Aerosol
An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols
can be natural or anthropogenic. Examples of natural aerosols are fog or mist, dust, forest exudates,
and geyser steam. Examples of anthropogenic aerosols include particulate air pollutants, mist from
the discharge at hydroelectric dams, irrigation mist, perfume from atomizers, smoke, dust, steam
from a kettle, sprayed pesticides, and medical treatments for respiratory illnesses. When a person
inhales the contents of a vape pen or e-cigarette, they are inhaling an anthropogenic aerosol.
The liquid or solid particles in an aerosol have diameters typically less than 1 μm (larger particles
with a significant settling speed make the mixture a suspension, but the distinction is not clear-cut).
In general conversation, aerosol often refers to a dispensing system that delivers a consumer
product from a can.
Diseases can spread by means of small droplets in the breath, sometimes called bio aerosols
Definitions
Photomicrograph made with a Scanning Electron Microscope (SEM): Fly ash particles at 2,000×
magnification.Most of the particles in this aerosol are nearly spherical.
Aerosol is defined as a suspension system of solid or liquid particles in a gas. An aerosol includes
both the particles and the suspending gas, which is usually air Meteorologists usually refer them as
particle matter - PM2.5 or PM10, depending on their size. Frederick G. Donnan presumably first
used the term aerosol during World War I to describe an aero-solution, clouds of microscopic
particles in air. This term developed analogously to the term hydrosol, a colloid system with water as
the dispersed medium. Primary aerosols contain particles introduced directly into the gas; secondary
aerosols form through gas-to-particle conversion.
Key aerosol groups include sulfates, organic carbon, black carbon, nitrates, mineral dust, and sea
salt, they usually clump together to form a complex mixture. Various types of aerosol, classified
according to physical form and how they were generated, include dust, fume, mist, smoke and fog.
Generation and applications
People generate aerosols for various purposes, including:
as test aerosols for calibrating instruments, performing research, and testing sampling
equipment and air filters
to deliver deodorants, paints, and other consumer products in sprays;
for dispersal and agricultural application
for medical treatment of respiratory disease; and
in fuel injection systems and other combustion technology.
Some devices for generating aerosols are:
Aerosol spray
Atomizer nozzle or nebulizer
Electrospray
Electronic cigarette
Vibrating orifice aerosol generator (VOAG)
Effects
Volcanic eruptions release large amounts of sulphuric acid, hydrogen sulfide and hydrochloric
acid into the atmosphere. These gases represent aerosols and eventually return to earth as acid
rain, having a number of adverse effects on the environment and human life.
Aerosols interact with the Earth's energy budget in two ways, directly and indirectly.
E.g., a direct effect is that aerosols scatter and absorb incoming solar radiation. This will
mainly lead to a cooling of the surface (solar radiation is scattered back to space) but may
also contribute to a warming of the surface (caused by the absorption of incoming solar
energy). This will be an additional element to the greenhouse effect and therefore
contributing to the global climate change.
The indirect effects refer to the aerosols interfering with formations that interact directly with
radiation. For example, they are able to modify the size of the cloud particles in the lower
atmosphere, thereby changing the way clouds reflect and absorb light and therefore
modifying the Earth's energy budget.
There is evidence to suggest that anthropogenic aerosols actually offset the effects of
greenhouse gases in some areas, which is why the Northern Hemisphere shows slower
surface warming than the Southern Hemisphere, although that just means that the Northern
Hemisphere will absorb the heat later through ocean currents bringing warmer waters from
the South. On a global scale however, aerosol cooling decreases greenhouse-gases-
induced heating without offsetting it completely.
When aerosols absorb pollutants, it facilitates the deposition of pollutants to the
surface of the earth as well as to bodies of water. This has the potential to be
damaging to both the environment and human health.
Aerosols in the 20 μm range show a particularly long persistence time in air
conditioned rooms due to their "jet rider" behaviour (move with air jets,
gravitationally fall out in slowly moving air); as this aerosol size is most effectively
adsorbed in the human nose, the primordial infection site in COVID-19, such
aerosols may contribute to the pandemic.
Aerosol particles with an effective diameter smaller than 10 μm can enter the
bronchi, while the ones with an effective diameter smaller than 2.5 μm can enter as
far as the gas exchange region in the lungs, which can be hazardous to human
health.
