A5003152912- Atmospheric chemistry and aerosols
- Air Quality and Health Impacts
- Atmospheric Ozone and Climate
- Air Quality Monitoring and Forecasting
- Catalytic Processes in Materials Science
- Atmospheric aerosols and clouds
- Indoor Air Quality and Microbial Exposure
- Advanced Chemical Sensor Technologies
- Vehicle emissions and performance
- Odor and Emission Control Technologies
- Advanced Chemical Physics Studies
- Conservation Techniques and Studies
- Catalysis and Oxidation Reactions
- Ion-surface interactions and analysis
- Atmospheric and Environmental Gas Dynamics
- Mass Spectrometry Techniques and Applications
- nanoparticles nucleation surface interactions
- Coagulation and Flocculation Studies
- Analytical Chemistry and Chromatography
- Toxic Organic Pollutants Impact
- Spectroscopy and Laser Applications
- ZnO doping and properties
- Isotope Analysis in Ecology
- Electron and X-Ray Spectroscopy Techniques
- Gas Sensing Nanomaterials and Sensors
Cooperative Institute for Research in Environmental Sciences
2016-2025
University of Colorado Boulder
2016-2025
University of Colorado System
2022-2025
University of California, Riverside
2008-2019
Hospital Universitario Fundación Jiménez Díaz
2015
In-Q-Tel
2015
Asia Center for Air Pollution Research
2009-2011
Aerodyne Research
2008-2009
University at Albany, State University of New York
2008
Universität Ulm
2004-2005
A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied ambient measurements. Atomic oxygen-to-carbon (O/C) ratios characterize oxidation state OA, O/C from urban OA ranges 0.2 0.8 with diurnal cycle that decreases primary emissions increases because photochemical processing secondary (SOA) production. Regional approaches ∼0.9. The...
Organonitrates (ON) are important products of gas-phase oxidation volatile organic compounds in the troposphere; some models predict, and laboratory studies show, formation large, multifunctional ON with vapor pressures low enough to partition particle phase. Organosulfates (OS) have also been recently detected secondary aerosol. Despite their potential importance, OS remain a nearly unexplored aspect atmospheric chemistry because few quantified particulate or ambient air. We report response...
A particle beam is produced when a particle-laden gas expands through nozzle into vacuum. This work discusses the theoretical basis of novel method for producing highly collimated and tightly focused beams. The approach to pass series axisymmetric contractions enlargements (so-called aerodynamic lenses) before expansion. Particles are moved closer axis by lens if sizes less than critical value particles can be confined very closely using multiple lenses in series. Since close experience...
The role of organic peroxides in secondary aerosol (SOA) formation from reactions monoterpenes with O3 was investigated a series environmental chamber experiments. Reactions were performed endocyclic (α-pinene and Δ3-carene) exocyclic (β-pinene sabinene) alkenes dry humid air the presence OH radical scavengers: cyclohexane, 1-propanol, formaldehyde. A thermal desorption particle beam mass spectrometer used to probe identity volatility SOA components, an iodometric−spectrophotometric method...
A particle-beam-forming apparatus for producing narrow particle beams was developed based on the theory discussed in paper I of this series. It consists a variable number aerodynamic lenses (short capillaries and/or thin-plate orifices with diameters ranging from 3.5 to 7.0 mm) followed by an accelerating nozzle (3 mm). evaluated using monodisperse DOS and NaCl particles (0.02–0.24 μm) at upstream pressures order 1 torr. The produced lens-nozzle system were focused through skimmer (1 into...
Abstract. The lightest Non Methane HydroCarbon (NMHC), i.e., acetylene (C2H2) is found to form secondary organic aerosol (SOA). Contrary current belief, the number of carbon atoms, n, for a NMHC act as SOA precursor lowered n=2 here. OH-radical initiated oxidation C2H2 forms glyoxal (CHOCHO) highest yield product, and >99% from attributed CHOCHO. formation CHOCHO was studied in photochemical dark simulation chamber. Further, experimental conditions were varied with respect chemical...
Abstract. The volatilities of different chemical species in ambient aerosols are important but remain poorly characterized. coupling a recently developed rapid temperature-stepping thermodenuder (TD, operated the range 54–230°C) with High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) during field studies two polluted megacities has enabled first direct characterization chemically-resolved urban particle volatility. Measurements Riverside, CA and Mexico City generally...
Gas-wall partitioning of organic compounds (OC) that included C 8 –C 16 n-alkanes and 1-alkenes 13 2-alcohols 2-ketones was investigated in two Teflon FEP chambers whose walls were either untreated, oxidized sunlight, or previously exposed to secondary aerosol (SOA). Partitioning nearly independent chamber treatment, reversible, obeyed Henry's law. The fraction an OC partitioned the at equilibrium ranged from 0 ∼ 65%. Values increased with increasing carbon number within class for similar...
The effect of hydrocarbon molecular structure on the measured yield and volatility secondary organic aerosol (SOA) formed from OH radical-initiated reactions linear, branched, cyclic alkanes in presence NOx was investigated an environmental chamber. SOA yields homologous series linear increased monotonically with increasing carbon number due to decreasing parent thus reaction products. For a given number, followed order > trend that appears be determined primarily by extent which alkoxy...
Abstract. Recent field studies have found large discrepancies in the measured vs. modeled SOA mass loadings both urban and regional polluted atmospheres. The reasons for these differences are unclear. Here we revisit a case study of formation Mexico City described by Volkamer et al. (2006), during photochemically active period when impact biomass burning is minor or negligible, show that observed increase OA/ΔCO consistent with results from several groups MILAGRO 2006. Then use to evaluate...
A newly modified fast temperature-stepping thermodenuder (TD) was coupled to a High Resolution Time-of-Flight Aerosol Mass Spectrometer for rapid determination of chemically resolved volatility organic aerosols (OA) emitted from individual sources. The TD-AMS system used characterize primary OA (POA) biomass burning, trash burning surrogates (paper and plastic), meat cooking as well chamber-generated secondary (SOA) alpha-pinene gasoline vapor. Almost all atmospheric models represent POA...
Partitioning of gas-phase organic compounds to the walls Teflon environmental chambers is a recently reported phenomenon than can affect yields reaction products and secondary aerosol (SOA) measured in laboratory experiments. Reported time scales for reaching gas-wall partitioning (GWP) equilibrium (τGWE) differ by up 3 orders magnitude, however, leading predicted effects that vary from substantial negligible. A new technique demonstrated here which semi- low-volatility oxidized (saturation...
Measurements of submicron particles by Fourier transform infrared spectroscopy in 14 campaigns North America, Asia, South and Europe were used to identify characteristic organic functional group compositions fuel combustion, terrestrial vegetation, ocean bubble bursting sources, each which often accounts for more than a third mass (OM), some is secondary aerosol (SOA) from gas-phase precursors. The majority the OM consists alkane, carboxylic acid, hydroxyl, carbonyl groups. groups formed...
Catechol (1,2-benzenediol) is emitted from biomass burning and produced a reaction of phenol with OH radicals. It has been suggested as an important secondary organic aerosol (SOA) precursor, but the mechanisms gas-phase oxidation SOA formation have not investigated in detail. In this study, catechol was reacted NO3 radicals presence NOx environmental chamber to simulate daytime nighttime chemistry. These reactions exceptionally high mass yields 1.34 ± 0.20 1.50 0.20, respectively,...
Organic aerosols are ubiquitous in the atmosphere and play a central role climate, air quality, public health. The aerosol size distribution is key determining its optical properties cloud condensation nucleus activity. dominant portion of organic formed through gas-phase oxidation volatile compounds, so-called secondary (SOAs). Typical experimental measurements SOA formation include total mass atomic oxygen-to-carbon ratio. These measurements, alone, generally insufficient to reveal extent...
Secondary organic aerosol (SOA) formation from reactions of n-alkanes with OH radicals in the presence NOx was investigated an environmental chamber using a thermal desorption particle beam mass spectrometer for analysis. SOA consisted both first- and higher-generation products, all which were nitrates. Major first-generation products δ-hydroxynitrates, while dinitrates, hydroxydinitrates, substituted tetrahydrofurans containing nitrooxy, hydroxyl, carbonyl groups. The are formed by series...
Measurements of hygroscopicity and cloud condensation nuclei (CCN) activity were conducted on secondary organic aerosol (SOA) formed in a smog chamber. SOA precursors included α ‐pinene, β Δ 3 ‐carene, toluene, representative both naturally anthropogenically emitted species. Measured CCN activation was comparable for all the species studied occurred at humidity conditions which are readily attained atmosphere. Further, there little variation hygroscopic growth between compounds. However,...
A thermodenuder (TD) system, based on the design of CitationWehner et al. (2002), was designed, constructed, and characterized in laboratory. The TD consists a heated tube (2.5 cm ID, 55 long) held at constant temperature by 3-zone controller, followed cooling zone with diffusion lined activated charcoal for adsorption evaporated gases. An important improvement over previous designs is ability to step through temperatures ∼ 10 min. per reduction thermal inertia, addition two fans....
Reactions of O3 with pure and mixed oleic acid particles bulk solutions were investigated using a thermal desorption particle beam mass spectrometer. The results provide information on the effect matrix reaction products, mechanisms, kinetics. major aerosol products are α-acyloxyalkyl hydroperoxides, secondary ozonides, α-alkoxyalkyl oxocarboxylic acids formed primarily through reactions Criegee intermediates or compounds. For example, it is estimated that for consist approximately 68%...
Mixing characteristics of particles different volatilities from a diesel engine were studied with two tandem differential mobility analyzers (TDMAs) and an aerosol particle mass analyzer (APM). In both TDMA systems, heater was located in the path between first second DMAs. Diesel exhaust that size-selected DMA passed through heater, change size due to loss volatile components determined by DMA. On basis volatility measurements, could be separated into overlapping modes varied peak diameter...
Gas phase (MgO)+n and (MgO)nMg+ clusters (n≤90) were produced in a gas aggregation source studied by using laser-ionization time-of-flight mass spectrometry. The abundance maxima observed the spectra indicate that form compact cubic structures similar to pieces of MgO crystal lattice. metal-rich show an interesting dependence on ionization wavelength appears be due different fragmentation pathways for cluster ions neutrals, may indicative excess electron behavior analogous solid state color...