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.
6. Two Very Important Factors in
Atmospheric Chemistry:
(i) Radiant solar energy
๏ Photons put high energy into individual molecules
(ii) Hydroxyl radical, HOโข
๏ Most important highly reactive intermediate
7. Loss of Excitation Energy from
Electronically Excited Species:
(i) Emission of a photon (light): NO2* ๏ฎ NO2 + h๏ฎ
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 ๏ฎ O2 + NO2* (luminescent species)
(ii) Direct reaction of an excited species
O2* + O3 ๏ฎ 2O2 + O
(iii) Dissociation
NO2* ๏ฎ NO + O (very important tropospheric reaction)
O2* ๏ฎ O + O (important in stratosphere leading to O3)
(iv) Photoionization (formation of ions in the ionsphere)
N2* ๏ฎ N2
+ + e-
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