Unique and Custom Built Instrumentation
Aerosol Optical Trap with Raman Spectroscopy. The aerosol optical trap consists of a 514 nm laser focused through a microscope objective into a trapping chamber. Aqueous aerosol particles are introduced, and their composition and size can be varied. Single particles are trapped indefinitely in the chamber, and we can change the environment of the chamber (i.e. humidity, temperature, etc.). The size of an individual droplet of micron scale can be determined to single nanometer resolution using Raman spectroscopy compared with Mie theory. This instrument can be used to observe properties of single, suspended particles.
Marine Aerosol Generator. The marine aerosol generator is a high capacity glass system that models processes in the ocean-atmosphere system. Bubbles are introduced to the model ocean using water and air pumped through a venturi. The bubbles rise to the model ocean surface and burst, emitting primary marine aerosol particles into the model atmosphere. These particles can be collected on filters for chemical analyses, or their number size distributions and hygroscopicity can be measured with the HTDTMA, SEMS, and/or APS.
Aerosol Particle Sizing and Characterization
Humidified Tandem Differential Mobility Analyzer (HTDMA). The HTDMA is used to measure the hygroscopic growth of aerosol particles of a specified diameter. The instrument consists of two Scanning Electrical Mobility Spectrometers (SEMS): an upstream (dried) SEMS and a humidified SEMS. The upstream SEMS creates a monodisperse flow of dry particles of a specific diameter, which is then split between a condensation particle counter (CPC) and the humidified SEMS. The humidified SEMS humidifies the dry, monodisperse particles to a given relative humidity and measures the resulting size distribution. The growth (or lack of growth) of aerosol particles as a function of relative humidity can show how aerosol particles uptake water and grow in the atmosphere. We can use this to measure hygroscopicity of particles and relate that to their composition.
Scanning Electrical Mobility Spectrometer (SEMS). The SEMS measures the number size distributions of aerosol particles using electrical mobility. The instrument is made up of a Differential Mobility Analyzer (DMA) to select particles of a given size and a Mixed Condensation Particle Counter (CPC) to count the monodisperse particles. Based on the electric field and sheath flow within the DMA, the aerosol particles will drift according to their electrical mobility which is a function of their size. By adjusting the voltage of the DMA, particles can be selected based on size and counted in order to give an overall number size distribution of the sample flow. The number size distribution of aerosol particles can give information about the size and number of particles and their fate in the atmosphere.
Aerodynamic Particle Sizer (APS). This instrument is used to measure particle size and number concentrations of particles 0.5 - 20 µm in diameter. Particles are counted and then sized using time of flight.
Fourier transformer infrared (FTIR) with Attenuated Total Reflectance (ATR). The FTIR-ATR uses a diamond crystal to directly analyze samples placed on the crystal. An infrared light source is directed onto the diamond crystal at an angle greater than its critical angle, creating internal reflection. Due to the direct contact between the sample and crystal, at each point of internal reflection, the infrared light is absorbed by the sample, at a limited depth. The resulting absorption spectrum from ATR mode or transmission mode provides information about the functional groups in a sample. The FTIR spectrum can be integrated at specific wavenumbers, based on the rotational and vibrational transitions of the molecular bonds within the functional groups, to quantify the mass of species in the sample. We can use ATR-FTIR to qualitatively identify functional groups present in liquid or deposited aerosol samples and measure their concentrations, based on calibrations.
Ion Chromatography (IC). The IC is used to qualitatively and quantitatively measures ions in liquid samples. It consists of both a cationic and an anionic system. Samples are each injected with equal volumes using an autosampler. Each system involves the transportation of sample by its similarly charged mobile phase, which is diluted in situ from a concentrated eluent cartridge and passed through the instrument at a regulated flow rate by an internal pump. The sample and eluent mixture pass through a guard column to remove contaminants and flow through a separatory column containing a stationary phase of opposite charge. Ions are retained on the separatory columns based on levels of attraction to the stationary phase and elute at unique retention times, while others continue through the system unaffected. A suppressor to improves the signal to noise ratio of the eluent before it is passed through a conductivity detector. Retention times and peak areas are compared to calibrated standard solutions of known ion compositions and concentrations to determine sample ionic composition. We use IC to measure the ionic composition of extracted aerosol particles and seawater.
Mass Spectrometry. The Proteomics and Mass Spectrometry Facility (PAMS) houses many types of mass spectrometers. With the proper training, lab members can operate the low resolution Bruker Esquire 3000 plus electrospray ion trap mass spectrometer (ESI-IT-MS). We use the Bruker Impact II quadrupole time of flight (ESI-Q-TOF) instrument for high resolution data with high mass accuracy. Additionally, the PAMS facility now has a Briker solariX XR 21 tesla Fourier-transform ion cyclotron resonance mass spectrometer (21T FT-ICR-MS) that can be used for ultra high resolution analyses. The Frossard group uses mass spectrometry to measure concentrations of surfactants in water and aerosol particle samples and identify individual surfactants based on their molecular formulas and the fragmentation patterns.
Solid Phase Extraction Manifold. For solid phase extractions (SPE), we use reversed-phase cartridges to separate and retain large, organic compounds from an aqueous sample. The organic compounds are eluted from the sorbent material using acetonitrile. Solid phase extractions to separate and concentrate large, organic compounds from extracted aerosol and water samples prior to other analyses.
Pendant Drop Tensiometer. The pendant drop tensiometer measures the equilibrium interfacial surface tension of liquid solutions. The physical constraints of a hanging droplet from a capillary tube are used to derive the surface energy. This method combines the two factors affecting the axisymmetric shape formed from a drop hanging on a needle tip. The elongation of the drop is the result of gravity, while the surface tension holds the drop in a spherical shape to minimize surface area. The surface energy is then calculated from a derivation of the Young-Laplace equation. We measure the surface tension of aqueous solutions and surfactant extracts. Surface tensions measured at a series of dilutions are used to calculate surface tension isotherms and critical micelle concentrations.