircraft and diesel engine soots indicates that the Mini-CAST soot is similar to real-world primary soot particles, which lends itself to a variety of process-based soot studies. The trends in soot properties uncovered here will guide selection of burner operating conditions to achieve optimum soot properties that are most relevant to such studies.
Journal of the Air & Waste Management Association, Jul 18, 2013
Characterization of Halyomorphahalys (brown marmorated stink bug) biogenic volatile organic compo... more Characterization of Halyomorphahalys (brown marmorated stink bug) biogenic volatile organic compound emissions and their role in secondary organic aerosol formation,
Environmental science, 2022
Volatile organic matter suspended in the atmosphere such as a-pinene and b-caryophyllene undergoe... more Volatile organic matter suspended in the atmosphere such as a-pinene and b-caryophyllene undergoes aging processes and chemical, and photo-oxidation reactions to create secondary organic aerosols (SOAs), which can influence the indirect effect of aerosol particles and the radiative budget. The presence and impact of water vapor and ammonium sulfate (ubiquitous species in the atmosphere) on the hygroscopicity and CCN activity of SOA have not been well characterized. In this research, three water-uptake measurement methods, cavity ring-down spectroscopy (CRD), humidified tandem differential mobility analysis (HTDMA), and cloud condensation nuclei counting (CCNC), were employed to study the hygroscopicity of a-pinene and bcaryophyllene SOAs formed by dark ozonolysis. We observed the changes in water uptake of SOAs in the absence and presence of water vapor at $70% RH and ammonium sulfate seeds. Measured hygroscopicity was represented by a single hygroscopicity parameter (k). Sesquiterpene SOA was observed to be insoluble, hydrophobic, and non-hygroscopic under all experimental conditions and at all initial concentrations, as bcaryophyllene SOA exhibited non-hygroscopic properties with values that were effectively 0. Conversely, monoterpene SOA water uptake is sensitive to increasing RH in the chamber during secondary aerosol formation. Dry and wet seeded monoterpene SOA showed a similar trend of increase despite variability in initial precursor concentrations. We conclude that differences in the viscosity, solubility and hydrophobicity of SOAs may be the primary factor that leads to changes in SOA hygroscopicity formed under low and high relative humidity conditions. Hygroscopicity of atmospheric aerosol particles governs the formation of droplets, clouds, and haze that can absorb, refract, or reect radiation, indirectly inuencing the Earth's net radiative budget. Hygroscopicity, and therefore the optical properties of atmospheric droplets are dependent on particle composition and relative humidity. In this research, we probed the effects of humidity and presence of ammonium sulfate seeds on the secondary organic aerosol (SOA) hygroscopicity from a-pinene and b-caryophyllene ozonolysis, two prevalent atmospheric terpenes. The results indicate that mixed organic-inorganic aerosols formed in high humidity regions may have different water-uptake properties than those in arid regions; and the hygroscopicity differences are more pronounced for monoterpene SOA mixtures compared to sesquiterpene SOA mixtures. The reported results contribute to the body of scientic knowledge on aerosol wateruptake that reduces uncertainty in climate models.
Aerosol Science and Technology
their own misconceptions and to learn new material by teaching and 'doing'.
Atmospheric Chemistry and Physics, 2016
Accurate estimates of particle surface tension are required for models concerning atmospheric aer... more Accurate estimates of particle surface tension are required for models concerning atmospheric aerosol nucleation and activation. However, it is difficult to collect the volumes of atmospheric aerosol required by typical instruments that measure surface tension, such as goniometers or Wilhelmy plates. In this work, a method that measures, ex situ, the surface tension of collected liquid nanoparticles using atomic force microscopy is presented. A film of particles is collected via impaction and is probed using nanoneedle tips with the atomic force microscope. This micro-Wilhelmy method allows for direct measurements of the surface tension of small amounts of sample. This method was verified using liquids, whose surface tensions were known. Particles of ozone oxidized α-pinene, a well-characterized system, were then produced, collected, and analyzed using this method to demonstrate its applicability for liquid aerosol samples. It was determined that oxidized α-pinene particles formed in dry conditions have a surface tension similar to that of pure α-pinene, and oxidized α-pinene particles formed in more humid conditions have a surface tension that is significantly higher.
International Journal of Engineering Education, 2018
Student-centered learning is known to lead to greater student knowledge gains and conceptual unde... more Student-centered learning is known to lead to greater student knowledge gains and conceptual understanding. In practice,implementation of these approaches can vary from the ideal implementation as defined by the original developer, leadingto differences in student outcomes compared to what might be expected. Fidelity of implementation, i.e., the extent towhich key practices of a pedagogical approach are used, must be considered in understanding how student-centeredpedagogies impact students. In this mixed method study, we examined how Process Oriented Guided Inquiry Learning(POGIL) was implemented across diverse institutional contexts and how those implementations affected students’conceptual understanding. The domains of curricula framework allowed us to understand how the curriculum as practicedby instructors and experienced by students differed from the ideal curriculum as originally designed. Our results show thatimplementation is impacted by the particular circumstances of a cl...
Bulletin of the American Meteorological Society, 2005
Environmental Science: Atmospheres, 2022
Aged atmospheric volatile organic matter create secondary organic aerosols (SOA), influencing the... more Aged atmospheric volatile organic matter create secondary organic aerosols (SOA), influencing the indirect effect of aerosols. A difference in viscosity and hydrophobicity of SOA may be the primary cause of changes in hygroscopicity.
2007 Annual Conference & Exposition Proceedings
Water-soluble organic compounds (WSOCs) readily uptake water and form atmospheric droplets. Under... more Water-soluble organic compounds (WSOCs) readily uptake water and form atmospheric droplets. Understanding the water-uptake ability of these WSOCs can improve our understanding of their radiative ef...
ABSTRACT Atmospheric aerosols affect both global and regional climate by altering the radiative b... more ABSTRACT Atmospheric aerosols affect both global and regional climate by altering the radiative balance of the atmosphere and acting as cloud condensation nuclei. Despite an increased focus on the research of atmospheric aerosols due to concerns about global climate change, current methods to measure the hygroscopic properties of aerosols are limited in various ways by experimental procedure. The objective of this research is to investigate the utility of environmental AFM for imaging atmospherically relevant aerosols as they respond to changes in relative humidity. Traditional aerosol generation and collection techniques were used in conjunction with environmental AFM to image sodium chloride aerosol as relative humidity increased for a variety of substrates and AFM probes. The results of this research demonstrated the utility of environmental AFM for measuring the hygroscopic properties of aerosols in addition to highlighting potential drawbacks. Further research in this area will lead to an increased understanding of the role of organic and inorganic aerosols in the atmosphere, allowing more accurate climate models to be developed.
ABSTRACT Over the summer of 2011, different methods were tested to imitate the generation of atmo... more ABSTRACT Over the summer of 2011, different methods were tested to imitate the generation of atmospheric aerosols from large bodies of water. A glass bubbler apparatus was used to create aerosol particles from real ocean samples and solutions mixed in the lab meant to imitate ocean water. Varying flows of carbon dioxide and air were bubbled through the two solutions, and particle size distributions between 10-600 nm were measured and analyzed. The peak particle sizes were compared to published sizes of particles found over the ocean. The addition of carbon dioxide to the air mix going into the bubbler had negligible effect on the particle size distributions within 0.0-1.0% CO2 by mass. In addition, a polycarbonate box was constructed so other techniques could be used to agitate water samples and produce particles. A small fountain pump was used to move the water. Pump setups meant to imitate small rapids or gently flowing water produced too few particles to be analyzed, so more vigorous agitation was used for a majority of the samples collected. River water was primarily used as samples; particle size distributions and cloud condensation nuclei activity were tested. In addition, conductivity of river samples was conducted to test for total dissolved solids.
ABSTRACT Solution atomization and subsequent drying is the primary method by which aerosols are g... more ABSTRACT Solution atomization and subsequent drying is the primary method by which aerosols are generated for laboratory studies such as CCN activity, hygroscopic growth, or smog chamber seeding experiments. The typical assumptions for this atomization process include: 1) The solvent does not affect the aerosol properties 2) The concentration of solution only affects the size distribution 3) The solution produces the same aerosols regardless of its age 4) The solution contains chemicals that do not react in any way We have conducted experiments using both organic and inorganic compounds and mixtures dissolved in a variety of solvents. We have investigated CCN activity and particle morphology of the resulting atomized particles after increasing aging of the solution. While Koehler theory accurately describes the activation of soluble inorganic salts, it is still not possible to accurately predict the water interaction behavior of organic aerosols. In recent years, several studies of CCN activity for organic aerosols have investigated the effects of solvents, organic coatings, mixed particles, and smog chamber-generated aerosols. The results of these studies are not in agreement and have resulted in conflicting findings. The current study has used a commercially available cloud chamber (DMT CCNC) and the recently reported Scanning Mobility CCN Activity (SMCA) method to measure several different organic species and mixtures of varying complexity. Additionally, we have investigated the morphology for atmospherically-relevant sized particles using Atomic Force Microscopy (AFM). Results have been analyzed to determine the relationships among chemistry, solvent, aging, and concentration. We have discovered that particle morphology may vary depending on the particle generation methods and conditions and that the morphology may influence properties such as CCN activity.
Tim received his BS in Chemical Engineering from Bucknell University in 1997 and his PhD from Car... more Tim received his BS in Chemical Engineering from Bucknell University in 1997 and his PhD from Carnegie Mellon University in 2002. He has taught a variety of courses since starting at Bucknell in 2002. He is interested in improving student learning by directing students to discover their own misconceptions and to learn new material by teaching and 'doing'.
ABSTRACT Over the summer of 2011, different methods were tested to imitate the generation of atmo... more ABSTRACT Over the summer of 2011, different methods were tested to imitate the generation of atmospheric aerosols from large bodies of water. A glass bubbler apparatus was used to create aerosol particles from real ocean samples and solutions mixed in the lab meant to imitate ocean water. Varying flows of carbon dioxide and air were bubbled through the two solutions, and particle size distributions between 10-600 nm were measured and analyzed. The peak particle sizes were compared to published sizes of particles found over the ocean. The addition of carbon dioxide to the air mix going into the bubbler had negligible effect on the particle size distributions within 0.0-1.0% CO2 by mass. In addition, a polycarbonate box was constructed so other techniques could be used to agitate water samples and produce particles. A small fountain pump was used to move the water. Pump setups meant to imitate small rapids or gently flowing water produced too few particles to be analyzed, so more vigorous agitation was used for a majority of the samples collected. River water was primarily used as samples; particle size distributions and cloud condensation nuclei activity were tested. In addition, conductivity of river samples was conducted to test for total dissolved solids.
A team-based cooperative learning environment for teaching Principles of Chemical Engineering (th... more A team-based cooperative learning environment for teaching Principles of Chemical Engineering (the material and energy balances course) has been used at Bucknell University for several years. This course has been carefully designed to include a variety of "best practices" to help prepare chemical engineering students in their first course in the curriculum. The course involves five two-week projects where students work in teams to complete problems covering a range of materials and, at the same time, practice team work and professional skills. Additionally, each project involves a complex laboratory experiment and use of process simulation software (HYSYS) problems. Assessment for this course has been ongoing and involves a range of data from team self-reports, before and after project concept inventories, individual surveys, team surveys, and final course evaluations. This presentation will explain the details of the course setup, the use and evaluation of various "b...
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Papers by Timothy Raymond