Since pollutants in the air are detrimental to human health, the public health is in crisis in cities. The Clean Ah Act of United States Environmental Protection Agency (EPA) is to protect public health by regulating the emissions of these harmful air pollutants. The main diseases caused by air pollution include respiratory and cardiovascular-related issues. CO,

NO, and soot are the main pollutants detrimental to health. CO attacks hemoglobin and as a result carboxyhemoglobin is formed and the oxygen- binging capacity of blood gets reduced. NO can form additional compounds with hemoglobin and thus enter into the bloodstream. Soot is a particulate matter and contains tiny chemical particles, smoke, dust particles, or other allergens. Contents of smog and soot are almost similar. The smallest airborne particles in soot cause health problems including bronchitis, asthma, heart attacks, irritation to eyes and throat, chronic obstructive pulmonary disease, and even death. Besides the above-mentioned pollutants, toxic components such as polynuclear hydrocarbons which are exhausts from traffic exhausts and wildfire also cause lung irritation, liver issues, and even deadly cancer. In addition to the above man-made pollutants, there are also natural air pollutants. Some allergens from trees, grass, and weeds which are known as pollen and mold also cause air pollution. They are carried by air and are hazardous to health. Although no human activity is involved in carrying these allergens, they are also considered air pollution. Some health issues cause by air pollution are mentioned below.


Neurodegenerative diseases may be associated with low-quality air. Organic air pollutants like particulate matter, NOx, SOx, etc. affect brain structure and neuronal degeneration may happen which might eventually lead to Alzheimer or Parkinson disease. Exposure to ozone also influence mental health and lead to depressive episodes. Air pollution may lead to mood disorders, depressive disorders, and even to suicide.4 Toxic air pollutants lead to mental health problems like anxiety.


Exposure to carbon monoxide and ozone may results in both birth disorders and abnormal birth. Premature mortality is happened by air pollutants. Anthropogenic sources of premature mortality by air pollution are agriculture, fossil fuel-fired by power plants, industry, biomass burning, and traffic. These contribute five out of six of air pollution while natural means contributes only one out of six.5


The air pollution which is a social evil can be reduced by prevention and control. Legal bodies must ensure by routine monitoring the level of pollution emitted by vehicles. Quality of the fuel must be ensured. Alternate sources of energy are highly recommended. Since higher energy consumption, electricity generation, and an increase in the number of vehicles lead to an increase in the multiple pollutant emissions, moderate use of these will also reduce air pollution. As all air pollution control techniques concentrate on stationary sources with easy treatment at a relatively low cost.6 The following biocompatible solutions may be recommended as low-cost means for the abatement of air pollution.


Designing automobile engines which emit minimal air pollutant when fossil fuels are burned is a current necessity. Automobiles are the main source of CO pollution and are mainly attributed to combustion under low stoichiometric ratio of fuel and air. Generally, fuel bum is completed at low temperatures and higher concentrations of oxygen. Internal engines are to be modified to reduce the production and emission CO to the atmosphere.


Substitutes for gasoline that produce fewer amount of CO are recommended. Substitute fuels for gasoline are highly recommended so that the amount of air pollutants on combustion may be reduced considerably. Unleaded petrol controls lead toxicity to a greater extent. Pyretic sulfur in coal must be removed and low-sulfur fuels are recommended.


Biofuels are fuels derived from biomass. Biodiesel, biogas, bioethanol, biomethanol, etc. are examples of biofuels. It reduces CO, emission and gives good fuel efficiencies. They are nontoxic and biodegradable too.

Biodiesel production involves transesterification reactions. Biodiesel is methyl esters. Diesel blended with 5% biodiesel is allowed in certain countries. Different crop plants are used for biodiesel production. Oil is generally extracted from their oilseeds. They include Jatropha curcus, Ponganna piimata, Colotropis gigantia, Euphorbia time alii, etc. Degraded land can be cultivated by plantation of these trees. One advantage of biodiesel can be used in conventional diesel engines without modification. The major advantage of using biodiesel engines, however, is the remarkable reduction in the emission of air pollutants like C02, CO, SOx, NOx, hydrocarbon, particulate matter, etc. It can be used as a domestic fuel as well and is user-friendly. The production and the storage of biodiesel need to be promoted because it can be stored safely than fossil diesel. Since it is harmless to aquatic system, even marine stores could be used. Thus, biofuel is environmentally renewable and efficient in the abatement of air pollution.

Nanomaterials like calcium oxide and magnesium oxide have been used as biocatalyst in oil transesterification reactions for biodiesel production.7 Biodiesel can be synthesized by transesterification of sunflower oil with methanol using nanocatalysts.s Ultrasonic-assisted transesterification using heterogeneous nanocatalysts for the production of biodiesel is a sustainable and environment-friendly approach.9 Heterogeneous catalysts have high activity and high water tolerance properties.10 Waste eggshell can also be used as a catalyst for biodiesel synthesis.11 Microwave-assisted pyrolysis and solvolysis reactions are used for lignin conversion leading to renewable fuel on large-scale.12


Vehicle engines require lubricants. Biolubricants are biodegradable and possesses antiwear protection, and are nontoxic. Due to polar nature, natural oils like com, soybean, olive, sunflower, peanut, etc. can be used as lubricants. Synthetic biodegradable lubricants include poly alpha olefins, diesters, polyglycols, etc. While esterification of oleic acid with small carbon chain alcohols yields biofuels, the same with long carbon chain alcohols yields biolubricants. Biolubricants can successfiilly be produced by enzyme-catalyzed esterification using ionic liquids.13 The biolubricant isoamyl oleate can be produced by the enzymatic reaction in microfluidic reactor using Novozym 435 enzyme. The bioconversion is done in solvent- free media.14 Synthesis of biolubricants may be extracted from effluents of palm oil mill enzymatic hydr olysis as well as noncatalytic esterification.15 Many renewable hydrocarbon biolubricants with added qualities can be prepared from hydrodeoxygenation of vegetable oils at 50 bar pressure and 450 °C. This opens a low-cost and high-quality technology for the preparation of renewable hydrocarbons that can do the functionalities of biolubricants.16


For clean development, hydrogen production from green, renewable, and sustainable energy resources are of higher priority. The splitting of water molecules into O, and H2 gases by a technology is the basic chemistry of hydrogen production, the technologies of hydrogen production from fossil fuels like natural gas, coal, etc. are what so far known and used. The environment friendly and green methodologies include renewable resources like combustion of biomass, biomass pyrolysis, biohydrogen production using anaerobic bacteria, etc. Although, Solar-based hydrogen fuel production is expensive. Photovoltaic cell-based hydrogen production is also important and may lead to fast development in industry and commerce. Hydrogen production from supercritical water gasification (SCWG) of moisturized biomass is an effective thermochemical process. Highly moisturized biomass is also utilized directly in SCWG without any high-cost drying process.17


Treatment of exhaust gases prior to release to the atmosphere will decrease the amount of pollutants in the air. Some technologies used in this field are the following:


Catalytic converters—two stages—remove NOx emission from the atmosphere. First converter consists of Pt catalyst for the conversion of the emitted NO to N7 NH,. Second converter facilitates an oxidation atmosphere for the efficient conversion of hydrocarbons/СО to H,0/ COv NO is also responsible for the depletion of 03 levels. Excess oxygen levels limit the levels of NO. Solid absorbents like activated charcoal, activated alumina, activated silica gel, and molecular zeolites can function as catalysts.


NOx and sulfur dioxide (SO,) are the main air pollutants. Awareness to protect the environment is progressively increasing. Catalytic reduction is the preferred technology used for onshore flue gas purification. Catalysts are useful for cleaning exhaust gases and they must work efficiently under large volumes of oxygen and moisture.18 Modem catalysts are based on nanotechnology and current candidate of catalytic reduction mostly nanocatalysts. Nano techno logy is a promising method to remove air pollutants. Nanotubes and nanoparticles can be used. Carbon nanotubes (CNTs) with cerium oxide (CeO,) effectively remove NO...19 Selective catalytic reduction of NO can be effected by CeO,-CNTs combinations.20 CeO, nanoparticles and CNTs can also be used to remove the harmful exhaust gas emissions from additives in Diesterol.21 Titanic acid nanotubes can also have catalytic capacity to remove NOx.22 Cr-MnOx mixed-oxide used to remove NO by oxidation of NO to nitrogen dioxide (NO,).23

The control of particulate emissions from renewable bioresources like biomass boiler plants using different scrubber systems like a washing tower, a Venturi scrubber, bubble-column scrubber show that they have good removal efficiency.24 Electro-scrubbing process is a green methodology for the removal of pollutant mist particles like CH3SH as a model air pollutant.25


Gaseous pollutants are adsorbed on solid adsorbents in a suitable container. Some adsorbents used and gaseous pollutants collected are given below:

TABLE 3.1 Solid Adsorbents for the Removal of Ah' Pollutants.





Zeolites, silica get


Iron oxides


Dolomite, alkaline alumina

Organic solvent vapors

Activated charcoal


Electrostatic precipitators working at very high potentials are able to remove pollutants in the precipitated form. This is based on the principle of acquiring charge by aerosol particles when an electric field is provided. It is given by the equation:

where, F = force, E = potential gradient, and q = electrostatic charge.

The charge acquired particles are attracted toward an electrostatic precipitator. It can removed large sized pollutants aluminum or stainless steel parallel plates. They use big filters or scrubbers to remove dust particles.


The high-gravity technology is the effective removal of particulate matter and gas pollutants from industries. Particulate collection is based on size, shape, velocity, gravity, momentum, etc. It works as follows: the effluent gas is applied to a big chamber and by decreasing velocities the particulate matter gets settled. The basic characteristics of high- gravity technique are mass transfer and high micro-mixing efficiency. According to this technology, the multiple air pollutants like SO.., NOx, CO„ particulate matter, etc. can be removed simultaneously with high efficiency. The benefits of the high-gravity technology are: it has zero secondary pollution, it is low cost, it requires only small space, etc. It can be scaled-up into large scale and the method is reliable. This high-gravity technology finds applications in integrated air pollution control in industries.6


Generally it helps remove liquid, solid, or gas contaminants. Scrubbers or adsorbers containing suitable liquid, generally water, the adsorbent, helps to remove pollutants present in a stream of gas. Chemical scrubbers like limestone and citric acid absorb SOx from the atmosphere. Wet collectors (scrubbers) are for the removal of fine particulates in a gas stream. Pollutant gases are effectively washed using atomized liquid. Marine air pollution has to be controlled using wet scrubbers containing electrolyzed seawater using a liquid, generally water, to eliminate particulate matter. Scrubbers contain several chambers and it is called scrubbing cloud of water. NOx and SOx from ship emissions can be removed by using wet scrubbers. Absorbents may be NaOH, Na,SOr NH4OH, Mg(OH)2, and Ca(OH),. The most attractive feature of wet scrubbing is that it can be done in low ambient temperatures.26


Greenhouse gases are mainly CO,, CH4, nitrous oxide, and fluorinated gases. The adsorption of air pollutants on nanomaterials is more efficient and cost-effective because of their high surface area, their adsorption capacity, and ability for regeneration. Solid adsorbents for CO, adsorption include calcium-based Nanomaterials, nanoparticles in combination with alkali metals, functionalized CNTs. For the decomposition of CH4 and nitrous oxides (NOx) metallic nickel nanoparticles, TiO, coated with stainless steel web net, titanate nanotubes and their derivatives etc. are suggested. Modified TiO-silver catalyst was suggested for the photodecomposition of (N,0) into nitrogen and oxygen. For the removal of SO,, activated carbon deposited on iron nanoparticles may be used as adsorbent. SO, adsorption process leads to some changes in the magnetism of magnetic nanoparticles.27 Household air pollution can be minimized by LPG by replacing biomass, wood, straw, and dung etc. for household cooking purpose.


Non thermal plasma is a kind of non-equilibrium plasma while in actual plasma state the components are in thermal equilibrium. Highly energetic electrons produce plasma state and the developed free radicals decompose the pollutants. NTP has ability to induce various chemical reactions at normal pressure and temperature. Generation of ozone for water disinfection and dust removal are the mam benefits of NTP related to air pollution control. Hybrid NTP system has a combined effect of adsorbents and catalysts and can be used in industries.28

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