Environmental Issues (Air Pollution)

Atmospheric Pollution (from Environmental Chemistry)

Atmospheric pollution refers to the contamination of the Earth's atmosphere by harmful substances (pollutants) that can adversely affect human health, ecosystems, and climate.

Tropospheric Pollution:

Tropospheric pollution refers to pollution in the lower layer of the atmosphere, the troposphere.

Gaseous Pollutants:

• Carbon Monoxide (CO):
  • Sources: Incomplete combustion of fossil fuels, vehicular exhaust, industrial processes.
  • Effects: Toxic; binds strongly to haemoglobin, reducing oxygen-carrying capacity of blood, leading to respiratory problems and cardiovascular issues.
• Hydrocarbons (HC):
  • Sources: Incomplete combustion, evaporation of fuels, industrial emissions.
  • Effects: Contribute to smog formation (photochemical smog), some are carcinogenic (e.g., benzene).
• Nitrogen Oxides ($NO_x$): ($NO$ and $NO_2$)
  • Sources: High-temperature combustion in engines and power plants, lightning.
  • Effects: Irritant to eyes and respiratory tract, contribute to acid rain and photochemical smog. $NO_2$ is a reddish-brown gas.
• Sulphur Dioxide ($SO_2$):
  • Sources: Burning of fossil fuels (coal, oil) containing sulphur, industrial processes (smelting of ores).
  • Effects: Respiratory problems, damages vegetation, contributes significantly to acid rain.
• Ozone ($O_3$): (In Troposphere)
  • Sources: Formed by photochemical reactions involving $NO_x$ and hydrocarbons.
  • Effects: Highly reactive and toxic; irritant to respiratory tract, damages plants, and contributes to smog.

Particulate Matter (PM):

• Sources: Combustion of fossil fuels, industrial emissions, construction sites, dust storms, smoke from forest fires.
• Types: Includes dust, soot, smoke, mist, fumes.
• Effects: Can penetrate deep into the lungs, causing respiratory and cardiovascular diseases. Smaller particles (PM2.5) are more dangerous. Can also affect visibility and climate.

Acid Rain:

• Formation: $SO_2$ and $NO_x$ react with atmospheric moisture to form sulphuric acid ($H_2SO_4$) and nitric acid ($HNO_3$).
• Effects: Damages aquatic ecosystems, forests, buildings (corrosion of marble), and human health.

Photochemical Smog:

• Formation: A complex mixture formed by photochemical reactions involving $NO_x$, hydrocarbons, and sunlight. Key components include ozone ($O_3$), peroxyacyl nitrates (PANs), and aldehydes.
• Effects: Irritates eyes and respiratory system, damages vegetation, reduces visibility.

Stratospheric Pollution:

Stratospheric pollution primarily refers to the depletion of the ozone layer in the stratosphere.

Ozone Layer Depletion:

• Ozone Layer: Located in the stratosphere (about 15-30 km above Earth), it absorbs most of the Sun's harmful ultraviolet (UV-B) radiation.
• Ozone Depleting Substances (ODS): Primarily Chlorofluorocarbons (CFCs) used in refrigerants, aerosols, and solvents. Other ODS include halons, carbon tetrachloride, and methyl chloroform.
• Mechanism: CFCs rise into the stratosphere, where UV radiation breaks them down, releasing chlorine free radicals ($Cl\cdot$). These radicals catalytically destroy ozone molecules.
  • $CFCl_3 \xrightarrow{UV} Cl\cdot + CFCl_2\cdot$
  • $Cl\cdot + O_3 \rightarrow ClO\cdot + O_2$
  • $ClO\cdot + O \rightarrow Cl\cdot + O_2$
  • Overall: $O_3 + O \xrightarrow{Cl\cdot} 2O_2$
• Effects of Ozone Depletion: Increased exposure to harmful UV-B radiation, leading to skin cancer, cataracts, immune system suppression, and damage to crops and aquatic ecosystems.
• Ozone Hole: A region of severely depleted ozone over Antarctica, particularly during spring.
• Control Measures: International agreements like the Montreal Protocol have phased out the production and use of CFCs.

Air Pollution And Its Control (from Environmental Issues)

Sources and Effects of Air Pollutants (Summary):

• Primary Pollutants: Emitted directly from sources. Examples: $CO$, $SO_2$, $NO_x$, hydrocarbons, particulate matter.
• Secondary Pollutants: Formed in the atmosphere through chemical reactions involving primary pollutants and atmospheric constituents. Examples: $O_3$, PANs, acid rain components.
• Major Air Pollution Issues: Smog (London smog - reducing, photochemical smog - oxidizing), acid rain, greenhouse effect leading to global warming, ozone layer depletion.

Control Measures:

1. Controlling Industrial Emissions:
• Scrubbers: Used to remove gaseous pollutants like $SO_2$. Wet scrubbers use a liquid absorbent (e.g., lime slurry), while dry scrubbers use solid absorbents.
• Electrostatic Precipitators: Used to remove particulate matter from industrial flue gases by imparting an electric charge to the particles and collecting them on oppositely charged plates.
• Catalytic Converters: Used in industrial stacks to convert harmful gases into less harmful ones.
• Switching to Cleaner Fuels: Using fuels with lower sulphur content or alternative energy sources.
2. Controlling Vehicular Air Pollution:
• Catalytic Converters: Installed in vehicles to convert harmful exhaust gases ($CO$, unburnt hydrocarbons, $NO_x$) into less harmful substances ($CO_2$, $H_2O$, $N_2$). This is a key technology for reducing vehicular pollution.

  Reactions: $2CO + O_2 \xrightarrow{Catalyst} 2CO_2$; $C_xH_y + (x+y/4)O_2 \xrightarrow{Catalyst} xCO_2 + (y/2)H_2O$; $2NO_x \xrightarrow{Catalyst} N_2 + xO_2$

• Leaded Petrol: Addition of lead compounds to petrol was used as an anti-knock agent, but these compounds are highly toxic and contribute to lead pollution. Unleaded petrol is now mandatory in many places.
• Fuel Efficiency: Improving fuel efficiency reduces emissions.
• Alternative Fuels: Use of CNG (Compressed Natural Gas), LPG (Liquefied Petroleum Gas), ethanol, and electric vehicles significantly reduces air pollution.
• Public Transportation: Encouraging the use of public transport reduces the number of individual vehicles on the road.
• Emission Standards: Government regulations and emission standards (e.g., Bharat Stage VI in India) enforce limits on pollutants from vehicles.
3. Controlling Indoor Air Pollution: Improving ventilation, using air purifiers, avoiding smoking indoors.
4. Afforestation: Planting trees helps absorb pollutants like $CO_2$ and provides oxygen.

Controlling Vehicular Air Pollution: A Case Study Of Delhi:

Delhi has been facing severe air pollution problems, largely attributed to vehicular emissions, industrial pollution, dust, and agricultural burning. Vehicular pollution is a major contributor.

• Problem: High levels of $CO$, hydrocarbons, $NO_x$, and particulate matter, leading to smog, respiratory illnesses, and poor visibility.
• Control Measures Implemented in Delhi:
  • Phasing out Leaded Petrol: Completed successfully.
  • Switching to Cleaner Fuels: Mandatory use of Compressed Natural Gas (CNG) for public transport (buses, auto-rickshaws) and taxis. This drastically reduced $SO_2$ and particulate matter emissions.
  • Upgradation of Emission Norms: Transition from Bharat Stage II to Bharat Stage VI (equivalent to Euro VI) emission standards for vehicles, mandating advanced catalytic converters and cleaner engines.
  • Improving Public Transport: Expansion of the Delhi Metro network and bus services to reduce reliance on private vehicles.
  • Road Congestion Reduction: Odd-Even scheme (allowing vehicles on alternate days based on registration numbers) implemented during periods of high pollution.
  • Control of Industrial Pollution: Stricter regulations on industrial emissions and use of cleaner technologies.
  • Dust Control Measures: Water sprinkling on roads, covering construction sites.
  • Restrictions on Crop Burning: Efforts to curb stubble burning in surrounding states.
• Impact: While significant improvements have been seen, especially with the adoption of CNG, Delhi continues to struggle with air quality issues due to the sheer volume of vehicles, geographic and meteorological factors, and pollution from neighbouring regions. Continuous monitoring and stricter enforcement are crucial.