*3.12.1 Urbanization and industrialization*

Urbanization and Industrialization are one of the major cause of air pollution due to urbanization there is increase in use of automobiles and due to industrialization there is an increase in cutting of trees which increase the air pollution rapidly [59].

### *3.12.2 Burning of fossil fuels*

Burning of fossil fuels is also the main cause of air pollution. Burning of fossil fuel can release a variety of primary and secondary pollutants as well as airborne oxide and also SO2, CO2, CO, hydrocarbons, organic compounds, chemicals, and nitrogen oxides (NOx). Due to burning of fossil fuel climates change and global warming is also increase due to release of major greenhouse gases (carbon dioxide, methane (CH4), nitrous oxide, and fluorinated gases) [59].

#### **3.13 Effect of air pollution**

The air pollution shows adverse effect on human health and causes many diseases like acute respiratory infection, pulmonary disease, cardiovascular disease etc.

### *3.13.1 Acute respiratory infection (ARI)*

Acute respiratory infection is one of the common disease causes by air pollution. In this the pollutants can effects the lungs and show some symptoms like cough, sinusitis and ditis media [60].

#### *3.13.2 Pulmonary disease*

Pulmonary disease can cause due to inhalation of air pollutants which cause allergic disease and pulmonary disease such as asthma, atopic dermatitis and allergic rhinitis and lung cancer [60].

#### *3.13.3 Cardiovascular disease (CVDs)*

The pollutants like PM, PAHs, CO, heavy metal, and other organic pollutants are the main cause of cardiovascular disease [61].

Cardiovascular disease is severe when particulate matter increases and shows symptoms like ischemic stroke, myocardial infarction, cardiac arrhythmia, heart failure, and atrial fibrillation [62].

Particulate matter is one of the major factors which cause CVDs and induce the oxidative stress, systemic inflammation and increases the blood coagulability, and autonomic and vascular imbalance [60].

#### **3.14 Nano-remediation of air pollution**

Air pollution can be remediated in many ways and one of the best ways is use of nanoparticles like nanocatalyst, nano-membranes and photocatalyst semiconductor.

Nanocatalyst helps in gaseous exchange by increasing the surface area for the reaction of gases which increases the chemical reaction and help in conversion of harmful gases which are release from cars and industries into harmless gases. Nanofibre catalysts are one of the examples which are used in industries for the removal of organic compounds from the smoke stacks.

Nanostructured membrane is another way to separate methane or carbon dioxide from smoke due to having small pores. The best example is the Carbon nanotubes (CNTs) which are more efficient than other membrane for trapping greenhouse gases which is released by the mining and power generation. CNTs have major advantages as it can trap gases hundred times faster than other membranes [61].

The other approach for the remediation of air pollution is using of nanosize semiconductor photocatalyst. Photocatalyst are the catalyst that oxidized organic pollutants into nontoxic materials for examples titanium dioxide (TiO2), zinc oxide (ZnO), iron (III) oxide (Fe2O3) and tungsten oxide (WO3) and used in many ways [11].

Photocatalyst and semiconductor can use together to remediate air pollution by using the principle of semiconductor i.e. oxidizing of organic molecules by light. The process includes, at a sufficient light exposure the charge is moved from valence band to conduction band and causes the oxidation of surrounding substance. The semiconductor photocatalyst can be modified according to reactivity and selectivity [63].
