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Cloud Condensation Nuclei (CCN) Properties of Ambient Aerosol

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Cloud Condensation Nuclei (CCN) Properties of Ambient Aerosol Tracey Alayne Rissman California Institute of Technology, Pasadena, CA Cloud Condensation Nuclei (CCN) Properties of Ambient Aerosol Environmental Issues Scientific Approach Aerosol/CCN Closures • Clouds and Climate Change • Instrument Development • CRYSTAL-FACE (July 2002) 4 10 9 0.85% Supersaturation 8 100% (NH ) SO 7 4 2 4 • Key West, FL: Marine Conditions • The Earth’s climate is the result of a delicate balance between • Designed and built one-column and three-column CCN log(N ) = m*log(N ) + b 6 P O µ(NP/NO) = 1.09 5 m = 1.04 σ(NP/NO) = 0.31 b = -0.08 4 ) -3 Flight 1 incoming and outgoing radiation. counters (CCNCs), based on previous Caltech CCNCs 3 • Closure was successful, probably Flight 2 ; cm P Flight 3 N 2 Flight 4 Flight 5 due to simple chemistry, mostly • Small changes in the Earth’s cloudiness can lead to changes in Flight 6 Flight 10 103 9 Flight 11 •Field Campaigns 8 Flight 12 7 (NH ) SO , of ambient particles. the overall energy balance on the globe, which can affect climate. 6 Flight 13 4 2 4 5 Flight 14 Flight 15 4 Flight 16 • Field campaigns allow the integration of data from many 3 Flight 17 • Important activation properties in Flight 18 Predicted CCN Concentration( 2 Flight 19 • Aerosols, Clouds, and the Indirect Effect Flight 20 different instruments at the same time. theory: aerosol size distribution 1:1 Line 2 Linear Fit in 10 9 8 Log-Log Space • Clouds form by water condensing on small particles suspended • Large CCN data sets are obtained during field missions 7 7 8 9 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 • VanReken et al. (2004) 102 103 104 Observed CCN Concentration (N ; cm-3) in the air (aerosols). Particles upon which cloud droplets form are by deploying a CCNC on an airplane and sampling at O called cloud condensation nuclei (CCN). various locations and altitudes. •ARM Aerosol IOP (May 2003) 4 2.8% Supersaturation: Flights 6-8,10 • Human emissions are increasing levels of aerosols in the 3 3.6% Supersaturation: Flight 9 • Lamont, OK: Continental Conditions 2.1% Supersaturation: Flights 12-17 2 • Aerosol/CCN Closure Studies 100% (NH4)2SO4 ) 4 atmosphere. The extent and mechanism of this impact are some -3 µ(N /N ) = 1.92 10 P O • Closure complicated by continental σ(N /N ) = 1.29 ; cm 7 P O P 6 N 5 • Compares CCN concentration observed by the CCNC to log(NP)=m*log(NO) + b of the key problems in the science of climate. 4 m = 0.90 character of ambient aerosol – Flight 6 3 b = 0.54 Flight 7 that predicted from the aerosol size distribution measured 2 Flight 8 • Aerosol particles alter cloud properties and, therefore, have an Flight 9 increased insoluble material, possibly Flight 10 3 10 Flight 12 by a Differential Mobility Analyzer (DMA). 7 Flight 13 indirect radiative forcing on climate. 6 Flight 14 5 organic, and external mixing Flight 15 4 Flight 16 Predicted CCN Concentration( • Can be complicated by chemistry and other properties of 3 Flight 17 2 • Important activation properties in 1:1 Line Linear Fit in Assumed 0.15% Ambient Supersaturation 2 For a given particle composition, only particles with 10 Log-Log Space the aerosol population. Sample Aerosol Size Distribution from DMA dry diameters greater than the critical diameter are 600 (One Time Scan, N is number concentration) able to activate into cloud droplets. 9 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 3 4 theory: insoluble material and mixing 0.4 2 3 4 Dry Diameter = 100 nm At 0.15% supersaturation, particles with the Area Under the Aerosol Size Distribution Curve for 10 10 -3 10 Particle Mass Fractions: given compositions have the following Observed CCN Concentration (NO;cm ) 100% (NH ) SO Diameters Greather than the Cut-Off Diameter 4 2 4 calculated critical diameters: = Number Concentration of Activated Particles 60% (NH ) SO , 40% Insoluble 500 0.3 4 2 4 40% (NH ) SO , 60% Insoluble state of the aerosol population 4 2 4 100% (NH ) SO : 100 nm *Images from 4 2 4 Total Number Concentration of Activated Particles: 20% (NH4)2SO4, 80% Insoluble -3 60% (NH4)2SO4, 40% Insoluble: 120 nm 100% (NH ) SO : 2628 cm 4 2 4 40% (NH4)2SO4, 60% Insoluble: 137 nm -3 Sample Ambient Supersaturation, 0.15% 60% (NH4)2SO4, 40% Insoluble: 1679 cm ) 400 0.2 20% (NH4)2SO4, 80% Insoluble: 173 nm -3 -3 40% (NH4)2SO4, 60% Insoluble: 882 cm terra.nasa.gov -3 (cm 20% (NH ) SO , 80% Insoluble: 620 cm P 4 2 4 Increasing Insoluble Mass Fraction 0.1 => Increasing Critical Supersaturation and 300 100 nm •CSTRIPE (July 2003) Critical Dry Diameter dN/dlogD 120 nm Supersaturation (%) Supersaturation 0.0 200 2 0.58% Supersaturation • Marina, CA: Marine and Continental At a sample ambient supersaturation of 0.15% and for a dry particle diameter of 100 nm, only the 100% (NH4)2SO4 particle would be able activate into a cloud 100% (NH4)2SO4 log(NP)=m*log(NO) + b droplet. 137 nm 4 µ(N /N ) = 1.36 10 P O m = 0.96 “Clean” “Polluted” -0.1 173 nm 100 The particles with insoluble material will activate into cloud droplets at 0.15% σ(NP/NO) = 0.38 b = 0.22 supersaturation at larger dry diameters (see figure to right). 7 Conditions 6 ) 5 -3 4 -0.2 0 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 3 4 5 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 ; cm 3 10 10 10 10 10 100 P • Low particle number • High particle number concentration Droplet Diameter (nm) N • Closure line shifted due to mixed Dry Diameter (D , nm) P 2 Flight 1 Flight 4 Flight 6 3 concentration = fewer, larger = more, smaller droplets formed 10 Flight 8 (marine and continental) character of 7 Flight 9 •Theoretical Development 6 Flight 10 5 Flight 11 4 droplets formed Flight 14 sampled aerosol populations • More visible radiation reflected 3 Flight 15 Flight 16 • Modify existing CCN activity theory to include more 2 Flight 17 Predicted CCN Concentration( Flight 18 • Important activation properties in • More visible radiation reaches back to space Flight 19 2 10 complicated parameters, such as chemical effects, that 7 1:1 Line 6 Linear Fit in 5 the Earth’s surface. Log-Log Space theory: insoluble material and mixing • Higher cloud albedo (reflectivity); 4 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 2 are discovered to be important in the activation process 2 3 4 10 10 -3 10 Observed CCN Concentration (N ; cm ) O state of the aerosol population • Lower cloud albedo (reflectivity) cools Earth’s surface from field campaign data analysis..
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