文档介绍：ATMOSPHERIC CHEMICAL SYSTEMS
Source: NASA
ATMOSPHERIC
CHEMISTRY
Climate Change
Regional Air Pollution
Acid Deposition
Stratospheric Ozone
IMPORTANCE OF ATMOSPHERIC CHEMISTRY
ATMOSPHERE STRUCTURE & POSITION
Pressure units
1 atm = x 106 g cm-1 s-2
1 mbar = 103 g cm-1 s-2
1 hPa = 103 g cm-1 s-2
Ideal gas law
p V = Rg T
p = ( Rg T)/Ma
Source: Environmental Science, Cunningham, P. W. and B. W. Saigo, 2001
ATMOSPHERIC TRANSPORT TIME SCALES
Source: Introduction to Atmospheric Chemistry, Jacob, D. J., 1999
TYPICAL POSITION
(mole fraction)
Typical units
Number concentration: molecules cm-3
Mixing ratio: ppm, ppb, ppt
Molecular weight of air
Ma = g mole-1
Trace chemistry
Reactants are present in trace amounts
OXIDIZING NATURE OF THE ATMOSPHERE
Earth’s atmosphere is oxidizing due to presence of O2
SO2 --> SO42-; CH4 --> CO; CO --> CO2; NO2 --> HNO3
Radicals are oxidizing agents in the atmosphere
OH is the cleansing agent of the atmosphere
Key to understanding atmospheric oxidant chemistry
Understand radical cycling but radical cycle is intimately connected to oxidant chemistry of other pounds including O3
Start with O3
O3 is important from chemical, climate, and health perspectives
ATMOSPHERIC O3 – A BRIEF HISTORY
1840: Ozone discovered in 1840 by C. F. Schönbein
– thought it was made up of oxygen and hydrogen
1848: Systematic measurement attempts – curiousity, growing
interest in env., health effects, ‘economy of nature’
1861: Odling suggested that ozone was O3
1930: Chemical mechanism for O3 layer postulated
1952: O3 identified ponent of chemical smog
Christian Frederich Schönbein
OZONE AND HEALTH
90% of O3 is in the stratosphere; O3 layer with max ~ 9 ppm
Absorption of = 200-320 nm (UV-B and UV-C) by strat. O3
Source: Stratospheric Ozone, NASA/GSFC
OZONE AND STRATOSPHERIC TEMPERATURE
Local heating of the stratosphere due to UV absorption by O3
Tropospheric O3 is also an important greenhouse gas
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