This document discusses important concepts in atmospheric chemistry including: 1) The vertical distribution of atmospheric layers and how UV rays interact with the Earth's surface. 2) Important chemical species in the atmosphere such as carbon monoxide, nitrogen dioxide, sulfur dioxide, oxidants, reductants, hydrocarbons, and aerosols. 3) Key aspects of atmospheric chemical processes including solar energy, the hydroxyl radical, excited state species, photochemistry, and aerosols acting as sites for surface reactions.

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: