Chapter 10: Environmental ChemistryLong Questions with Answers

1. Carbon dioxide (CO₂)

Higher levels of carbon dioxide lead to increased global warming, which can cause ice caps to melt and oceans to warm, causing sea levels to rise. Extreme weather changes such as heat waves, heavy rains and wildfires also occur.

2. Carbon monoxide (CO)

It is an extremely poisonous gas that can cause suffocation and death. It stops the red blood cells in the blood from carrying the oxygen that the body needs.

3. Oxides of nitrogen (NOₓ)

NOₓ can damage lungs, irritate the eyes and damage vegetation. It can also cause acid rain, which affects buildings and statues made of limestone, and forms photochemical smog.

4. Oxides of sulphur (SOₓ)

SO₂ irritates the eyes and causes breathing difficulties and acid rain, and haze.

5. Hydrocarbons

They can cause pneumonia, coughing and many other breathing and lung diseases. They also cause global warming (methane).

6. Particulate matter

It irritates the eyes and can cause severe breathing problems for people with asthma. It also makes clothes dirty, and visibility is reduced because it produces haze; it increases the risk of cancer.

7. Ozone

Breathing ozone can cause a variety of health problems including chest pain, coughing, throat irritation and congestion.

Smog

Smog leads to allergies, asthma and lung infections and inhibits plant growth by reducing the CO₂ absorbed in photosynthesis.

Greenhouse effect

The progressive warming up of the Earth's surface due to the blanketing effect of man-made carbon dioxide, methane, water vapour and other gases in the atmosphere is called the greenhouse effect.

How it works

The Sun emits short-wave radiation that passes through greenhouse gases to heat the surface of the Earth. The hot Earth's surface emits long-wave radiation that is mostly absorbed by greenhouse gases. This absorption prevents the radiation from reaching space, reducing the speed at which the Earth can cool off. The higher the concentration of greenhouse gases, the greater the warming.

Greenhouse gases

CO₂ from burning coal, oil and gas (rising for 300 years; forests that absorb it are being cut); methane from decaying vegetation, animal digestion and rice fields; water vapour, about half of the effect.

Dangers of global warming

Definition

The air quality index (AQI) is a rating system that shows how bad the atmosphere around you is. It is calculated from the levels of the main pollutants: particulate matter (PM2.5, PM10), ozone, NO₂, SO₂ and CO.

Scale

Information it conveys

An AQI under 50 is good; an AQI over 300 is hazardous.

High-risk groups

Why more dangerous

Effects

Breathing polluted air may affect their lungs, heart and brain. Pollutants can enter their blood stream and cause coughing or itching of eyes, which may lead to poor quality of life, hospitalisation, cancer or even premature death.

Precautions

Check the AQI, stay indoors and reduce activity on bad days, wear N95 masks, keep indoor air clean, and see a doctor about worrying symptoms.

1. Planting trees

Planting trees is very helpful in removing air pollution. Plants clean the air through photosynthesis, absorbing carbon dioxide and releasing oxygen in sunlight, catalysed by chlorophyll. They also trap particulate matter on their leaves and trunks.

2. Catalytic converters and cleaner fuels

Catalytic converters are used in the exhaust of modern automobiles. A three-way converter reduces NOₓ to N₂ and O₂, oxidises CO to CO₂, and oxidises hydrocarbons to CO₂ and H₂O. The emission of SO₂ is reduced by using low-sulphur fuels or flue gas desulphurisation with calcium oxide (up to 95 % removed).

3. Renewable energy

To discourage the excessive use of fossil fuels, renewable resources (Sun, wind, water, geothermal, biomass) should be used. Solar and wind energy generate electricity without damaging the environment. Hydrogen fuel, which burns to water only, is another clean option.

Others

Sources of pollutants

Weather that traps them

Smog is caused by a combination of industrial pollution, vehicle emission and crop burning, which build up NOₓ, SO₂, particulate matter and volatile organic compounds.

Summer air is not always clean: dust storms can raise PM10, and ground-level ozone forms on sunny days, but the dangerous winter smog does not form.

Pakistan produces less than 1 % of the world's greenhouse gases but is among the countries most affected by climate change.

Composition

Earth is covered with a blanket of air called the atmosphere, made up of several layers of gases. Its constituents are divided into major and minor ones; the amounts vary slightly from place to place, season to season and day to night.

Air pollutants

Any substance in the air which has an adverse effect on human health and quality of life is an air pollutant. Seven substances make up over 90 % of air pollution:

Main factors

The complete and incomplete combustion of fossil fuels is alone responsible for most of our pollution. Rapid growth of population, urbanisation, industrialisation and transportation are the main factors.

Definition

Rain water with pH between 4.2 and 4.4 is known as acid rain.

Role of sulphur

Burning of fossil fuels releases SO₂ and SO₃, produced because of the sulphur present in fossil fuels.

Role of oxides of nitrogen

Oxides of nitrogen are produced by the direct combination of atmospheric nitrogen and oxygen in combustion, in automobile engines and by lightning. They act directly, forming nitric acid, and catalytically, helping SO₂ change to SO₃:

Fall

The gases mix with moisture to form acid droplets that wind carries to huge distances, returning as acid rain, hail, snow or fog.

Effects

Control

Catalytic converters, low-sulphur fuels, flue gas desulphurisation with CaO, and adding lime to acidic soils and lakes.

Formation of pollutants in engines

At the very high temperature of burning fuel inside the engine, nitrogen and oxygen of the air combine: N₂ + O₂ → 2NO; NO then forms NO₂ in air. Due to non-availability of enough oxygen the carbon fuel does not burn completely into CO₂ and water; toxic CO and hydrocarbons are produced.

Catalytic converter

A catalytic converter is used in the exhaust system of automobiles to reduce emissions. The catalysts are platinum, palladium and rhodium, coated on a honeycomb with a large surface.

Three functions

Result

Toxic CO, NOₓ and unburnt fuel are turned into CO₂, N₂ and water. CO₂ still comes out and adds to global warming, so fuel saving and electric vehicles are still needed.

Definition

Photosynthesis is the reaction between carbon dioxide and water to produce glucose and oxygen in the presence of chlorophyll, using energy from light.

How plants control pollution

Why deforestation is harmful

As human beings cut down forests, the capacity of trees to remove CO₂ from the air is diminished. So planting trees (such as Pakistan's tree-plantation campaigns) is a key strategy against climate change and smog.

Know the air quality

Check the air quality index (AQI): under 50 is good; above 150 unhealthy; over 300 hazardous.

Steps when air quality is bad

Extra care for high-risk people

Children, the elderly, heart and lung patients, diabetics and outdoor workers should take these steps first.

Personal habits

Do not burn rubbish; keep heaters and stoves serviced and rooms ventilated; avoid smoking; use public transport.