Environmental Chemistry — Long Questions

Pollutants and their Harmful Effects

No. Pollutants Harmful Effects

i. 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 wild fires also occur.

ii. Carbon monoxide It is extremely poisonous gas that can cause suffocation and death. Carbon monoxide is very toxic gas that stops the red blood cells in animal's blood from carrying oxygen that ·body needs.

iii. 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.
NO, NO2

iv. Oxides of sulphur (SOx), SOx irritates the eyes and causes breathing difficulties and acid rain.
SO2, SO3

v. Hydrocarbons They can cause pneumonia, coughing, many other breathing and lung diseases. They also cause global warming.

vi. Particulate matter Irritates the eyes and can also cause severe breathing problems for people with asthma. It also makes clothes dirty. Also, visibility is reduced because it produces haze in the air.

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

viii. Smog It can lead to health complications like allergies, asthma and lung infections. Inhibits the proper growth of plants.

Greenhouse Effect The process warming up of the Earth's surface due to covering effect of man - made carbon dioxide, methane, water vapours and other gases in the atmosphere is called Greenhouse Effect.

Phenomenon The sun emits short wave length radiation (UV) that passes through greenhouse gases to heat the surface of the Earth. At night the hot Earth's surface emits infrared radiation (IR) that is mostly absorbed by green house gases. This process of absorption prevents the radiation to reach space, reducing the speed at which the Earth can cool off. This increases the temperature of the Earth and causes global warming.

Effects of Greenhouse effect

i. Rise in Sea level
Higher temperature will make the water of the seas and oceans expand. Ice melting in the Antarctic and Greenland will flow into the sea and it results in higher sea levels. This phenomenon will threaten the low-lying coastal areas of the world such as the Netherlands and Bangladesh.

ii. Increase in Rainfall
There may be enormous increase in rainfall in a few regions which may increase the sea level. This ultimately will cause worldwide floods endangering survival of living species.

iii. Effects on Agriculture
The changes in the weather will affect the types of crops grown in different parts of the world. Some crops such as wheat and rice grow better in higher temperature but other plants such as maize and sugar cane do not.

iv. Hot summer and winter
In moderate region, the winter will be shorter and warmer and the summer will be longer and hotter

Air Quality Index

Definition of AQI Air quality index(AQI) is a rating system that shows how bad is the atmosphere around you.

Beneficial AQI An (AQI) value under 50 is considered good in quality. This means that is safe for you to spend time outdoors without posing a risk to your health.

Hazardous AQI As the (AQI) number increases, so does the risk to health. An (AQI) over 300 is considered hazardous. Children under 18, adults over 65, people with chronic heart or lung disease and diabetic people are high risk groups. Outdoor workers can also be considered at higher risk because of prolonged exposure.

Definition of AQI Air quality index(AQI) is a rating system that shows how bad is the atmosphere around you.

Beneficial AQI An (AQI) value under 50 is considered good in quality. This means that is safe for you to spend time outdoors without posing a risk to your health.

Hazardous AQI As the (AQI) number increases, so does the risk to health. An (AQI) over 300 is considered hazardous. Children under 18, adults over 65, people with chronic heart or lung disease and diabetic people are high risk groups. Outdoor workers can also be considered at higher risk because of prolonged exposure.

Control Measurements

The following steps should be taken when air quality is bad:

i. Reduced the time you spend outdoors. Also reduce the intensity of outdoor activity. According to experts the changes of being affected by unhealthy atmosphere increase the longer a person spends outdoors and the more laborious the activity.

ii. If you are forced to go out then consider wearing a mask. Unfortunately, not all the mask provides adequate safety against particulate matter. Cloth or dust mask may not effectively filter out the finer particles. However, well fitted N95 masks have better filtration capabilities and may be safer to use.

iii. Keep your indoor healthy by keeping the windows and doors closed. If it is difficult to maintain clean air in the entire room, then create a clean room by switching on air conditioner or air cleaner

iv. If you experience such symptoms that worry you, talk to your doctor

v. Install carbon monoxide detector to detect the increased level of carbon monoxide. These higher levels of CO may occur due to faulty fuel burning appliances.

Effects Breathing in polluted air by these high risk groups may affect their lungs, heart and brain. Air pollutants can enter their blood stream and can cause coughing or itching of eyes which may lead to poor quality of life hospitalization, cancer or even premature death.

Huge amount of pollutant gases are thrown out in the atmosphere by burning fossil fuels. Automobiles, aeroplanes, industrial machines and coal-fired electricity generating plants, etc. are mainly responsible for the extremely polluted air especially in big cities. Scientists have developed a number of different ways to control this menace of pollution.

i. Tree Plantation

Planting trees is thought to be very helpful in removing the air pollution. A well-known process carried out by plants is photosynthesis in which plants clean the air through absorption of carbon dioxide and releasing oxygen. This famous reaction takes place in the presence of sunlight and it is catalyzed by chlorophyll, the green pigments present in leaves.

6 CO2(g) + 6H2O(l) → (Chlorophyll/Sunlight) → C6H12O6(s) + 6O2(g)

The particulate matter present in the atmosphere is also removed by plants when it deposits on leaves, branches and trunk surfaces.

ii. Catalytic Converters

Catalytic converters are used in the exhaust system of modern-day automobiles to reduce the emissions from an internal combustion engine. Due to non-availability of enough oxygen the carbon fuel in engine does not burn completely into carbon dioxide and water. Thus, toxic by-products like CO and hydrocarbons are produced.

A three-way catalytic converter performed the following three functions simultaneously.

1. It reduces nitrogen oxides into elemental nitrogen and oxygen.
2NO x(g) → N2(g) + xO2(g)

2. It oxidizes CO to CO2:
2CO(g) + O2(g) → 2CO2(g)

3. It oxidizes hydrocarbons into CO2 and H2O
CxHy2+(g) + 2O2(g) → x CO2(g) + 2H2O(l)

iii. Flue gas desulfurization process

The emission of sulphur dioxide can be decreased either by using fuels which have significantly less sulphur contents or using flue gas desulfurization process. This process can remove sulphur dioxide gas from the exhaust gases of fossil fuel. Flue gas is the mixture of waste gases produced when fossil fuels are burnt in power plants. The desulfurization process involves the addition of adsorbents like calcium oxide which can remove upto 95% of the sulphur dioxide from the flue gas.

iv. Use of harmless renewable resources

To discourage the excessive use of fossil fuels in our daily lives it is urgently required to use the renewable resources to meet our energy needs. Renewable resources are those resources that can continue to exist despite being consumed over a period of time even as they are used.

Air Quality Index

Air quality index (AQI) is a rating system that shows how bad is the atmosphere around you. An AQI below 50 is considered good in quality, meaning it is safe for you to spend time outdoor without posing a risk to your health. As the AQI number increases, so does the risk to health.

Quality Rating Considerations
0 - 50 Good
51 - 100 Moderate
101 - 150 Unhealthy for sensitive group
151 - 200 Unhealthy
201 - 300 Very unhealthy
301 + Hazardous

High Risk Group

An AQI over 300 is considered as hazardous. Children under 18, adults over 65, people with chronic heart or lung disease and diabetic individuals are considering high risk group. Outdoor workers can also be considered at higher risk because of prolonged exposure

Effects of Hazardous AQI

Breathing polluted air can effect the lungs, heart and brain. Air pollutant can enter their blood stream and can cause coughing or itching of eyes which may lead to poor quality of life, hospitalization, cancer or even premature death

Major causes of high AQI

High AQI is due to following factors

i. Crop Burning

Farmers burn their crops in fields after harvesting. They burn the crop residues to make land prepare for next crop.

ii. Fossil fuel Burning

Fossil fuels like petroleum products, coal, natural gas etc. are burnt to get energy for transportation, heat and electricity generation

iii. Destruction of Green-Land area:

Concrete structures has been installed in place of green land area Decrease in number of plants increase AQI.

iv. Industrial emission

Smoke coming from chimneys of industries is playing a major role for bad AQI.

The air quality index (AQI) in Pakistan often remain moderate during hot summer days due to following reasons.

i. High Temperature

High temperature creates surface heating resulting in mixing up of layers of air. This mix up dilute air pollutants in atmosphere.

ii. Reduced Photochemical Reactions

Hot summer reduces the precursor of photochemical reactions like volatile organic compounds and nitrogen oxides (NOx). They cannot combine helping in less ozone formation

iii. Low Humidity

Low humidity in many regions decreases formation of secondary aerosols (major component of particulate matter)

iv. Wind Pattern

Hot weather often brings strong winds in plain areas. These winds disperse transport pollutants away from urban center.

v. Chemical Kinetics of pollutant

Dry and windy conditions due to reduced moisture render formation of secondary pollutants

Climate change has significantly impacted Pakistan over last five years causing environment, economic and agriculture losses. Following are effects of climate change.

i. Heatwaves

Pakistan experienced record breaking heatwave since last five years. Temperature exceeds 50°C in some areas of Pakistan.

ii. Rise in sea level

High temperature will make water of seas and oceans expand. Ice melting in Antarctic and Greenland will flow into sea and it result in higher sea level. This phenomenon will threaten low lying coastal areas of Pakistan.

iii. Increase in Rainfall

There may be sufficient increase in rainfall in a few regions that may increase sea level. This ultimately will cause worldwide flood endangering survival of living species.

iv. Effects on agriculture

It will affect type of crops grown in different parts of Pakistan. Some crops such as wheat and rice grow better in higher temperature but other like maize and sugarcane do not.

i. Human activities

Millions of tonnes of pollutants are emitted into the atmosphere each year as a result of human activities. The major activity among them is the completed and incomplete combustion of fossils fuels which along is responsible for most of our pollution problem.

ii. Combustion

Burning of fossil fuels (oil natural gas, coal) produce carbon dioxide carbon monoxide, NOx, SOx, CH4, ash, smoked and suspended particles. Many of these pollutants are also released into the air by natural process e.g. volcanic eruption releases large quantities of CO2, SO2 and particulates. Methane is released in the air by the decomposition of vegetation. It is also present in waste gases produced during digestion in animals.

iii. Over Population

Rapid growth of population, urbanization, industrialization and transportation are the main factors which are responsible for environmental pollution. All these factors are increasing in every city of the world especially in the last half century. These pollutants are affecting the environment very badly.

iv. Ozone

Another pollutant ozone (O3) is formed when heat and sunlight cause chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (hydrocarbons).

Definition

When rain water has pH less than 5.6, it is known as acid rain.

Historical Background

In 1852, Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester, England. He is sometimes referred to as the "Father of Acid Rain.

Causes

Burning of fossil fuels releases harmful gases into the atmosphere. These gases (SO2,SO3) are produced due to the presence of sulphur in the fossil fuels. SO2 is converted to SO3 in the presence of oxides of nitrogen of the atmosphere. Oxides of nitrogen are produced mostly by the direct combination of atmospheric oxygen and nitrogen in the industrial and domestic combustion processes. They are also produced by the combustion of atmospheric nitrogen and oxygen in the presence of lightning. Significant amount of nitrogen oxides is produced by the reactions taking place in automobile engines.

Formation These gases mix with the moisture that is always present in the air to form acid droplets. Wind can carry these acidic droplets to huge distance.

Finally, these droplets return to the ground as acid rain, acid hail, snow and even fog. Acid rain looks, feels and tastes like clean rain. Its corrosive nature causes widespread damage to the environment.

S(s) + O2(g) → SO2(g)
2SO2(g) + O2(g) → 2SO3(g)
SO3(g) + H2O(l) → H2SO4(aq)
N2(g) + O2(g) → 2NO(g)
2NO(g) + O2(g) → 2NO2(g)
2NO2(g) + H2O(l) → HNO3(aq) + HNO2(aq)

Effects of Acid Rain

Acid rain causes a number of adverse effects. It tends to increase acidity of the soil, threatens human and aquatic life, destroy forests and reduces agricultural productivity. Besides it corrode building, monuments, statues, bridges and railings. Most important adverse effects of acid rain are as follows:

i. Soil

Acid rain makes soil more acidic. It dissolves and washes away nutrients present in the soil which are needed by plants. It can also dissolve toxic substances such as aluminium and mercury which are naturally present in the soil.

ii. Plants

Many plants cannot live or grow in acidic soil. It can damage vegetation and plants. Tree roots hold the soil together on bills and mountain areas. If the trees are destroyed, then the soil is washed away and new plants cannot grow there.

iii. Aquatic Life

Acid rain falls into drains streams, lakes, marshes, rivers and damages the aquatic life. Acid rain can make water too acidic for animals to live in. Due to this, many lakes and rivers no longer have fish.

iv. Human Health

The acidification of surface water does not affect life directly. However, toxic substances leached from the soil can pollute land water supplies and damage human health.

v. Agriculture

Crops are less affected by the acid rain than forest. Farmers can prevent acid rain damage by monitoring the conditions of the soil and when necessary adding crushed lime to neutralize the acid.

vi. Human-made Structure

Acid rain and the dry deposition of acidic particles damage buildings, statues, automobiles and other structures made of stone, metal etc. Historical buildings like Parthenon in Athens (Greece) and the Taj Mahal in Agra (India) are deteriorating due to acid rain.