Air pollution is a mix of hazardous substances from both human-made and natural sources.

• Vehicle emissions, fuel oils and natural gas to heat homes, by-products of manufacturing and power generation, particularly coal-fueled power plants, and fumes from chemical production are the primary sources of human-made air pollution.
• Nature releases hazardous substances into the air, such as smoke from wildfires, which are often caused by people; ash and gases from volcanic eruptions; and gases, like methane, which are emitted from decomposing organic matter in soils.

Smog

• Smog is a specific type of air pollution. It is a combination of harmful pollutants (often appearing relatively low to the ground as a yellow-brown haze) that are introduced into the atmosphere by both natural and human induced processes. It was first described over 5 decades ago as a mixture of smoke and fog, hence the name “smog”—but today it has a more specific definition and composition.
• Smog is made up of many chemicals including nitrogen oxides (NOx), sulphur dioxide (SOx), carbon monoxide (CO), and volatile organic compounds (VOCs), but the two main components of smog are particulate matter (PM) and groundlevel ozone (O3 ).
• Normal smog is mainly a product of burning large amounts of high sulfur coal. Whereas photochemical smog is a more modern phenomena commonly produced by vehicle emissions in contact with sunlight—mostly from burning gasoline and diesel. Photochemical smog forms in warm, densely populated cities with many vehicles.

Formation of Smog

• Smog forms when pollutants are released into the air. The pollutants are formed both naturally and by humans, however, the human-induced pollutants are of most concern due to the magnitude of pollutants produced by the burning and extraction of fossil fuels, which are known to cause extreme health effects. The location of smog formation is also of great concern, especially for human health, as a good portion of it is produced within cities where large portions of the population live.
• One of the primary constituents, ozone, is created through chemical reactions between sunlight and certain pollutants. The other primary constituent, particulate matter can also form through chemical reactions but is introduced to the atmosphere through other means as well. Wind may disperse these particles among land, thereby decreasing the amount within a given area. In addition, rainfall may wash these pollutants out of the local atmosphere; however, this can result in other unwanted events like acid rain. When smog encounters an inversion layer (caused by warm areas in the upper atmosphere) it can stay over a region for an extended period of time—exposing people to its effects for longer. Visit the inversion layer page to see how this phenomenon occurs.

Health Effects of Smog 

• The health effects from smog and its components can be severe, and depend on many variables. Smog is harmful when inhaled, with the severity of it depending on the amount inhaled, the types of pollutants contained in it, as well as the individual’s age, weight, activity level, and well-being. However studies show that any exposure to these pollutants is harmful, with extended exposure and higher doses obviously causing the most damage. 
• Types of effects smog has include:
  • Eye, nose and throat irritation 
  • Decreased lung function 
  • Aggravation of respiratory or heart disease 
  • In some cases, death

Indoor Air Pollution

• It is created by the release of harmful pollutants inside. These can include fine particulate matter, carbon monoxide, and various other toxins.
• Indoor air pollution is a big problem in developing countries, where people often burn fuels indoors for cooking and heating. It is also a concern for people living in energy-efficient homes. These properties tend to be relatively airtight, meaning that the air inside can quickly become stagnant and pollutant levels can rise rapidly.
• And while pollution in all forms can be harmful, indoor air pollution is particularly pernicious because people are often steeped in it for long periods of time.

Sources of Indoor Air Pollution

• Asbestos 
• Biological Pollutants
• Carbon Monoxide (CO)
• Cookstoves
• Formaldehyde/Pressed Wood Products
• Lead (Pb)
• Nitrogen Dioxide (NO2)
• Pesticides
• Radon (Rn)
• Indoor Particulate Matter
• Secondhand Smoke/ Environmental Tobacco Smoke
• Volatile Organic Compounds (VOCs)
• Wood Smoke

Effects of Indoor Air Pollution on Health

• The ill-effects of indoor air pollution result in about 2 million premature deaths per year, wherein 44% are due to pneumonia, 54% from chronic obstructive pulmonary disease (COPD), and 2% from lung cancer. The most affected groups are women and younger children, as they spend maximum time at home. The morbidities associated with indoor air pollution are respiratory illnesses, viz., acute respiratory tract infection and COPD, poor perinatal outcomes like low birth weight and still birth, cancer of nasopharynx, larynx, lung,and leukemia. The harmful health effects of formaldehyde range from being an acute irritant, reducing vital capacity, causing bronchitis, to being a carcinogen causing leukemia and lung cancer.

What is a Smog Tower?

• Smog towers are structures designed as large-scale air purifiers to reduce air pollution.
• Smog towers work on the principle of HEPA filtration or air ionisation technology to remove PM2.5 particles. That is, air flowing through a smog tower passes through a filter to provide clean air coming out of it. These methods of cleaning air are scientifically well established and used widely for cleaning indoor air where the air exchange with the outdoors is minimal. The first prototype of a smog tower was built in 2017 by Dutch artist Daan Roosegaarde in Beijing as a demonstration and art project that converts the carbon in filtered particles into diamonds.

Scenario in Delhi 

• According to the World Health Organization (WHO), India has six of the top 10 most polluted cities in the world, with Delhi on the top of the list. A 2020 study in The Lancet found there were 1.67 million deaths in India attributable to air pollution in 2019, including almost 17,500 in Delhi. The Supreme Court in January 2020 directed the central government to construct a smog tower to reduce pollution at Anand Vihar and the Delhi government to install another such structure at Connaught Place in three months.

Fly ash

• It is a fine gray powder consisting mostly of spherical, glassy particles that are produced as a byproduct in coal-fired power stations. Fly ash has pozzolanic properties, meaning that it reacts with lime to form cementitious compounds. It is commonly known as a supplementary cementitious material. Fly ash is also known as flue-ash or simply ash. Fly ash is suitable for a wide variety of applications and uses, including:
  • Concrete 
  • Dams
  • Flowable fill
  • Mines
  • Landfills
  • Geopolymer concrete

Advantages of Fly Ash

• It is highly economical. 
• Use of Fly Ash is environmentally friendly as the waste materials from industries are effectively being used to create quality building materials.
• Fly Ash has very small particles which makes the concrete highly dense and reduces the permeability of concrete. It can add greater strength to the building.
• The concrete mixture generates a very low heat of hydration which prevents thermal cracking.
• Fly Ash concrete is resistant to acid and sulphate attacks.
• The shrinkage of fly ash concrete is very less.
• The use of fly ash gives concrete good work ability, durability and finish.

Disadvantages of Fly Ash 

• The quality of fly ash can affect the quality and strength of Cement concrete.
• Poor quality fly ash can increase the permeability of the concrete and cause damage to the building.

Various Initiatives undertaken by Government for mitigation of Air Pollution Action Plans for Improvement of Air Quality

• The Central Government has launched National Clean Air Programme (NCAP) under the Central Sector “Control of Pollution” Scheme as a long-term, time-bound, national level strategy to tackle the air pollution problem across the country in a comprehensive manner with targets to achieve 20 % to 30 % reduction in PM10 and PM2.5 concentrations by 2024 keeping 2017 as the base year for the comparison of concentration.102 non-attainment cities mostly in IndoGangetic Plains have been identified based on ambient air quality data for the period 2011 – 2015 and WHO report 2014/2018. The city specific Action Plans have been approved for all 102 non-attainment cities for implementation on ground.
• The Central Government has notified a Comprehensive Action Plan (CAP) in 2018 identifying timelines and implementing agencies for actions identified for prevention, control and mitigation of air pollution in Delhi and NCR. 
• Graded Response Action Plan (GRAP) was notified on January 12, 2017, for prevention,    control and abatement of air pollution in Delhi and NCR. It identifies graded measures and implementing agencies for response to four AQI categories, namely, Moderate to Poor, Very Poor, Severe and Severe + or Emergency.
• Several steps have been taken for creating awareness amongst the general population. These steps are as follows.
  • SAMEER app has been launched wherein air quality information is available to public along with provision for registering complaints against air polluting activities.
  • Air quality information collection and dissemination are done from a centralized location. It provides real time air quality status to all stakeholders.
  • A dedicated media corner, Twitter and Facebook accounts have been created for access to air quality related information and to provide a platform for lodging complaints by general population.
  • Crowd sourcing of innovative ideas/ suggestions/proposals from public is done through CPCB website to strengthen efforts for improving air quality in Delhi-NCR.
  • The Ministry of Environment, Forest and Climate Change is implementing Environment Education, Awareness and Training Scheme with the objective to promote environmental awareness among all sections of the society and to mobilize people’s participation for conservation of environment. Under the National Green Corps (NGC) programme of the Ministry, about one lakh schools have been identified as Eco-clubs, wherein, nearly thirty lakh students are actively participating in various environment protection and conservation activities, including the issues related to the air pollution.
  • Ministry is promoting peoples participation and awareness building among citizens for environmental conservation that focus on promotion of cycling, saving water and electricity, growing trees, proper maintenance of vehicles, following of lane discipline and reducing congestion on roads by car pooling etc.
  • For field feedback on air polluting activities in Delhi and major NCR towns, 46 teams of Central Pollution Control Board have been deployed since October 7, 2019.

National Air Quality Index 

• Air Quality Index is a tool for effective communication of air quality status to people in terms, which are easy to understand. It transforms complex air quality data of various pollutants into a single number (index value), nomenclature and colour.

• There are six AQI categories, namely Good, Satisfactory, Moderately polluted, Poor, Very Poor, and Severe. Each of these categories is decided based on ambient concentration values of air pollutants and their likely health impacts (known as health breakpoints). AQ sub-index and health breakpoints are evolved for eight pollutants (PM10, PM2.5, NO2 , SO2, CO, O3 , NH3 , and Pb) for which short-term (upto 24-hours) National Ambient Air Quality Standards are prescribed.
• Based on the measured ambient concentrations of a pollutant, sub-index is calculated, which is a linear function of concentration (e.g. the sub-index for PM2.5 will be 51 at concentration 31 µg/m3 , 100 at concentration 60 µg/m3 , and 75 at concentration of 45 µg/m3 ). The worst sub-index determines the overall AQI. AQI categories and health breakpoints for the eight pollutants are as follow:

Acid rain

• Acid rain occurs when Sulphur dioxide (SO2 ) and oxides of Nitrogen (NOx ) are emitted into the atmosphere, undergo chemical transformations and are absorbed by water droplets in clouds. This causes the formation of sulphuric and nitric acids in rain clouds. The droplets then fall to earth as rain, snow or mist. If rain falls through polluted air it picks up more of these gases and increases its acidity. This is called acid rain. This can increase the acidity of the soil, and affect the chemical balance of lakes and streams. Thus, acid rain is defined as any type of precipitation with a pH that is unusually low. A pH of less than about 5 is used as a definition of acid rain. Acid rain is a serious environmental problem that affects large parts of the world.

Sources of acid rain

• Sulphur dioxide (SO2 ) is generally a by-product of industrial processes and burning of fossil fuels. Ore smelting, coal-fired power generators and natural gas processing are the main contributors to sulphur dioxide in the atmosphere. The main source of oxides of nitrogen (NOx) emissions is the combustion of fuels in motor vehicles, residential and commercial furnaces, industrial and electrical utility boilers and engines, and other equipments.

Effects of acid rain

• It causes acidification of lakes and streams and contributes to the damage of trees any many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including heritage buildings, statues, and sculptures that are part of our nation’s cultural heritage. Prior to falling to the earth, sulphur dioxide (SO2 ) and nitrogen oxide (NOx) gases and their particulate matter derivatives— sulphates and nitrates- contribute to visibility degradation and harm public health.

Prevention of acid rain

• Coal can be crushed and washed before burning.
• Oil can be treated to remove sulphur. 
• Cleaning systems can be fitted into chimneys to remove sulphur dioxide before it can be released into the atmosphere.
• Improved furnaces can be built which burn fuel more effectively and produce less pollution.
• Vehicle exhausts can be fitted in vehicles, which remove pollutants from engine emissions.