Justify the statement “ the size and chemical characteristics of particles in the atmosphere are more significant than their concentration”
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Answer:
Small particles—ranging in size from about one nanometer to tens of microns—are ubiquitous in the natural and engineered worlds. In the atmosphere, small particles impact both warming and cooling of the climate. In Earth’s subsurface, small particles impact soil and water quality. In living systems, small particles impact organism health and viability. In catalysis and reaction engineering, small particles enhance reaction specificity and rates. In materials design and synthesis, small particles provide new and enhanced properties. However, in all of these scientific and engineering domains, a lack of understanding about the properties and chemical composition of small particles limits our ability to understand, predict, and control their applications and impacts. Speakers in this session discussed the crucial types of information that need to be determined about small particles in different media.
Research has determined that gaseous precursors form low-volatility products that nucleate to form new particles, but little is known about how this occurs, even after decades of research. Furthermore, little is known about how the particles then grow into nanoparticles. Because of their size, nanoparticles have a high surface-to-volume ratio, which means that the properties of the particles, in terms of their chemistry and photochemistry, will not necessarily be the same as those of the bulk material (because size is one of the unique and desirable characteristics of nanoparticles). Little is known about that chemistry as well.
Finlayson-Pitts explained that a major research objective is to determine the three-dimensional structure of particles in the atmosphere. Based on a large body of chemical data accumulated over many years, it is known that atmospheric nanoparticles contain a large number of polar groups, including carboxylic acids, amines, and alcohols. However, little is known about how the particles assemble. Other unanswered questions include the following: Do particles self-assemble in air? Do the polar groups end up inside a hydrophobic shell, or do they end up on the outside?
Many factors contribute to understanding climate, according to Finlayson-Pitts. For example, understanding the three-dimensional arrangement of the particles is extremely important. If polar groups are on the outside of the particles, then they will be expected to take up water and act as cloud condensation nuclei more efficiently than if they are buried inside the particles. Some of the studies performed in Finlayson-Pitts’s laboratory revealed that it is not unusual to find polar groups on the inside at the nanoscale. From a bulk chemical composition point of view, significant water uptake might be expected; however, that does not happen because the hydrophobic shell forms at the nanoscale
