Aerosol
[3] Several types of atmospheric aerosol have a significant effect on Earth's climate: volcanic, desert dust, sea-salt, that originating from biogenic sources and human-made.
Volcanic aerosol forms in the stratosphere after an eruption as droplets of sulfuric acid that can prevail for up to two years, and reflect sunlight, lowering temperature.
Desert dust, mineral particles blown to high altitudes, absorb heat and may be responsible for inhibiting storm cloud formation.
Human-made sulfate aerosols, primarily from burning oil and coal, affect the behavior of clouds.
Water molecules collect around the tiny particles (aerosols) from exhaust to form a cloud seed.
In 2020, regulations on fuel significantly cut sulfur dioxide emissions from international shipping by approximately 80%, leading to an unexpected global geoengineering termination shock.
Larger particles with a significant settling speed make the mixture a suspension, but the distinction is not clear.
In everyday language, aerosol often refers to a dispensing system that delivers a consumer product from a spray can.
[11] Frederick G. Donnan presumably first used the term aerosol during World War I to describe an aero-solution, clouds of microscopic particles in air.
[10] Various types of aerosol, classified according to physical form and how they were generated, include dust, fume, mist, smoke and fog.
[13] Liquid droplets are almost always nearly spherical, but scientists use an equivalent diameter to characterize the properties of various shapes of solid particles, some very irregular.
Volcanic aerosol forms in the stratosphere after an eruption as droplets of sulfuric acid that can prevail for up to two years, and reflect sunlight, lowering temperature.
Desert dust, mineral particles blown to high altitudes, absorb heat and may be responsible for inhibiting storm cloud formation.
Human-made sulfate aerosols, primarily from burning oil and coal, affect the behavior of clouds.
These gases represent aerosols and eventually return to earth as acid rain, having a number of adverse effects on the environment and human life.
Water molecules collect around the tiny particles (aerosols) from exhaust to form a cloud seed.
In 2020, regulations on fuel significantly cut sulfur dioxide emissions from international shipping by approximately 80%, leading to an unexpected global geoengineering termination shock.
[42] For low values of the Reynolds number (<1), true for most aerosol motion, Stokes' law describes the force of resistance on a solid spherical particle in a fluid.
A second set of processes internal to a given volume of gas include particle formation (nucleation), evaporation, chemical reaction, and coagulation.
[49] Change in time = Convective transport + brownian diffusion + gas-particle interactions + coagulation + migration by external forces Where: As particles and droplets in an aerosol collide with one another, they may undergo coalescence or aggregation.
This process leads to a change in the aerosol particle-size distribution, with the mode increasing in diameter as total number of particles decreases.
As such, they behave similarly to gas molecules, tending to follow streamlines and diffusing rapidly through Brownian motion.
The mass flux equation in the free molecular regime is: where a is the particle radius, P∞ and PA are the pressures far from the droplet and at the surface of the droplet respectively, kb is the Boltzmann constant, T is the temperature, CA is mean thermal velocity and α is mass accommodation coefficient.
Nucleation is the process of forming aerosol mass from the condensation of a gaseous precursor, specifically a vapor.
This process causes the diameter at the mode of particle-size distribution to increase with constant number concentration.
Some available in situ measurement techniques include: Remote sensing approaches include: Particles can deposit in the nose, mouth, pharynx and larynx (the head airways region), deeper within the respiratory tract (from the trachea to the terminal bronchioles), or in the alveolar region.
[65] Examples of these subsets of the particle-size distribution of an aerosol, important in occupational health, include the inhalable, thoracic, and respirable fractions.
[67] The thoracic fraction is the proportion of the particles in ambient aerosol that can reach the thorax or chest region.
It is common to use cyclonic separation for the pre-collector, but other techniques include impactors, horizontal elutriators, and large pore membrane filters.
