Air Pollution in Indian Cities — Definition
Definition
Air pollution refers to the presence of harmful or excessive quantities of substances in the Earth's atmosphere that can cause adverse effects on humans, animals, vegetation, and materials. These substances, known as air pollutants, can be in the form of solid particles, liquid droplets, or gases.
The air we breathe is a complex mixture of gases, primarily nitrogen (about 78%) and oxygen (about 21%), with smaller amounts of argon, carbon dioxide, and other trace gases. When this natural composition is altered by the introduction of contaminants, it leads to air pollution.
Pollutants are broadly categorized into two types: primary and secondary. Primary pollutants are emitted directly from a source, such as carbon monoxide from vehicle exhausts, sulfur dioxide from industrial smokestacks, or particulate matter from construction sites.
Secondary pollutants, on the other hand, are not directly emitted but form in the atmosphere when primary pollutants react with each other or with other atmospheric constituents. A classic example is ground-level ozone, which forms when nitrogen oxides and volatile organic compounds react in the presence of sunlight.
Key air pollutants of concern in Indian cities include Particulate Matter (PM2.5 and PM10), Sulfur Dioxide (SO2), Nitrogen Dioxide (NO2), Carbon Monoxide (CO), Ozone (O3), Ammonia (NH3), and Lead (Pb).
PM2.5 and PM10 refer to particulate matter with diameters less than 2.5 and 10 micrometers, respectively. These tiny particles are particularly dangerous because they can penetrate deep into the lungs and even enter the bloodstream, causing respiratory and cardiovascular diseases.
SO2 and NO2 are primarily emitted from industrial processes and vehicular exhaust, contributing to acid rain and respiratory problems. CO is a colorless, odorless gas produced by incomplete combustion, which can reduce oxygen delivery to the body's organs.
O3, at ground level, is a harmful pollutant that irritates the respiratory system. NH3 is often associated with agricultural activities and waste decomposition, contributing to secondary particulate formation.
Lead, though largely phased out from petrol, can still be found in some industrial emissions and older paint, posing severe neurological risks.
To monitor and communicate air quality, India uses the Air Quality Index (AQI). The AQI is a tool that converts complex air quality data into a single, easy-to-understand number and color-coded category, indicating whether air pollution levels are healthy or unhealthy.
It considers eight major pollutants: PM2.5, PM10, SO2, NO2, CO, O3, NH3, and Pb. The AQI ranges from 0 to 500, with lower numbers indicating better air quality. Each range (e.g., 0-50 'Good', 51-100 'Satisfactory', 101-200 'Moderate', 201-300 'Poor', 301-400 'Very Poor', 401-500 'Severe') has associated health implications and recommended public actions.
The AQI is calculated based on the highest concentration of any single pollutant, providing a snapshot of the worst air quality at a given time and location. Understanding these basics is crucial for UPSC aspirants to grasp the multifaceted challenge of air pollution in India.