**2. Potential air pollutants**

As described earlier, the air pollutants are generated from the various sources and undergo a series of complex mechanisms that ultimately affect the natural environment. However, the major identified pollutants generated from the above sources are discussed as below:

#### **2.1 Particulate matter (PM)**

Particulate matter (PM) is one of the basic air pollutants, which is formed when different pollutants react chemically. The particulate matter has different particle sizes ranging from 10 μm to very fine particles having particle size of 0.5 μm or less. Such particles are made up of tiny drops of liquid or solid that can be breathed in by human and cause serious health issues such as lung infections and contamination of even bloodstream [25–28]. Both short-term and long-term effects are caused by PMs. Several epidemiological studies have been conducted to investigate such effects. Such effects include asthma, pneumonia, respiratory, and heart diseases [29, 30].
