Learning Science through Environmental Measurements
Learners of all ages and abilities can use an array of tools and instruments to learn about the world in which they live. Just as PhD-level scientists make detailed measurements of the chemistry of Earth’s atmosphere, so can school-age students use simpler tools, measure air pollutants in their classroom, and work together to find ways to clean up the air they breathe every day!
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Direct Dynamics Reactive Scattering-adaptive QM/MM
The reactive uptake of atmospherically-relevant gases (such as N2O5) by model aerosol surfaces will be simulated using the direct dynamics reactive scattering with adaptive quantum mechanics/molecular mechanics (DDRS-adQM/MM) approach. While the interactions of all molecules in the system would ideally be treated quantum mechanically, a fully-quantum mechanical description is often impractical due to computational expense. Alternatively, the system can be studied at a mixed quantum/classical level, where, for instance, the colliding molecule (N2O5) and the surface water molecules are treated quantum mechanically (QM) and the solvent molecules in the environment region are treated with classical molecular mechanics (MM). Contrary to conventional QM/MM methods, adQM/MM enables a fully QM representation of reactive processes in condensed phases by allowing solvent molecules to diffuse into and out of the active QM region.
Park, K., Go, A. W., Walker, R. C., & Paesani, F.,J. Chem. Theory Comput., 2012, 8(2868).
Detailed simulations of global climate in the past, present, and future require precise knowledge of the role of aerosols within the radiation balance of the atmosphere. How well do they scatter light? How well do they make both liquid and ice clouds? CAICE is working to understand how chemistry can help climate scientists predict these properties.
Interface Selective Experimentation
Sum Frequency Generation Spectroscopy
Sum frequency generation (SFG) is a type of vibrational spectroscopy in which infrared and visible laser pulses are overlapped in time and space at an interface. Unlike most spectroscopic techniques, SFG provides information exclusively about the chemistry of interfaces, which allows us to study the surfaces of SSA particles, without contributions from the bulk. Probing the surface through C-H bond vibrations allows for an understanding of the surface orientation of organic molecules, while probing O-H vibrations provides information about the structure of water at the gas-liquid interface and its interactions with solutes and thin organic films.
Gas-Liquid Molecular Beam Scattering
In order to understand the fundamental physical chemistry of reactions at complex environmental interfaces, the Nathanson Research Group will use a gas-liquid molecular beam scattering technique. This apparatus directs a beam of gaseous reagent molecules at a liquid surface, inducing a chemical reaction at the gas-liquid interface. A mass spectrometer is used to determine the identity and quantity of the product gases. These studies will complement heterogeneous chemistry studies performed by the Bertram (experimental) and Paesani (computational) research groups.
CAICE Chemistry and Climate Activity Kit
The CAICE Chemistry and Climate Activity Kit is designed to facilitate education and outreach in chemistry and climate science in informal learning environments (e.g. at home, in the classroom, and at STEM fairs). These materials may be used individually or in series. Together, they support student understanding of the radiative balance of the earth and anthropogenic influences on climate. The activity on surface albedo relates the brightness of a surface to its absorption of heat. Light scattering by particles affects the transmission of light and describes why the sky is blue and sunsets are red. As the Earth’s reflectively is largely attributed to clouds, the exploration of cloud formation logically follows. However, consideration of surfaces and clouds alone grossly underestimates the temperature of the earth, because it does not account for the heat trapping capabilities of greenhouse gases. The molecular structure of greenhouse gases and how they trap heat is explored through a guided-inquiry using molecular models. Graphs provide a glimpse of historic and recent trends in greenhouse gas concentrations and the average temperature of the Earth. Oceans are affected by carbon dioxide levels in the atmosphere, and are becoming more acidic. Explore acid base chemistry and dissolution of calcium carbonate with a red cabbage experiment. Whether used together or alone, these activities provide a way of sharing chemistry and climate science.
Learning materials were prepared by University of Iowa researchers Olga Laskina, Holly Morris, Joshua Grandquist, Jonathon Trueblood, Thilina Jayarathne, Jennifer Schmidt, Miranda Neff, Richard Cochran, and Elizabeth A. Stone. We thank Haim Weizman and Kayla Busby of the University of California – San Diego for reviewing these materials. This project was supported by an ACS Climate Science Challenge Grant and the National Science Foundation under Grant No. CHE 1305427. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
Sea Spray Generators
In order to properly reproduce the properties of aerosol particles generated in nature, it is essential to accurately mimic the mechanisms that create them. Towards this goal, an artificial ocean was created in the glass wave channel in the Scripps Institution of Oceanography Hydraulics Laboratory. In Phase I, real seawater from off the Scripps Pier was transported to fill the 33m x 0.5m x 0.5m tank. Wave packets were generated using an electro-hydraulic powered paddle to mimic the wave properties and bubble size distribution encountered in nature. The tank was sealed and filtered air was directed through the channel to provide a clean background from which to measure the properties of particles generated during the process. Beyond measuring properties of particles generated from clean seawater, biological material can easily be added to simulate increased concentrations of eukaryotes, bacteria, and organic carbon in order to probe the impacts of changing seawater composition on aerosol properties. This experimental setup has allowed for the first measurement of the chemical properties of nascent sea spray.
The amount of material contained within a single aerosol particle is about one trillionth of a gram. Many important reactive trace gases in the atmosphere exist as only one 1 molecule in a billion molecules of whole air. As one of the most sensitive chemical analysis techniques, mass spectrometry is well suited to the task.
Microscopy and Spectroscopy
Electron Microscopy with Energy Dispersive X-ray Spectroscopy
The ability for an aerosol particle to accomodate water or react with trace gases in the atmosphere is key to its influence on atmospheric chemistry and climate. While some instruments, like ATOFMS, have been designed to analyze many individual particles in a short amount of time, the level of detail in the chemical composition is not always sufficient for fully understanding their climatic properties. Spatial information is key, and can be provided by scanning (SEM) or transmission electron microscopy (TEM) coupled with energy dispersive x-ray spectroscopy (EDX). This technique can provide not only information on the shape of aerosol particles, but also spatial relationships between the compounds that comprise those particles.