Friebel, Franz

Kanji, Zamin A.

Lohmann, Ulrike

Mahrt, Fabian

Mensah, Amewu A.

Neubauer, David

KITopen

The role of black carbon in cloud formation and climate   Ulrike LohmannF. Friebel, Z.A. Kanji, F. Mahrt, A.A. Mensah, D. Neubauer Source: wikipediaBond et al., 2013Bond et al., 2013Climate forcing of soot and co-emitted species (1750-2005)• Can soot particles act as cloud condensation nuclei (CCN) at atmospheric conditions?• Can soot particles act as ice nucleating particles (INPs) at atmospheric conditions?• Can cloud processing of soot particles improve their INP ability? Is soot a good cloud condensation nucleus?16.05.2019Franz Friebel7• 100nm soot particles• 16h aging time• miniCAST brown (organic carbon rich soot)Ozone0- 200ppbTemperature5- 35°CContinuous-flow Stirred Tank Reactor (CSTR) The minionFriebel and Mensah, AMT, 2019Ozone oxidation of 100 nm organic-rich sootAdding 200 ppb ozone → adsorptionContinuous exposure to 200 ppb ozonetact = 3 - 12 hActivation time tactZurich LuganoMexico CityOzone x 8tact x 1.7Activation time vs. ozone concentrationMoscowZurichPhoenixTemperature dependency at 200 ppb O3tact x 5Activation times of soot in ZürichClimate impact of ozone-aged soot→ 93% increase in cloud droplet burden north of 60 ºN for 10h activation timeCCN competitionlow CCN backgroundfew susceptible cloudsor low soot emissionsrelatively strong increasecloud dropletsClimate impact of ozone-aged soot--> Largest impact of ozone as CCN at around 60 ºNIs soot a good ice nucleating particle?Hoose and Möhler, 2012Ice nucleation onset supersaturations (Si) and temperaturesKanji et al., 2017Ice nucleation onset for different soot typesWater saturation (RHw = 100%)Homogeneous freezing of solution dropletsIce nucleation activity of soot particlesIce nucleation activity of soot particles▪ Different soot typeshave different physicochemicalproperties.▪ Strong temperaturedependence of iceformation.▪ Implies involvement ofliquid water.Water freezes homogeneouslyHNT = 235 KCloud dropletMahrt et al., ACP, 2018Pore condensation and freezingRHw ≥ 100 %Porous particleRHw < 100 %Non-porous particleParticle surfaceCondensed water▪ Water is taken up by capillarycondensation at RHw < 100%.▪ Pore water freezes homogeneouslyat T < 235 KT < HNTIceMarcolli, ACP, 2014; David et al., PNAS, 2019How often do we find soot with pores?Mahrt et al., ACP, 2018Atmo-spherically aged sootDiesel sootLamb blackAircraft sootCloud processing for cirrus cloudsCloud processingIce cloud processingMixed-phase cloudprocessingMahrt et al., JGR, subm.Water saturation (RHw = 100%)Homogeneous freezing of solution dropletsUnprocessed sootCloud processingWater saturation (RHw = 100%)Homogeneous freezing of solution dropletsUnprocessed sootProcessed (Cirrus)High RH& low TCloud processedsoot is muchmore ice active.Cloud processingTransition T = 233 KImpact of processing vs. transitionCan ice be retained in pores duringtransition ? 1stCloud cycleTransition2ndCloud cycleUnprocessedProcessed (Cirrus)Transition T = 233 KTransition T = 293 K Can ice be retained in pores duringtransition ? 1stCloud cycleTransition2ndCloud cycleImpact of processing vs. transitionWater saturation (RHw = 100%)Homogeneous freezing of solution dropletsUnprocessed sootProcessed (Cirrus)Processed (MPC)Pre-coolingCloud processingEnhanced icenucleation controlledby hydrometeorformation.Low RH& low THigh RH& low THigh RH& high THydrometeor formation changes sootmorphological propertiesUnprocessedProcessedPerfectcircle▪ Cloud processed sootaggregates are morecompacted.Impact on ice crystal number concentrationonly accumulation +coarse modeall modes→ Cloud processing of soot makes soot potentially as important as mineral dustImpact on ice crystal number concentrations (ICNC)1. How important is soot as a CCN? ➢ It depends on the organic carbon content➢ It can be important if aged with ozone at atmospheric conditions and can increase the cloud droplet burden significantly on the Northern Hemisphere1. How important is soot as an INP?➢ This depends on the soot type; in general soot types with pores are favoured➢ Soot INP could noticeably increase the ice crystal concentration in mid latitudes2. How important is cloud processing of soot for cirrus clouds?➢ It lowers onset RHw by 10% and can then rival with other INPs➢ Depending on how much soot act as INPs, the global ice crystal burden can be decreased or increasedTake-home messagesQuestions?Active Fraction =𝑵(𝑰𝒄𝒆)𝑵(𝑨𝒆𝒓𝒐𝒔𝒐𝒍)Quantifying the ice nucleation activity of soot using the Horizontal Ice Nucleation Chamber (HINC)NABEL station: Jungfraujochtact = A ∙ e−EAR∙T ∙Keq ∙ Cozone1+ Keq ∙ Cozone−1Keq = 0.0229 ppb-1p = 650 mbarDifferent soot typesMahrt et al., ACP, 2018Atmo-spherically aged sootDiesel sootLamb blackAircraft sootCirrus cloud regime: 400 nm soot particlesCan particle morphology (pores)give insight?Mahrt et al., ACP, 2018Which mechanism is responsible for ice nucleation? Low RH (and steep) activation curves of FW200 soot suggest PCF type mechanismθ =Keq ∙ Cozone1+ Keq ∙ CozoneLangmuir-adsorption: O3 adsorption is the bottleneck for soot agingCirrusCloud processing1stCloud cycleTransition2ndCloud cycle

The role of black carbon in cloud formation and climate

https://publikationen.bibliothek.kit.edu/1000096742/35307922

The role of black carbon in cloud formation and climate

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