1. CVEN 5424 Environmental Organic Chemistry Lecture 9 – Air-Water Exchange Kinetics

2. Announcements Reading  Chapter 6, Air-Water Partition  Chapters 18, 19, and 20 (for next lecture) Problem sets PS 4 due Tuesday Office hours – semester Thursday 4-5:30 pm Monday 9-10:30 am

3. Announcements Exam 1 Tues Feb 16, noon, to Thurs Feb 18, 10 am open book, open notes, open web, etc.  eligible sources of data will be specified in some cases  closed colleague  Honor Code  Problem sets 1, 2, 3, and 4  Chapters 2, 3, 4, 5, 6, 18, 19, 20  topics p, C w sat, K dom, K H, k vol  20% of total grade  PSs 30%, two third-terms 40%, final 30%

4. Air-Water Exchange  Estimating Henry’s Law constant  Vapor pressure / solubility  Structural contributions  linear free energy relationship (LFER)  Hine and Mookerjee (1975)  Meyland and Howard (1991)

5. Air-Water Exchange K aw 10 -0.84 10 0.71 10 1.58 10 1.69 10 -0.65 10 -0.80 10 1.69 10 -1.49  Based on the K aw values given for the compounds to the right, rank the following bonds in order of their contribution to making K aw more positive from highest to lowest: A. C–F > C–H > C–Cl > C– O B. C–H > C–F > C–Cl > C– O C. C–O > C–Cl > C–F > C– H  log K aw +1.55 +0.11 -0.15 -3.18

6. Air-Water Exchange  Structural contribution method  effect of each bond on  aw G  good approximation if minimal interactions between functional groups  accuracy only good to a factor of 2 or 3  use only if no vapor pressure and solubility data

7.  Subscripts  d – olefinic (double bond)  t – triple bond  ar – aromatic  Aromatic carbon/oxygen  C ar -OH – oxygen part of OH  C ar -O – oxygen not connected to hydrogen  inconsistency  Aromatic carbon/carbon  f – intraring aromatic carbon to carbon  g – inter-ring aromatic carbon to carbon (e.g., biphenyl)

8.  Correction factors for certain structures  linear or branched alkane SGI: +0.75  positive correction  more in air  negative correction  more in water  presence of more than one alcohol difficult to account for (e.g., ethylene glycol, two – OH), correction factor of +3.00  (signs of all corrections changed because Meylan and Howard calculated K aw -1 )

9. Air-Water Exchange  benzene bondnumbercontribtotalknown C ar —H6+0.1543+0.9258 C ar –C ar 6-0.2638-1.5828 log K aw -0.66-0.68 measured

10. Air-Water Exchange  n-hexane bondnumbercontribtotal C—C5-0.1163-0.5815 C—H14+0.1197+1.6758 linear/branched alkane factor* +0.75 log K aw +1.84+1.74 estimated using p* and C w sat * not shown in Table 6.4; in text

11. Air-Water Exchange  1-hexanol bondnumbercontribtotal C—C5-0.1163-0.5815 C—H13+0.1197+1.6758 C–O1-1.0855 O–H1-3.2318 linear/branched aliphatic alcohol -0.20 log K aw -3.4230-3.15

12. Air-Water Exchange  Which compound has a higher Henry’s Law constant? A. B. K aw 10 -1.32 10 0.16 C w sat 10 -1.47 M lower C w sat 10 -2.01 M p L * 10 -1.40 bar higher p L * 10 -0.78 bar

13. Air-Water Exchange  trichloroethanes bondnumbercontribtotalknown C—H3+0.1197+0.3591 C—Cl3-0.3335-1.0005 C—C1-0.1163 log K aw -0.76 -1.32 1,1,2-trichloroethane log K aw -0.76 0.16 1,1,1-trichloroethane

14. Air-Water Exchange  trichloroethene bondnumbercontribtotal C d –C d 10.0 C d —H1+0.1005 C d —Cl3-0.0426-0.1278 log K aw -0.03-0.40 measured * * each of the bonds to the carbons include ¼ of the contribution of the C=C bond, so the C=C bond is never actually counted.

15. Air-Water Exchange  phenol bondnumbercontribtotalknown C ar —H5+0.1543+0.7715 C ar –C ar 6-0.2638-1.5828 C ar —OH1-0.5967 log K aw -1.41-4.79 measured

16. Air-Water Exchange  phenol bondnumbercontribtotalknown C ar —H5+0.1543+0.7715 C ar –C ar 6-0.2638-1.5828 C ar —O1-0.3473 O—H1-3.2318 log K aw -4.39-4.79 measured

17. Air-Water Exchange  permethrin bondnumbercontribtotal C ar –C ar 12-0.2638-3.1656 C ar —O9+0.1543+1.3887 C ar —O2-0.3473-0.6946 C—C ar 1-0.1619 C—O2-1.0855-2.1710 C—CO1-1.7057 C—C5-0.1163-0.5815 C d —C1-0.0635 C d —H1+0.1005 C d —Cl2-0.0426-0.0852 C—H10+0.1197+1.1970 log K aw -5.95?

18. Air-Water Exchange  permethrin  C w sat  0.006 mg L -1 at 20  C  USDS Pesticide Data Base  p s *  2.18  10 -8 mm Hg at 25  C  USDS Pesticide Data Base  K H  1.87  10 -6 atm m 3 mol -1 at 25  C  p s */C w sat estimate

19. Air-Water Exchange  permethrin  K H  1.87  10 -6 atm m 3 mol -1 at 25  C  1000 L per m 3  1.87  10 -3 atm L mol -1  1.013 bar per atm  1.89  10 -3 bar L mol -1

20. Air-Water Exchange  permethrin bondnumbercontribtotal C ar –C ar 12-0.2638-3.1656 C ar —O9+0.1543+1.3887 C ar —O2-0.3473-0.6946 C—C ar 1-0.1619 C—O1-1.0855 C—CO1-1.7057 C—C5-0.1163-0.5815 C d —C1-0.0635 C d —H1+0.1005 C d —Cl2-0.0426-0.0852 C—H10+0.1197+1.1970 log K aw -5.95-4.11

21.  Correction factors for certain structures  linear or branched alkane SGI: +0.75  positive correction  more in air  negative correction  more in water  presence of more than one alcohol difficult to account for (e.g., ethylene glycol, two – OH), correction factor of +3.00  (signs of all corrections changed because Meylan and Howard calculated K aw -1 )

22. Air-Water Exchange  permethrin bondnumbercontribtotal C ar –C ar 12-0.2638-3.1656 C ar —O9+0.1543+1.3887 C ar —O2-0.3473-0.6946 C—C ar 1-0.1619 C—O1-1.0855 C—CO1-1.7057 C—C5-0.1163-0.5815 C d —C1-0.0635 C d —H1+0.1005 C d —Cl2-0.0426-0.0852 C—H10+0.1197+1.1970 cyclic alkane1+0.28 log K aw -5.67-4.11

23. Air-Water Exchange Kinetics  A barge carrying chloroform down the Mississippi River runs aground and ruptures. The spill contaminates a large volume of water at C w sat of CHCl 3. The wind speed at 2 m height is 3 m s -1. The mean depth of the river is 10 m. The water and air temperature are 20  C.  What is the initial flux of chloroform from the river?  What is the half-life of chloroform volatilization?

24. Air-Water Exchange Kinetics  Diffusion in air  inversely proportional to molar volume compound mw (g mol -1 ) V (cm 3 mol -1 ) D a (cm 2 s -1 ) H2OH2O18 0.26 methane16250.28 benzene78890.12 tetrachloroethene1661110.086 2,2’,4,4’,5,5’- hexachlorobiphenyl 3613230.059

25. Air-Water Exchange Kinetics  Molar volume calculation  density   liquid  temperature 25  C (often 20  C)  solid or gas  density as a liquid at some temperature higher or lower than 25  C

26. Air-Water Exchange Kinetics  Molar volume calculation

27. Air-Water Exchange Kinetics  Molar volume estimation element contribution (cm 3 mol -1 ) C16.5 H2.0 O5.5 N5.7 S17.0 Cl19.5 rings-20.2 Fuller et al. (1966), Table 18.2; see also Abraham and McGowan (1987), Box 5.1

28. Air-Water Exchange Kinetics  Molar volume estimation element contribution (cm 3 mol -1 ) C16.5 H2.0 O5.5 N5.7 S17.0 Cl19.5 rings-20.2 Fuller et al. (1966), Table 18.2

29. Air-Water Exchange Kinetics  Estimating D a (Fuller et al., 1966)  T absolute temperature (K)  mw air average molecular mass of air (28.97 g mol -1 )  mw c molecular mass of compound (g mol -1 )  P air total pressure of the air (atm)  V air average molar volume of air (20.1 cm 3 mol -1 )  V c molar volume of compound (cm 3 mol -1 )

30. Air-Water Exchange Kinetics  Estimating D a  relative to known compound  water, benzene, etc.

31. Air-Water Exchange Kinetics  Diffusion of tetrachloroethene in air at 25  C

32. Air-Water Exchange Kinetics  Diffusion of tetrachloroethene in air at 25  C

33. Air-Water Exchange Kinetics  Diffusion in water  inversely proportional to molar volume compound mw (g mol -1 ) V (cm 3 mol -1 ) D w (cm 2 s -1 ) O2O2 3218 2.1  10 -5 methane1625 3.0  10 -5 benzene7889 1.3  10 -5 tetrachloroethene166111 0.92  10 -5 2,2’,4,4’,5,5’- hexachlorobiphenyl 361323 0.63  10 -5

34. Air-Water Exchange Kinetics  Estimating D w   viscosity of the water (cp, 10 -2 g cm -1 s -1 )  V molar volume of the compound

35. Air-Water Exchange Kinetics  Estimating D w  diffusion volume  molecular weight

36. Air-Water Exchange Kinetics  Diffusion of PCE in water at 25  C

37. Air-Water Exchange Kinetics  Diffusion of PCE in water at 25  C

38. Air-Water Exchange Kinetics  Diffusion of PCE in water at 25  C

39. Air-Water Exchange Kinetics  Flux of molecules across air-water interface  driven by concentration gradient  controlled by molecular diffusion  Water across air-water interface  evaporation  Gases across air-water interface  oxygen  carbon dioxide

40. Air-Water Exchange Kinetics Evaporation, that random breach of surface tension by molecules "which happen to acquire exceptionally high velocities.“ Brave "happening"! – they fly the minute distance across and join another state of matter, sacrificing, as they depart, heat to the attraction of the molecules still water, like a wedlocked beauty leaving behind her filmy nightgowns as she flees to a better lover. John Updike, Ode to Evaporation

41. Air-Water Exchange Kinetics  Three models:  stagnant film  surface renewal  boundary layer

42. Air-Water Exchange Kinetics  Stagnant film model  stagnant air layer below well-mixed air  stagnant water layer above well- mixed water  equilibrium applies only in boundary layers  most applicable to ocean, lakes, slow rivers well-mixed water well-mixed air C zwzw zaza 0 CwCw C a/w C w/a CaCa stagnant water ~0.01 cm stagnant air ~0.1 cm

43. Air-Water Exchange Kinetics  Surface renewal model  parcels of air spend some time at interface  parcels of water spend some time at interface  equilibrium between parcels at interface  most applicable to smaller, faster-flowing streams in which stagnant films unlikely water air C 0 CwCw C a/w C w/a CaCa

44. Air-Water Exchange Kinetics  Boundary layer model  similar to stagnant film model  continuous, not step-like, drop in diffusivity  accounts for turbulence  most versatile, recommended by SGI

45. Air-Water Exchange Kinetics  A barge carrying chloroform down the Mississippi River runs aground and ruptures. The spill contaminates a large volume of water at C w sat of CHCl 3. The wind speed at 2 m height is 3 m s -1. The mean depth of the river is 10 m. The water and air temperature are 20  C.  What is the initial flux of chloroform from the river?  What is the half-life of chloroform volatilization?

46. Air-Water Exchange Kinetics  Spills in the Mississippi River  oil (crude, diesel)  at least 44 major spills post-Katrina  27,000,000 L  xylene  tanker collided with barge  160,000 L  “pyrolysis gasoline”  tanker collided with barge  product of ethylene manufacture; benzene  17,000 L  cumene  barge accident at lock  31,000 L

47. Air-Water Exchange Kinetics  Spills in the Mississippi River  ethylene glycol  leaking railroad tank car  77,000 L  pentachlorophenol  ship accident; required dredging  16 tons  fluorosilicic acid (H 2 SiF 6 )  highly corrosive acid; used for fluoridation  leaking tank; causing damage to other tanks at chemical transfer facility; pumped into river  1,700,000 L  chloroform  barge sank near Baton Rouge  500,000 L

50. Air-Water Exchange Kinetics  A barge carrying chloroform down the Mississippi River runs aground and ruptures. The spill contaminates a large volume of water at C w sat of CHCl 3. The wind speed at 2 m height is 3 m s -1. The mean depth of the river is 10 m. The water and air temperature are 20  C.  What is the initial flux of chloroform from the river?  What is the half-life of chloroform volatilization?

51. Air-Water Exchange Kinetics  Flux  v w water piston velocity  resistance of the water side  CO 2 moving through water  v a air piston velocity  resistance of the air side  H 2 O moving through air piston velocity (cm s -1 ) “resistance” conc. gradient (mol cm -3 ) “driving force” flux (mol cm -2 s -1 )

52. Air-Water Exchange Kinetics  C w  chloroform solubility, C w sat  C w = 10 -1.19 M = 10 -4.19 mol cm -3  this is the initial concentration, so the flux is only initial  C a  wind continuously brings air free of chloroform  C a  0  K aw  chloroform K H = 10 0.60 bar L mol -1 (at 25  C)  K aw = 0.16

53. Air-Water Exchange Kinetics  Boundary layer model (Deacon, 1977)  gradual change in diffusivity between well-mixed and stagnant film  well-mixed (turbulent diffusion)  stagnant film (molecular diffusion)  turbulent to molecular transition zone  depends on viscosity of fluid   a and  w of stagnant film model  separate viscosity effect from wind effect  incorporate effect or temperature (air or water) on piston velocities  means to estimate v w and v a

54. Air-Water Exchange Kinetics  Boundary layer model (Deacon, 1977)  transport controlled by two processes  transport of chemicals  molecular diffusivity D a and D w  transport of turbulence  kinematic viscosity a and w subscript  is a or w

55. Air-Water Exchange Kinetics  Boundary layer model (Deacon, 1977)  D  and  combined to characterize boundary layer  Schmidt number  water piston velocity from Sc  VOCs that are “water-side-limited”  high K a/w  smooth, rigid water surface  Sc > 100  piston velocity increases as D w increases, as w decreases

56. Air-Water Exchange Kinetics water film “bottleneck”

57. Air-Water Exchange Kinetics  Smooth water surface (“SSR”)  lower wind speed, u 10  4.2 m s -1  Rough water surface (“RSR,” “BSR”)  higher wind speed, u 10 > 4.2 m s -1

58. Air-Water Exchange Kinetics T (  C) kinematic viscosity (cm 2 s -1 ) 01.79 x 10 -2 51.52 x 10 -2 101.31 x 10 -2 151.14 x 10 -2 201.00 x 10 -2 250.89 x 10 -2 300.80 x 10 -2  Kinematic viscosity of water

59. Air-Water Exchange Kinetics  Using CO 2 for v w reference  Sc w (CO 2,20  C) = 600 (595) at 20  C  Sc w (unknown,T 2 )  lower wind speed, u 10  5 m s -1  higher wind speed, u 10 > 5 m s -1

60. Air-Water Exchange Kinetics  Using CO 2 for v w reference (same w )  lower wind speed, u 10  5 m s -1  higher wind speed, u 10 > 5 m s -1

62. “ I entered upon the small enterprise of ‘learning’ twelve or thirteen hundred miles of the great Mississippi with the easy confidence of my time of life. If I had really known what I was about to require of my faculties, I should not have had the courage to begin. I supposed that all a pilot had to do was to keep his boat in the river, and I did not consider that that could be much of a trick, since it was so wide.” - Mark Twain, Life on the Mississippi

63. Air-Water Exchange Kinetics “The idea of you being a pilot—you! Why, you don’t know enough to pilot a cow down a lane... Look here! What do you suppose I told you the names of those points for?” I tremblingly considered a moment, and then the devil of temptation provoked me to say:— “Well— to—to—be entertaining, I thought.” “My boy, you must get a little memorandum-book, and every time I tell you a thing, put it down right away. There’s only one way to be a pilot, and that is to get this entire river by heart. You have to know it just like A B C.” - Mark Twain, Life on the Mississippi

64. Air-Water Exchange Kinetics  Half-life of chloroform volatilization  volatilization rate coefficient:

65. Air-Water Exchange Kinetics  Piston velocity of chloroform through air v a  estimate for water, relate to CHCl 3  depends solely on wind speed (Eqn. 20-15)

66. Air-Water Exchange Kinetics  Piston velocity of chloroform through air v a  relating CHCl 3 to H 2 O (Eqn. 20-27)

67. Air-Water Exchange Kinetics  Piston velocity of chloroform through air v a

68. Air-Water Exchange Kinetics  Piston velocity of chloroform through water v w  estimate for CO 2, relate to CHCl 3  depends solely on wind speed (Eqn. 20-16)

69. Air-Water Exchange Kinetics  Piston velocity of chloroform through water v w  relating CHCl 3 to CO 2 (Eqn 20-24a)  “SSR” – u 10 < 5 m s -1 ; use exponent of 0.67

70. Air-Water Exchange Kinetics  Piston velocity of chloroform through water v w

71. Air-Water Exchange Kinetics  Volatilization rate coefficient

72. Air-Water Exchange Kinetics  Volatilization half-life, boundary layer

73. Next Lecture  Octanol-water partition coefficient  More estimation techniques