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Relationship Between Growth Factor and Critical Supersaturation for Aerosol Particles

This study explores the hygroscopic growth factor at 90% relative humidity for various aerosol particles, including pure ammonium sulfate and sodium chloride. By plotting the growth factor against the critical supersaturation necessary for cloud droplet activation, we observe key trends influenced by the Kelvin effect. The "kappa Köhler" equation facilitates predictions of critical supersaturation based on growth factors and dry diameters. Measured data is compared to these predictions, providing insights into aerosol behavior and activation fractions across varying dry sizes and supersaturations.

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Relationship Between Growth Factor and Critical Supersaturation for Aerosol Particles

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Presentation Transcript

  1. HTMDA & CCN Celtic Explorer Cruise

  2. Plot of hygroscopic growth factor at 90% relative humidity for a given dry diameter vs. the critical supersaturation required for cloud droplet activation of that sized particle

  3. e.g. if we plot pure ammonium sulphate and sodium chloride aerosol in this way: • The growth factor decreases with decreasing dry size due to the Kelvin effect • And the critical supersaturation decreases with increasing dry size

  4. Solving the “kappa köhler “ equation at 90% relative humidity, assuming the surface tension of pure water for growth factors between 1.0 and 2.5 we can see the predicted critical supersaturations for any growth factor and dry diameter pairing.

  5. The measured data can be plotted in the same way, i.e. the growth factor at 90% RH is plotted against the measured critical supersaturation for each dry size the HTDMA measures at a given time.

  6. The measured data can now be compared to the predictions made using the “kappa köhler” equation As the growth factor is the only variable in the model, for a single dry size the predicted critical supersaturation fall along a single curve on the plot

  7. To better represent the relationship between the measured and predicted data, the model predictions are plotted as a box and whiskers plot for each dry size

  8. Activated Fraction (CCN/CN)

  9. Using the activated fractions measured at for each dry size for the 5 different supersaturations, the critical supersaturation can calculated:

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