Alla Zelenyuk - Profile on Academia.edu (original) (raw)

Papers by Alla Zelenyuk

2017 New York Scientific Data Summit (NYSDS), 2017

Clustering has become an unavoidable step in big data analysis. It may be used to arrange data in... more Clustering has become an unavoidable step in big data analysis. It may be used to arrange data into a compact format, making operations on big data manageable. However, clustering of big data requires not only the capability of handling data with large volume and high dimensionality, but also the ability to process streaming data, all of which are less developed in most current algorithms. Furthermore, big data processing is seldom interactive, which stands at conflict with users who seek answers immediately. The best one can do is to process incrementally, such that partial and, hopefully, accurate results can be available relatively quickly and are then progressively refined over time. We propose a clustering framework which uses Multi-Dimensional Scaling for layout and GPU acceleration to accomplish these goals. Our domain application is the clustering of mass spectral data of individual aerosol particles with 8 million data points of 450 dimensions each.

Pragmatic markers, considered as one of the best-known sources of troubles in translation, have r... more Pragmatic markers, considered as one of the best-known sources of troubles in translation, have received considerable attention from researchers. This study therefore, offers a contrastive analysis of "well" and "so" occurring in an extract of the film Finding Nemo and their translation in the Vietnamese dubbed and subtitled versions. The occurrences of "well and "so" in the data were analyzed according to a functional classification framework and compared with their translation equivalents by contrastive analysis (CA) to find out the translation strategies applied and to evaluate translation effectiveness. The findings reveal that "well" tends to be omitted more often than "so" in the Vietnamese translations while "so" appears to be the easier item whose functions are usually well captured by single-word equivalents. The study also shows how careful analysis may help the translators achieve effective and natural translation. Implications for EFL teaching and translating tasks as well as suggestions for further research are also discussed.

Bulletin of the American Meteorological Society, 2021

The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to impro... more The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft. A multitude of atmospheric processes and cloud conditions were obser...

Atmospheric Chemistry and Physics Discussions, 2019

We present measurements utilizing the Filter Inlet for Gases and Aerosols (FIGAERO) applied to ch... more We present measurements utilizing the Filter Inlet for Gases and Aerosols (FIGAERO) applied to chamber measurements of isoprene-derived epoxydiol (IEPOX) reactive uptake to aqueous acidic particles and associated SOA formation. Similar to recent field observations with the same instrument, we detect two molecular components desorbing from the IEPOX SOA in high abundance: C5H12O4 and C5H10O3. The thermal desorption signal of the former, presumably 2-methyltetrols, exhibits two distinct maxima, suggesting it arises from at least two different SOA components with significantly different effective volatilities. Isothermal evaporation experiments illustrate that the most abundant component giving rise to C5H12O4 is semi-volatile, undergoing nearly complete evaporation within 1 hour, while the second, less volatile, component remains unperturbed and even increases in abundance. We thus confirm, using controlled laboratory studies, recent analyses of ambient SOA measurements showing that IEPOX SOA is of very low volatility and commonly measured IEPOX SOA tracers, such as 2methyltetrols and C5-alkene triols, result predominantly from artifacts of measurement techniques associated with thermal decomposition and/or hydrolysis. We further show that IEPOX SOA volatility continues to evolve via acidity enhanced accretion chemistry on the timescale of hours, potentially involving both 2-methyltetrols and organosulfates. , and IEPOX has been shown to react in aqueous acidic particles, forming SOA. Commonly measured species from IEPOX reactive uptake include 2-methyltetrols (Lin et al.,

Atmospheric Chemistry and Physics, 2018

Biological particles, including bacteria and bacterial fragments, have been of much interest due ... more Biological particles, including bacteria and bacterial fragments, have been of much interest due to the special ability of some to nucleate ice at modestly supercooled temperatures. This paper presents results from a recent study conducted on two strains of cultivated bacteria which suggest that bacterial fragments mixed with agar, and not whole bacterial cells, serve as cloud condensation nuclei (CCN). Due to the absence of whole bacteria cells in droplets, they are unable to serve as ice nucleating particles (INPs) in the immersion mode under the experimental conditions. Experiments were conducted at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber at the Karlsruhe Institute of Technology (KIT) by injecting bacteria-containing aerosol samples into the cloud chamber and inducing cloud formation by expansion over a temperature range of -5 to -12 • C. Cloud droplets and ice crystals were sampled through a pumped counterflow virtual impactor inlet (PCVI) and their residuals were characterized with a single particle mass spectrometer (miniSPLAT). The size distribution of the overall aerosol was bimodal, with a large particle mode composed of intact bacteria and a mode of smaller particles composed of bacterial fragments mixed with agar that were present in higher concentrations. Results from three expansions with two bacterial strains indicate that the cloud droplet residuals had virtually the same size distribution as the smaller particle size mode and had mass spectra that closely matched those of bacterial fragments mixed with agar. The characterization of ice residuals that were sampled through an ice-selecting PCVI (IS-PCVI) also shows that the same particles that activate to form cloud droplets, bacteria fragments mixed with agar, were the only particle type observed in ice residuals. These results indicate that the unavoidable presence of agar or other growth media in all laboratory studies conducted on cultivated bacteria can greatly affect the results and needs to be considered when interpreting CCN and IN activation data.

Environmental science & technology, Jan 21, 2018

We developed a parametrizable box model to empirically derive the yields of semivolatile products... more We developed a parametrizable box model to empirically derive the yields of semivolatile products from VOC oxidation using chamber measurements, while explicitly accounting for the multigenerational chemical aging processes (such as the gas-phase fragmentation and functionalization and aerosol-phase oligomerization and photolysis) under different NO levels and the loss of particles and gases to chamber walls. Using the oxidation of isoprene as an example, we showed that the assumptions regarding the NO -sensitive, multigenerational aging processes of VOC oxidation products have large impacts on the parametrized product yields and SOA formation. We derived sets of semivolatile product yields from isoprene oxidation under different NO levels. However, we stress that these product yields must be used in conjunction with the corresponding multigenerational aging schemes in chemical transport models. As more mechanistic insights regarding SOA formation from VOC oxidation emerge, our box ...

Environmental science & technology, Jan 15, 2017

Low bulk diffusivity inside viscous semisolid atmospheric secondary organic aerosol (SOA) can pro... more Low bulk diffusivity inside viscous semisolid atmospheric secondary organic aerosol (SOA) can prolong equilibration timescale, but its broader impacts on aerosol growth and size distribution dynamics are poorly understood. Here we present quantitative insights into the effects of bulk diffusivity on the growth and evaporation kinetics of SOA formed under dry conditions from photooxidation of isoprene in the presence of a bimodal aerosol consisting of Aitken (ammonium sulfate) and accumulation (isoprene or -pinene SOA) mode particles. Aerosol composition measurements and evaporation kinetics indicate that isoprene SOA is composed of several semivolatile organic compounds (SVOCs), with some reversibly reacting to form oligomers. Model analysis shows that liquid-like bulk diffusivities can be used to fit the observed evaporation kinetics of accumulation mode particles, but fail to explain the growth kinetics of bimodal aerosol by significantly under-predicting the evolution of the Ait...

Aerosol Science and Technology, 2016

Understanding and modeling the behavior of quartz dust particles, commonly found in the atmospher... more Understanding and modeling the behavior of quartz dust particles, commonly found in the atmosphere, requires knowledge of many relevant particle properties, including particle shape. This study uses a single particle mass spectrometer, a differential mobility analyzer, and an aerosol particle mass analyzer to measure quartz aerosol particles mobility (d m ), vacuum aerodynamic, and volume equivalent diameters, mass, composition, effective density, and dynamic shape factor as a function of particle size, in both the free molecular and transition flow regimes. The results clearly demonstrate that dynamic shape factors can vary significantly as a function of particle size. For the quartz samples studied here, the dynamic shape factors increase with size, indicating that larger particles are significantly more aspherical than smaller particles. In addition, dynamic shape factors measured in the free-molecular (x v ) and transition (x t ) flow regimes can be significantly different, and these differences vary with the size of the quartz particles. For quartz, x v of small (d m < 200 nm) particles is 1.25, while x v of larger particles (d m » 440 nm) is 1.6, with a continuously increasing trend with particle size. In contrast, x t of small particles starts at 1.1 increasing slowly to 1.34 for 550 nm diameter particles. The multidimensional particle characterization approach used here goes beyond determination of average properties for each size, to provide additional information about how the particle dynamic shape factor may vary even for particles with the same mass and volume equivalent diameter.

Proceedings of the National Academy of Sciences of the United States of America, Feb 7, 2017

Polycyclic aromatic hydrocarbons (PAHs) have toxic impacts on humans and ecosystems. One of the m... more Polycyclic aromatic hydrocarbons (PAHs) have toxic impacts on humans and ecosystems. One of the most carcinogenic PAHs, benzo(a)pyrene (BaP), is efficiently bound to and transported with atmospheric particles. Laboratory measurements show that particle-bound BaP degrades in a few hours by heterogeneous reaction with ozone, yet field observations indicate BaP persists much longer in the atmosphere, and some previous chemical transport modeling studies have ignored heterogeneous oxidation of BaP to bring model predictions into better agreement with field observations. We attribute this unexplained discrepancy to the shielding of BaP from oxidation by coatings of viscous organic aerosol (OA). Accounting for this OA viscosity-dependent shielding, which varies with temperature and humidity, in a global climate/chemistry model brings model predictions into much better agreement with BaP measurements, and demonstrates stronger long-range transport, greater deposition fluxes, and substantia...

Environmental science & technology, Jun 13, 2016

Multiphase chemistry of isomeric isoprene epoxydiols (IEPOX) has been shown to be the dominant so... more Multiphase chemistry of isomeric isoprene epoxydiols (IEPOX) has been shown to be the dominant source of isoprene-derived secondary organic aerosol (SOA). Recent studies have reported particles composed of ammonium bisulfate (ABS) mixed with model organics exhibit slower rates of IEPOX uptake. In the present study, we investigate the effect of atmospherically-relevant organic coatings of α-pinene (AP) SOA on the reactive uptake of trans-β-IEPOX onto ABS particles under different conditions and coating thicknesses. Single particle mass spectrometry was used to characterize in real-time particle size, shape, density, and quantitative composition before and after reaction with IEPOX. We find that IEPOX uptake by pure sulfate particles is a volume-controlled process, which results in particles with uniform concentration of IEPOX-derived SOA across a wide range of sizes. Aerosol acidity was shown to enhance IEPOX-derived SOA formation, consistent with recent studies. The presence of wate...

Atmospheric Chemistry and Physics Discussions, 2016

Measurements of the optical properties (absorption, scattering and extinction) of…

Fuel-Neutral Studies of PM Transportation Emissions

New gasoline engine technologies such as Spark Ignition Direct Injection (SIDI), Gasoline Direct ... more New gasoline engine technologies such as Spark Ignition Direct Injection (SIDI), Gasoline Direct Injection Compression Ignition (GDICI), and Reaction Controlled Compression Ignition (RCCI) offer the possibility of dramatically increasing the fuel efficiency of future vehicles. One drawback to these advanced engines is that they have the potential to produce higher levels of exhaust particulates than current Port Fuel Injection (PFI) engines. Regulation of engine particulate emissions in Europe is moving from mass-based standards toward number-based standards. Due to growing health concerns surrounding nano-aerosols, it is likely that similar standards will eventually be applied in the United States. This would place more emphasis on the reliable removal of smaller particles, which make up the vast majority of the particulates generated on a number basis. While Diesel Particulate Filters (DPF) have become standard, different filter systems would likely be required for advanced gasoline vehicles, due to factors such as differing particulate properties and higher exhaust temperatures. High exhaust temperatures can limit the accumulation of a soot cake, which performs most of the actual filtration in a typical DPF system.

Secondary Organic Aerosol (SOA) Formation From the NO3 Radical Oxidation of Alpha pinene

ABSTRACT

Atmospheric Chemistry and Physics, 2014

We have developed the novel Aerosol Dynamics, gas- and particle-phase chemistry model for laborat... more We have developed the novel Aerosol Dynamics, gas- and particle-phase chemistry model for laboratory CHAMber studies (ADCHAM). The model combines the detailed gas-phase Master Chemical Mechanism version 3.2 (MCMv3.2), an aerosol dynamics and particle-phase chemistry module (which considers acid-catalysed oligomerization, heterogeneous oxidation reactions in the particle phase and non-ideal interactions between organic compounds, water and inorganic ions) and a kinetic multilayer module for diffusion-limited transport of compounds between the gas phase, particle surface and particle bulk phase. In this article we describe and use ADCHAM to study (1) the evaporation of liquid dioctyl phthalate (DOP) particles, (2) the slow and almost particle-size-independent evaporation of α-pinene ozonolysis secondary organic aerosol (SOA) particles, (3) the mass-transfer-limited uptake of ammonia (NH₃) and formation of organic salts between ammonium (NH<sub>4</sub&gt...

New Developments and Needs in Hygroscopicity Measurements of the Ambient Aerosol

A review of water uptake measurements conducted over the past 25 years using the Humidified Tande... more A review of water uptake measurements conducted over the past 25 years using the Humidified Tandem Differential Mobility Analyzer (HTDMA) technique reveals that ambient Aitken and accumulation mode particles typically grow substantially less at a given relative humidity compared to pure ammonium sulfate. Multiple hygroscopic modes at a single particle size are routinely observed, revealing that ambient particles are externally mixed with respect to their chemical composition. The observed growth of the multiple hygroscopic modes is typically less than that for particles composed of purely soluble salts, indicating that the externally mixed populations are themselves internally mixed with more and less-water soluble species. Therefore, the HTDMA is a powerful tool for quantitative measurements of size-dependent hygroscopic growth factors and for qualitative observations of the complex chemical composition responsible for the observed growth. The strengths and limitations of the HTDMA...

Amine–Amine Exchange in Aminium–Methanesulfonate Aerosols

The Journal of Physical Chemistry C, 2014

Aerosol particles are ubiquitous in the atmosphere and have been shown to impact the Earth’s clim... more Aerosol particles are ubiquitous in the atmosphere and have been shown to impact the Earth’s climate, reduce visibility, and adversely affect human health. Modeling the evolution of aerosol systems requires an understanding of the species and mechanisms involved in particle growth, including the complex interactions between particle- and gas-phase species. Here we report studies of displacement of amines (methylamine, dimethylamine, or trimethylamine) in methanesulfonate salt particles by exposure to a different gas-phase amine, using a single particle mass spectrometer, SPLAT II. The variation of the displacement with the nature of the amine suggests that behavior is dependent on water in or on the particles. Small clusters of methanesulfonic acid with amines are used as a model in quantum chemical calculations to identify key structural elements that are expected to influence water uptake, and hence the efficiency of displacement by gas-phase molecules in the aminium salts. Such molecular-level understa...

Role of Ozone in Particle Formation and Growth From the Nitrate Radical-Initiated Oxidation of alpha-Pinene

The three major atmospheric oxidants involved in SOA formation from biogenic volatile organic com... more The three major atmospheric oxidants involved in SOA formation from biogenic volatile organic compounds are O3, OH and nitrate radical (NO3). While O3 and OH-initiated oxidation occur during the day, NO3 radical-initiated oxidation is recognized to be a major contributor to the night-time chemistry of volatile organic compounds in the troposphere. Specifically, the reaction of biogenic hydrocarbons with NO3 is

Construction, Modeling and Testing of a Low-Flow, Large-Diameter Aerosol Flow System for the Study of the Formation and Reactions of Tropospheric Aerosols

A unique, high-volume, low-flow, stainless steel aerosol flow system for the study of the formati... more A unique, high-volume, low-flow, stainless steel aerosol flow system for the study of the formation and reactions of aerosols relevant to the troposphere has been constructed, modeled and experimentally tested. The total flow tube length is 7.3 m which includes a 1.2 m section used for mixing. The flow tube is equipped with ultraviolet lamps for photolysis. The diameter of

Particulate Matter Sampling and Volatile Organic Compound Removal for Characterization of Spark Ignited Direct Injection Engine Emissions

SAE International Journal of Fuels and Lubricants, 2011

More stringent emissions regulations are continually being proposed to mitigate adverse human hea... more More stringent emissions regulations are continually being proposed to mitigate adverse human health and environmental impacts of internal combustion engines. With that in mind, it has been proposed that vehicular particulate matter (PM) emissions should be regulated based on particle number in addition to particle mass. One aspect of this project is to study different sample handling methods for number based aerosol measurements, specifically, two different methods for removing volatile organic compounds (VOCs). One method is a thermodenuder (TD) and the other is an evaporative chamber/diluter (EvCh). These sample handling methods have been implemented in an engine test cell with a spark ignited direct injection (SIDI) engine. The engine was designed for stoichiometric, homogeneous combustion. SIDI is of particular interest for improved fuel efficiency compared to other SI engines, however, the efficiency benefit comes with greater PM emissions and may therefore be subject to the proposed number based PM regulation. Another aspect of this project is to characterize PM from this engine in terms of particle number and composition.

Particulate Characteristics for Varying Engine Operation in a Gasoline Spark Ignited, Direct Injection Engine

SAE Technical Paper Series, 2011

2017 New York Scientific Data Summit (NYSDS), 2017

Clustering has become an unavoidable step in big data analysis. It may be used to arrange data in... more Clustering has become an unavoidable step in big data analysis. It may be used to arrange data into a compact format, making operations on big data manageable. However, clustering of big data requires not only the capability of handling data with large volume and high dimensionality, but also the ability to process streaming data, all of which are less developed in most current algorithms. Furthermore, big data processing is seldom interactive, which stands at conflict with users who seek answers immediately. The best one can do is to process incrementally, such that partial and, hopefully, accurate results can be available relatively quickly and are then progressively refined over time. We propose a clustering framework which uses Multi-Dimensional Scaling for layout and GPU acceleration to accomplish these goals. Our domain application is the clustering of mass spectral data of individual aerosol particles with 8 million data points of 450 dimensions each.

Pragmatic markers, considered as one of the best-known sources of troubles in translation, have r... more Pragmatic markers, considered as one of the best-known sources of troubles in translation, have received considerable attention from researchers. This study therefore, offers a contrastive analysis of "well" and "so" occurring in an extract of the film Finding Nemo and their translation in the Vietnamese dubbed and subtitled versions. The occurrences of "well and "so" in the data were analyzed according to a functional classification framework and compared with their translation equivalents by contrastive analysis (CA) to find out the translation strategies applied and to evaluate translation effectiveness. The findings reveal that "well" tends to be omitted more often than "so" in the Vietnamese translations while "so" appears to be the easier item whose functions are usually well captured by single-word equivalents. The study also shows how careful analysis may help the translators achieve effective and natural translation. Implications for EFL teaching and translating tasks as well as suggestions for further research are also discussed.

Bulletin of the American Meteorological Society, 2021

The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to impro... more The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft. A multitude of atmospheric processes and cloud conditions were obser...

Atmospheric Chemistry and Physics Discussions, 2019

We present measurements utilizing the Filter Inlet for Gases and Aerosols (FIGAERO) applied to ch... more We present measurements utilizing the Filter Inlet for Gases and Aerosols (FIGAERO) applied to chamber measurements of isoprene-derived epoxydiol (IEPOX) reactive uptake to aqueous acidic particles and associated SOA formation. Similar to recent field observations with the same instrument, we detect two molecular components desorbing from the IEPOX SOA in high abundance: C5H12O4 and C5H10O3. The thermal desorption signal of the former, presumably 2-methyltetrols, exhibits two distinct maxima, suggesting it arises from at least two different SOA components with significantly different effective volatilities. Isothermal evaporation experiments illustrate that the most abundant component giving rise to C5H12O4 is semi-volatile, undergoing nearly complete evaporation within 1 hour, while the second, less volatile, component remains unperturbed and even increases in abundance. We thus confirm, using controlled laboratory studies, recent analyses of ambient SOA measurements showing that IEPOX SOA is of very low volatility and commonly measured IEPOX SOA tracers, such as 2methyltetrols and C5-alkene triols, result predominantly from artifacts of measurement techniques associated with thermal decomposition and/or hydrolysis. We further show that IEPOX SOA volatility continues to evolve via acidity enhanced accretion chemistry on the timescale of hours, potentially involving both 2-methyltetrols and organosulfates. , and IEPOX has been shown to react in aqueous acidic particles, forming SOA. Commonly measured species from IEPOX reactive uptake include 2-methyltetrols (Lin et al.,

Atmospheric Chemistry and Physics, 2018

Biological particles, including bacteria and bacterial fragments, have been of much interest due ... more Biological particles, including bacteria and bacterial fragments, have been of much interest due to the special ability of some to nucleate ice at modestly supercooled temperatures. This paper presents results from a recent study conducted on two strains of cultivated bacteria which suggest that bacterial fragments mixed with agar, and not whole bacterial cells, serve as cloud condensation nuclei (CCN). Due to the absence of whole bacteria cells in droplets, they are unable to serve as ice nucleating particles (INPs) in the immersion mode under the experimental conditions. Experiments were conducted at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber at the Karlsruhe Institute of Technology (KIT) by injecting bacteria-containing aerosol samples into the cloud chamber and inducing cloud formation by expansion over a temperature range of -5 to -12 • C. Cloud droplets and ice crystals were sampled through a pumped counterflow virtual impactor inlet (PCVI) and their residuals were characterized with a single particle mass spectrometer (miniSPLAT). The size distribution of the overall aerosol was bimodal, with a large particle mode composed of intact bacteria and a mode of smaller particles composed of bacterial fragments mixed with agar that were present in higher concentrations. Results from three expansions with two bacterial strains indicate that the cloud droplet residuals had virtually the same size distribution as the smaller particle size mode and had mass spectra that closely matched those of bacterial fragments mixed with agar. The characterization of ice residuals that were sampled through an ice-selecting PCVI (IS-PCVI) also shows that the same particles that activate to form cloud droplets, bacteria fragments mixed with agar, were the only particle type observed in ice residuals. These results indicate that the unavoidable presence of agar or other growth media in all laboratory studies conducted on cultivated bacteria can greatly affect the results and needs to be considered when interpreting CCN and IN activation data.

Environmental science & technology, Jan 21, 2018

We developed a parametrizable box model to empirically derive the yields of semivolatile products... more We developed a parametrizable box model to empirically derive the yields of semivolatile products from VOC oxidation using chamber measurements, while explicitly accounting for the multigenerational chemical aging processes (such as the gas-phase fragmentation and functionalization and aerosol-phase oligomerization and photolysis) under different NO levels and the loss of particles and gases to chamber walls. Using the oxidation of isoprene as an example, we showed that the assumptions regarding the NO -sensitive, multigenerational aging processes of VOC oxidation products have large impacts on the parametrized product yields and SOA formation. We derived sets of semivolatile product yields from isoprene oxidation under different NO levels. However, we stress that these product yields must be used in conjunction with the corresponding multigenerational aging schemes in chemical transport models. As more mechanistic insights regarding SOA formation from VOC oxidation emerge, our box ...

Environmental science & technology, Jan 15, 2017

Low bulk diffusivity inside viscous semisolid atmospheric secondary organic aerosol (SOA) can pro... more Low bulk diffusivity inside viscous semisolid atmospheric secondary organic aerosol (SOA) can prolong equilibration timescale, but its broader impacts on aerosol growth and size distribution dynamics are poorly understood. Here we present quantitative insights into the effects of bulk diffusivity on the growth and evaporation kinetics of SOA formed under dry conditions from photooxidation of isoprene in the presence of a bimodal aerosol consisting of Aitken (ammonium sulfate) and accumulation (isoprene or -pinene SOA) mode particles. Aerosol composition measurements and evaporation kinetics indicate that isoprene SOA is composed of several semivolatile organic compounds (SVOCs), with some reversibly reacting to form oligomers. Model analysis shows that liquid-like bulk diffusivities can be used to fit the observed evaporation kinetics of accumulation mode particles, but fail to explain the growth kinetics of bimodal aerosol by significantly under-predicting the evolution of the Ait...

Aerosol Science and Technology, 2016

Understanding and modeling the behavior of quartz dust particles, commonly found in the atmospher... more Understanding and modeling the behavior of quartz dust particles, commonly found in the atmosphere, requires knowledge of many relevant particle properties, including particle shape. This study uses a single particle mass spectrometer, a differential mobility analyzer, and an aerosol particle mass analyzer to measure quartz aerosol particles mobility (d m ), vacuum aerodynamic, and volume equivalent diameters, mass, composition, effective density, and dynamic shape factor as a function of particle size, in both the free molecular and transition flow regimes. The results clearly demonstrate that dynamic shape factors can vary significantly as a function of particle size. For the quartz samples studied here, the dynamic shape factors increase with size, indicating that larger particles are significantly more aspherical than smaller particles. In addition, dynamic shape factors measured in the free-molecular (x v ) and transition (x t ) flow regimes can be significantly different, and these differences vary with the size of the quartz particles. For quartz, x v of small (d m < 200 nm) particles is 1.25, while x v of larger particles (d m » 440 nm) is 1.6, with a continuously increasing trend with particle size. In contrast, x t of small particles starts at 1.1 increasing slowly to 1.34 for 550 nm diameter particles. The multidimensional particle characterization approach used here goes beyond determination of average properties for each size, to provide additional information about how the particle dynamic shape factor may vary even for particles with the same mass and volume equivalent diameter.

Proceedings of the National Academy of Sciences of the United States of America, Feb 7, 2017

Polycyclic aromatic hydrocarbons (PAHs) have toxic impacts on humans and ecosystems. One of the m... more Polycyclic aromatic hydrocarbons (PAHs) have toxic impacts on humans and ecosystems. One of the most carcinogenic PAHs, benzo(a)pyrene (BaP), is efficiently bound to and transported with atmospheric particles. Laboratory measurements show that particle-bound BaP degrades in a few hours by heterogeneous reaction with ozone, yet field observations indicate BaP persists much longer in the atmosphere, and some previous chemical transport modeling studies have ignored heterogeneous oxidation of BaP to bring model predictions into better agreement with field observations. We attribute this unexplained discrepancy to the shielding of BaP from oxidation by coatings of viscous organic aerosol (OA). Accounting for this OA viscosity-dependent shielding, which varies with temperature and humidity, in a global climate/chemistry model brings model predictions into much better agreement with BaP measurements, and demonstrates stronger long-range transport, greater deposition fluxes, and substantia...

Environmental science & technology, Jun 13, 2016

Multiphase chemistry of isomeric isoprene epoxydiols (IEPOX) has been shown to be the dominant so... more Multiphase chemistry of isomeric isoprene epoxydiols (IEPOX) has been shown to be the dominant source of isoprene-derived secondary organic aerosol (SOA). Recent studies have reported particles composed of ammonium bisulfate (ABS) mixed with model organics exhibit slower rates of IEPOX uptake. In the present study, we investigate the effect of atmospherically-relevant organic coatings of α-pinene (AP) SOA on the reactive uptake of trans-β-IEPOX onto ABS particles under different conditions and coating thicknesses. Single particle mass spectrometry was used to characterize in real-time particle size, shape, density, and quantitative composition before and after reaction with IEPOX. We find that IEPOX uptake by pure sulfate particles is a volume-controlled process, which results in particles with uniform concentration of IEPOX-derived SOA across a wide range of sizes. Aerosol acidity was shown to enhance IEPOX-derived SOA formation, consistent with recent studies. The presence of wate...

Atmospheric Chemistry and Physics Discussions, 2016

Measurements of the optical properties (absorption, scattering and extinction) of…

Fuel-Neutral Studies of PM Transportation Emissions

New gasoline engine technologies such as Spark Ignition Direct Injection (SIDI), Gasoline Direct ... more New gasoline engine technologies such as Spark Ignition Direct Injection (SIDI), Gasoline Direct Injection Compression Ignition (GDICI), and Reaction Controlled Compression Ignition (RCCI) offer the possibility of dramatically increasing the fuel efficiency of future vehicles. One drawback to these advanced engines is that they have the potential to produce higher levels of exhaust particulates than current Port Fuel Injection (PFI) engines. Regulation of engine particulate emissions in Europe is moving from mass-based standards toward number-based standards. Due to growing health concerns surrounding nano-aerosols, it is likely that similar standards will eventually be applied in the United States. This would place more emphasis on the reliable removal of smaller particles, which make up the vast majority of the particulates generated on a number basis. While Diesel Particulate Filters (DPF) have become standard, different filter systems would likely be required for advanced gasoline vehicles, due to factors such as differing particulate properties and higher exhaust temperatures. High exhaust temperatures can limit the accumulation of a soot cake, which performs most of the actual filtration in a typical DPF system.

Secondary Organic Aerosol (SOA) Formation From the NO3 Radical Oxidation of Alpha pinene

ABSTRACT

Atmospheric Chemistry and Physics, 2014

We have developed the novel Aerosol Dynamics, gas- and particle-phase chemistry model for laborat... more We have developed the novel Aerosol Dynamics, gas- and particle-phase chemistry model for laboratory CHAMber studies (ADCHAM). The model combines the detailed gas-phase Master Chemical Mechanism version 3.2 (MCMv3.2), an aerosol dynamics and particle-phase chemistry module (which considers acid-catalysed oligomerization, heterogeneous oxidation reactions in the particle phase and non-ideal interactions between organic compounds, water and inorganic ions) and a kinetic multilayer module for diffusion-limited transport of compounds between the gas phase, particle surface and particle bulk phase. In this article we describe and use ADCHAM to study (1) the evaporation of liquid dioctyl phthalate (DOP) particles, (2) the slow and almost particle-size-independent evaporation of α-pinene ozonolysis secondary organic aerosol (SOA) particles, (3) the mass-transfer-limited uptake of ammonia (NH₃) and formation of organic salts between ammonium (NH<sub>4</sub&gt...

New Developments and Needs in Hygroscopicity Measurements of the Ambient Aerosol

A review of water uptake measurements conducted over the past 25 years using the Humidified Tande... more A review of water uptake measurements conducted over the past 25 years using the Humidified Tandem Differential Mobility Analyzer (HTDMA) technique reveals that ambient Aitken and accumulation mode particles typically grow substantially less at a given relative humidity compared to pure ammonium sulfate. Multiple hygroscopic modes at a single particle size are routinely observed, revealing that ambient particles are externally mixed with respect to their chemical composition. The observed growth of the multiple hygroscopic modes is typically less than that for particles composed of purely soluble salts, indicating that the externally mixed populations are themselves internally mixed with more and less-water soluble species. Therefore, the HTDMA is a powerful tool for quantitative measurements of size-dependent hygroscopic growth factors and for qualitative observations of the complex chemical composition responsible for the observed growth. The strengths and limitations of the HTDMA...

Amine–Amine Exchange in Aminium–Methanesulfonate Aerosols

The Journal of Physical Chemistry C, 2014

Aerosol particles are ubiquitous in the atmosphere and have been shown to impact the Earth’s clim... more Aerosol particles are ubiquitous in the atmosphere and have been shown to impact the Earth’s climate, reduce visibility, and adversely affect human health. Modeling the evolution of aerosol systems requires an understanding of the species and mechanisms involved in particle growth, including the complex interactions between particle- and gas-phase species. Here we report studies of displacement of amines (methylamine, dimethylamine, or trimethylamine) in methanesulfonate salt particles by exposure to a different gas-phase amine, using a single particle mass spectrometer, SPLAT II. The variation of the displacement with the nature of the amine suggests that behavior is dependent on water in or on the particles. Small clusters of methanesulfonic acid with amines are used as a model in quantum chemical calculations to identify key structural elements that are expected to influence water uptake, and hence the efficiency of displacement by gas-phase molecules in the aminium salts. Such molecular-level understa...

Role of Ozone in Particle Formation and Growth From the Nitrate Radical-Initiated Oxidation of alpha-Pinene

The three major atmospheric oxidants involved in SOA formation from biogenic volatile organic com... more The three major atmospheric oxidants involved in SOA formation from biogenic volatile organic compounds are O3, OH and nitrate radical (NO3). While O3 and OH-initiated oxidation occur during the day, NO3 radical-initiated oxidation is recognized to be a major contributor to the night-time chemistry of volatile organic compounds in the troposphere. Specifically, the reaction of biogenic hydrocarbons with NO3 is

Construction, Modeling and Testing of a Low-Flow, Large-Diameter Aerosol Flow System for the Study of the Formation and Reactions of Tropospheric Aerosols

A unique, high-volume, low-flow, stainless steel aerosol flow system for the study of the formati... more A unique, high-volume, low-flow, stainless steel aerosol flow system for the study of the formation and reactions of aerosols relevant to the troposphere has been constructed, modeled and experimentally tested. The total flow tube length is 7.3 m which includes a 1.2 m section used for mixing. The flow tube is equipped with ultraviolet lamps for photolysis. The diameter of

Particulate Matter Sampling and Volatile Organic Compound Removal for Characterization of Spark Ignited Direct Injection Engine Emissions

SAE International Journal of Fuels and Lubricants, 2011

More stringent emissions regulations are continually being proposed to mitigate adverse human hea... more More stringent emissions regulations are continually being proposed to mitigate adverse human health and environmental impacts of internal combustion engines. With that in mind, it has been proposed that vehicular particulate matter (PM) emissions should be regulated based on particle number in addition to particle mass. One aspect of this project is to study different sample handling methods for number based aerosol measurements, specifically, two different methods for removing volatile organic compounds (VOCs). One method is a thermodenuder (TD) and the other is an evaporative chamber/diluter (EvCh). These sample handling methods have been implemented in an engine test cell with a spark ignited direct injection (SIDI) engine. The engine was designed for stoichiometric, homogeneous combustion. SIDI is of particular interest for improved fuel efficiency compared to other SI engines, however, the efficiency benefit comes with greater PM emissions and may therefore be subject to the proposed number based PM regulation. Another aspect of this project is to characterize PM from this engine in terms of particle number and composition.

Particulate Characteristics for Varying Engine Operation in a Gasoline Spark Ignited, Direct Injection Engine

SAE Technical Paper Series, 2011