Atmospheric Pollution — Revision Notes

⚡ 30-Second Revision

Primary Pollutants: — Directly emitted (CO, $SO_2$, $NO_x$, PM, hydrocarbons).
Secondary Pollutants: — Formed in atmosphere ($O_3$ (tropospheric), PAN, $H_2SO_4$, $HNO_3$).
Acid Rain: — pH < 5.6. Caused by $SO_2 \rightarrow SO_3 \rightarrow H_2SO_4$ and $NO_x \rightarrow HNO_3$.
Photochemical Smog: — $NO_x + VOCs + Sunlight \rightarrow O_3 + PAN + Aldehydes$. Warm, sunny conditions.
Classical Smog: — Smoke + Fog + $SO_2$. Cool, humid conditions.
Greenhouse Gases: — Trap heat ($CO_2$, $CH_4$, $N_2O$, CFCs, tropospheric $O_3$).
Ozone Depletion: — Stratospheric $O_3$ destroyed by CFCs ($cdot Cl$ radical).
CO Toxicity: — Binds to hemoglobin ($Hb$) 200-250x stronger than $O_2$, forming carboxyhemoglobin ($HbCO$).
PM Effects: — Respiratory & cardiovascular diseases, reduced visibility.
Control: — Catalytic converters (gases), Scrubbers ($SO_2$), Electrostatic precipitators (PM).

2-Minute Revision

Atmospheric pollution involves harmful substances in the air, categorized as primary (directly emitted like CO, $SO_2$, $NO_x$) or secondary (formed via reactions, e.g., tropospheric ozone, acid rain components).

Key pollutants include sulfur dioxide ($SO_2$) and nitrogen oxides ($NO_x$), which are precursors to acid rain ($H_2SO_4$, $HNO_3$), damaging ecosystems and structures. Carbon monoxide (CO) from incomplete combustion is highly toxic, binding to hemoglobin.

Particulate matter (PM) causes respiratory and cardiovascular issues.

Ozone has dual roles: 'good' stratospheric ozone protects from UV, but 'bad' tropospheric ozone is a pollutant in photochemical smog (formed from $NO_x$ and VOCs in sunlight). Chlorofluorocarbons (CFCs) deplete the stratospheric ozone layer. Greenhouse gases like $CO_2$, $CH_4$, and $N_2O$ trap heat, leading to global warming. Control measures include catalytic converters for vehicular emissions, scrubbers for $SO_2$, and electrostatic precipitators for PM.

5-Minute Revision

Atmospheric pollution is the contamination of air by substances harmful to life and the environment. Pollutants are either primary (directly emitted, e.g., Carbon Monoxide (CO) from incomplete combustion, Sulfur Dioxide ($SO_2$) from fossil fuels, Nitrogen Oxides ($NO_x$) from high-temperature combustion, Particulate Matter (PM)) or secondary (formed in the atmosphere, e.g., tropospheric Ozone ($O_3$), Peroxyacetyl Nitrate (PAN), Sulfuric Acid ($H_2SO_4$), Nitric Acid ($HNO_3$)).

Key Phenomena:

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Acid Rain: — pH < 5.6. Caused by $SO_2$ and $NO_x$ reacting with atmospheric water to form $H_2SO_4$ and $HNO_3$. Damages monuments (e.g., Taj Mahal's marble, $CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + H_2O + CO_2$), forests, and aquatic life.
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Smog:

* Classical Smog (London Smog): Smoke + Fog + $SO_2$. Cool, humid conditions. Causes respiratory problems. * Photochemical Smog (Los Angeles Smog): $NO_x + VOCs + Sunlight \rightarrow O_3 + PAN + Aldehydes$. Warm, sunny conditions. Causes eye irritation, respiratory issues, plant damage.

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Greenhouse Effect & Global Warming: — Greenhouse gases ($CO_2$, $CH_4$, $N_2O$, CFCs, tropospheric $O_3$) trap infrared radiation, warming Earth. Increased anthropogenic emissions lead to enhanced greenhouse effect and global warming.
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Ozone Depletion: — Stratospheric ozone layer ($O_3$) protects from harmful UV-B radiation. CFCs release $cdot Cl$ radicals in the stratosphere, which catalytically destroy $O_3$ molecules ($cdot Cl + O_3 \rightarrow cdot ClO + O_2$; $cdot ClO + O \rightarrow cdot Cl + O_2$). This leads to increased UV-B radiation, causing skin cancer, cataracts, etc.

Health Impacts: CO causes oxygen deprivation by forming carboxyhemoglobin ($HbCO$). $SO_2$, $NO_x$, and PM cause respiratory diseases. Tropospheric $O_3$ irritates eyes and lungs.

Control Measures:

Vehicular Emissions: — Catalytic converters (convert $CO, NO_x$, hydrocarbons to $CO_2, N_2, H_2O$).
Industrial Emissions: — Scrubbers (remove gaseous pollutants like $SO_2$ using liquid absorbents), Electrostatic Precipitators (remove particulate matter by charging and collecting).

Example Reaction: Formation of tropospheric ozone: $NO_2 xrightarrow{h u} NO + O$ $O + O_2 \rightarrow O_3$ This highlights the role of sunlight and primary pollutants in forming secondary pollutants.

Prelims Revision Notes

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Pollutant Classification:

* Primary: Directly emitted. E.g., CO, $SO_2$, $NO$, $NO_2$, PM, unburnt hydrocarbons. * Secondary: Formed by reactions in atmosphere. E.g., Tropospheric $O_3$, PAN, $H_2SO_4$, $HNO_3$.

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Major Pollutants & Sources:

* CO: Incomplete combustion (vehicles, furnaces). * **$SO_2$:** Burning sulfur-containing fossil fuels (thermal power plants, industries). * **$NO_x$ (NO, $NO_2$):** High-temperature combustion (vehicles, power plants).

* PM: Industrial emissions, vehicles, construction, natural dust. * CFCs: Refrigerants, aerosols, fire extinguishers. * **$CH_4$:** Anaerobic decomposition (paddy fields, cattle), natural gas leaks.

* **$CO_2$:** Complete combustion of fossil fuels, deforestation.

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Acid Rain:

* pH < 5.6. Normal rain pH $approx$ 5.6 (due to $H_2CO_3$). * Formation: $SO_2 xrightarrow{O_2} SO_3 xrightarrow{H_2O} H_2SO_4$. $NO_x xrightarrow{H_2O} HNO_3$. * Effects: Corrosion of marble ($CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + H_2O + CO_2$), damage to forests, acidification of lakes.

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Smog:

* Classical Smog (London Smog): Smoke + Fog + $SO_2$. Cool, humid. Reducing smog. * Photochemical Smog (Los Angeles Smog): $NO_x + VOCs + Sunlight \rightarrow O_3 + PAN + Aldehydes$. Warm, dry. Oxidizing smog.

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Ozone:

* **Stratospheric $O_3$ (Good):** 10-50 km altitude. Absorbs UV-B. Depleted by CFCs ($cdot Cl$ radical catalyst: $cdot Cl + O_3 \rightarrow cdot ClO + O_2$; $cdot ClO + O \rightarrow cdot Cl + O_2$). * **Tropospheric $O_3$ (Bad):** Ground level. Secondary pollutant in photochemical smog. Respiratory irritant.

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Greenhouse Effect & Global Warming:

* Greenhouse Gases (GHGs): $CO_2$ (most significant anthropogenic), $CH_4$ (more potent per molecule), $N_2O$, CFCs, tropospheric $O_3$. * Mechanism: Trap infrared radiation, warming Earth. Enhanced by human emissions.

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Health Effects:

* CO: Binds to $Hb$ (carboxyhemoglobin, $HbCO$), causes oxygen deprivation. * **$SO_2$, $NO_x$, PM:** Respiratory problems (asthma, bronchitis), cardiovascular issues. * **UV-B (due to $O_3$ depletion):** Skin cancer, cataracts, immune suppression.

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Control Measures:

* Vehicles: Catalytic converters (convert $CO, NO_x$, hydrocarbons to $CO_2, N_2, H_2O$). * Industries: Scrubbers (for gaseous pollutants like $SO_2$), Electrostatic Precipitators (for particulate matter).

Vyyuha Quick Recall

To remember the main components of Photochemical Smog: PAN, Ozone, Nitrogen oxides, Volatile Organic Compounds. Think: P.O.N.V.O.C. (Pronounced 'Pon-voc') - 'Photochemical Smog is a PONVOC!'