Trees, Aerosols, and Clouds Colby J. Fronk1, Gwenore F. Pokrifka2, Jerry Y. Harrington2, and Jose D. Fuentes2

1. Department of Chemical Engineering, Rochester Institute of Technology

2. Department of Meteorology and Atmospheric Science, The Pennsylvania State University

We are grateful for the support from The National Science Foundation (NSF), grant No. AGS-1560339. This research was part of the NSF's REU program and was conducted at The Pennsylvania State University within the Department of Meteorology and Atmospheric Science.

Changing Aerosol Composition: (Eastern United States)

Traditional Köhler Theory:

Modified Köhler Theory: Air Parcel Model: Results

References

Acknowledgements Assumptions:

• Equilibrium for drop formed on solute aerosol

• Original, solid core aerosol is dissolved

• The solute is dilute, concentration <10

Slowly Dissolving Aerosol Core • The solute saturation concentration and amount of solvent

present determines how much of the aerosol dissolves

• The remaining aerosol, the aerosol core, is assumed to stay at the center of the droplet during the dissolution process

• Dissolved solute diffuses radially away from the core toward the droplet’s surface

• As a result of diffusion, the solute has a concentration gradient within the droplet that varies radially outward from the core

𝑆𝑒𝑞 = exp4𝑀𝑤𝜎

𝑅𝑇𝜌𝑤∗1

𝐷𝑝

𝜆𝑤

1 +𝑀𝑤𝜌𝑤

∗ 𝑣𝑖∗ 𝐶𝑖𝑠𝑢𝑟𝑓𝑎𝑐𝑒

Unmodified Kelvin Term Modified Solution Term

[Miyawaki et. al, 1997] 𝜆𝑤 = exp(𝛼 ∗ 𝑋𝑖2 + 𝛽 ∗ 𝑋𝑖

3)

Water Activity Coefficient

Solute Surface Concentration

𝐶𝑖𝑠𝑢𝑟𝑓𝑎𝑐𝑒

=

max(1

2𝐶𝑠𝑎𝑡,𝑖 ,

𝐶𝑠𝑎𝑡,𝑖

1 + (1 −𝐷𝑐𝐷𝑠)(𝐷𝑐𝐷𝑠)𝐷𝑝(𝑆 − 𝑆𝑒𝑞)4𝐷𝑐𝐺𝐷𝑖,𝑤

6𝑚𝑖

𝜋𝑀𝑖(𝐷𝑝3 − 𝐷𝑐

3)

[Asa-Awuku & Nenes, 2007]

Equilibrium Saturation Ratio

Air Parcel Model: Overview

How does the changing aerosol composition affect cloud formation and growth processes?

Fig 5. The parcel model was ran for all of the chemical species with varying maximum updraft speeds, wmax. With the exception of the

first panel, the distribution is shown at the time immediately after all of the particles are finished activating. In all simulations, the initial

conditions were: RH0=0.80, Z0=300 m, T0=15 deg C, and P0=919000 Pa. The CCN size distribution was kept constant with the

following lognormal distribution: geometric standard deviation=1.8 , NCCN=100 particles cm-3 bin-1, and median=0.05 um.

a.) H2SO4 b.) Pinic Acid c.) 𝜶-Pinene

Solute Mass

Fig 4. Modified Köhler curves

Fig 2. Traditional Köhler curve

Fig 1. Changing aerosol source and composition for the eastern United States

Fig 3. Slowly dissolving aerosol core with

concentration gradient

Table 1: Percentage of activated droplets for the time corresponding to the subfigures in Fig 5.

Compound b.)Wmax=25 cm/s c.) Wmax=100 cm/s d.) Wmax=250 cm/s e.) Wmax= 500 cm/s f.) Wmax=750 cm/s g) Wmax=1000 cm/s

H2SO4 76.81% 95.48% 99.56% 100.00% 100.00% 100.00%

(NH4)2SO4 69.92% 92.99% 98.98% 99.88% 100.00% 100.00%

A-Pinene 8.30% 20.52% 39.76% 62.06% 75.44% 81.08%

B-Pinene 8.32% 20.56% 39.81% 62.10% 75.48% 81.12%

General SOA 8.32% 26.28% 47.14% 61.98% 75.29% 80.90%

Pinic Acid 45.61% 74.20% 89.18% 97.03% 98.43% 99.40%

Pinonic Acid 45.22% 73.88% 89.00% 96.97% 98.39% 99.38%

Norpinonic

Acid

45.61% 74.20% 89.18% 97.03% 98.43% 100.00%

• A set of ordinary differential equations for vertical velocity, ambient temperature, ambient pressure, saturation ratio, and equations for the growth 200 droplet bins are solved

• Constraints for conservation of mass and conservation of energy are imposed.

• Based on a droplet model developed by Feingold and Chuang [2002] and numerically integrated using the Variable Order Differential Equation (VODE) solver

(while dissolving)

(for completely dissolved aerosol)

𝑆𝑒𝑞 = exp(4𝑀𝑤𝜎

𝑅𝑇𝜌𝑤∗1

𝐷𝑝−6𝑣𝑠𝑚𝑠𝑀𝑤

𝜋𝜌𝑤𝑀𝑠∗1

𝐷𝑝3)

[Lamb & Verlinde, 2011]

Equilibrium Saturation Ratio

Kelvin Term (Drop Curvature Effect)

Solution Term (Raoult’s Law)

We need to modify this equation for organics with low solubility

1Asa-Awuku, A., & Nenes, A. (2007). Effect of solute dissolution kinetics on cloud droplet formation: Extended Köhler theory. Journal of Geophysical Research,112(D22). doi:10.1029/2005jd006934 2Brown, P. N., Byrne, G. D., & Hindmarsh, A. C. (1989). VODE: A Variable-Coefficient ODE Solver. SIAM Journal on Scientific and Statistical Computing,10(5), 1038-1051. doi:10.1137/0910062 3Engelhart, G. J., Asa-Awuku, A., Nenes, A., & Pandis, S. N. (2008). CCN activity and droplet growth kinetics of fresh and aged monoterpene secondary organic aerosol. Atmospheric Chemistry and Physics,8(14), 3937-3949. doi:10.5194/acp-8-3937-2008 4Feingold, G., & Chuang, P. Y. (2002). Analysis of the Influence of Film-Forming Compounds on Droplet Growth: Implications for Cloud Microphysical Processes and Climate. Journal of the Atmospheric Sciences,59(12), 2006-2018. doi:10.1175/1520-0469(2002)0592.0.co;2 5Lamb, D., & Verlinde, J. (2011). Physics and chemistry of clouds. Cambridge: Cambridge University Press. 6Lebo, Z. J., Johnson, N. C., & Harrington, J. Y. (2008). Radiative influences on ice crystal and droplet growth within mixed-phase stratus clouds. Journal of Geophysical Research,113(D9). doi:10.1029/2007jd009262 7Miyawaki, O., Saito, A., Matsuo, T., & Nakamura, K. (1997). Activity and Activity Coefficient of Water in Aqueous Solutions and Their Relationships with Solution Structure Parameters. Bioscience, Biotechnology, and Biochemistry,61(3), 466-469. doi:10.1271/bbb.61.466 8Raymond, T. M. (2002). Cloud activation of single-component organic aerosol particles. Journal of Geophysical Research,107(D24). doi:10.1029/2002jd002159