Atmospheric Pollution by Gaseous Pollutants

Pollutant: Substance present in nature, but conc ↑ due to human activities and cause harmful effects.
1° eg: Dust, CO₂, CO, Pb, Hg, NO.... etc
2° eg: NO₂, SO₃.... etc

Contaminant: Substance not present in nature, but released due to human activities.
eg: MIC (1989) Bhopal tragedy
CFC (Chloro Fluoro Carbon)
DDT (Di chloro Diphenyl Trichloro ethane)

Receptor: The medium effected by the pollutant
eg: Eyes, Skin etc...

Sink: The medium which reacts with pollutants
eg: Oceans, trees etc... microorganisms

Threshold Limit value (TLV): The value upto which a person is exposed to, in shown

COD: The amount of O₂ required to oxidise the organic matter
→ measure of quality of water.
Pure water 1ppm; polluted water → 17ppm
\tt COD=\frac{weight\ of\ K_{2}Cr_{2}O_{7}\left(mg\right)\times1000}{49\times weight\ of \ water\left(g\right)}\times8

BOD: The amount of O₂ required by microorganism in 5 days at 20°C
It also decides the quality of water.
\tt BOD=\frac{No.of\ mg\ of\ O_{2}\ consumed}{No.of\ lit\ of\ water}

Oxides of Sulphur:
S + O₂ → SO₂
2SO₂ + O₂ → 2SO₃ Particles
SO₂ + O₃ → SO₃ + O₂
SO₃ + H₂O → H₂SO₄
2SO₂ + O₂ + H₂O → H₂SO₄
→ Irritation
→ respiratory problems

Oxides of nitrogen:
\tt N_{2}+O_{2}\xrightarrow{10,000^{0}C}2NO
2NO + O₂ → 2NO₂

→ Harmful effects on plants
→ Respiratory problems

Acid rains pH < 5.6
→ Stratospheric
\tt CCl_{2}F_{2}\xrightarrow{UV}\dot{C}F_2+\dot{Cl}
\tt O_{3}+C\dot{l}\longrightarrow\dot{C}lO+O_{2}
\tt \dot{C}lO+O\longrightarrow\dot{C}l_2+O
1 CFC(Cl free radical) can damage 1 lakh molecules of ozone.

Summer (Antarctica) Depletion ↓
\tt CH_{4}+\dot{C}l\rightarrow \dot{C}H_{3}+HCl
\tt NO_{2}+\dot{C}lO\rightarrow ClONO_2
acts as sinks, for 'cl' free radical

Winter:
\tt ClONO_2 + H_2O\longrightarrow HOCl + HNO_3
\tt ClONO_2 + HCl\longrightarrow Cl_2 + HNO_3

Springs: \tt HClO \xrightarrow {h\nu} OH+\dot{C}l