Publications by authors named "Markus Petters"

Article Synopsis
  • Airborne microorganisms can influence cloud formation and disease spread, and their ability to survive is affected by water availability in the atmosphere.
  • Researchers studied the hygroscopic properties (water-attracting ability) of a plant pathogen that aids in cloud formation using a specialized analyzer.
  • The study found that while pure cells absorbed little water and had a growth factor of 1.09 at high humidity, cells mixed with salt showed significantly greater hydration, with a growth factor of 1.74, indicating the crucial role of salt in water uptake.
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Anthropogenically derived aerosols have been hypothesized to influence convective precipitation by increasing the available pool of cloud condensation nuclei. Here, we present a synthesis of aerosol size distribution and subsaturated hygroscopicity measurements between 15 and 250 nm diameter particles during the TRacking Aerosol Convection interactions ExpeRiment (TRACER). We found that the aerosol is externally mixed and can be described by a quasi-two-component description comprising a more and less hygroscopic mode.

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The amorphous phase state of suspended nanoparticles affects their atmospheric lifetimes and environmental impact. Influence of relative humidity and chemical composition on the glass-to-liquid transition is well-known. However, the influence of the particle size on the phase transition remains uncertain.

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Aerosol particles with rare specific properties act as nuclei for ice formation. The presence of ice nucleating particles in the atmosphere leads to heterogeneous freezing at warm temperatures and thus these particles play an important role in modulating microphysical properties of clouds. This work presents an ice nucleation cold stage instrument for measuring the concentration of ice nucleating particles in liquids.

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Article Synopsis
  • Ice-nucleating particles (INPs) are key aerosols in the atmosphere that trigger ice formation, but predicting their concentrations in climate models is difficult.
  • Researchers developed a method to differentiate INP sources from dust, sea spray aerosol (SSA), and bioaerosol, using data from Bodega Bay, California.
  • Findings showed that bioaerosols were the main contributor to INPs at certain temperatures, while current models accurately reflected dust and SSA INP levels but struggled with bioaerosols, indicating the need for further study on their emission and efficiency.
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Electrostatic precipitators are devices that remove charged particles from an air stream. We present the design and characterization of an electrostatic precipitator that is intended to be incorporated into aerosol sampling equipment. Hardware and software components of the design are open, all components can be directly purchased from vendors, and the device can be assembled with standard tools.

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Atmospheric aerosols can assume liquid, amorphous semi-solid or glassy, and crystalline phase states. Particle phase state plays a critical role in understanding and predicting aerosol impacts on human health, visibility, cloud formation, and climate. Melting point depression increases with decreasing particle diameter and is predicted by the Gibbs-Thompson relationship.

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Ultrafine particles with diameters less than 100 nm suspended in the air are a topic of interest in air quality and climate sciences. Sub-10 nm particles are of additional interest due to their health effects and contribution to particle growth processes. Ambient measurements were carried out at North Carolina State University in Raleigh, NC between April to June 2019 and November 2019 to May 2020 to investigate the temporal variability of size distribution and number concentration of ultrafine particles.

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Responding to changes in the surrounding environment, aerosol particles can grow by water condensation changing rapidly in composition and changing dramatically in viscosity. The timescale for growth is important to establish for particles undergoing hydration processes in the atmosphere or during inhalation. Using an electrodynamic balance, we report direct measurements at -7.

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A Dimer Coagulation, Isolation and Coalescence (DCIC) technique is used to probe the phase behaviour and glass transition temperatures of ternary aerosol mixtures. The DCIC technique is used to perform temperature and relative humidity dependent viscosity measurements at viscosities near 5 × 106 Pa s. Measurements include organic-organic and organic-inorganic mixtures composed of sucrose-citric acid and sucrose-sodium nitrate.

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Article Synopsis
  • Organic aerosol particles are crucial for cloud dynamics, sunlight interaction, and human health, affecting the atmosphere's overall composition.
  • Recent findings indicate that these particles may be more like viscous semi-solids or glassy solids rather than just liquids, challenging previous assumptions.
  • The review discusses how the phase state of these particles, especially their viscosity, influences atmospheric chemistry, climate, and air quality.
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The albedo and microphysical properties of clouds are controlled in part by the hygroscopicity of particles serving as cloud condensation nuclei (CCN). Hygroscopicity of complex organic mixtures in the atmosphere varies widely and remains challenging to predict. Here we present new measurements characterizing the CCN activity of pure compounds in which carbon chain length and the numbers of hydroperoxy, carboxyl, and carbonyl functional groups were systematically varied to establish the contributions of these groups to organic aerosol apparent hygroscopicity.

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Atmospheric aerosols can exist in amorphous semi-solid or glassy phase states. These states are determined by the temperature (T) and relative humidity (RH). New measurements of viscosity for amorphous semi-solid nanometer size sucrose particles as a function of T and RH are reported.

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Organic aerosols can exist in highly viscous or glassy phase states. A viscosity database for organic compounds with atmospherically relevant functional groups is compiled and analyzed to quantify the influence of number and location of functional groups on viscosity. For weakly functionalized compounds the trend in viscosity sensitivity to functional group addition is carboxylic acid (COOH) ≈ hydroxyl (OH) > nitrate (ONO) > carbonyl (CO) ≈ ester (COO) > methylene (CH).

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Quantifying how atmospheric particles interact with water vapor is critical for understanding the effects of aerosols on climate. We present a novel method to measure the mass-based hygroscopicity of particles while characterizing their elemental and carbon functional group compositions. Since mass-based hygroscopicity is insensitive to particle geometry, it is advantageous for probing the hygroscopic behavior of atmospheric particles, which can have irregular morphologies.

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Organic aerosols in the atmosphere are composed of a wide variety of species, reflecting the multitude of sources and growth processes of these particles. Especially challenging is predicting how these particles act as cloud condensation nuclei (CCN). Previous studies have characterized the CCN efficiency for organic compounds in terms of a hygroscopicity parameter, κ.

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Atmospheric heterogeneous reactions can potentially change the hygroscopicity of atmospheric aerosols as they undergo chemical aging processes in the atmosphere. A particle's hygroscopicity influences its cloud condensation nuclei (CCN) properties with potential impacts on cloud formation and climate. In this study, size-selected calcite mineral particles were reacted with controlled amounts of nitric acid vapour over a wide range of relative humidities in an aerosol flow tube to study the conversion of insoluble and thus apparently non-hygroscopic calcium carbonate into soluble and hygroscopic calcium nitrate.

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The interaction of water with laboratory soots possessing a range of properties relevant for atmospheric studies is examined by two complementary methods: gravimetrical measurement of water uptake coupled with chemical composition and porosity analysis and HTDMA (humidified tandem differential mobility analyzer) inference of water uptake accompanied by separate TEM (transmission electron microscopy) analysis of single particles. The first method clarifies the mechanism of water uptake for bulk soot and allows the classification of soot with respect to its hygroscopicity. The second method highlights the dependence of the soot aerosol growth factor on relative humidity (RH) for quasi-monodisperse particles.

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