1. Ozone

What causes Ozone formation?

Motor vehicle exhaust and industrial emissions, vapours from burning fuel and chemical solvents as well as natural sources emit Nitrous Oxides that help form ozone. In the earth's lower atmosphere, ground-level ozone is considered "bad." Sunlight and hot weather cause ground-level ozone to form in harmful concentrations in the air. Ground-level ozone is the primary constituent of smog.

Is it a phenomenon only near chemical factories or busy roads?

Urban areas tend to have high levels of "bad" ozone, but even rural areas are subject to increased ozone levels because wind carries ozone and pollutants hundreds of miles away from their original source.

Why is it harmful?

Ozone exposure irritates the mucous membranes of the nose, throat, and airways. Short-term ozone exposure (up to 8 hours) may cause the lungs to function with reduced vigour and some or all of the following respiratory symptoms:

• Cough
• Pain on inhaling deeply
• Shortness of breath
• Irritation of the eyes and nose
• Increased airway obstruction
• Reduced volume of forced air, when exhaled

2. Particulate matter

What causes particulate matter to form in the air?

Generally, particles in the air that are 10 micrometers in diameter or smaller can pass from the mouth and nose to enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects.

Particulate matters are of two types:

• Inhalable coarse particles near roadways and dusty industries
• Fine particles such as those found in smoke and haze. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react with other compounds the air.

Why are they harmful?

Particle pollution, especially when caused by fine particles contains microscopic solid or liquid droplets that are so small that they can get deep into the lungs and cause serious health problems.

3. Carbon monoxide (CO)

What causes formation of Carbon monoxide in large quantities?

Higher levels of Carbon monoxide (CO) generally occur in areas with heavy traffic congestion. The highest levels of CO in the outside air typically occur during the colder months of the year when inversion conditions are more frequent. The air pollution becomes trapped near the ground beneath a layer of warm air.

The main constituents of CO are:

• Motor vehicle exhaust may cause 85 to 95 percent of all CO emissions cities
• Industrial processes (such as metals processing and chemical manufacturing)
• Residential fuel such as burning wood, woodstoves, gas stoves, and unvented gas and kerosene space heaters
• Cigarette smoke
• Natural sources such as forest fires.

4. Nitrogen oxide (NO₂)

This is a common pollutant, which combines with particles in the air and can often be seen as a reddish-brown layer over many urban areas.

5. Sulphur dioxide (SO₂)

Sulphur dioxide (SO2) dissolves in water vapour to form acid, and interacts with other gases and particles in the air to form sulphates and other products that can be harmful to people and their environment.

What causes SO2?

All raw materials, including crude oil, coal, and ore that contain common metals like aluminum, copper, zinc, lead, and iron react with other compounds in the air and lead to the formation of this chemical compound. Gases are formed when fuel containing sulphur, such as coal and oil are burned, and when petroleum is extracted from crude oil, or metals are extracted from ore.

6. Lead (Pb)

What causes lead to be present in the air we breathe?

• Motor vehicles (such as cars and trucks)
• Industrial sources
• The highest levels of lead in air are usually found near lead smelters
• Other stationary sources are waste incinerators, utilities, and lead-acid battery manufacturers.

How does it affect health?

• Irritation of the airways
• Coughing, or difficulty in breathing
• Decreased lung function
• Aggravated asthma
• Development of chronic bronchitis
• Irregular heartbeat
• Non-fatal heart attacks
• Premature death in people with heart or lung disease

7. Tobacco Smoking

The lung and the airways work as a filter for several thousand damaging substances, which are contained in cigarette smoke. The harmful substances in cigarettes and smoking them are by far, the largest preventable risk factor for developing chronic lung diseases.

How does it affect health?

A markedly high proportion of cigarette and beedi smokers are known to suffer from:

• Airway obstruction
• Clinical symptoms leading to chronic obstructive pulmonary diseases (COPD)
• Recurrent respiratory tract infections.

As a result, smokers show an elevated mortality rate caused by lung cancer as well as development of Chronic Obstructive Pulmonary Disease.

8. Indoor air pollution

When we think of the word ‘pollution’ we usually picture heavy traffic or exhaust from large factories, but never our own home. It may come as a surprise that the problem of indoor air pollution far outweighs ambient air pollution.

A recent report of the World Health Organization (WHO) asserts the rule of 1000 which states that a pollutant released indoors is one thousand times more likely to reach people’s lung than a pollutant released outdoors. It has been estimated that about half a million women and children die each year from indoor air pollution in India. Compared to other countries, India has household fuels and 28% of all deaths due to indoor air pollution in developing countries occur here. Indoor air pollution may cause irritation in breathing to everyone, but people who already suffer from respiratory problems usually become more sensitive to indoor irritants and prone to developing complications.

What causes indoor pollution?

There are four principal sources of indoor pollutants:

• Combustion • Building material • Ground below the building • Bioaerosols

In developed countries, the most important indoor air pollutants are radon, asbestos, volatile organic compounds, pesticides, heavy metals, animal dander, mites, moulds and environmental tobacco smoke. However, in developing countries like India, the most important indoor air pollutants are the combustion products of unprocessed solid biomass fuels for cooking and heating. Approximately half the world’s population and up to 90% of rural households in developing countries rely on unprocessed biomass fuels such as wood, dung and crop residues.

Special Note on Household Dust

Dust is made up of a variety of things from blowing dirt, bacteria, pollen, pollutants, molds, animal dander, hair, decomposing insects, fibres, insulation, dust mites and their excrement, and mostly, skin flakes that humans shed. Household dust comes from a variety of sources including plants, roads, wind, windows, electronics, attics, basements, air conditioning and heating ducts and vents, pets, pollen, insects and carpeting. Dust creates lots of problems, from eye irritation to lingering colds and allergies to that annoying itchy or runny nose. It makes a house dirty and that attracts more dust.