CVEN 4424 Environmental Organic Chemistry Lecture 7 Sorption of Neutral Organic Compounds to Dissolved Organic Matter and Air-Water Exchange Equilibrium

Announcements Reading Problem sets Office hours Exam 1 Chapter 5, Aqueous solubility Chapter 9, Sorption (more of this later) Problem sets PS 3 due Thursday PS 4 out Thursday Office hours Monday, 10-11 am, ECES 115, Joe Tuesday, 5-6:30 pm, ECES 115, Alejandro Wednesday, 10-11 am, ECES 115, Joe Wednesday, 4:30-6 pm, ECES 115, Alejandro Exam 1 Tuesday, February 17, in class closed book; equations and data available on exam

Aqueous Solubility Organic liquid mixtures petroleum – gasoline, oil, kerosene coal tar PCBs – Arochlor

Aqueous Solubility Solubility of an organic liquid assumptions xL  1 (essentially no water in organic phase) L = 1 (pure liquid; ideal interactions) w L

Aqueous Solubility Solubility of an organic liquid mixture assumptions xL is the mole fraction of the compound of interest L  1 (not a pure liquid, but nearly ideal interactions) w L

Coal tar BTEX PAHs

Aqueous Solubility Organic liquid mixtures org mix  1 to 5 xorg mix need average mw of organic liquid mixture e.g., coal tar 150 g mol-1 no melting costs compound is already in liquid phase in organic mixture

Aqueous Solubility Organic liquid mixtures example: What concentration of benzene should we find in water in equilibrium with gasoline containing benzene at a concentration of 1 vol%?

Aqueous Solubility Benzene in water in equilibrium with gasoline containing 1 vol% benzene? Need estimates for and

Aqueous Solubility Benzene in water in equilibrium with gasoline containing 1 vol% benzene? activity coefficient of benzene in gasoline, mole fraction of benzene in gasoline,

Aqueous Solubility Benzene in water in equilibrium with gasoline containing 1 vol% benzene? activity coefficient of benzene in water,

Aqueous Solubility Benzene in water in equilibrium with gasoline containing 1 vol% benzene? benzene MCL: 5 g L-1

Solubility and Organic Matter

DOM Suwannee River humic acid Suwannee River fraction 10 mgC L-1 fulvic acid fraction 10 mgC L-1 Everglades hydrophobic acid fraction 10 mgC L-1 Williams Lake hydrophobic acid fraction 10 mgC L-1

Solubility and Organic Matter Dissolved organic matter (DOM) terrestrial source plants; “allochthonous” more soluble, higher molecular weight, more aromatic aquatic source organisms; “autochthonous” less soluble, lower molecular weight, less aromatic Kerner et al., 2003, Nature 422, 150-154.

Solubility and Organic Matter Dissolved organic matter “dissolved” is operational membrane filtration 0.45 m glass fiber filtration 0.7-0.8 m ultrafiltration molecular weight cutoffs 1,000-10,000 Da tangential flow filtration

Solubility and Organic Matter

Solubility and Organic Matter

Solubility and Organic Matter Ultraviolet light absorption

Solubility and Organic Matter Fractionation glass fiber-filtered sample at pH 2 fulvic acid hydrophobic organic acid “transphilic” organic acid NaOH NaOH pH 2 XAD-8 resin humic acid XAD-4 resin hydrophobic organic neutral “transphilic” organic neutral CH3CN CH3CN hydrophilic organic acid

Solubility and Organic Matter Adoc Aw + =

Solubility and Organic Matter Binding to DOM binding, not absorption one molecule of solute bound by a single DOM molecule like co-solvency readily reversible solute release from DOM not diffusion-limited like release from SOM

Solubility and Organic Matter Measurement of Kdoc: techniques headspace analysis volatile compounds only solid phase microextraction only for low solubility compounds solubility enhancement microcrystals/emulsions? fluorescence quenching fluorescent compounds only “dynamic quenching” questions

Solubility and Organic Matter Solubility enhancement

Solubility and Organic Matter If you use headspace analysis for measurement of Kdoc for a volatile organic compound (VOC), which trend would you expect? A. the amount of VOC in the headspace increases as DOC increases B. the amount of VOC in the headspace decreases as DOC increases ? ? ?

Air-Water Exchange Equilibrium

p* Cwsat Air-Water Exchange Phase transfers vaporization/sublimation aqueous solution vapor p* Cwsat pure liquid pure liquid aqueous solution

= Air-Water Exchange Another phase exchange air-water exchange vapor pure liquid aqueous solution aqueous solution

Air-Water Exchange Phase exchange Awater  Aair Henry’s Law constants (bar L mol-1) dimensionless (mol La-1 mol-1 Lw)

Air-Water Exchange compound Henry’s Law constant Kaw (dimensionless) benzene 10-0.65 phenol 10-4.59 trichloroethene 10-0.31 phenanthrene 10-2.85 2,2’,5,5’-tetrachlorobiphenyl 10-1.70

Air-Water Exchange Estimates by vapor pressure / solubility

Air-Water Exchange Example: chloroethene (a gas) estimated Kaw = 10-0.04 experimental Kaw = 10-0.05

Air-Water Exchange Example: chlorobenzene (a liquid) estimated Kaw = 10-0.80 experimental Kaw = 10-0.82

Air-Water Exchange Example: pyrene (a solid) estimated Kaw = 10-3.32 experimental Kaw = 10-3.36

Air-Water Exchange Temperature dependence enthalpy of liquid-air phase change, alH Two components of alH: vapH - wHE enthalpy to vaporize vapH, related to pL* (excess) enthalpy to solubilize wHE, related to Cwsat for solids and gases, melting and condensation enthalpies cancel out

gas already in gas phase Air-Water Exchange Liquid: Solid: Gas: (getting to gas phase) (getting out of water phase) gas already in gas phase

Air-Water Exchange dichlorodifluoromethane (gas) toluene (liquid) naphthalene (solid) pyrene (solid)

+ = Air-Water Exchange Temperature dependence liquids (e.g., benzene, tetrachloroethylene) ln p* 1/T ln Cwsat 1/T ln KH 1/T + =

+ = Air-Water Exchange Temperature dependence solids (e.g., naphthalene, 1,4-dichlorobenzene) ln p* 1/T ln Cwsat 1/T ln KH 1/T + =

+ = Air-Water Exchange Temperature dependence gases (e.g., vinyl chloride, chloromethane) ln p* 1/T ln Cwsat 1/T ln KH 1/T + =

Air-Water Exchange Effect of salt Salting out decreases solubility; increases Kaw

Air-Water Exchange Effect of salt pyrene, Kaw = 10-3.32 seawater [salt]tot = 0.5 M KS = 0.30

Air-Water Exchange Effect of co-solvents Co-solvents increase solubility; decrease KH

Air-Water Exchange Effect of co-solvents naphthalene, Kaw = 10-1.74 20% acetone solution fv = 0.2 c = 6.5

Air-Water Exchange Partition between air and water importance of keeping bubbles out of water samples for VOCs 40 mL vial 39 mL water, 1 mL bubble VOC is chloromethane Kaw = 100.16 what fraction of the chloromethane is in the bubble?

Air-Water Exchange Partition between air and water

Next Lecture Air-Water Exchange Kinetics Read Chapters 18, 19, and 20