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 = P o e -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 N 2 :O 2 :Ar) Exercise: Calculate the partial pressure of O 2 at 6 km if P Total is 0.5 bar.

Atmospheric Composition

Species

N 2 O 2 Ar CO 2 Ne He CH 4

Species

O 3 NO + NO 2 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/cm 3 (use ideal gas law) 1 atm = 2.5 x 10 19 molecules cm -3 at 298 K if P Total = 1 atm, 1 ppmv = 2.5 x 10 13 P Total = 1 Torr  3.2 x 10 16 molecules cm molecules cm -3 -3 At 220 K, 1 Torr = 4.3 x 10 16 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