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Related Concept Videos

Diffusion01:12

Diffusion

Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
Gas Exchange and Transport01:20

Gas Exchange and Transport

Gas exchange, the intake of molecular oxygen (O2) from the environment and the outflow of carbon dioxide (CO2) into the environment, is necessary for cellular function. Gas exchange during respiration occurs largely via the movement of gas molecules along pressure gradients. Gas travels from areas of higher partial pressure to areas of lower partial pressure. In mammals, gas exchange occurs in the alveoli of the lungs, which are adjacent to capillaries and share a membrane with them.
Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion03:48

Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

Although gaseous molecules travel at tremendous speeds (hundreds of meters per second), they collide with other gaseous molecules and travel in many different directions before reaching the desired target. At room temperature, a gaseous molecule will experience billions of collisions per second. The mean free path is the average distance a molecule travels between collisions. The mean free path increases with decreasing pressure; in general, the mean free path for a gaseous molecule will be...
Diffusion01:21

Diffusion

Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...
Diffusion on Chromatography Columns01:07

Diffusion on Chromatography Columns

In column chromatography, when an analyte is introduced as a narrow band at the top of the column, the solutes begin to separate and broaden, developing a Gaussian profile. This broadening occurs due to various factors, such as longitudinal diffusion.
Longitudinal diffusion occurs when the solute molecules in the mobile phase diffuse from the more concentrated center of the chromatographic band to the more dilute regions on either side, both towards and against the flow direction. This...
External and Internal Respiration01:24

External and Internal Respiration

External respiration occurs in the lungs, and it is the first step in the journey of oxygen inside the body. When we inhale, oxygen enters our lungs and diffuses across the thin alveolar membrane. The alveoli are tiny, air-filled sacs that provide a vast surface area for gas exchange. Oxygen in the alveoli has a higher partial pressure (105 mmHg) than in the adjacent pulmonary capillaries (40 mmHg), establishing a pressure gradient. As a result, oxygen molecules move from the alveoli into the...

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Whole-Body Nanoparticle Aerosol Inhalation Exposures
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Whole-Body Nanoparticle Aerosol Inhalation Exposures

Published on: May 7, 2013

Diffusive separation of the lower atmosphere.

Yosuke Adachi1, Kenji Kawamura, Laurence Armi

  • 1Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093-0244, USA.

Science (New York, N.Y.)
|March 11, 2006
PubMed
Summary

Atmospheric gases separate by gravity, a phenomenon previously undetectable in the lower atmosphere due to turbulence. Researchers detected this gravitational separation in near-surface air, driven primarily by thermal influences.

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Area of Science:

  • Atmospheric Science
  • Geophysics
  • Physical Chemistry

Background:

  • Gravitational separation of atmospheric gases has been theorized for nearly 200 years.
  • Turbulent mixing in the lower atmosphere has historically prevented empirical detection of this phenomenon.
  • Strong nocturnal inversions create stable atmospheric conditions conducive to observing subtle effects.

Purpose of the Study:

  • To experimentally detect and quantify gravitational separation of atmospheric constituents.
  • To investigate the influence of thermal and gravimetric factors on gas separation in near-surface layers.
  • To determine the relative importance of thermal versus gravimetric contributions to observed separation.

Main Methods:

  • Collected air samples from near-surface layers during strong nocturnal inversions.
  • Utilized precise measurements of the Argon/Nitrogen (Ar/N2) ratio in collected air samples.
  • Analyzed data to identify and quantify variations in atmospheric constituent ratios attributable to separation.

Main Results:

  • Successfully detected gravitational separation of atmospheric constituents in near-surface air.
  • Observed separation is consistent with the combined effects of thermal and gravimetric forces.
  • The thermal contribution to the separation effect was found to be more significant than the gravimetric contribution.

Conclusions:

  • Gravitational separation of atmospheric gases is detectable under specific conditions, such as strong nocturnal inversions.
  • Thermal gradients play a dominant role in driving gas separation in the near-surface atmosphere.
  • This finding validates long-standing theories and opens new avenues for atmospheric composition studies.