Air Pollution and its Control — Revision Notes

⚡ 30-Second Revision

Air Pollutants: — Harmful substances in air (gases, PM).
Primary Pollutants: — Directly emitted ($SO_2$, CO, $NO_x$, PM, Lead, VOCs).
Secondary Pollutants: — Formed in atmosphere (Ground-level $O_3$, PAN).
Sources: — Vehicular, industrial, domestic combustion, natural (volcanoes).
Effects: — Respiratory/cardiovascular diseases, neurological damage (Lead), acid rain, smog, plant damage.
Control Devices:

- Electrostatic Precipitator (ESP): Removes particulate matter (>99% efficiency) by charging and collecting. - Scrubber: Removes gaseous pollutants ($SO_2$) using water/lime spray. - Catalytic Converter: In vehicles, converts CO, HCs, $NO_x$ to $CO_2$, $H_2O$, $N_2$. Requires unleaded petrol (lead inactivates catalysts).

Noise Pollution: — Unwanted high-level sound. Measured in dB. Causes stress, hearing loss. Control: sound-absorbing materials, green belts.

2-Minute Revision

Air pollution involves harmful substances contaminating the atmosphere, originating from natural events or, more significantly, human activities like burning fossil fuels. Pollutants are categorized as primary (directly emitted, e.

g., $SO_2$, CO, PM) or secondary (formed in the atmosphere, e.g., ground-level ozone). These pollutants cause severe health issues, including respiratory and cardiovascular diseases, and neurological damage from lead.

They also lead to environmental problems like acid rain, which damages ecosystems and infrastructure, and smog, reducing visibility and harming health. Key control technologies include Electrostatic Precipitators (ESPs) for particulate matter, which charge particles for collection; Scrubbers for gaseous pollutants like $SO_2$, using liquid sprays for absorption; and Catalytic Converters in vehicles, which convert toxic gases into less harmful ones, necessitating unleaded petrol to prevent catalyst inactivation.

Noise pollution, another environmental concern, is controlled by reducing sources and using sound-absorbing materials.

5-Minute Revision

Air pollution is the presence of harmful substances in the atmosphere, impacting living organisms and the environment. These pollutants are classified into primary pollutants, directly emitted from sources (e.

g., sulfur dioxide ($SO_2$) from power plants, carbon monoxide (CO) from incomplete combustion, nitrogen oxides ($NO_x$) from vehicles, particulate matter (PM) from industries, and lead), and secondary pollutants, formed through atmospheric reactions (e.

g., ground-level ozone ($O_3$) and peroxyacetyl nitrate (PAN) from $NO_x$ and VOCs in sunlight).

Effects of Air Pollution:

Human Health: — Respiratory diseases (asthma, bronchitis, lung cancer), cardiovascular issues, neurological damage (lead), reduced oxygen transport (CO forming carboxyhemoglobin).
Plants: — Reduced growth, chlorophyll damage, acid rain effects.
Materials: — Corrosion of buildings and monuments (acid rain).
Environment: — Acid rain, smog (photochemical and industrial), global warming contribution.

Control Measures:

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For Particulate Matter:

* Electrostatic Precipitator (ESP): Used in thermal power plants. High voltage electrode creates corona, charging dust particles. Charged particles move to grounded collecting plates. Efficiency >99%. * *Example:* An ESP reduces $100,\text{g}$ of dust to less than $1,\text{g}$ per unit volume of air.

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For Gaseous Pollutants:

* Scrubber: Removes $SO_2$. Exhaust gas passes through water or lime slurry spray. $SO_2$ reacts with lime to form calcium sulfate/sulfite. * *Example:* $SO_2 + CaCO_3 \rightarrow CaSO_3 + CO_2$.

* Catalytic Converters: In automobiles, with platinum, palladium, rhodium catalysts. Convert unburnt hydrocarbons to $CO_2$ and $H_2O$; CO to $CO_2$; $NO_x$ to $N_2$. Crucially, requires unleaded petrol as lead inactivates catalysts.

* *Example:* $2CO + O_2 xrightarrow{\text{Catalyst}} 2CO_2$.

Noise Pollution: Unwanted high-level sound. Measured in decibels (dB). Causes hearing loss, stress, sleep disturbance. Control involves sound-absorbing materials, regulating horn use, and green belts. Understanding these mechanisms and their specific applications is vital for NEET.

Prelims Revision Notes

Air pollution refers to the presence of harmful substances in the atmosphere. These are categorized as primary pollutants (emitted directly, e.g., $SO_2$, CO, $NO_x$, PM, Lead, VOCs) and secondary pollutants (formed in the atmosphere, e.g., ground-level $O_3$, PAN). Major sources include vehicular emissions, industrial activities, and burning of fossil fuels.

Key Pollutants and their Effects:

Particulate Matter (PM2.5, PM10): — Causes respiratory problems (asthma, bronchitis), cardiovascular diseases. Can penetrate deep into lungs.
Sulfur Dioxide ($SO_2$): — Respiratory irritation, acid rain precursor (from burning sulfur-rich fossil fuels).
Nitrogen Oxides ($NO_x$): — Respiratory irritation, acid rain precursor, component of photochemical smog (from high-temperature combustion).
Carbon Monoxide (CO): — Highly toxic, binds to hemoglobin to form carboxyhemoglobin, reducing oxygen transport. Causes headaches, dizziness, death (from incomplete combustion).
Ozone ($O_3$) (ground-level): — Secondary pollutant, respiratory irritant, causes eye irritation, damages plants (component of photochemical smog).
Lead (Pb): — Neurotoxin, especially harmful to children, causes neurological damage (historically from leaded petrol, now industrial).

Environmental Phenomena:

Acid Rain: — Caused by $SO_2$ and $NO_x$ reacting with water to form $H_2SO_4$ and $HNO_3$. Damages ecosystems, buildings.
Smog:

* Industrial Smog (Sulfurous Smog): From $SO_2$ and particulates, common in cold, humid conditions. * Photochemical Smog: From $NO_x$, VOCs, and sunlight, forms ground-level $O_3$ and PAN.

Control Technologies:

Electrostatic Precipitator (ESP): — Removes particulate matter from industrial exhaust. Works by charging particles and collecting them on charged plates. Efficiency >99%.
Scrubber: — Removes gaseous pollutants like $SO_2$. Exhaust gas passed through a spray of water or lime slurry, which absorbs/reacts with $SO_2$.
Catalytic Converter: — Used in automobiles. Contains Pt, Pd, Rh catalysts. Converts CO to $CO_2$, HCs to $CO_2$ and $H_2O$, $NO_x$ to $N_2$. Requires unleaded petrol because lead inactivates the catalysts.

Noise Pollution: Unwanted sound. Measured in decibels (dB). Causes hearing impairment, stress, hypertension. Control measures include using sound-absorbing materials, regulating noise sources, and planting green belts.

Vyyuha Quick Recall

Please Stop Noxious Carbon Outbursts, Let's Eliminate Smog Completely!

Particulate Matter, Sulfur Dioxide, Nitrogen Oxides, Carbon Monoxide, Ozone, Lead (major pollutants). Electrostatic Precipitator, Scrubber, Catalytic Converter (major control devices).