Cloud Condensation Nuclei Hygroscopic Parameter Kappa Covers Reading Material in Chapter 17.5 Atmospheric Sciences 5200 Physical Meteorology III: Cloud Physics
Cloud Condensation Nuclei (CCN) Form a cloud droplet under atmospheric saturations Reported CCN concentrations always refer to specific supersaturations, for example CCN(1%) or CCN(0.5%) + Number distribution of aerosol population CCN s = & n D ) dd ) CCN @ supersaturation, - Activation diameter for supersaturation
Cloud Condensation Nuclei (CCN) + CCN s = & f / D ) n(d ) )dd ), - Fraction of the aerosol particles of D p that are activated at supersaturation s% f / D ) is will be either 0 or 1, if the aerosol particles are internally mixed (all particles of the same diameter have the same chemical composition)
Realistic
Relative humidity RH = e e / (T) Supersaturation e > e / (T) S RH 100% S 0.5 2% in convective updrafts
CCN data
Ambient CCN Depends on both Size and Composition
Results from a spruce wood fire Average CCN/CN ratios as function of supersaturation and particle diameter. P. Frank, G & Ulrike, Dusek & Andreae, Meinrat. (2006). Technical note: A method for measuring sizeresolved CCN in the atmosphere. Atmospheric Chemistry and Physics Discussions. 6.. 10.5194/acpd-6-4879- 2006.
P. Frank, G & Ulrike, Dusek & Andreae, Meinrat. (2006). Technical note: A method for measuring sizeresolved CCN in the atmosphere. Atmospheric Chemistry and Physics Discussions. 6.. 10.5194/acpd-6-4879- 2006. Results from a peat fire. Average CCN/CN ratios as function of supersaturation. The 50 and 100 nm particles show similar behavior to the wood fire, whereas the 250 and 325 nm particles behave different
Ambient CCN Depends on both Size and Composition Size Dominates
Fig. 1. (A) An example of size-resolved 6-hour averaged CCN spectra for particle diameters between 40 and 120 nm. U. Dusek et al. Science 2006;312:1375-1378 Published by AAAS
Fig. 2. (A to D) Particle number size distributions and CCN size distributions for the four chosen case studies. U. Dusek et al. Science 2006;312:1375-1378 Published by AAAS
Are scenarios where composition changes do matter Aging of dust
Giant CCN Small fraction of particles with relatively large dry diameters (>1um) that activate at low supersaturations (<0.02%) These particles can grow to a large size (>10um) even before becoming actually activated. First to activate, grow rapidly, reduce the supersaturation reached in the cloud. Sea spray over ocean Large Ash from biomass burning, mineral dust, salt particles from evaporating lakes
Köhler Curve Koehler curve for two drops: N s =1x10-17 moles (blue solid line), N s =5x10-17 moles (red dashed line). Credit: W. Brune
Hygroscopic Parameter Kappa Many many organic compounds in aerosols are unknown and not individually measured Difficult to predict CCN behavior of these ambient aerosols from 1 st principals (Köhler theory)
Hygroscopic Parameter Kappa Kroll et al., Nature Chemistry 3, 133 139 (2011)
Hygroscopic Parameter Kappa Kroll et al., Nature Chemistry 3, 133 139 (2011)
Hygroscopic Parameter Kappa Many many organic compounds in aerosols are unknown and not individually measured Difficult to predict CCN behavior of these ambient aerosols from 1 st principals (Köhler theory) Petter and Kreidenweis (2007) introduced a hygroscopicity parameter, kappa Relates the volume of water taken up by a particle to the water activity. Values of kappa determined experimentally by fitting CCN activity κ
Köhler Curve e / (D ) ) e / y D x D = exp 4M Dσ D R L Tρ D D ) x D = Mole fraction of pure water e / = saturation vapor pressure of water adjacent to a pure water droplet of the same size and at the same temperature. y D = Activity Coefficient, accounts for non ideal behavior y D 1, for dilute solution M w = Molecular Weight of substance ρ D = water density
Hygroscopic Parameter Kappa e / (D ) ) e / y D x D = exp 4M Dσ D R L Tρ D D ) S = a D exp 4v Dσ D R L TD ) a D = water activity in the solution
Hygroscopic Parameter Kappa e / (D ) ) e / y D x D = exp 4M Dσ D R L Tρ D D ) S = a D exp 4v Dσ D R L TD ) a D = water activity in the solution Need to put this in something that we can measure
Hygroscopic Parameter Kappa S = a D exp 4v Dσ D R L TD ) a D = water activity in the solution 1 a D = 1 + κ V / V D Volume of the dry particle Volume of the water S = D )` D à D )` D à (1 κ) exp 4v Dσ D R L TD )
Hygroscopic Tandem Differential Mobility Analyser
Hygroscopic Tandem Differential Mobility Analyser