A5101623864- Atmospheric chemistry and aerosols
- Atmospheric aerosols and clouds
- Atmospheric Ozone and Climate
- nanoparticles nucleation surface interactions
- Crystallization and Solubility Studies
- X-ray Diffraction in Crystallography
- Air Quality and Health Impacts
- Crystallography and molecular interactions
- Industrial Gas Emission Control
- Icing and De-icing Technologies
- Air Quality Monitoring and Forecasting
- Chemical Analysis and Environmental Impact
- Planetary Science and Exploration
- Vehicle emissions and performance
- Advanced Chemical Physics Studies
- Freezing and Crystallization Processes
- Chemical and Physical Properties in Aqueous Solutions
- Molecular Junctions and Nanostructures
- Spectroscopy and Laser Applications
- Catalytic Processes in Materials Science
- Groundwater and Isotope Geochemistry
- UAV Applications and Optimization
- Oil Spill Detection and Mitigation
- Adsorption, diffusion, and thermodynamic properties of materials
- Additive Manufacturing and 3D Printing Technologies
Maryland Aerospace (United States)
2022
University of Colorado Boulder
2003-2019
Concordia University
2012-2019
University of Portland
2019
University of Montana
2016
Cooperative Institute for Research in Environmental Sciences
2002-2013
Arizona State University
2005-2009
Aerodyne Research
2005
Harvard University
2005
Boston College
2005
Abstract. The light-absorbing organic aerosol (OA) commonly referred to as “brown carbon” (BrC) has attracted considerable attention in recent years because of its potential affect atmospheric radiation balance, especially the ultraviolet region and thus impact photochemical processes. A growing amount data indicated that BrC is prevalent atmosphere, which motivated numerous laboratory field studies; however, our understanding relationship between chemical composition optical properties...
Recent studies have shown that tropospheric aerosols composed of internal mixtures organics with sulfates are quite common the organic composing up to 50% particle mass. The influences on chemical and physical properties aerosol not known. In this paper, we report solubility a series dicarboxylic acids in saturated ammonium sulfate solution as function temperature. We also deliquescence relative humidity (DRH) pure sulfate. For systems studied, find presence water‐soluble caused occur at...
Abstract. Sea-salt aerosol (SSA) particles are ubiquitous in the marine boundary layer and over coastal areas. Therefore SSA have ability to directly indirectly affect Earth's radiation balance. The influence on climate is related their water uptake ice nucleation characteristics. In this study, optical microscopy coupled with Raman spectroscopy was used detect formation of a crystalline NaCl hydrate that could form under atmospheric conditions. NaCl(s) (~1 10 μm diameter) deliquesced at...
In this study chemical compositions of background aerosol and ice nuclei were examined through laboratory investigations using Raman spectroscopy field measurements by single‐particle mass spectrometry. Aerosol sampling took place at Storm Peak Laboratory in Steamboat Springs, Colorado (elevation 3210 m). A cascade impactor was used to collect coarse‐mode particles for analysis spectroscopy; the composition, mixing state, heterogeneous nucleation activity individual examined. For situ...
Abstract. Amorphous (semi-)solid organic aerosol particles have the potential to serve as surfaces for heterogeneous ice nucleation in cirrus clouds. Raman spectroscopy and optical microscopy been used conjunction with a cold stage examine water uptake on individual amorphous at atmospherically relevant temperatures (200–273 K). Three compounds considered proxies atmospheric secondary (SOA) were this investigation: sucrose, citric acid glucose. Internally mixed consisting of each ammonium...
Recent studies have shown that tropospheric sulfate aerosols commonly contain 50% by mass organic species. The influence of these organics on the chemical and physical properties is not fully established. We measured water activity pure dicarboxylic acids eutonic mixtures ammonium sulfate/dicarboxylic at 25°C calculated van't Hoff factors for each individual system. also used vapor pressure data to determine hygroscopic growth curves provide power law fits data. For systems studied we find...
The hygroscopic behavior of 0.1 to 4 μ m NaBr, CsCl, NaCl, (NH4)2SO4, and KBr particles were monitored using a transmission electron microscope (TEM) equipped with an environmental cell into which gases can be introduced. This instrument, commonly called or ETEM, allowed us observe phase transitions small at relative humidities between 0 100%. We used deliquescence humidity efflorescence values from the literature for each salt calibrate in cell. Using our methodology, we reliably accurately...
The ozonolysis of mixed oleic-acid/stearic-acid (OL/SA) aerosol particles from 0/100 to 100/0 wt % composition is studied. magnitude the divergence particle beam inside an mass spectrometer shows that, in concentration range 60/40, OL/SA are liquid prior reaction. Upon ozonolysis, having compositions 75/25 and 60/40 change shape, indicating that they have solidified during Transmission electron micrographs show SA(s) forms needles. For 75/25, greater SA content, reaction kinetics exhibit...
Abstract. Heterogeneous ice nucleation on solid ammonium sulfate and glutaric acid particles was studied using optical microscopy Raman spectroscopy. Optical used to detect selective events as water vapor slowly introduced into an environmental sample cell. Particles that nucleated were dried via sublimation examined in detail Depositional is highly occurred preferentially just a few each sample. For freezing temperatures between 214 K 235 average saturation ratio of S = 1.10±0.07 for...
We used conventional and environmental transmission electron microscopes to determine morphology, composition, water uptake of individual natural inorganic aerosol particles collected from industrial pollution plumes clean polluted marine environments. Five particle types are described in detail. They range relatively insoluble mineral grains internally mixed containing NaCl with other soluble or material. studied the hygroscopic behavior these 0 100% relative humidity (RH). Relatively...
Using an environmental transmission electron microscope (ETEM), we show that a significant amount of water, far exceeding the multilayers caused by surface adsorption, is reversibly associated prior to deliquescence with substrate-supported NaCl particles (dry diameters ∼ 40 nm 1.5 μ m; 18°C). We hypothesize water present as aqueous solution containing dissolved Na and Cl ions. Water uptake occurs at relative humidities (RH) low 70%, resulting liquid layer coating stable over extended times...
Abstract. We present measurements utilizing the Filter Inlet for Gases and Aerosols (FIGAERO) applied to chamber of isoprene-derived epoxydiol (IEPOX) reactive uptake aqueous acidic particles associated secondary organic aerosol (SOA) formation. Similar recent field observations with same instrument, we detect two molecular components desorbing from IEPOX SOA in high abundance: C5H12O4 C5H10O3. The thermal desorption signal former, presumably 2-methyltetrols, exhibits distinct maxima,...
Cirrus clouds are ubiquitous in the tropical tropopause region and play a major role Earth’s climate. Any changes to cirrus abundance due natural or anthropogenic influences must be considered evaluate future climate change. The detailed impact of on depends ice particle number, size, morphology, composition. These properties depend turn nucleation mechanism particles. Although it is often assumed that nucleates via homogeneous mechanism, recent work points possibility heterogeneous...
Sea‐salt aerosol (SSA) particles affect the Earth's radiative balance and moderate heterogeneous chemistry in marine boundary layer. Using conventional environmental transmission electron microscopes (ETEM), we investigated hygroscopic growth liquid‐layer compositions of generated from three types aqueous salt solutions: sodium chloride, laboratory‐synthesized seawater (S‐SSA particles), natural (N‐SSA particles). Three levels morphological change were observed with ETEM as...
General equations are derived for predicting the change in fluorescent intensity of zinc-sulphide phosphors containing more than one kind impurity activating center, according to theory hole migration. The effect on blue fluorescence efficiency exciting intensity, temperature, and other center is discussed. If this a killer which produces no visible radiation, it shown that observed ZnS-Ag-Co quantitatively agrees with if probability particular excited Co will recombine an electron...
Abstract. While water insoluble organics are prevalent in the atmosphere, it is not clear how presence of such species alters chemical and physical properties atmospheric aerosols. Here we use a combination FTIR spectroscopy, Transmission Electron Microscopy (TEM) Aerosol Mass Spectrometry (AMS) to characterize ammonium sulfate particles coated with palmitic acid. Coated aerosols were generated by atomizing pure sulfate, mixing heated flow nitrogen acid vapor, then flowing mixture through an...
A temperature controlled flow tube system equipped with Fourier transform infrared (FTIR) detection of particle phase and relative humidity was used to measure the deliquescence efflorescence ammonium sulfate, maleic acid, internally mixed acid/ammonium sulfate particles. Our results indicate that acid aerosols begin take up water starting at a low humidity, ∼20%, continue constant uptake until final (DRH), 89%, is reached. Internally particles containing were found deliquesce lower (RH)...
The aerosol direct effect, which characterizes the interaction of radiation with particles, remains poorly understood. By determining composition, shape, and internal structure, we can predict optical properties. In this study, performed a feasibility study to determine if tapping-mode atomic force microscopy (TM-AFM) Raman be effectively used obtain information on structure. These techniques are advantageous because they operate under ambient pressure temperature. We worked model particles...
Cirrus clouds are composed of ice particles and expected to form in the upper troposphere when highly dilute sulfate aerosols cool become supersaturated with respect ice. In laboratory we have used Fourier transform infrared spectroscopy monitor nucleation from for relevant compositions sulfuric acid/water ammonium sulfate/water aerosols. Measured freezing temperatures presented as a function aerosol composition, results compared existing data. We find that acid solution exhibits greater...
Recent studies have shown that tropospheric sulfate aerosols commonly contain 50% or more by mass organic species. The influence of these organics on the chemical and physical properties is not fully established. Using an aerosol flow tube technique, we determined ice nucleation temperatures for particles composed ammonium mixtures with a series dicarboxylic acids. A calibration curve was developed to allow us convert freezing saturation ratio required nucleation. At levels detectable our...
Abstract. Cirrus clouds are composed of ice particles and their formation pathways have been studied extensively in the laboratory. The ability ammonium sulfate to act as nuclei for cirrus has particular importance because ubiquitous presence upper troposphere. results past laboratory experiments homogeneous nucleation from show a wide range freezing conditions. In present study, flow tube apparatus equipped with Fourier transform infrared spectroscopy was used reexamine these discrepancies....