Program Abstracts: Formation and Growth of Atmospheric Aerosols

DOE provided $11,000 to sponsor the Workshop on New Particle Formation in the Atmosphere, which was held at The Riverwood Inn and Conference Center near Minneapolis, MN from September 7 to 9, 2006. Recent work has shown that new particle formation is an important atmospheric process that must be better understood due to its impact on cloud cover and the Earth's radiation balance. The conference was an informal gathering of atmospheric and basic scientists with expertise pertinent to this topic. The workshop included discussions of: • atmospheric modeling; • computational chemistry pertinent to clustering; • ions and ion induced nucleation; • basic laboratory and theoretical studies of nucleation; • studies on neutral molecular clusters; • interactions of organic compounds and sulfuric acid; • composition of freshly nucleated particles. Fifty six scientists attended the conference. They included 27 senior scientists, 9 younger independent scientists (assistant professor or young associate professor level), 7 postdocs, 13 graduate students, 10 women, 35 North Americans (34 from the U.S.), 1 Asian, and 20 Europeans. This was an excellent informal workshop on an important topic. An effort was made to include individuals from communities that do not regularly interact. A number of participants have provided informal feedback indicating that the workshop led to research ideas and possible future collaborations

Transfer Functions and Penetrations of Five Differential Mobility Analyzers for Sub-2 nm Particle Classification

The transfer functions and penetrations of five differential mobility analyzers (DMAs) for sub-2 nm particle classification were evaluated in this study. These DMAs include the TSI nanoDMA, the Caltech radial DMA (RDMA) and nanoRDMA, the Grimm nanoDMA, and the Karlsruhe-Vienna DMA. Measurements were done using tetra-alkyl ammonium ion standards with mobility diameters of 1.16, 1.47, and 1.70 nm. These monomobile ions were generated by electrospray followed by high resolution mobility classification. Measurements were focused at an aerosol-to-sheath flow ratio of 0.1. A data inversion routine was developed to obtain the true transfer function for each test DMA, and these measured transfer functions were compared with theory. DMA penetration efficiencies were also measured. An approximate model for diffusional deposition, based on the modified Gormley and Kennedy equation using an effective length, is given for each test DMA. These results quantitatively characterize the performance of the test DMAs in classifying sub-2 nm particles and can be readily used for DMA data inversion

An experimental and numerical study of particle nucleation and growth during low-pressure thermal decomposition of silane

Abstract This paper discusses an experimental and numerical study of the nucleation and growth of particles during low-pressure (∼1:0 Torr) thermal decomposition of silane (SiH 4 ). A Particle Beam Mass Spectrometer was used to measure particle size distributions in a parallel-plate showerhead-type semiconductor reactor. An aerosol dynamics moment-type formulation coupled with a chemically reacting uid ow model was used to predict particle concentration, size, and transport in the reactor. Particle nucleation kinetics via a sequence of chemical clustering reactions among silicon hydride molecular clusters, growth by heterogeneous chemical reactions on particle surfaces and coagulation, and transport by convection, di usion, and thermophoresis were included in the model. The e ect of pressure, temperature, ow residence time, carrier gas, and silane concentration were examined under conditions typically used for low-pressure (∼1 Torr) thermal chemical vapor deposition of polysilicon. The numerical simulations predict that several pathways involving linear and polycyclic silicon hydride molecules result in formation of particle "nuclei," which subsequently grow by heterogeneous reactions on the particle surfaces. The model is in good agreement with observations for the pressure and temperature at which particle formation begins, particle sizes and growth rates, and relative particle concentrations at various process conditions. A simpliÿed, computationally inexpensive, quasi-coupled modeling approach is suggested as an engineering tool for process equipment design and contamination control during low-pressure thermal silicon deposition.

Emissions from Ethanol-Gasoline Blends: A Single Particle Perspective

Due to its agricultural origin and function as a fuel oxygenate, ethanol is being promoted as an alternative biomass-based fuel for use in spark ignition engines, with mandates for its use at state and regional levels. While it has been established that the addition of ethanol to a fuel reduces the particulate mass concentration in the exhaust, little attention has been paid to changes in the physicochemical properties of the emitted particles. In this work, a dynamometer-mounted GM Quad-4 spark ignition engine run without aftertreatment at 1,500 RPM and 100% load was used with four different fuel blends, containing 0, 20, 40 and 85 percent ethanol in gasoline. This allowed the effects of the fuel composition to be isolated from other effects. Instrumentation employed included two Aerosol Time-of-Flight Mass Spectrometers covering different size ranges for analysis of single particle composition, an Aethalometer for black carbon, a Scanning Mobility Particle Sizer for particle size distributions, a Photoelectric Aerosol Sensor for particle-bound polycyclic aromatic hydrocarbon (PAH) species and gravimetric filter measurements for particulate mass concentrations. It was found that, under the conditions investigated here, additional ethanol content in the fuel changes the particle size distribution, especially in the accumulation mode, and decreases the black carbon and total particulate mass concentrations. The molecular weight distribution of the PAHs was found to decrease with added ethanol. However, PAHs produced from higher ethanol-content fuels are associated with NO2 − (m/z—46) in the single-particle mass spectra, indicating the presence of nitro-PAHs. Compounds associated with the gasoline (e.g., sulfur-containing species) are diminished due to dilution as ethanol is added to the fuel relative to those associated with the lubricating oil (e.g., calcium, zinc, phosphate) in the single particle spectra. These changes have potential implications for the health effect impacts of particulate emissions from biofuel blends

Electrical Mobility Spectrometer Using a Diethylene Glycol Condensation Particle Counter for Measurement of Aerosol Size Distributions Down to 1 nm. Aerosol Sci.

We report a new scanning mobility particle spectrometer (SMPS) for measuring number size distributions of particles down to ∼1 nm mobility diameter. This SMPS includes an aerosol charger, a TSI 3085 nano differential mobility analyzer (nanoDMA), an ultrafine condensation particle counter (UCPC) using diethylene glycol (DEG) as the working fluid, and a conventional butanol CPC (the "booster") to detect the small droplets leaving the DEG UCPC. The response of the DEG UCPC to negatively charged sodium chloride particles with mobility diameters ranging from 1-6 nm was measured. The sensitivity of the DEG UCPC to particle composition was also studied by comparing its response to positively charged 1.47 and 1.70 nm tetra-alkyl ammonium ions, sodium chloride, and silver particles. A high resolution differential mobility analyzer was used to generate the test particles. These results show that the response of this UCPC to sub-2 nm particles is sensitive to particle composition. The applicability of the new SMPS for atmospheric measurement was demonstrated during the Nucleation and Cloud Condensation Nuclei (NCCN) field campaign (Atlanta, Georgia, summer 2009). We operated the instrument at saturator and condenser temperatures that allowed the efficient detection of sodium chloride particles but not of air ions having the same mobility. We found that particles as small as 1 nm were detected during nucleation events but not at other times. Factors affecting size distribution measurements, including aerosol charging in the 1-10 nm size range, are discussed. For the charger used in this study, bipolar charging was found to be more effective for sub-2 nm particles than unipolar charging. No ion induced nucleation inside the charger was observed during the NCCN campaign

Representing glycophenotypes: semantic unification of glycobiology resources for disease discovery.

While abnormalities related to carbohydrates (glycans) are frequent for patients with rare and undiagnosed diseases as well as in many common diseases, these glycan-related phenotypes (glycophenotypes) are not well represented in knowledge bases (KBs). If glycan-related diseases were more robustly represented and curated with glycophenotypes, these could be used for molecular phenotyping to help to realize the goals of precision medicine. Diagnosis of rare diseases by computational cross-species comparison of genotype-phenotype data has been facilitated by leveraging ontological representations of clinical phenotypes, using Human Phenotype Ontology (HPO), and model organism ontologies such as Mammalian Phenotype Ontology (MP) in the context of the Monarch Initiative. In this article, we discuss the importance and complexity of glycobiology and review the structure of glycan-related content from existing KBs and biological ontologies. We show how semantically structuring knowledge about the annotation of glycophenotypes could enhance disease diagnosis, and propose a solution to integrate glycophenotypes and related diseases into the Unified Phenotype Ontology (uPheno), HPO, Monarch and other KBs. We encourage the community to practice good identifier hygiene for glycans in support of semantic analysis, and clinicians to add glycomics to their diagnostic analyses of rare diseases

GA4GH Phenopackets: A Practical Introduction.

The Global Alliance for Genomics and Health (GA4GH) is developing a suite of coordinated standards for genomics for healthcare. The Phenopacket is a new GA4GH standard for sharing disease and phenotype information that characterizes an individual person, linking that individual to detailed phenotypic descriptions, genetic information, diagnoses, and treatments. A detailed example is presented that illustrates how to use the schema to represent the clinical course of a patient with retinoblastoma, including demographic information, the clinical diagnosis, phenotypic features and clinical measurements, an examination of the extirpated tumor, therapies, and the results of genomic analysis. The Phenopacket Schema, together with other GA4GH data and technical standards, will enable data exchange and provide a foundation for the computational analysis of disease and phenotype information to improve our ability to diagnose and conduct research on all types of disorders, including cancer and rare diseases

GA4GH Phenopackets: A Practical Introduction

The Global Alliance for Genomics and Health (GA4GH) is developing a suite of coordinated standards for genomics for healthcare. The Phenopacket is a new GA4GH standard for sharing disease and phenotype information that characterizes an individual person, linking that individual to detailed phenotypic descriptions, genetic information, diagnoses, and treatments. A detailed example is presented that illustrates how to use the schema to represent the clinical course of a patient with retinoblastoma, including demographic information, the clinical diagnosis, phenotypic features and clinical measurements, an examination of the extirpated tumor, therapies, and the results of genomic analysis. The Phenopacket Schema, together with other GA4GH data and technical standards, will enable data exchange and provide a foundation for the computational analysis of disease and phenotype information to improve our ability to diagnose and conduct research on all types of disorders, including cancer and rare diseases