A5012711441- Atmospheric chemistry and aerosols
- Atmospheric aerosols and clouds
- Atmospheric Ozone and Climate
- Air Quality and Health Impacts
- Coagulation and Flocculation Studies
- nanoparticles nucleation surface interactions
- Particle Dynamics in Fluid Flows
- Catalytic Processes in Materials Science
- Indoor Air Quality and Microbial Exposure
- Thermochemical Biomass Conversion Processes
- Atmospheric and Environmental Gas Dynamics
- Aeolian processes and effects
- Air Quality Monitoring and Forecasting
- Combustion and flame dynamics
- Electrohydrodynamics and Fluid Dynamics
- Silicon Nanostructures and Photoluminescence
- Allergic Rhinitis and Sensitization
- Aerosol Filtration and Electrostatic Precipitation
- Cyclone Separators and Fluid Dynamics
- Vehicle emissions and performance
- Electrostatics and Colloid Interactions
- Semiconductor materials and devices
- Coal Properties and Utilization
- Spectroscopy and Quantum Chemical Studies
- Photonic and Optical Devices
California Institute of Technology
2015-2024
University of Arizona
2015
Division of Chemistry
2004-2013
University of Wisconsin–Madison
2003-2010
University of California, Riverside
2009
Alion Science and Technology (United States)
2008
University of Antwerp
2006-2008
Environmental Protection Agency
2006-2008
Brechtel (United States)
2007
National Oceanic and Atmospheric Administration
2007
Secondary organic aerosol (SOA) formation is considered in the framework of gas/particle partitioning absorption model outlined by Pankow. Expressions for fractional SOA yield (Y) are developed within this and shown to be a function mass concentration, M_o. These expressions applied over 30 individual reactive gas (ROG) photooxidation smog chamber experiments. Analysis data from these experiments clearly shows that Y strong M_o secondary best described model. In addition ROG experiments,...
Isoprene is a significant source of atmospheric organic aerosol; however, the oxidation pathways that lead to secondary aerosol (SOA) have remained elusive. Here, we identify role two key reactive intermediates, epoxydiols isoprene (IEPOX = β -IEPOX + δ -IEPOX) and methacryloylperoxynitrate (MPAN), which are formed during under low- high-NO x conditions, respectively. low-NO SOA enhanced in presence acidified sulfate seed (mass yield 28.6%) over neutral 1.3%). Increased uptake IEPOX by...
Current single-molecule detection techniques require labeling the target molecule. We report a highly specific and sensitive optical sensor based on an ultrahigh quality (Q) factor (Q > 10(8)) whispering-gallery microcavity. The silica surface is functionalized to bind molecule; binding detected by resonant wavelength shift. Single-molecule confirmed observation of events that shift frequency, as well statistics for these shifts over many events. These result from thermo-optic mechanism....
The Aerodyne Aerosol Mass Spectrometer (AMS) has been designed to measure size‐resolved mass distributions and total loadings of volatile semivolatile chemical species in/on submicron particles. This paper describes the application this instrument ambient aerosol sampling. AMS uses an aerodynamic lens focus particles into a narrow beam, roughened cartridge heater vaporize them under high vacuum, quadrupole spectrometer analyze vaporized molecules. Particle size is measured via particle...
Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up half global cloud condensation nuclei. Aerosols can cause a net cooling climate by scattering sunlight and leading smaller but more numerous droplets, which makes clouds brighter extends their lifetimes. Atmospheric aerosols derived human activities are have compensated for large fraction the warming caused greenhouse gases. However, despite its importance climate, nucleation poorly understood. Recently,...
The measurement of particle size distributions using electrical mobility can be accelerated significantly by an alternate mode operating instruments. Rather than changing the electric field in discrete steps to select particles a given range, scanned continuously. are classified time-varying field, but for exponential ramp strength there remains one-to-one correspondence between time enters classifier and it leaves. By this method, complete scans with as many 100 measurements have been made...
Recent work has shown that the atmospheric oxidation of isoprene (2-methyl-1,3-butadiene, C5H8) leads to formation secondary organic aerosol (SOA). In this study, mechanism SOA by photooxidation is comprehensively investigated, measurements yields over a range experimental conditions, namely and NOx concentrations. Hydrogen peroxide used as radical precursor, substantially constraining observed gas-phase chemistry; all dominated OH radical, peroxy radicals (RO2) react only with HO2 (formed...
Abstract About half of present-day cloud condensation nuclei originate from atmospheric nucleation, frequently appearing as a burst new particles near midday 1 . Atmospheric observations show that the growth rate often accelerates when diameter is between one and ten nanometres 2,3 In this critical size range, are most likely to be lost by coagulation with pre-existing 4 , thereby failing form typically 50 100 across. Sulfuric acid vapour involved in nucleation but too scarce explain...
A series of outdoor chamber experiments has been used to establish and characterize the significant atmospheric aerosol‐forming potentials most prevalent biogenic hydrocarbons emitted by vegetation. These compounds were also studied elucidate effect structure on aerosol yield for these types compounds. Because oxidation products partition between gas phases, yields parent depend concentration organic into which can be absorbed. For mass concentrations 5 40 μg m −3 , mass‐based in...
Abstract. Secondary organic aerosol (SOA) formation from the photooxidation of m-xylene, toluene, and benzene is investigated in Caltech environmental chambers. Experiments are performed under two limiting NOx conditions; high-NOx conditions peroxy radicals (RO2) react only with NO, while low-NOx they HO2. For all three aromatics studied (m-xylene, benzene), SOA yields (defined as ratio mass formed to parent hydrocarbon reacted) substantially exceed those conditions, suggesting importance...
Abstract Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood 1 . Globally, around half cloud condensation nuclei originate from nucleation atmospheric vapours 2 It is that sulfuric acid essential initiate most particle formation in atmosphere 3,4 , ions have a relatively minor role 5 Some laboratory studies, however, reported organic without intentional addition acid, although...
Recent work in our laboratory has shown that the photooxidation of isoprene (2-methyl-1,3-butadiene, C(5)H(8)) leads to formation secondary organic aerosol (SOA). In current study, chemical composition SOA from over full range NO(x) conditions is investigated through a series controlled chamber experiments. studied using wide experimental techniques: electrospray ionization-mass spectrometry, matrix-assisted laser desorption high-resolution mass online gas chromatography/mass and an...
Organosulfates of isoprene, α-pinene, and β-pinene have recently been identified in both laboratory-generated ambient secondary organic aerosol (SOA). In this study, the mechanism ubiquity organosulfate formation biogenic SOA is investigated by a comprehensive series laboratory photooxidation (i.e., OH-initiated oxidation) nighttime oxidation NO3-initiated under dark conditions) experiments using nine monoterpenes (α-pinene, β-pinene, d-limonene, l-limonene, α-terpinene, γ-terpinene,...
Recent work has shown that particle-phase reactions contribute to the formation of secondary organic aerosol (SOA), with enhancements SOA yields in presence acidic seed aerosol. In this study, chemical composition from photooxidations α-pinene and isoprene, or absence sulfate aerosol, is investigated through a series controlled chamber experiments two separate laboratories. By using electrospray ionization−mass spectrometry, esters produced laboratory photooxidation are identified for first...
Atmospheric new-particle formation affects climate and is one of the least understood atmospheric aerosol processes. The complexity variability atmosphere has hindered elucidation fundamental mechanism from gaseous precursors. We show, in experiments performed with CLOUD (Cosmics Leaving Outdoor Droplets) chamber at CERN, that sulfuric acid oxidized organic vapors concentrations reproduce particle nucleation rates observed lower atmosphere. reveal a involving clusters containing molecules...
series of sunlight-irradiated, smog-chamber experiments confirmed that the atmospheric organic aerosol formation potential whole gasoline vapor can be accounted for solely in terms aromatic fraction fuel. The total amount secondary produced from oxidation represented as sum contributions individual molecular constituents urban atmospheric, anthropogenic hydrocarbon profile is approximated well by evaporated gasoline, and thus these results suggest it possible to model formation.
Observations made in the CLOUD chamber at CERN illuminate atmospheric particle formation.
The photooxidation of isoprene, eight monoterpenes, three oxygenated and four sesquiterpenes were conducted individually at the Caltech Indoor Chamber Facility under atmospherically relevant HC:NO x ratios to monitor time evolution yields SOA gas‐phase oxidation products using PTR‐MS. Several calibrated in PTR‐MS, including formaldehyde, acetaldehyde, formic acid, acetone, acetic nopinone, methacrolein + methyl vinyl ketone; other inferred from known fragmentation patterns, such as...
Abstract. Secondary organic aerosol (SOA) formation from the photooxidation of one monoterpene (α-pinene) and two sesquiterpenes (longifolene aromadendrene) is investigated in Caltech environmental chambers. The effect NOx on SOA for these biogenic hydrocarbons evaluated by performing experiments under varying conditions. dependence α-pinene follows same trend as that observed previously a number precursors, including isoprene, which yield (defined ratio mass formed to parent hydrocarbon...
Abstract. Chamber studies of glyoxal uptake onto ammonium sulphate aerosol were performed under dark and irradiated conditions to gain further insight into processes controlling ambient aerosol. Organic fragments from dimers trimers observed within the conditions. Glyoxal monomers oligomers dominant organic compounds formed this study; oligomer formation overall growth found be reversible Analysis high-resolution time-of-flight mass spectra provides evidence for irreversible carbon-nitrogen...