What are Particulates?
Particulates, commonly known as Particulate Matter are basically small-sized particles that are present in the air. These particles can be present naturally in air or sometimes these are the result of man-made or anthropogenic activities.
The particulates can either exist in the form of small solid particles or liquid droplets. There is a large number of such particles that exist in the atmosphere and when exist in a plentiful amount then it can lead to cause air pollution up to a serious level.
Basics of Particulate Matter
On average, the diameter of a particulate varies between 0.0002 μ to 500 μ. The life span of these particles can be a few seconds to several months.
One should note here that the settling rate is the parameter which decides the lifespan of particulates. The setting rate shows dependency on particle density and size along with turbulence of air.
In the environment of the atmosphere, the overall amount of particulates varies in such a manner that if the air is clean then the number of particles will be several hundred in each cm3 while if the air is highly polluted then its quantity will be more than 100,000 in each cm3.
As particulates are known to be part of air thus their optical properties are important to consider. So, the optical properties like the ability of matter to scatter light or reduce the visibility are so much important to check how these particles affect solar radiation.
Sources of Particulates
Some of the major sources that give rise to particulate matter are as follows:
Transportation sources: These include the exhaust fumes and particles emitted from the clutch, and brake wear along with the flyash generated from thermal power plants.
Agricultural sources: Particulates are also generated from processes like the production of fertilizers, pesticides, various chemicals, etc. Not only this, the combustion of fossil fuels like coal, and wood also gives rise to particulate matter.
Industrial and Non-industrial Fugitive sources: The industrial fugitive processes include actions like handling, loading and transferring of material matter. While non-industrial fugitive processes include actions like constructing buildings, bridges, roads, etc.
It is not wrong to say that the combustion of fossil fuels, as well as thermal power plants, are crucial sources of particulates and the reason behind this is that flyash and cold dust are generated in very large amounts in India which get collected in the atmosphere.
When industrial activities take place then a large amount of smoke and dust are produced through stone crushers and cement factories. Basically, the dust particles get to settle on the objects present in our surroundings and stop the penetration of light rays. This sometimes leads to cause variation in the temperature of air and so the surface of the earth. When dust particles exist in the air then they absorb the light rays thereby leading to cause respiratory disorders.
Cotton dust which is known to exist near textile mills induces a disease called Byssinosis.
When particulates are generated due to the emission of fuel through vehicles in the form of smoke then it is commonly referred to as diesel particulates. These are very much dangerous to humans.
Types of Particulates
In general, the classification of particulates is done according to their size, nature or the optical properties possessed by them. The various types of particulates are as follows:
- Smoke: This type of particulate has solid and liquid particles with sizes in between 0.05 to 1.0 micron. The smoke particles are generally produced when incomplete combustion of carbonaceous materials takes place.
- Dust: It is particularly present in solid form and the size varies between 1 to 100 microns. Generally, mechanical processing gives rise to dust particles.
- Spray: It is a liquid form of particulates where the particles exist in the form of droplets. Basically, these are generated from liquid when mechanical disintegration takes place.
- Fumes: Fumes are the condensed form of vapours which is produced during chemical processes like sublimation, boiling, distillation, etc.
- Mist: It is produced when condensation of water vapour takes place. However, the size of the water vapour, in this case, must be less than 10 microns.
Organic and Inorganic Particulates
The inorganic form of particulates originated from metallic oxides, sulphides and carbonates. More specifically, these are the result of the burning of such metals that contain fuel.
Some of the examples of the formation of inorganic particulates are as follows:
3FeS2 + 😯2 = Fe3O4 + 6SO2
When pyrites that have coal are burnt in the presence of oxygen then particulate Fe3O4 is formed.
On the other side, organic particulate matter is the result of the combustion of fuels. An example of organic particulate matter is polycyclic aromatic hydrocarbons, abbreviated as PAHs. These are found in urban regions and are very hazardous to health. The size is around 1μ.