Atmosphere Chemistry

Atmosphere –Water Interactions
C. P. Huang

Stumm W. and J. J. Morgan. Chapter 5. Aquatic Chemistry
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Environmental Systems

2

5.2 Atmospheric generation of acidity

3

Genesis of acid rain

4

Chemical processes and Chemical
Composition of Water Droplets

5

uM ueq/L NO360
60

SO4244
88

Cl 25
25

S(X)
173

Mg2+
4.5
9

Ca2+
16
32

NH4+
85
85

K+
2
2

Na +
5
5

H+
50
50

S(M)
183

CH3COOH
5
5

6

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8

Total Annual Atmospheric Deposition

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5.3 Gas-Water Partitioning:
Henry’s Law

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Henry’s Law
A (g)  A(l)
[A(aq)] = H [A(g)]

(mol/L)
[A(aq)] [A]w= PA/(RT) (mol/L)
[A(aq)] = KHRT [A(g)]
H = KH RT

(A(aq)) = [A(aq)] q mol/m3 mol/L

L/m3

KH= M/atm

R= 0.082057 (L-atm/K)
[A(aq)] = H [A(g)]

q: content of water per m3 of the entire system q = 5x10-5 – 5x10-4 L-m-3 for fog q = 1x10-4 – 1x10-3 L-m-3 for clouds

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Henry’s Law

[A(aq)] = H [A(g)]
(A(aq)) = [A(g)] q

[A(aq] = KHRT [A(g)]
(A(aq)) = (A)w
[A(aq)] = [A]w

mol/m3

mol/L

L/m3

(A)T = (A)g + (A)w = pA/RT +[A]w q

[A(aq)] = H [A(g)]
H = KH RT (L(g)/L(aq)
R = 0.082057 (L-atm-mol-1-K-1)

(A)T = (A)g + KHRT (A)gq = (A)g (1+KHRTq)
(A)T = (A)g (1+ Hq) fg = (A)g/(A)T = 1/(1+qH) fw = (A)w/(A)T =qH/(1+qH)

R = 8.2057x10-5 (m3-atm-mol-1-K-1) q: content of water per m3 of the entire system
H = KH RT (m3/L)
-5 – 5x10-4 L-m-3 for fog q = 5x10 q = 1x10-4 – 1x10-3 L-m-3 for clouds

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Solubility of oxygen
O2(g) = O2(aq); H = 0.038
[O2(aq)] = KH p(O2) = (H/RT)[O2(g)]

RT = 0.024465 (m3-atm-mol-1)
RT = 6.132946 (L-atm-mol-1)

KH(O2) = H/(RT) =0.038/6.1632946 = 1.26x10-3 M-atm-1
In freshwater KH(O2) = 3.1x10-3 M-atm-1
In 10 o% estuarine water KH(O2) = 3.73x10-3 M-atm-1
In 35 o% sea water KH(O2) = 3.32x10-3 M-atm-1
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Important Gas-Water Equilibria

14

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5.4 Gas-water equilibria in closed and open systems

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5.4 gas-water