Air Pollution

Air is a mixture of gases and in this mixture is water vapour (nitrogen – 78%, oxygen – 21%, CO2
– 0.04% and inert gases – 1%)
Air pollution refers to the contamination of the air by harmful substances, including gases,
particulate matter, and biological molecules, which can adversely affect human health, ecosystems,
and the climate.
Air pollutants can be categorized into two major sources; natural and anthropogenic.
Natural sources refers to pollution as a result of naturally occurring events such as volcanoes, dust
storms and forest fires. While natural sources can contribute significantly to air pollution, they are
generally more diffuse and less controllable than anthropogenic sources.
Anthropogenic refers to pollution as a result of human activities. These sources are directly linked
to industrialization, urbanization, transportation, agriculture, and other human-driven processes.
Anthropogenic pollution is often more concentrated and localized, making it a significant
contributor to environmental degradation and health issues.
Types and sources of (anthropogenic) gaseous air pollutants
 Sulfur oxides – It is produced from combustion sources such as coal-fired power plants
and industries. This oxidizes the Sulfur to form Sulphur oxide compounds including SO3
and SO2. One effect of sulfur oxide pollution is the formation of acid rain, which results
when sulfur dioxide (as well as other gases such as nitrogen dioxide) reacts with water and
atmospheric oxygen to produce sulfuric acid (H2SO4), acid-rain's main constituent.
Acid rain has several detrimental effects on human health and the environment, including
respiratory problems, cardiovascular issues, skin or eye irritation, weakened immune
systems, damaging aquatic ecosystems by killing fish and other organisms, harming forests
and vegetation, corroding buildings and structures, and impacting soil quality by altering
its chemistry, ultimately affecting the entire food chain across affected areas.
 Carbon monoxide - CO is a product of the incomplete combustion of carbon-containing
compounds. CO is majorly produced in transportation, also wood and tobacco.
 Volatile Organic Compounds - (VOCs) are a group of carbon-based chemicals that easily
evaporate at room temperature. They are commonly found in a wide range of products and
environments, and they can have significant impacts on indoor air quality, human health,
and the environment.
 Hydrocarbons – major source of this gaseous pollutant is transportation. They include
methane CH4, propane C2H8, ethane C2H6, butane C4H10etc.
 Carbon dioxide – It is a product of further oxidation of carbon monoxide. Because they are
heavier than oxygen and nitrogen, they are more concentrated close to the earth's surface
and can be thought to form a "canopy" of gas, similar to the glass canopy of a greenhouse
and with a similar result: Heat is trapped that would otherwise be lost.
 Chlorofluorocarbons
 Lead – like other metals lead can accumulate in the body and is especially destructive to
the nervous system. Lead poisoning can lead to brain damage causing learning disabilities,
seizures and death at high concentrations.
Airborne lead particles are heavy and therefore occur close to the source such as in paint
flaking off from a contaminated window.
 Oxides of nitrogen (NO and NO2) – Oxides of nitrogen are majorly produced from
transportation and coal-fired power plants. Nitric oxide is formed by the combustion of
nitrogen-containing compounds during burning of fossil fuels and in transportation. NO, is
then oxidized further to NO2.
 Photochemical pollutants are produced when sunlight initiates chemical reactions among
the oxides of nitrogen (NOX), hydrocarbons and other components of air. These pollutants
include ground-level ozone, NO2 and hydroxyl radicals (OH).
 Ozone – It is the result of chemical reactions in the ambient air
There are two types of ozone – ground-level ozone in the (troposphere layer) and
stratospheric ozone in the stratosphere layer.
Ground-level ozone is a major pollutant and forms the primary constituent of smog.
(Smog is a type of air pollutant referring to a brown haze of photochemical pollutants in
urban areas that irritates membranes and reduces visibility.)
Ground-level ozone damages foliage of plants and is associated with increased
susceptibility of plants to diseases, pests and environmental stresses.
Ozone (O3) molecule is highly reactive and it also erodes rubber and irritates the
respiratory system.
The stratospheric ozone occurs naturally and serves primary functions such as protecting
the surface of Earth from high levels of ultraviolent radiation.
The primary stratospheric pollutants include - ozone-depleting substances (ODSs) such as
chlorofluorocarbons & halons, greenhouse gases (GHGs) such as CO2, methane CH4, &
nitrous oxide N2O, and aerosols from natural and anthropogenic sources such as black
carbon and soot, sulfate aerosols.
Stratospheric Ozone layer depletion leads to 1. UV- B radiation causing skin cancer and
eye damage (cataracts), weakened immune systems in both animals and humans and crop
damage.
The GHGs and aerosols cause global warming.

 Particulates – They are often described by size. PM2.5 refers to “fine” particulate matter,
and PM10, referring to “coarse” particulates which are bigger than the fine ones. Generally,
particulates include,
Dust, consisting of solid particles such as cement dust, wood dust, and sand.
Fume, that is, solid particles formed by the condensation of vapors by sublimation,
distillation, calcination, or other chemical reactions. Examples include zinc and lead
oxides.
Mist, liquid particles formed by the condensation of a vapor and sometimes by chemical
reaction as, for example, the formation of sulfuric acid mist.
 Smoke, which consists of solid particles formed by incomplete combustion of
carbonaceous materials.
Spray, which is a liquid particle formed by the atomization of a parent liquid.

Indoor air pollution

Indoor air pollution refers to the contamination of indoor air by harmful substances, which can
adversely affect the health and well-being of occupants.
Indoor air pollution can be more dangerous than outdoor pollution because people spend a
majority of their time indoors, and pollutants can accumulate to higher concentrations in
enclosed spaces.
Sources include –
 Burning solid fuels (wood, coal, dung, crop residues) in traditional stoves or open fires.
 Tobacco smoke.
 Building materials such as asbestos (mesothelioma, a rare type of cancer), paints and
varnishes.
 Biological pollutants - Mold and Mildew- Damp environments promote the growth of
mold, which releases spores and mycotoxins.
o Dust Mites and Pet Dander: These allergens can trigger asthma and
allergic reactions.
o Bacteria and Viruses: Poor ventilation can lead to the buildup of
pathogens in indoor air.
  Outdoor Sources: Radon: A naturally occurring radioactive gas that can enter homes
through cracks in the foundation.
Common Indoor Pollutants – CO, particulate matter, NOx, volatile organic compounds, radon.

(Primary and secondary types of pollutants) – read on this

Effects of Air Pollution
Health effects.
Air pollution has a variety of health effects, ranging from immediate to delayed and from slight
irritation to potentially life-threatening conditions.
Immediate health effects include, shortness of breath, eye irritation and even death.
Incidences of colds, coughs, rhinitis (nose irritation) among other symptoms.
Chronic health effects include – chronic bronchitis, emphysema, asthma attacks, lung cancer,
cardiovascular diseases.
Effects on plants and non-human animals
 Damage to Leaves - Pollutants like ozone (O₃) and sulfur dioxide (SO₂) enter leaves
through tiny pores, causing yellowing, spotting, and reduced photosynthesis.
 Reduced Growth - Acid rain (from SO₂ and NOₓ) leaches nutrients from soil, stunting
plant growth.
 Ecosystem Disruption - Sensitive species, like lichens, which mainly obtain
nourishment from the air, rain and snow make them extremely vulnerable to air pollution,
causing them to disappear hence, reducing biodiversity.
Effects on Animals
 Health Problems - Animals breathe in pollutants like particulate matter
(PM) and ozone, leading to respiratory and heart issues.
 Toxic Chemicals - Heavy metals like lead and mercury accumulate in animals, causing
poisoning and reproductive issues. Example: Eagles suffer lead poisoning from eating
contaminated prey.
 Habitat Damage - Acid rain harms aquatic life by acidifying water bodies. Example:
Fish in acidified lakes struggle to reproduce.
 Food Chain Disruption - Pollution damages plants, reducing food for herbivores and, in
turn, predators. Example: Insects decline due to ozone, reducing food for birds and bats.
 Behavioral Changes

Effect on materials
  Corrosion of Metals - SO₂ reacts with moisture in the air to form sulfuric acid (H₂SO₄),
which corrodes metals like iron, steel, and copper. Example: Bridges and statues made of
metal develop rust and weaken over time. Metal roofs and car exteriors corrode faster in
polluted urban areas.
 Deterioration of Stone and Concrete - Acid rain (formed from SO₂ and NOₓ) dissolves
calcium carbonate in limestone, marble, and concrete, causing erosion and loss of detail.
Particulate Matter (PM) - Dust and soot settle on surfaces, staining and degrading stone
and concrete.
 Damage to Paints and Coatings - Ozone breaks down the chemical bonds in paints and
coatings, causing them to crack and peel. Dust and soot stick to painted surfaces, making
them dirty and reducing their lifespan.
 Weakening of Rubber and Plastics - Ozone reacts with rubber, causing it to become
brittle and crack. Example: Car tires and rubber seals degrade faster in areas with high
ozone levels.
 Ultraviolet (UV) Radiation - Air pollution enhances the effects of UV radiation,
breaking down plastics and synthetic materials. Example: Plastic outdoor furniture
becomes brittle and discolored in polluted environments.
 Economic Costs - Maintenance and Repair - Frequent cleaning, repairs, and
replacements of materials increase costs for individuals, businesses, and governments.
 Loss of Cultural Heritage - Historic monuments and artifacts are irreversibly damaged,
leading to a loss of cultural heritage.

Air Pollution Control

Industry emission control
 Bag filters – Bag filters are primarily used to remove dust and fine particles from exhaust
gases in industrial processes. They are especially effective for capturing particles smaller
than 10 micrometers (PM₁₀) and even finer particles like PM₂.₅.
 Cyclones - They are simple, cost-effective devices that separate dust, particles, and other
pollutants from gas streams using centrifugal force before they are released into the
atmosphere.
 Electrostatic precipitators - Use electric charges to remove particulate matter from
industrial emissions. Used in cement factories and steel plants.
 Scrubber - Devices that remove pollutants like sulfur dioxide (SO₂) and particulate matter
(PM) from industrial exhaust gases.
 Mobile sources
Use of new-combustion technologies (clean coal technologies)
 Magnetohydrodynamics - MHD power generation involves converting the thermal energy
of coal combustion directly into electricity using a conducting fluid (typically ionized gas
or plasma) and a magnetic field. The process can be integrated with conventional steam
turbines to create a combined-cycle system, significantly improving overall efficiency.
  Fluidized bed combustion (FBC) - FBC involves burning coal in a bed of solid
particles (e.g., sand, limestone, or ash) that are suspended by an upward flow of air or gas.
This creates a fluid-like state that enhances combustion efficiency and heat transfer while
minimizing emissions.
 Chemical Looping Combustion (CLC) – It is a novel technology that separates oxygen
from air using a metal oxide as an oxygen carrier, allowing for efficient combustion with
inherent CO₂ capture.
 Low-NOx Burners - They are designed to minimize the formation of nitrogen oxides (NOₓ)
during combustion by controlling flame temperature and oxygen availability.
 Oxy-Fuel Combustion – It uses pure oxygen instead of air for combustion, reducing the
volume of flue gas and eliminating nitrogen from the process.
 Catalytic Combustion- It uses catalysts to enable complete combustion of fuel at lower
temperatures, reducing the formation of pollutants.
 Hydrogen Combustion - uses hydrogen as a fuel, producing only water vapor as a
byproduct and eliminating CO₂ and other pollutants.
 Carbon Capture and Storage (CCS) - It captures carbon dioxide (CO₂) emissions from
industrial sources and stores them underground to prevent their release into the atmosphere.
Innovation policy and regulatory measures
 Cap-and-Trade Systems - A market-based approach that sets a cap on emissions and
allows companies to buy and sell emission allowances.
 Low Emission Zones (LEZs) and Zero Emission Zones (ZEZs) - Areas where only
low- or zero-emission vehicles are allowed, reducing traffic-related pollution.
 Pollution Taxes and Incentives - Taxes on polluting activities (e.g., carbon tax) and
incentives for clean technologies (e.g., subsidies for electric vehicles).
 Integrated Air Quality Management Plans - Comprehensive plans that address multiple
pollution sources (e.g., transport, industry, agriculture) and involve stakeholders at all
levels.
Nature based Solutions
 Urban forests and green corridors - involves planting trees and creating green spaces in
cities to absorb pollutants and improve air quality.
 Phytoremediation - uses plants to absorb and break down pollutants from soil, water,
and air. Sunflowers and willow trees, for instance, are employed to clean up
contaminated sites and improve air quality in polluted areas.
 Blue-green infrastructure - combines water management (blue) and vegetation (green)
to reduce pollution and enhance urban resilience. Projects like rain
gardens and constructed wetlands not only improve air quality but also manage
stormwater and reduce urban heat islands.
 Agroforestry and afforestation.
Controlling indoor air pollution – (Check on this)
Assignment 3: Discuss legal and social solutions that Kenya has taken to enhance air pollution
control.

Noise Pollution
Noise pollution refers to the presence of excessive or harmful levels of sound in the environment
that disrupts the natural balance and causes discomfort to living beings.
Sound can be described in terms of its loudness, pitch or frequency. (Sound is longitudinal)
Loudness is measured by decibels (dB), and the lowest sound a human ear can detect is set at 0dB.
Pitch or frequency is a measure of how high or low a sound is, and is measured in cycles (i.e
waves) per second commonly termed as Hertz (Hz).
In cast iron, sound waves travel at about 3440 m/sec. What is the wavelength of a sound from a
train if it rumbles at 50 cycles/sec and one listens to it placing an ear on the track?

It is typically generated by human activities such as industrial operations, transportation (like cars,
airplanes, and trains), construction work, loud music, and urban development.
Prolonged exposure to high levels of noise can have detrimental effects on human health, including
hearing loss, stress, sleep disturbances, and even cardiovascular issues.
Temporary threshold shift is a momentary decrease in our ability to hear, while permanent
threshold shift is a permanent loss of hearing.
Additionally, noise pollution can disrupt wildlife, interfering with animal communication,
breeding patterns, and habitat use.
As urbanization and industrialization continue to grow, managing and mitigating noise pollution
has become a critical environmental and public health challenge.
Noise is partly subjective. (why do you think so)

Noise control
Controlling noise at the source - Reducing noise at the source. This includes using quieter
machinery, implementing soundproofing technologies in industries, and enforcing vehicle noise
limits through improved engine designs and exhaust systems.
Transmission control - Focuses on reducing the spread of noise. Constructing sound barriers along
highways, using noise-absorbing materials in buildings.
Protecting the person - In workplaces, installing acoustic panels and using noise-dampening
flooring can help control indoor noise pollution. For individuals, wearing earplugs or noise-
canceling headphones in high-noise environments.
Policies and Legal framework. (Do further research on this)