scholarly journals Droplet activation behaviour of atmospheric black carbon particles in fog as a function of their size and mixing state

2018 ◽  
Author(s):  
Ghislain Motos ◽  
Julia Schmale ◽  
Joel Christopher Corbin ◽  
Marco Zanatta ◽  
Urs Baltensperger ◽  
...  
Keyword(s):  
Black Carbon ◽  
Single Particle ◽  
Radiative Forcing ◽  
Cloud Condensation Nuclei ◽  
Mixing State ◽  
Scanning Mobility Particle Sizer ◽  
Carbon Particles ◽  
Hygroscopic Properties ◽  
Droplet Activation ◽  
Aerosol Cloud Interactions

Abstract. Among the variety of particle types present in the atmosphere, black carbon (BC), emitted by combustion processes, is uniquely associated with harmful effects to the human body and substantial radiative forcing of the Earth. Pure BC is known to be non-hygroscopic, but its ability to acquire a coating of hygroscopic organic and inorganic material leads to increased hygroscopicity as well as diameter, facilitating droplet activation. This affects BC radiative forcing through aerosol-cloud interactions (aci) and BC life cycle. To gain insights into these processes, we performed a field campaign in winter 2015/16 in a residential area of Zurich which aimed at distinguishing different particle mixing states regarding hygroscopic properties in the cloud condensation nuclei (CCN)-activated fraction spectrum of urban aerosol and establishing relations between the mixing state of BC and its activation to form droplets in fog. This was achieved by operating a CCN counter (CCNC), a scanning mobility particle sizer (SMPS), a single particle soot photometer (SP2) and an aerosol chemical speciation monitor (ACSM) behind a combination of a total- and an interstitial-aerosol inlet. Our results indicate that, depending on the time of the day, we sampled both heavily aged internally mixed BC from background air advected to the site and freshly emitted externally mixed BC from local or regional traffic sources. During rush hours in the morning of weekdays, we found clear evidence that the enhanced traffic emissions caused peaks in the number fraction of externally mixed BC particles which do not act as CCN within the CCNC. The mixing state of BC particles was also found to play a key role in their ability to form fog droplets. The very low effective peak supersaturations (SSpeak) occurring in fog (between approximately 0.03 and 0.06 % during this campaign) restrict droplet activation to a minor fraction of the aerosol burden (around 0.5 to 1 % of total particle number concentration between 20 and 593 nm) leading to very selective criteria on diameter and chemical composition. We show that bare BC cores are unable to activate to fog droplets at such low SSpeak, while BC particles surrounded by thick coating have a very similar activation behavior as BC-free particles. The threshold coating thickness required for activation was shown to decrease with increasing BC core size. Using simplified κ-Köhler theory combined with the ZSR mixing rule assuming spherical core-shell particle geometry constrained with single particle measurements of respective volumes, we found good agreement between the predicted and the directly observed size and mixing state resolved droplet activation behaviour of BC-containing particles in fog. This successful closure demonstrates the predictability of their droplet activation in fog with a simplified theoretical model only requiring size and mixing state information, which can also be applied in a consistent manner in model simulations.

scholarly journals Droplet activation behaviour of atmospheric black carbon particles in fog as a function of their size and mixing state

2019 ◽  
Vol 19 (4) ◽  
pp. 2183-2207 ◽  
Author(s):  
Ghislain Motos ◽  
Julia Schmale ◽  
Joel C. Corbin ◽  
Marco Zanatta ◽  
Urs Baltensperger ◽  
...  
Keyword(s):  
Black Carbon ◽  
Single Particle ◽  
Radiative Forcing ◽  
Mixing State ◽  
Scanning Mobility Particle Sizer ◽  
Carbon Particles ◽  
Kohler Theory ◽  
Droplet Activation ◽  
Aerosol Cloud Interactions ◽  
A Minor

Abstract. Among the variety of particle types present in the atmosphere, black carbon (BC), emitted by combustion processes, is uniquely associated with harmful effects to the human body and substantial radiative forcing of the Earth. Pure BC is known to be non-hygroscopic, but its ability to acquire a coating of hygroscopic organic and inorganic material leads to increased diameter and hygroscopicity, facilitating droplet activation. This affects BC radiative forcing through aerosol–cloud interactions (ACIs) and BC life cycle. To gain insights into these processes, we performed a field campaign in winter 2015–2016 in a residential area of Zurich which aimed at establishing relations between the size and mixing state of BC particles and their activation to form droplets in fog. This was achieved by operating a CCN counter (CCNC), a scanning mobility particle sizer (SMPS), a single-particle soot photometer (SP2) and an aerosol chemical speciation monitor (ACSM) behind a combination of a total- and an interstitial-aerosol inlet. Our results indicate that in the morning hours of weekdays, the enhanced traffic emissions caused peaks in the number fraction of externally mixed BC particles, which do not act as CCN within the CCNC. The very low effective peak supersaturations (SSpeak) occurring in fog (between approximately 0.03 % and 0.06 % during this campaign) restrict droplet activation to a minor fraction of the aerosol burden (around 0.5 % to 1 % of total particle number concentration between 20 and 593 nm) leading to very selective criteria on diameter and chemical composition. We show that bare BC cores are unable to activate to fog droplets at such low SSpeak, while BC particles surrounded by thick coating have very similar activation behaviour to BC-free particles. Using simplified κ-Köhler theory combined with the ZSR mixing rule assuming spherical core–shell particle geometry constrained with single-particle measurements of respective volumes, we found good agreement between the predicted and the directly observed size- and mixing-state-resolved droplet activation behaviour of BC-containing particles in fog. This successful closure demonstrates the predictability of their droplet activation in fog with a simplified theoretical model only requiring size and mixing state information, which can also be applied in a consistent manner in model simulations.

scholarly journals Temporal variations of the hygroscopicity and mixing state of black carbon aerosols in a polluted megacity area

2018 ◽  
Author(s):  
Kangning Li ◽  
Xingnan Ye ◽  
Hongwei Pang ◽  
Xiaohui Lu ◽  
Hong Chen ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Black Carbon ◽  
Single Particle ◽  
Radiative Forcing ◽  
Temporal Variations ◽  
Mixing State ◽  
Atmospheric Aging ◽  
Secondary Organic Carbon ◽  
Bc Aerosols ◽  
Mixing States

Abstract. Black carbon (BC) aerosols in the atmosphere strongly affect radiative forcing. They are mainly removed from the air by wet deposition, and their lifetime is controlled by their water uptake ability or hygroscopicity, which is a function of the aerosol mixing states. It is well known that atmospheric aging processes coat various materials on BC aerosols and affect their mixing states and hygroscopicity. However, detailed relations between the aging processes, the hygroscopicity and mixing state of BC aerosol particles in polluted city areas are not well understood. Here, we studied the temporal variation of the hygroscopicity and its correlation with the mixing state of ambient BC particles during 2017 summer in Shanghai, China using a hygroscopicity tandem differential mobility analyzer in-line with a single particle soot photometer (HTDMA-SP2 system) as well as a single particle aerosol mass spectrometer (SPAMS). BC particles with 120 nm, 240 nm and 360 nm dry diameter were humidified at RH = 85 %. After humidification, particles with growth factors (GFs) of 1.0, 1.2 and 1.4, representing the BC particles with different hygroscopicities (hydrophobic, transition and hydrophilic modes, respectively), were analyzed by a SP2 to obtain their BC mixing states. The diurnal trends of coating thickness and chemical mixing state show that coating materials of BC particles were distinct between daytime and nighttime. The differences were associated with the hygroscopicity of BC particles. Single particle mass spectrometry and other chemical characterization techniques revealed that during nighttime with lower temperature and higher relative humidity (RH), formation or condensation of nitrates resulted in an enhanced hygroscopicity of BC particles. During daytime, secondary organic carbon formation was mainly responsible for the change of hygroscopicity of BC particles. Due to the high hygroscopicity of inorganic nitrate, a thinner nitrate coating on BC particles could convert fresh BC particles to aged hygroscopic ones during nighttime while a thicker coating layer of secondary materials was required to reach the same overall hygroscopicity during daytime since the participation of secondary organic carbon. Different atmospheric aging processes between daytime and nighttime led to the change of BC particles' mixing states, which play a fundamental role in determining their hygroscopicity. To our knowledge, this is the first report of links between temporal variations of the hygroscopic growth of BC particles and atmospheric aging processes in polluted environment. These findings have significant ramification of understanding the aging process, wet removal as well as climate effects of BC particles.

scholarly journals Cloud droplet activation properties and scavenged fraction of black carbon in liquid-phase clouds at the high-alpine research station Jungfraujoch (3580 m a.s.l.)

2019 ◽  
Vol 19 (6) ◽  
pp. 3833-3855 ◽  
Author(s):  
Ghislain Motos ◽  
Julia Schmale ◽  
Joel C. Corbin ◽  
Rob. L. Modini ◽  
Nadine Karlen ◽  
...  
Keyword(s):  
Particle Size ◽  
Black Carbon ◽  
Single Particle ◽  
Aerosol Particles ◽  
Cloud Droplet ◽  
Water Soluble ◽  
Core Size ◽  
Mixing State ◽  
Cloud Droplets ◽  
Droplet Activation

Abstract. Liquid clouds form by condensation of water vapour on aerosol particles in the atmosphere. Even black carbon (BC) particles, which are known to be slightly hygroscopic, have been shown to readily form cloud droplets once they have acquired water-soluble coatings by atmospheric aging processes. Accurately simulating the life cycle of BC in the atmosphere, which strongly depends on the wet removal following droplet activation, has recently been identified as a key element for accurate prediction of the climate forcing of BC. Here, to assess BC activation in detail, we performed in situ measurements during cloud events at the Jungfraujoch high-altitude station in Switzerland in summer 2010 and 2016. Cloud droplet residual and interstitial (unactivated) particles as well as the total aerosol were selectively sampled using different inlets, followed by their physical characterization using scanning mobility particle sizers (SMPSs), multi-angle absorption photometers (MAAPs) and a single-particle soot photometer (SP2). By calculating cloud droplet activated fractions with these measurements, we determined the roles of various parameters on the droplet activation of BC. The half-rise threshold diameter for droplet activation (Dhalfcloud), i.e. the size above which aerosol particles formed cloud droplets, was inferred from the aerosol size distributions measured behind the different inlets. The effective peak supersaturation (SSpeak) of a cloud was derived from Dhalfcloud by comparing it to the supersaturation dependence of the threshold diameter for cloud condensation nuclei (CCN) activation measured by a CCN counter (CCNC). In this way, we showed that the mass-based scavenged fraction of BC strongly correlates with that of the entire aerosol population because SSpeak modulates the critical size for activation of either particle type. A total of 50 % of the BC-containing particles with a BC mass equivalent core diameter of 90 nm was activated in clouds with SSpeak≈0.21 %, increasing up to ∼80 % activated fraction at SSpeak≈0.50 %. On a single-particle basis, BC activation at a certain SSpeak is controlled by the BC core size and internally mixed coating, which increases overall particle size and hygroscopicity. However, the resulting effect on the population averaged and on the size-integrated BC scavenged fraction by mass is small for two reasons: first, acquisition of coatings only matters for small cores in clouds with low SSpeak; and, second, variations in BC core size distribution and mean coating thickness are limited in the lower free troposphere in summer. Finally, we tested the ability of a simplified theoretical model, which combines the κ-Köhler theory with the Zdanovskii–Stokes–Robinson (ZSR) mixing rule under the assumptions of spherical core–shell particle geometry and surface tension of pure water, to predict the droplet activation behaviour of BC-containing particles in real clouds. Predictions of BC activation constrained with SSpeak and measured BC-containing particle size and mixing state were compared with direct cloud observations. These predictions achieved closure with the measurements for the particle size ranges accessible to our instrumentation, that is, BC core diameters and total particle diameters of approximately 50 and 180 nm, respectively. This clearly indicates that such simplified theoretical models provide a sufficient description of BC activation in clouds, as previously shown for activation occurring in fog at lower supersaturation and also shown in laboratory experiments under controlled conditions. This further justifies application of such simplified theoretical approaches in regional and global simulations of BC activation in clouds, which include aerosol modules that explicitly simulate BC-containing particle size and mixing state.

scholarly journals Ambient black carbon particle hygroscopic properties controlled by mixing state and composition

2012 ◽  
Vol 12 (11) ◽  
pp. 28955-28992 ◽  
Author(s):  
D. Liu ◽  
J. Allan ◽  
J. Whitehead ◽  
D. Young ◽  
M. Flynn ◽  
...  
Keyword(s):  
Ammonium Nitrate ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Western Europe ◽  
Carbon Particle ◽  
Chemical Compositions ◽  
Mixing State ◽  
Additional Material ◽  
Considerable Uncertainty ◽  
Hygroscopic Properties

Abstract. The wet removal of black carbon aerosol (BC) in the atmosphere is a crucial factor in determining its atmospheric lifetime and thereby the vertical and horizontal distributions, dispersion on local and regional scales, and the direct, semi-direct and indirect radiative forcing effects. The in-cloud scavenging and wet deposition rate of freshly emitted hydrophobic BC will be increased on acquisition of more-hydrophilic components by coagulation or coating processes. The lifetime of BC is still subject to considerable uncertainty for most of the model inputs, which is largely due to the insufficient constraints on the BC hydrophobic-to-hydrophilic conversion process from observational field data. This study was conducted at a site along UK North Norfolk coastline, where the BC particles were transported from different regions within Western Europe. A hygroscopicity tandem differential mobility analyser (HTDMA) was coupled with a single particle soot photometer (SP2) to measure the hygroscopic properties of BC particles and associated mixing state in real time. In addition, a Soot Particle AMS (SP-AMS) measured the chemical compositions of additional material associated with BC particles. The ensemble of BC particles persistently contained a less-hygroscopic mode at a growth factor (gf) of around 1.05 at 90% RH (dry diameter 163 nm). Importantly, a more-hygroscopic mode of BC particles was observed throughout the experiment, the gf of these BC particles extended up to ~1.4–1.6 with the minimum between this and the less hygroscopic mode at a gf ~1.25, or equivalent effective hygroscopicity parameter κ = ~0.1. The gf of BC particles (gfBC) was highly influenced by the composition of associated soluble material: increases of gfBC were associated with secondary inorganic components, and these increases were more pronounced when ammonium nitrate was in the BC particles; however the presence of secondary organic matter suppressed the gfBC below that of pure inorganics. The Zdanovskii-Stokes-Robinson (ZSR) mixing rule captures the hygroscopicity contributions from different compositions within ±30% compared to the measured results, however is subject to uncertainty due to the complex morphology of BC component and potential artefacts associated with semivolatile particles measured with the HTDMA. This study provides detailed insights on BC hygroscopicity associated with its mixing state, and the results will importantly constrain the microphysical mixing schemes of BC as used by a variety of high level models. In particular, this provides direct evidence to highlight the need to consider ammonium nitrate ageing of BC particles because this will result in particles becoming hydrophilic on much shorter timescales than for sulphate formation, which is often the only mechanism considered.

scholarly journals Temporal variations in the hygroscopicity and mixing state of black carbon aerosols in a polluted megacity area

2018 ◽  
Vol 18 (20) ◽  
pp. 15201-15218 ◽  
Author(s):  
Kangning Li ◽  
Xingnan Ye ◽  
Hongwei Pang ◽  
Xiaohui Lu ◽  
Hong Chen ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Black Carbon ◽  
Single Particle ◽  
Radiative Forcing ◽  
Temporal Variations ◽  
Mixing State ◽  
Atmospheric Aging ◽  
Secondary Organic Carbon ◽  
Bc Aerosols ◽  
Mixing States

Abstract. Black carbon (BC) aerosols in the atmosphere strongly affect radiative forcing. They are mainly removed from the air by wet deposition, and their lifetime is controlled by their water uptake ability or hygroscopicity, which is a function of aerosol mixing states. It is well known that atmospheric aging processes coat various materials on BC aerosols and affect their mixing states and hygroscopicity. However, detailed relations between the aging processes and the hygroscopicity and mixing state of BC aerosol particles in polluted city areas are not well understood. Here, we studied the temporal variation in hygroscopicity and its correlation with the mixing state of ambient BC particles during the summer of 2017 in Shanghai, China, using a hygroscopic tandem differential mobility analyzer inline with a single-particle soot photometer (HTDMA–SP2 system) as well as a single-particle aerosol mass spectrometer (SPAMS). BC particles with 120, 240, and 360 nm in dry diameter were humidified at relative humidity (RH)  =  85 %. After humidification, particles with growth factors (GFs) of 1.0, 1.2, and 1.4, representing the BC particles with different hygroscopicities (hydrophobic, transition, and hydrophilic modes, respectively), were analyzed with a SP2 to obtain their BC mixing states. The diurnal trends in coating thickness and chemical mixing state show that coating materials of BC particles were distinct between daytime and nighttime. The differences were associated with the hygroscopicity of BC particles. Single-particle mass spectrometry and other chemical characterization techniques revealed that with lower temperature and higher RH during nighttime, formation or condensation of nitrates resulted in an enhanced hygroscopicity of BC particles. During daytime, secondary organic carbon formation was mainly responsible for the change of hygroscopicity of BC particles. Due to the high hygroscopicity of inorganic nitrate, a thinner nitrate coating on BC particles could convert fresh BC particles to aged hygroscopic ones during nighttime while a thicker coating layer of secondary materials was required to reach the same overall hygroscopicity during daytime because of the participation of secondary organic carbon. Different atmospheric aging processes between daytime and nighttime led to the change of BC particles' mixing states, which play a fundamental role in determining their hygroscopicity. To our knowledge, this is the first report of links between temporal variations in the hygroscopic growth of BC particles and atmospheric aging processes in polluted environments. These findings have significant ramifications in understanding the aging process, wet removal, and climate effects of BC particles.

scholarly journals Supplementary material to "Droplet activation behaviour of atmospheric black carbon particles in fog as a function of their size and mixing state"

2018 ◽  
Author(s):  
Ghislain Motos ◽  
Julia Schmale ◽  
Joel Christopher Corbin ◽  
Marco Zanatta ◽  
Urs Baltensperger ◽  
...  
Keyword(s):  
Black Carbon ◽  
Mixing State ◽  
Carbon Particles ◽  
Supplementary Material ◽  
Droplet Activation

scholarly journals Ambient black carbon particle hygroscopic properties controlled by mixing state and composition

2013 ◽  
Vol 13 (4) ◽  
pp. 2015-2029 ◽  
Author(s):  
D. Liu ◽  
J. Allan ◽  
J. Whitehead ◽  
D. Young ◽  
M. Flynn ◽  
...  
Keyword(s):  
Ammonium Nitrate ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Western Europe ◽  
Carbon Particle ◽  
Chemical Compositions ◽  
Mixing State ◽  
Additional Material ◽  
Considerable Uncertainty ◽  
Hygroscopic Properties

Abstract. The wet removal of black carbon aerosol (BC) in the atmosphere is a crucial factor in determining its atmospheric lifetime and thereby the vertical and horizontal distributions, dispersion on local and regional scales, and the direct, semi-direct and indirect radiative forcing effects. The in-cloud scavenging and wet deposition rate of freshly emitted hydrophobic BC will be increased on acquisition of more-hydrophilic components by coagulation or coating processes. The lifetime of BC is still subject to considerable uncertainty for most of the model inputs, which is largely due to the insufficient constraints on the BC hydrophobic-to-hydrophilic conversion process from observational field data. This study was conducted at a site along UK North Norfolk coastline, where the BC particles were transported from different regions within Western Europe. A hygroscopicity tandem differential mobility analyser (HTDMA) was coupled with a single particle soot photometer (SP2) to measure the hygroscopic properties of BC particles and associated mixing state in real time. In addition, a Soot Particle AMS (SP-AMS) measured the chemical compositions of additional material associated with BC particles. The ensemble of BC particles persistently contained a less-hygroscopic mode at a growth factor (gf) of around 1.05 at 90% RH (dry diameter 163 nm). Importantly, a more-hygroscopic mode of BC particles was observed throughout the experiment, the gf of these BC particles extended up to ~1.4–1.6 with the minimum between this and the less hygroscopic mode at a gf ~1.25, or equivalent effective hygroscopicity parameter κ ~0.1. The gf of BC particles (gfBC) was highly influenced by the composition of associated soluble material: increases of gfBC were associated with secondary inorganic components, and these increases were more pronounced when ammonium nitrate was in the BC particles; however the presence of secondary organic matter suppressed the gfBC below that of pure inorganics. The Zdanovskii-Stokes-Robinson (ZSR) mixing rule captures the hygroscopicity contributions from different compositions within ±30% compared to the measured results, however is subject to uncertainty due to the complex morphology of BC component and potential artefacts associated with semivolatile particles measured with the HTDMA. This study provides detailed insights on BC hygroscopicity associated with its mixing state, and the results will importantly constrain the microphysical mixing schemes of BC as used by a variety of high level models. In particular, this provides direct evidence to highlight the need to consider ammonium nitrate ageing of BC particles because this will result in particles becoming hydrophilic on much shorter timescales than for sulphate formation, which is often the only mechanism considered.

scholarly journals The single-particle mixing state and cloud scavenging of black carbon at a high-altitude mountain site in southern China

2017 ◽  
Author(s):  
Guohua Zhang ◽  
Qinhao Lin ◽  
Long Peng ◽  
Xinhui Bi ◽  
Duohong Chen ◽  
...  
Keyword(s):  
Black Carbon ◽  
Single Particle ◽  
Southern China ◽  
Climate Impacts ◽  
Limited Information ◽  
Mixing State ◽  
Cloud Droplets ◽  
Mountain Site ◽  
Cloud Scavenging ◽  
Scavenging Efficiency

Abstract. In the present study, a ground-based counterflow virtual impactor (GCVI) was used to sample cloud droplet residual (cloud RES) particles, while a parallel PM2.5 inlet was used to sample cloud-free or cloud interstitial (cloud INT) particles. The mixing state of black carbon (BC)-containing particles in a size range of 0.1–1.6 µm and the mass concentrations of BC in the cloud-free, RES and INT particles were investigated using a single particle aerosol mass spectrometer (SPAMS) and two aethalometers, respectively, at a mountain site (1690 m a.s.l.) in southern China. The measured BC-containing particles were internally mixed extensively with sulfate, and were activated into cloud droplets to the same extent as all the measured particles. The results indicate the preferential activation of larger particles and/or that the production of secondary compositions shifts the BC-containing particles towards larger sizes. BC-containing particles with an abundance of both sulfate and organics were activated less than those with sulfate but limited organics, implying the importance of the mixing state on the incorporation of BC-containing particles into cloud droplets. The mass scavenging efficiency of BC with an average of 33 % was similar for different cloud events independent of the air mass. This is the first time that both the mixing state and cloud scavenging of BC in China have been reported. Since limited information on BC-containing particles in the free troposphere is available, the results also provide an important reference for the representation of BC concentrations, properties, and climate impacts in modeling studies.

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