1. Handled by: Atun RoyChoudhury
Discipline: Environmental
Semester: 1st

2. Vertical distribution of
atmospheric layers:

3. Direct interaction of UV rays
with earth surface:

4. Important Atmospheric
Chemical Species:
 Inorganic oxides: CO, CO2, NO2, SO2
 Oxidants: O3, H2O2, HO• radical, HO2• radical, ROO• radicals, NO3 radical
 Reductants: CO, SO2, H2S
 Hydrocarbons: Natural CH4, pollutant alkanes, alkenes, aromatics
 Oxidized organics: Aldehydes, ketones, acids, organic nitrates
 Photochemically active species: NO2, formaldehyde
 Acids: H2SO4, H2SO3, HNO3
 Bases: NH3
 Salts: NH4HSO4
 Unstable reactive species: Electronically excited nitrogen dioxide (NO2*), HO•
Solid and liquid particles in aerosols and clouds
 Sources and sinks for gas-phase species
 Sites for surface reactions on solids
 Aqueous phase reactions in water droplets

5. Important aspects of
atmospheric chemical
processes:

6. Two Very Important Factors in
Atmospheric Chemistry:
(i) Radiant solar energy
 Photons put high energy into individual molecules
(ii) Hydroxyl radical, HO•
 Most important highly reactive intermediate

7. Loss of Excitation Energy from
Electronically Excited Species:
(i) Emission of a photon (light): NO2*  NO2 + h
Called luminescence if instantaneous, phosphorescence if
slower and
Chemiluminescence when the excited species that emits a
photon is formed as the result of a chemical reaction
O3 + NO  O2 + NO2* (luminescent species)
(ii) Direct reaction of an excited species
O2* + O3  2O2 + O
(iii) Dissociation
NO2*  NO + O (very important tropospheric reaction)
O2*  O + O (important in stratosphere leading to O3)
(iv) Photoionization (formation of ions in the ionsphere)
N2*  N2
+ + e-

8. Photochemical Reaction:

9. Photochemical cycle:

10. Basic elements of SMOG:

11. Photochemical smog
generation:

12. Pictorial representation of
Smog:

13. Basics of Photochemical
reaction:

14. Other important
compound:

15. Beijing location showing
smog effect:

16. Introduction of Ozone:
 O3
 a gas composed of three atoms of
oxygen
 bluish gas that is harmful to breathe
 Nearly 90% of the Earth's ozone is in
the stratosphere and is referred to as
the ozone layer
 Ozone absorbs a band of ultraviolet
radiation called UVB

17. Formation of Ozone:

18. Ozone depleting substances:
 CFCs,
 HCFCs,
 halons,
 methyl bromide,
 carbon tetrachloride, and
 methyl chloroform.

19. Anthropogenic activities
causing depletion of Ozone:

20. Study of Ozone layer with
respect to time:

21. Effects of ozone layer
depletion: