In the
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which rel ...
of
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 ant ...
s, aerosol impaction is the process in which
particle
In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass.
They vary greatly in size or quantity, fro ...
s are removed from an
air stream by forcing the
gases to make a sharp bend. Particles above a certain size possess so much
momentum
In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass ...
that they can not follow the air stream and strike a collection surface, which is available for later analysis of
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different element ...
and composition. Removal of particles from an air-stream by impaction followed by mass and composition analysis has always been a different approach as to filter sampling, yet has been little utilized for routine analysis because of lack of suitable analytical methods.
Advantages
The most clear and important advantage of impaction, as opposed to filtration, is that two key
aerosol parameter
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 anthropogen ...
s,
size
Size in general is the Magnitude (mathematics), magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to linear dimensions (length, width, height, diameter, perimeter), area, or volume ...
and
composition, can be simultaneously established.
Inertial Impaction, Size and Time
There are many advantages of impaction as a sampling method. For two of the most common configurations, an orifice and an infinite slot
Infinite may refer to:
Mathematics
* Infinite set, a set that is not a finite set
*Infinity, an abstract concept describing something without any limit
Music
*Infinite (group), a South Korean boy band
*''Infinite'' (EP), debut EP of American m ...
, theoretical prediction
A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research. Theories may ...
s can be made and empirically verified that give the cuts point and shape of the collection efficiency of an impaction stage. The air stream moves over the sample, not through it as in filtration, reducing desiccation
Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. ...
and chemical transformations of the collected sample. Almost complete control of the type of surface on which the particles are impacted, as opposed to the limited choice of filter types. By varying the speed of the air stream and the sharpness of the bend, one can separate particles into numerous size classifications while retaining a sample for analysis.
Disadvantages
There are also several disadvantages to impaction as a sampling method. Only a limited amount of material is available for mass and compositional analysis, as one can not collect more than a few monolayer A monolayer is a single, closely packed layer of atoms, molecules, or cells. In some cases it is referred to as a self-assembled monolayer. Monolayers of layered crystals like graphene and molybdenum disulfide are generally called 2D materials.
...
s of particles before particle bounce and mis-sizing are a potential problem.
See also
*Deposition (aerosol physics)
In the physics of aerosols, deposition is the process by which aerosol particles collect or deposit themselves on solid surfaces, decreasing the concentration of the particles in the air. It can be divided into two sub-processes: ''dry'' and '' ...
* Cascade impactor
References
{{Reflist
Particulates
Aerosols