Unit – 4

AIR POLLUTION

4.1 Environment and Human health - Air pollution: sources- effects- control

Air Pollution

Air pollution refers to any physical, chemical or biological change in the air. It is the contamination of air by harmful gases, dust and smoke which affects the plants, animals, and humans drastically.

There is a certain percentage of gases present in the atmosphere. An increase or decrease in the composition of these gases is harmful to survival. This imbalance in the gaseous composition has resulted in an increase in earth’s temperature, which is known as global warming.

Types of Air Pollution

1. Primary Pollutants

The pollutants that directly cause air pollution are known as primary pollutants. Sulphur-dioxide emitted from factories is a primary pollutant.

2.     Secondary Pollutants

The pollutants formed by the intermingling and reaction of primary pollutants are known as secondary pollutants. Smog, formed by the intermingling of smoke and fog, is a secondary pollutant.

Causes of Air Pollution

Following are the important causes of air pollution:

The combustion of fossil fuels emits a large amount of sulphur dioxide. Carbon monoxide released by incomplete combustion of fossil fuels also results in air pollution.

The gases emitted from vehicles such as jeeps, trucks, cars, buses, etc. pollute the environment. These are the major sources of greenhouse gases and also result in diseases among individuals.

Ammonia is one of the most hazardous gases emitted during agricultural activities. The insecticides, pesticides and fertilizers emit harmful chemicals in the atmosphere and contaminate it.

Factories and industries are the main source of carbon monoxide, organic compounds, hydrocarbons, and chemicals. These are released into the air, degrading its quality.

In the mining process, the minerals below the earth are extracted using large pieces of equipment. The dust and chemicals released during the process not only pollute the air, but also deteriorate the health of the workers and people living in the nearby areas.

The household cleaning products and paints contain toxic chemicals that are released in the air. The smell from the newly painted walls is the smell of the chemicals present in the paints. It not only pollutes the air but also affects breathing.

Effects of Air Pollution

The hazardous effects of air pollution on the environment include:

Air pollution has resulted in several respiratory disorders and heart diseases among humans. The cases of lung cancer have increased in the last few decades. Children living near polluted areas are more prone to pneumonia and asthma. Many people die every year due to the direct or indirect effects of air pollution.

Due to the emission of greenhouse gases, there is an imbalance in the gaseous composition of the air. This has led to an increase in the temperature of the earth. This increase in earth’s temperature is known as global warming. This has resulted in the melting of glaciers and an increase in sea levels. Many areas are submerged underwater.

The burning of fossil fuels releases harmful gases such as nitrogen oxides and sulphur oxides in the air. The water droplets combine with these pollutants, become acidic, and fall as acid rain which damages human, animal and plant life.

The release of chlorofluorocarbons, halons, and hydro chlorofluorocarbons in the atmosphere is the major cause of depletion of the ozone layer. The depleting ozone layer does not prevent the harmful ultraviolet rays coming from the sun and causes skin diseases and eye problems among individuals.

The air pollutants suspend on the water bodies and affect the aquatic life. Pollution also compels the animals to leave their habitat and shift to a new place. This renders them stray and has also led to the extinction of a large number of animal species.

Control Measures

Following are the measures one should adopt, to control air pollution:

People should avoid using vehicles for shorter distances. Rather, they should prefer public modes of transport to travel from one place to another. This not only prevents pollution, but also conserves energy.

A large number of fossil fuels are burnt to generate electricity. Therefore, do not forget to switch off the electrical appliances when not in use. Thus, you can save the environment at the individual level. Use of energy-efficient devices such CFLs also controls pollution to a greater level.

4.2           Particulate emission     

“Particulate matter” (PM) is the general term used to describe solid particles and liquid droplets found in the air. The composition and size of these airborne particles and droplets vary. Some particles are large enough to be seen as dust or dirt, while others are so small they can only be seen using a powerful microscope. Two size ranges, known as PM10 and PM2.5, are widely monitored, both at major emissions sources and in ambient air. PM10 includes particles that have aerodynamic diameters less than or equal to 10 micrometers (m), approximately equal to one-seventh the diameter of human hair. PM 2.5 is the subset of PM10 particles that have aerodynamic diameters less than or equal to 2.5 m. Particles within the two size ranges behave differently in the atmosphere. PM2.5, or fine particles, can remain airborne for long periods and travel hundreds of miles. Coarse particles, or the subset of PM10 that is larger than 2.5 m, do not remain airborne as long and their spatial impact is typically limited because they tend to deposit on the ground downwind of emissions sources. Larger coarse particles are not readily transported across urban or broader areas because they are generally too large to remain suspended in air and they tend to be removed easily on contact with surfaces. In short, as the particle size increases, the amount of time the particles remain airborne decreases. The PM Concentrations indicator describes the various ways PM can harm human health and the environment.

PM can be emitted directly or formed in the atmosphere. “Primary” particles are those released directly to the atmosphere. These include dust from roads and black and/or elemental carbon from combustion sources. In general, coarse PM is composed largely of primary particles. “Secondary” particles, on the other hand, are formed in the atmosphere from chemical reactions involving primary gaseous emissions. Thus, these particles can form at locations distant from the sources that release the precursor gases. Examples include sulphates formed from sulphur dioxide emissions from power plants and industrial facilities and nitrates formed from nitrogen oxides released from power plants, mobile sources, and other combustion sources. Unlike coarse PM, a much greater portion of fine PM (PM2.5) contains secondary particles.

4.3           Air quality standards

Ambient air quality refers to the condition or quality of air surrounding us in the outdoors. National Ambient Air Quality Standards are the standards for ambient air quality set by the Central Pollution Control Board (CPCB) that is applicable nationwide. The CPCB has been conferred this power by the Air (Prevention and Control of Pollution) Act, 1981.

Ambient Air Quality Standards in India

The Air (Prevention and Control of Pollution) Act 1981 was enacted by the Central Government with the objective of arresting the deterioration of air quality. The Air (Prevention and Control of Pollution) Act 1981 describes the main functions of the Central Pollution Control Board (CPCB) as follows:

• To advise the Central Government on any matter concerning the improvement of the quality the air and the prevention, control and abatement of air pollution.
• To plan and cause to be executed a nation-wide programme for the prevention, control and abatement of air pollution.
• To provide technical assistance and guidance to the State Pollution Control Board.
• To carry out and sponsor investigations and research related to prevention, control and abatement of air pollution.
• To collect, compile and publish technical and statistical data related to air pollution; and
• To lay down and annul standards for the quality of air

The mandate provided to the CPCB under the Air (Prevention and Control of Pollution) Act empowers it to set standards for the quality of air.

The current National Ambient Air Quality Standards were notified on 18 November 2009 by the Central Pollution Control Board. 

4.4           Measurement of air pollution.

Air quality is measured with the Air Quality Index, or AQI. The AQI works like a thermometer that runs from 0 to 500 degrees. However, instead of showing changes in the temperature, the AQI is a way of showing changes in the amount of pollution in the air. Air quality measurement are commonly reported in terms of: micrograms per cubic meter (µg/m3) parts per million (ppm) or parts per billion (ppb)

Air quality control agencies measure pollutants in the ambient air to determine whether an area is meeting EPA’s air quality standards. Ambient air monitoring is conducted via networks of monitors located throughout the country that measure actual concentrations of various air pollutants, including sulphur dioxide, nitrogen dioxide, ozone, lead, particulate matter, carbon monoxide, and several toxic air pollutants. In addition, new standards from EPA require the establishment of a monitoring network near major roadways in metropolitan areas across the country that will measure near roadway emissions of nitrogen dioxide, carbon monoxide, and particulate matter. Agencies also use air quality modelling to project emissions of pollutants from stationary and mobile sources. Modelling is used to help identify appropriate air quality controls during the permitting process, develop state implementation plans for meeting air quality goals, and, in some cases, determine air quality in areas where a monitor is not available.

Reference Books

1. Environmental pollution and Control  by Ruth Weiner et al
2. Environmental Pollution Control Engineering  by C S Rao
3. Environmental Engineering-1  by H.S Vishwanath et al