Allison Schwier 25 April 2013

2 The McNeill Group McNeill Group 1 Postdoc 2 Grad Students 1 Fulbright Scholar 1 Visiting Professor 4 Undergrads

3 Aerosol-CIMS

4 Aerosol Chamber

Surfactants N 2 O 5 (g) “Inverted micelle” Can also form other morphologies: lenses, crystals, oils or lamellar phases hydrophilic hydrophobic 5 Atmospheric Aerosols Health Effects Air Quality 10 – 90% organic material 2 nm - 20 μ m Aerosol composition can be solid, liquid, or complex ina.html?_r=1

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Mechanism Primary ch Secondary 7

8 1. Organic Films can depress surface tension Cl - H2OH2O H2OH2O H2OH2ONa+ H 2 O Cl - H2OH2O Na+ H2OH2O Effects of Surfactants 3. Can affect trace gas uptake (N 2 O 5, HO 2, etc.) 2. Can affect water uptake H2OH2O H2OH2O H2OH2O N2O5N2O5 N2O5N2O5 N2O5N2O5 Seinfeld & Pandis, 2006 Kelvin/Curvature Effect: Raoult/Solute Effect: When Kelvin > Raoult GROWTH Köhler Theory- cloud condensation nuclei activity (CCN) Unknowns: Complex systems Natural conditions untested (pH, salt, organics) 8

9 Cl - H2OH2O H2OH2O H2OH2ONa+ H 2 O Cl - H2OH2O Na+ H2OH2O Cl - H2OH2O H2OH2O H2OH2ONa+ H 2 O Cl - Na+ H2OH2O SOA

10 Oleic acid (OA) – C 18 H 34 O 2 Stearic acid (SA) – C 18 H 36 O 2

Bulk Solutions Pendant Drop Tensiometry 11 Adamson & Gast,1997 Juza, 1997

12 Oleic Acid in 3.1 M AS, pH = 3Stearic Acid in 3.1 M AS, pH = 3 Solutionσ o (dyn cm -1 ) a ×10 2 (K -1 ) b (kg water/mol carbon) SA ± ± 128 OA ± 0.05(7.3 ± 4.9) ×10 6

mM Stearic Acid at pH 3

14 Saturated oleic acid and stearic acid in saturated NaCl, (NH 4 ) 2 SO 4, and water with varying pH.

Long chain fatty acids form surface films at all atmospherically relevant conditions. Impact: Organic films could exist if surfactants are present. 15 Schwier, Mitroo, McNeill, Atmospheric Environment, 2012

16 Glyoxal Methylglyoxal

Aerosol-CIMS Aerosol CIMS = Chemical Ionization Mass Spectrometer with a volatilization inlet flow tube (VFT) Low fragmentation High sensitivity (O~ppt) 17

Cross products make up to 55(±5%) product mass CIMS Data 18 Hydrated G Hydrated MG MG - Sulfate MG - MG MG – MG MG -G G – G MG -G MG – MG MG -G Hydrated MG

19 GlyoxalMethylglyoxalGlyoxal- Methylglyoxal a ± ± b0140±3483±13 a = (dyn cm -1 K -1 ); b = kg H 2 O (mol C) -1 Surface Tension

20 Varying concentrations (1:1 G:MG) in 3.1 M AS Light absorbing products

21 k A II 5 × k B II 1 × k C II 3.25 × k D II 0.15 εGεG 750 ε MG 7500 Self- and cross-reactions have the same rate- limiting step (protonation of the carbonyl) Kinetic Model

Cross-reaction products make up a large fraction of product mass. Absorption kinetics and surface tension can be modeled in parallel. Impact: Knowledge of reaction products might not be required to accurately describe an aerosol system. Schwier, Sareen, Mitroo, Shapiro, McNeill, Environmental Science & Technology,

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24 Henning et al Schwier et al How do we account for salt? 2 ways:Explicitlyand Implicitly Tuckermann et al. 2007

25 Complex Organic Mixture Glyoxal Methylglyoxal Oxalic Acid Succinic Acid Acetaldehyde Formaldehyde

26 Leucine + Acetaldehyde What is the model missing?? ~Structurally dissimilar molecule reaction pathways

27 Modeling structurally similar molecules is possible. However, we are still missing key information about structurally dissimilar molecules. Impact: Can we use this information in Köhler Theory? Schwier, Viglione, Li, McNeill, Atmospheric Chemistry and Physics Discussion, 2012

III. If an organic film is oxidized, how does this change the CCN activity? 28 Cl - H2OH2O H2OH2O H2OH2ONa+ H 2 O Cl - H2OH2O Na+ H2OH2O O3O3 O3O3 O3O3 28

Sodium Oleate and Oleic Acid Azelaic Acid Nonanaldehyde (nonanal)Nonanoic Acid 9-oxononanoic Acid + Humid conditions + 29

DMA = Differential Mobility Analyzer CPC = Condensation Particle Counter CFSTGC = Continuous Flow Streamwise Thermal Gradient Cloud Condensation Nuclei Counter Methodology M and 0.01 M SO 0.05 M NaCl CFSTGC O 3 + N 2 Flow Tube Reactor CPC DMA Drier Atomizer TSI 3076 Sodium Oleate (SO) Solutions Humidified N 2 t r = 3 min Control Experiments: M SO 0.06 M Na 2 SO 4 Oxidation controls with salt Acidified Experiments 7 30

CCN Data 8 31

32 Ozone oxidation of acidified particles slightly decreases CCN activity at higher critical SS 32

Power Law Fits κ -Köhler Petters & Kreidenweis, Power Log Fit κ (avg) M SO, Water, (fit to NaCl SS%) ± NaCl ± M SO, NaCl ± M SO, NaCl, 1 ppm O ± M SO, NaCl, H 2 SO ± M SO, NaCl, H 2 SO 4, 1 ppm O ± Na 2 SO ± M SO, Na 2 SO ± M SO, Na 2 SO 4, 1 ppm O ± M SO, Na 2 SO 4, H 2 SO ± M SO, Na 2 SO 4, H 2 SO 4, 1 ppm O ±

Köhler Theory Analysis Inferred surface tension for acidified aerosols, assuming in-particle concentrations of or 1.76 M oleate in either 8.6 M NaCl or 10.6 M Na 2 SO 4. σ (mN/m) [0.176 M]σ (mN/m) [1.76 M] Before Oxidation After Oxidation (1ppm) Before Oxidation After Oxidation (1ppm) NaCl Na 2 SO Padró et al

Oxidation depresses CCN activity, especially for acidic aerosols; it also makes the organic film disappear. Impact: Can this change cloud nucleation? Schwier, Sareen, Lathem, Nenes, McNeill, Journal of Geophysical Research,

Surfactant systems in aerosols are incredibly complex Organic films form at atmospherically relevant conditions Modeling of reaction mixtures could be simplified depending on the organic species Oxidation does not always increase CCN activity Conclusions 36 Cl - H2OH2O H2OH2O H2OH2ONa+ H 2 O Cl - H2OH2O Na+ H2OH2O

Acknowledgements: V. Faye McNeill Dhruv Mitroo Giuliana Viglione Neha Sareen McNeill Group Terry Lathem Athanasios Nenes Koberstein Group Funding: 37

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Impact Direct Effect: scattering/absorbing solar radiation Indirect Effect: cloud properties such as cloud lifetime and albedo Aerosols mostly believed to have a cooling effect Global radiation budget and climate Scientific Understanding is LOW 40

41 Taken from Isaksen et al. [2009], adapted from AR4 IPCC [2007]

Mechanisms (Hemi)acetal formation Aldol Condensation

Mechanisms Imidazole Formation + 43

Köhler Theory Consider the change of Gibbs free energy of formation of a single drop from a flat surface Write in terms of vapor and liquid and curvature Rewrite and relate n to R p Evaluate g l - g v : Use Gibbs fundamental equation and laws of ideality, simplify, write in terms of pressure, integrate, and re-substitute Solve for maximum Δ G, then re-arrange in terms of saturation ratio Kelvin Equation Pure Water Droplet Following Seinfeld & Pandis 44

Köhler Theory cont. Flat Water Solution Write out chemical potential of gas phase and liquid phase in terms of partial pressures, activity coefficients, combine, simplify Aqueous Solution Droplets Combine these cases Solve for molar volume, substitute, use dilute approximation Solve molar volume, write in terms of A and B 45

Empirical Model Szyszkowski – Langmuir equation Henning (2005) describes complex non reacting organic species by modifying the above equation: σ and σ w are the surface tension of solution and water T is the temperature C is the concentration of soluble carbon (mol C/kg water) a and b constants related to the organic χ Is the carbon content of each species (mol C/kg water) 46

“Salting Out” ~ Salt ions surround themselves with a shell of water  Electrostriction ~ Decreases amount of available water for organic ~ “SALT IN” or “SALT OUT” γ and γ o are activity coefficients of organic in salt and water S and S o are solubility of organic in salt and water K s is Setschenow constant C s is salt concentration Setschenow, 1889 Varies on factors such as polarity of the organic, and type of salt 47

 Control experiments:  At pH 1, ratio of dissociated vs. non- dissociated using pKa and pH, will remain mostly non dissociated at acidic conditions  Bulk depletion effects – used solid precipitate  Nitric acid effect on surface tension depression 48

 Time spent in aerosol form: 3.5 s, so oligomerization products were formed in bulk solutions 49

 Ozone concentration 0.2 & 1 ppm  Particle concentration: 9 x 10 4 cm -3, 200 nm diameter  Acidified aerosols, pH ~8 to pH ~0.4  Internally mixed aerosols: sum of components for κ -Köhler theory 50