168
100 ~-y~~-------------------------, zxxxxxxxx
•••
xxx
90
80
70
~ 60
~
.~ 50
'"
~
~
~
40
30
20
10
• • • •
Xx
• • •
Xx
•• •
x
• • • •
Xx
•
•
x
•
•
x
•
•
x
• • •
•
•
x
•
•
Xx
• •
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
• •
•
•
•
•
• •
•
•
•
•
•
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•••
o +---~---+----~--+---~---+--~
270
275
280
285
290
295
300
305
Temperature (K)
M.R. Preston
Fig. 7.3. The percentage particle association for homologous PCB congeners 128(2) (+),145(4) (.6.),
149{J) (_),156(1) (e) and 169(0) (x) plotted against temperature for aerosol with urban characteristics.
Each congener has a total of 6 chlorine atoms, and numbers in parentheses are the number of ortho
substituted chlorine atoms
7.3.5
Gas Phase Exchange Processes
Gas phase processes are rather more difficult to model than either of the wet and dry
deposition processes described above. The flux of a gas (F g ) between air and water (in
either direction) is driven by the concentration difference (de) and the rate term K
(the piston or transfer velocity) such that