Here is the long-form, highly informative article titled ‘Exploring non-soluble particles in hailstones through innovative analytical techniques’ for the Air Cooled Heat Exchangers blog:
Understanding the role of atmospheric particles in hailstone formation and growth
The analysis of hailstone samples has been a subject of increasing interest owing to its potential to provide valuable insights into microphysics and the development of hailstorms. Consider a hailstone a miniature chronicle of time that preserves a rich history of its formation and growth within its crystalline structure. Understanding hailstones’ microphysics and developmental processes is crucial for improving weather forecasting, mitigation strategies, and climate change modeling.
Atmospheric particles play a crucial role in hailstone microphysics. Particles may be ingested into convective-cloud updrafts, serving as cloud condensation nuclei (CCN) or ice-nucleating particles (INPs), which are necessary to form hydrometeors like cloud droplets and ice crystals that are essential for hail formation. Furthermore, hailstones can accumulate particles from the surrounding environment in the cloud during their growth, which could have sizes larger than those that serve as CCN and INPs and would provide information about the source environments involved in hail formation.
Particle size and chemical composition are essential to quantify because they influence the nucleation efficiency and growth rate within hailstones. Characterizing these particles allows us to reconstruct their potential influence on hailstone properties, such as fall speed rates and growth regimes, furthering our understanding of hail formation and its complex interplay with atmospheric conditions.
Innovative microscopy techniques for hailstone analysis
Previous studies have investigated hailstone composition and properties using various techniques to determine their chemical constituents. However, these approaches have relied on the melting of the hailstones, which obscures the spatial distribution of non-soluble particles within the hailstone.
To overcome this limitation, a new method has been developed to preserve the in situ non-soluble particles within hailstones using a protective porous plastic coating. This approach allows the analysis of non-soluble particles through powerful microscopy techniques, including confocal laser scanning microscopy (CLSM) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS).
Confocal laser scanning microscopy (CLSM)
CLSM is a high-resolution optical imaging technique that uses a diffraction-limited spot to produce a point source of light and reject out-of-focus light, allowing for imaging of deep tissues and 3-D reconstructions of imaged samples. CLSM provides insights into physical attributes like particle size and surface topography, enhancing our understanding of ice nucleation.
Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS)
SEM and EDS are techniques often used together to analyze the surface of a sample. SEM works by scanning a focused beam of electrons onto a sample, inducing the emission of secondary electrons and backscattered electrons, which can be detected and used to create a high-resolution image of a surface. EDS allows the analysis of the elemental composition of a sample by detecting characteristic X-rays emitted from the sample when bombarded with a beam of electrons.
By combining CLSM and SEM-EDS, researchers can characterize the non-soluble particles trapped within hailstones, providing valuable data on their physical attributes, such as size and surface topography, as well as their elemental composition. This information can give insights into hail developmental processes by enhancing our understanding of the role of atmospheric particles.
Preserving the in situ particle distribution
A key aspect of this innovative methodology is the use of a protective porous plastic coating to preserve the spatial distribution of non-soluble particles within the hailstone. This coating, made of polyvinyl formal (Formvar) dissolved in ethylene dichloride, is applied to the hailstone sample before the sublimation process.
The hailstone is then left to gradually sublimate in a controlled, low-humidity environment, allowing the ice to transition directly from the solid to the gas phase. During this process, the non-soluble particles become trapped beneath the Formvar coating, maintaining their original spatial distribution within the hailstone.
This approach eliminates the need to melt the hailstone, which would otherwise disrupt the particle arrangement and distribution. By preserving the in situ particle locations, researchers can examine the characteristics of individual particles and their spatial relationship to the hailstone’s structure, providing valuable insights into the hail formation and growth processes.
Analyzing particle properties through microscopy
The hailstone samples coated with Formvar are then analyzed using CLSM and SEM-EDS techniques to characterize the non-soluble particles.
Confocal laser scanning microscopy (CLSM) analysis
The CLSM is used to create a 2-D cross-section of the sublimated hailstone, centered on the embryo location, along an axis in the equatorial plane. At the lowest available magnification, the 2-D cross-section is scanned to locate the non-soluble particles trapped in the Formvar coating.
Subsectors of the 2-D cross-section are then selected for higher magnification analysis, providing high-resolution 3-D particle surface topography and size information for individual particles. The particle size is determined by assessing the maximum length along the x and y axes.
Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis
The 2-D cross-section created with the CLSM is used as a reference point to investigate the elemental composition of the individual particles through SEM-EDS analysis. The sample is coated with a thin layer of gold to ensure a conductive surface for accurate X-ray chemical analysis.
The SEM operating conditions, such as accelerating voltage and working distance, are carefully optimized to achieve the best imaging resolution and X-ray excitation for the particle sizes of interest, typically down to 1 μm. EDS analysis is then conducted for every particle identified in the SEM imagery to determine the major and minor element composition of the non-soluble particles.
By combining the physical insights from CLSM and the elemental composition data from SEM-EDS, researchers can classify the trapped particles based on their size, surface topography, and chemical characteristics. This comprehensive analysis provides valuable information about the distribution and properties of non-soluble particles within the hailstone, which can be correlated with the hailstone’s growth and development.
Insights into hailstone composition and development
The innovative microscopy techniques have been applied to analyze hailstones collected during a supercell storm event in Argentina. The results reveal interesting insights into the composition and distribution of non-soluble particles within the hailstones.
Particle size distribution
The CLSM analysis of the hailstone samples shows that the particle sizes range from 2 to 150 μm, with variations observed between different cross-sections and hailstones. Larger particles, up to 100 μm, were identified in all the analyzed hailstones, despite being collected from the same storm event.
These findings suggest that the particle size distribution within hailstones can vary depending on the hailstone’s size and growth history, highlighting the importance of examining multiple cross-sections and hailstones to gain a comprehensive understanding of the particle characteristics.
Elemental composition and particle classification
The SEM-EDS analysis of the trapped particles revealed that the majority were carbonaceous (both C-based and C-heavy), followed by silicates (Si-based and Si-heavy) and salts (Cl-based). Interestingly, the particle composition within the embryo region of the hailstone differed from the outer layers, with the absence of salts in one of the cross-sections examined.
By combining the particle size, surface topography, and elemental composition data, the researchers were able to classify the non-soluble particles into five categories: C-based, C-heavy, Si-based, Si-heavy, and Cl-based. This detailed characterization provides insights into the potential sources and roles of these particles in the hail formation and growth processes.
Advantages and future applications of the innovative methodology
The proposed methodology, which combines the use of a protective Formvar coating and advanced microscopy techniques, offers several advantages over traditional hailstone analysis approaches:
-
Preservation of in situ particle distribution: The Formvar coating allows for the preservation of the spatial distribution of non-soluble particles within the hailstone, preventing disruption during sample preparation.
-
Comprehensive particle characterization: The integration of CLSM and SEM-EDS enables the analysis of both physical (size, surface topography) and chemical (elemental composition) properties of individual particles.
-
Insights into hail formation and growth: The detailed particle data can be correlated with the hailstone’s structure and growth history, providing valuable insights into the role of atmospheric particles in hail development.
-
Potential for wider applicability: While this study focused on hailstones, the innovative methodology could be adapted for the analysis of other types of natural ice, such as snowflakes or ice cores, to investigate their trapped particle characteristics.
As researchers continue to explore the potential of this approach, further refinements and enhancements may be made. For example, the incorporation of complementary techniques like Raman spectroscopy and scanning transmission X-ray microscopy (STXM) could enable more precise differentiation between organic and inorganic carbon-based particles.
Additionally, the application of computer-controlled SEM-EDS (CCSEM) systems could streamline the analysis process and enable the examination of a larger number of particles, providing more statistically robust data.
By expanding the use of this innovative methodology to hailstones from diverse storm environments and regions, researchers can continue to unravel the complex interplay between atmospheric particles and hail formation, ultimately contributing to advancements in weather forecasting, mitigation strategies, and climate change modeling.
For the latest updates and insights on air-cooled heat exchangers, be sure to visit the Air Cooled Heat Exchangers website. Our team of experts is dedicated to providing practical tips and in-depth knowledge to help you optimize the performance and maintenance of your air-cooled heat exchangers across various industries.
