Air pollutants are one of the environmental problems that the people of the world are facing, especially in populated cities and metropolises. In general, there are three types of troposphere pollutants: suspended particles (or Particulate Matter (PM)), pollutant gases such as NOx and smog. These pollutants create destructive consequences in the environment. For example, they cause acid rain in different areas.
Particulate Matter (PM)
The suspended particles in the air are a heterogeneous mixture. These particles, in a given mass of air, have neither the same size nor the same chemical composition. Most suspended particles, especially particles smaller than 10 micrometers, can enter the lungs and remain there, causing acute respiratory diseases.
Suspended particles are made up of various sources. Examples of these sources are:
- Storm
- Desert
- Asbestos
- Aerosols
Interestingly, even the braking of cars can cause suspended particles. Because the brake pad often contains silica compounds that affect the suspended particles by abrasion.
Air pollutant gases
These gases are:
- NOxs: NO2, NO
- SOxs: SO2, SO3
- CO
- NH3
- VOCs
- H2S
- CH4
These gases have resources in the troposphere and are regularly manufactured and then destroyed by radical OH and eventually removed from the air.
Smog
Smog is a type of air pollution that reduces vision and is also called Urban Ozone. The term “smog” was first used in the early 1900s to describe a combination of smoke and fog. This phenomenon was first raised in Los Angeles around the 1980s, but the most important smog that happened in the world was in London in 1952, which killed thousands of people.
Smog is caused by a chemical reaction between nitric acid, unburned hydrocarbons and semi-burned hydrocarbons.
The most important conditions for smog formation are:
- The presence of air pollutants like VOCs, NOxs
- Existence of sunlight with high intensity
- High temperature
- Heavy traffic
- No air displacement in the cities
Cities such as Los Angeles, London, Tokyo, Tehran, Mexico, etc. are more subject to geographical reasons (e.g. because of the mountains) and the dense population.
All of the above is my understanding of the information I have obtained from various sources.