atmospheric chemistry ppt

LAYERS OF ATMOSPHERE AND

VARIOUS REACTIONS IN IT

Handled by: Atun RoyChoudhuryDiscipline: Environmental

Semester: 1st

Vertical distribution of atmospheric layers:

Direct interaction of UV rays with earth surface:

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

Important aspects of atmospheric chemical processes:

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

Loss of Excitation Energy from Electronically Excited Species:

(i) Emission of a photon (light): NO2* NO2 + h

Called luminescence if instantaneous, phosphorescence if slower andChemiluminescence when the excited species that emits a photon is

formed as the result of a chemical reactionO3 + NO O2 + NO2* (luminescent species)

(ii) Direct reaction of an excited speciesO2* + O3 2O2 + O

(iii) DissociationNO2* 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-

Photochemical Reaction:

Photochemical cycle:

Basic elements of SMOG:

Photochemical smog generation:

Pictorial representation of Smog:

Basics of Photochemical reaction:

Other important compound:

Beijing location showing smog effect:

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

Formation of Ozone:

Ozone depleting substances:

CFCs, HCFCs, halons, methyl bromide, carbon tetrachloride, and methyl chloroform.

Anthropogenic activities causing depletion of Ozone:

Study of Ozone layer with respect to time:

Effects of ozone layer depletion: