Atmospheric Structure
Theodore S. Dibble
Chemistry Department
SUNY-Environmental Science and Forestry Syracuse, NY
Temperature defines regions of the atmosphere
Altitude
(km)
Pressure
(mbar)
Pressure and the Barometric Law
P = Poe-Mgh/RT applies to individual compounds at equilibrium
Atmosphere not at equilbrium!
Below 130 km, long lived gases have constant mole fraction
Pressure behaves as if M =28.8 g/mole (78:21:1 N2:O2:Ar)
Exercise: Calculate the partial pressure of
O2 at 6 km if PTotal is 0.5 bar.
Atmospheric Composition
Species
N2
O2
Ar
CO2
Ne
He
CH4
Species
O3
NO + NO2
HOO
OH
O
Mole Fraction
0.781
0.209
9.34 x 10-3
3.6 x 10-4
1.8 x 10-5
5 x 10-6
1.8 x 10-6
Sunny Noon
Mole Fraction
0.5 - 2 x 10-7
10-12 - 10-8
0.4 -4 x 10-11
0.5- 4 x 10-13
1-4
x 10-14
How can chemistry
(reactions) occur?
Units
Part per million, etc. by volume = mole fraction
1 ppmv = mole fraction 1 x 10-6
1 ppbv = mole fraction 1 x 10-9
1 pptv = mole fraction 1 x 10-12
Molecules/cm3 (use ideal gas law)
1 atm = 2.5 x 1019 molecules cm-3 at 298 K
if PTotal = 1 atm, 1 ppmv = 2.5 x 1013 molecules cm-3
PTotal = 1 Torr  3.2 x 1016 molecules cm-3
At 220 K, 1 Torr = 4.3 x 1016 molecules cm-3
Ozone Concentration in Different Units
Mixing Times in Troposphere
3 months
2 weeks
2 years
Mixing in Troposphere
Vertical
ground to tropopause in 1 week
Horizontal
Around a latitude line in weeks
Mid-latitude to equator in months
Cross equator in 1 year
[CO] = 120 ppbv in N.H. and 60 ppbv in S.H.
Question: CO has a lifetime of ~2 months
Will it be evenly distributed over oceans and remote
continental regions within the N.H.?
Troposphere-Stratosphere Exchange
Key Points
• Temperature structure
• Most of mass in troposphere
• Chemistry competes with transport