scholarly journals Impact of isolated atmospheric aging processes on the cloud condensation nuclei activation of soot particles

2019 ◽  
Vol 19 (24) ◽  
pp. 15545-15567 ◽  
Author(s):  
Franz Friebel ◽  
Prem Lobo ◽  
David Neubauer ◽  
Ulrike Lohmann ◽  
Saskia Drossaart van Dusseldorp ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Cloud Condensation Nuclei ◽  
Particle Diameter ◽  
Cloud Droplet ◽  
High Sensitivity ◽  
Condensation Nuclei ◽  
Soot Particles ◽  
Atmospheric Aging ◽  
Ccn Activity

Abstract. The largest contributors to the uncertainty in assessing the anthropogenic contribution in radiative forcing are the direct and indirect effects of aerosol particles on the Earth's radiative budget. Soot particles are of special interest since their properties can change significantly due to aging processes once they are emitted into the atmosphere. Probably the largest obstacle for the investigation of these processes in the laboratory is the long atmospheric lifetime of 1 week, requiring tailored experiments that cover this time span. This work presents results on the ability of two types of soot, obtained using a miniCAST soot generator, to act as cloud condensation nuclei (CCN) after exposure to atmospherically relevant levels of ozone (O3) and humidity. Aging times of up to 12 h were achieved by successful application of the continuous-flow stirred tank reactor (CSTR) concept while allowing for size selection of particles prior to the aging step. Particles of 100 nm diameter and rich in organic carbon (OC) that were initially CCN inactive showed significant CCN activity at supersaturations (SS) down to 0.3 % after 10 h of exposure to 200 ppb of O3. While this process was not affected by different levels of relative humidity in the range of 5 %–75 %, a high sensitivity towards the ambient/reaction temperature was observed. Soot particles with a lower OC content required an approximately 4-fold longer aging duration to show CCN activity at the same SS. Prior to the slow change in the CCN activity, a rapid increase in the particle diameter was detected which occurred within several minutes. This study highlights the applicability of the CSTR approach for the simulation of atmospheric aging processes, as aging durations beyond 12 h can be achieved in comparably small aerosol chamber volumes (<3 m3). Implementation of our measurement results in a global aerosol-climate model, ECHAM6.3-HAM2.3, showed a statistically significant increase in the regional and global CCN burden and cloud droplet number concentration.

scholarly journals Impact of Isolated Atmospheric Aging processes on the Cloud Condensation Nuclei-activation of Soot Particles

2019 ◽  
Author(s):  
Franz Friebel ◽  
Prem Lobo ◽  
David Neubauer ◽  
Ulrike Lohmann ◽  
Saskia Drossaart van Dusseldorp ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Cloud Condensation Nuclei ◽  
Particle Diameter ◽  
High Sensitivity ◽  
Condensation Nuclei ◽  
Soot Particles ◽  
Atmospheric Aging ◽  
Aerosol Chamber ◽  
Small Aerosol ◽  
Ccn Activity

Abstract. The largest contributors to the uncertainty in assessing the anthropogenic contribution in radiative forcing are the direct and indirect effects of aerosol particles on the Earth's radiative budget. Soot particles are of special interest since their properties can change significantly due to aging processes once they are emitted to the atmosphere. Probably the largest obstacle for the investigation of these processes in the laboratory is the long atmospheric lifetime of one week, demanding tailored experiments that cover this time span. This work presents results on the ability of two types of soot to act as cloud condensation nuclei (CCN) after exposure to atmospherically relevant levels of ozone and humidity. Aging times of up to 12 h were achieved by successful application of the continuous-flow stirred tank reactor (CSTR) concept while allowing for size-selection of particles prior to the aging step. 100 nm particles rich in organic carbon (OC) that were initially CCN-inactive showed significant CCN-activity at supersaturations (SS) down to 0.3 % after 10 h of exposure to 200 ppb of ozone. While this process was not affected by different levels of relative humidity in the range 5–75 %, a high sensitivity towards the ambient/reaction temperature was observed. Soot particles with a lower OC-content demanded an approximately four-fold longer aging duration to show CCN-activity for the same SS. Prior to the slow change in the CCN-activity, a rapid increase in the particle diameter was detected which occurred within several minutes. This study highlights the applicability of the CSTR-approach for the simulation of atmospheric aging processes, as aging durations beyond 12 h can be achieved in comparably small aerosol chamber volumes (

scholarly journals Cloud droplet activity changes of soot aerosol upon smog chamber ageing

2014 ◽  
Vol 14 (18) ◽  
pp. 9831-9854 ◽  
Author(s):  
C. Wittbom ◽  
A. C. Eriksson ◽  
J. Rissler ◽  
J. E. Carlsson ◽  
P. Roldin ◽  
...  
Keyword(s):  
Uv Radiation ◽  
Organic Material ◽  
Mass Fraction ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Particle Morphology ◽  
Organic Aerosol ◽  
Condensation Nuclei ◽  
Soot Particles ◽  
Kohler Theory

Abstract. Particles containing soot, or black carbon, are generally considered to contribute to global warming. However, large uncertainties remain in the net climate forcing resulting from anthropogenic emissions of black carbon (BC), to a large extent due to the fact that BC is co-emitted with gases and primary particles, both organic and inorganic, and subject to atmospheric ageing processes. In this study, diesel exhaust particles and particles from a flame soot generator spiked with light aromatic secondary organic aerosol (SOA) precursors were processed by UV radiation in a 6 m3 Teflon chamber in the presence of NOx. The time-dependent changes of the soot nanoparticle properties were characterised using a Cloud Condensation Nuclei Counter, an Aerosol Particle Mass Analyzer and a Soot Particle Aerosol Mass Spectrometer. The results show that freshly emitted soot particles do not activate into cloud droplets at supersaturations ≤2%, i.e. the BC core coated with primary organic aerosol (POA) from the exhaust is limited in hygroscopicity. Before the onset of UV radiation it is unlikely that any substantial SOA formation is taking place. An immediate change in cloud-activation properties occurs at the onset of UV exposure. This change in hygroscopicity is likely attributed to SOA formed from intermediate volatility organic compounds (IVOCs) in the diesel engine exhaust. The change of cloud condensation nuclei (CCN) properties at the onset of UV radiation implies that the lifetime of soot particles in the atmosphere is affected by the access to sunlight, which differs between latitudes. The ageing of soot particles progressively enhances their ability to act as cloud condensation nuclei, due to changes in: (I) organic fraction of the particle, (II) chemical properties of this fraction (e.g. primary or secondary organic aerosol), (III) particle size, and (IV) particle morphology. Applying κ-Köhler theory, using a κSOA value of 0.13 (derived from independent input parameters describing the organic material), showed good agreement with cloud droplet activation measurements for particles with a SOA mass fraction ≥0.12 (slightly aged particles). The activation properties are enhanced with only a slight increase in organic material coating the soot particles (SOA mass fraction < 0.12), however not as much as predicted by Köhler theory. The discrepancy between theory and experiments during the early stages of ageing might be due to solubility limitations, unevenly distributed organic material or hindering particle morphology. The change in properties of soot nanoparticles upon photochemical processing clearly increases their hygroscopicity, which affects their behaviour both in the atmosphere and in the human respiratory system.

New evidence of soot particles affecting past and future cloud formation and climate

2020 ◽  
Author(s):  
Ulrike Lohmann ◽  
Franz Friebel ◽  
Zamin A. Kanji ◽  
Fabian Mahrt ◽  
Amewu A. Mensah ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Hydrological Cycle ◽  
Global Climate ◽  
Cloud Condensation Nuclei ◽  
Critical Role ◽  
Carbon Dioxide Concentration ◽  
Radiative Properties ◽  
Cloud Formation ◽  
Condensation Nuclei ◽  
Soot Particles

&lt;p&gt;Clouds play a critical role in the hydrological cycle and modulating the Earth&amp;#8217;s climate via precipitation and radiative forcing. Aerosol particles acting as cloud condensation nuclei and ice nucleating particles aid in cloud formation, shaping their microphysical structure. Previously thought to be unimportant for cloud formation, soot particles that undergo oxidation by ozone and/or aging with aqueous sulfuric acid result in being both good centers for cloud droplets and ice crystals formation. However, the associated changes in cloud radiative properties and the consequences for Earth&amp;#8217;s climate remain uncertain, because these processes have not been considered in global climate models. Here we present both past and future global climate simulations, which for the first time consider the effect of such aged soot particles as cloud condensation nuclei and ice nucleating particles. Our results constitute the first evidence that aging of soot particles produce a 0.2 to 0.25 Wm&lt;sup&gt;-2&lt;/sup&gt; less negative shortwave indirect aerosol forcing compared to previous estimates. We also conducted equilibrium climate sensitivity simulations representing a future warmer climate in which the carbon dioxide concentration is doubled compared to pre-industrial levels. Accounting for these soot aging processes significantly exacerbates the global mean surface temperature increase by 0.4 to 0.5 K. Thus, reducing emissions of soot particles will be beneficial for many aspects including air pollution and future climate.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals The challenge of simulating the sensitivity of the Amazonian cloud microstructure to cloud condensation nuclei number concentrations

2020 ◽  
Vol 20 (3) ◽  
pp. 1591-1605 ◽  
Author(s):  
Pascal Polonik ◽  
Christoph Knote ◽  
Tobias Zinner ◽  
Florian Ewald ◽  
Tobias Kölling ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Climate Model ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Number Concentration ◽  
Effective Radius ◽  
Cloud Base ◽  
Atmospheric Conditions ◽  
Condensation Nuclei ◽  
Aerosol Cloud

Abstract. The realistic representation of aerosol–cloud interactions is of primary importance for accurate climate model projections. The investigation of these interactions in strongly contrasting clean and polluted atmospheric conditions in the Amazon region has been one of the motivations for several field campaigns, including the airborne “Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON-CHUVA)” campaign based in Manaus, Brazil, in September 2014. In this work we combine in situ and remotely sensed aerosol, cloud, and atmospheric radiation data collected during ACRIDICON-CHUVA with regional, online-coupled chemistry-transport simulations to evaluate the model's ability to represent the indirect effects of biomass burning aerosol on cloud microphysical and optical properties (droplet number concentration and effective radius). We found agreement between the modeled and observed median cloud droplet number concentration (CDNC) for low values of CDNC, i.e., low levels of pollution. In general, a linear relationship between modeled and observed CDNC with a slope of 0.3 was found, which implies a systematic underestimation of modeled CDNC when compared to measurements. Variability in cloud condensation nuclei (CCN) number concentrations was also underestimated, and cloud droplet effective radii (reff) were overestimated by the model. Modeled effective radius profiles began to saturate around 500 CCN cm−3 at cloud base, indicating an upper limit for the model sensitivity well below CCN concentrations reached during the burning season in the Amazon Basin. Additional CCN emitted from local fires did not cause a notable change in modeled cloud droplet effective radii. Finally, we also evaluate a parameterization of CDNC at cloud base using more readily available cloud microphysical properties, showing that we are able to derive CDNC at cloud base from cloud-side remote-sensing observations.

scholarly journals Brightening of the global cloud field by nitric acid and the associated radiative forcing

2012 ◽  
Vol 12 (16) ◽  
pp. 7625-7633 ◽  
Author(s):  
R. Makkonen ◽  
S. Romakkaniemi ◽  
H. Kokkola ◽  
P. Stier ◽  
P. Räisänen ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Indirect Effect ◽  
Radiative Forcing ◽  
Climate Model ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
So2 Emissions ◽  
Cloud Droplets ◽  
Cloud Albedo ◽  
Albedo Effect

Abstract. Clouds cool Earth's climate by reflecting 20% of the incoming solar energy, while also trapping part of the outgoing radiation. The effect of human activities on clouds is poorly understood, but the present-day anthropogenic cooling via changes of cloud albedo and lifetime could be of the same order as warming from anthropogenic addition in CO2. Soluble trace gases can increase water condensation to particles, possibly leading to activation of smaller aerosols and more numerous cloud droplets. We have studied the effect of nitric acid on the aerosol indirect effect with the global aerosol-climate model ECHAM5.5-HAM2. Including the nitric acid effect in the model increases cloud droplet number concentrations globally by 7%. The nitric acid contribution to the present-day cloud albedo effect was found to be −0.32 W m−2 and to the total indirect effect −0.46 W m−2. The contribution to the cloud albedo effect is shown to increase to −0.37 W m−2 by the year 2100, if considering only the reductions in available cloud condensation nuclei. Overall, the effect of nitric acid can play a large part in aerosol cooling during the following decades with decreasing SO2 emissions and increasing NOx and greenhouse gases.

scholarly journals Cloud droplet activity changes of soot aerosol upon smog chamber ageing

2014 ◽  
Vol 14 (7) ◽  
pp. 8851-8914 ◽  
Author(s):  
C. Wittbom ◽  
J. H. Pagels ◽  
J. Rissler ◽  
A. C. Eriksson ◽  
J. E. Carlsson ◽  
...  
Keyword(s):  
Black Carbon ◽  
Uv Radiation ◽  
Organic Material ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Particle Morphology ◽  
Organic Aerosol ◽  
Condensation Nuclei ◽  
Soot Particles ◽  
Kohler Theory

Abstract. Particles containing soot, or black carbon, are generally considered to contribute to global warming. However, large uncertainties remain in the net climate forcing resulting from anthropogenic emissions of black carbon (BC), to a large extent due to the fact that BC is co-emitted with gases and primary particles, both organic and inorganic, and subject to atmospheric ageing processes. In this study, diesel exhaust particles and particles from a flame soot generator spiked with light aromatic secondary organic aerosol (SOA) precursors were processed by UV-radiation in a 6 m3 Teflon chamber in the presence of NOx. The time-dependent changes of the soot nanoparticle properties were characterised using a Cloud Condensation Nuclei Counter, an Aerosol Particle Mass Analyzer and a Soot Particle Aerosol Mass Spectrometer. The results show that freshly emitted soot particles do not activate into cloud droplets at supersaturations ≤ 2%, i.e. the black carbon core coated with primary organic aerosol (POA) from the exhaust is limited in hygroscopicity. Before the onset of UV radiation it is unlikely that any substantial SOA formation is taking place. An immediate change in cloud-activation properties occurs at the onset of UV exposure. This change in hygroscopicity is likely attributed to SOA formed from intermediate volatile organic compounds (IVOC) in the diesel engine exhaust. The change of cloud condensation nuclei (CCN) properties at the onset of UV radiation implies that the lifetime of soot particles in the atmosphere is affected by the access to sunlight, which differs between latitudes. The ageing of soot particles progressively enhances their ability to act as cloud condensation nuclei, due to changes in: (I) organic fraction of the particle, (II) chemical properties of this fraction (POA or SOA), (III) particle size, and (IV) particle morphology. Applying κ-Köhler theory, using a κSOA value of 0.13 (derived from independent input parameters describing the organic material), showed good agreement with cloud droplet activation measurements for particles with a SOA mass fraction (mfSOA(APM)) ≥ 0.12 (slightly aged particles). The activation properties are enhanced with only a slight increase in organic material coating the soot particles (mfSOA(APM) < 0.12), however not as much as predicted with Köhler theory. The discrepancy between theory and experiments might be due to solubility limitations, unevenly distributed organic material or hindering particle morphology. The change in properties of soot nanoparticles upon photochemical processing clearly increases their hygroscopicity, which affects their behaviour both in the atmosphere and in the human respiratory system.

scholarly journals Aerosol hygroscopicity and CCN activity obtained from a combination analysis based on size-resolved CCN and aerosol chemical composition observations during the AC<sup>3</sup>Exp13 campaign

2014 ◽  
Vol 14 (10) ◽  
pp. 14889-14931 ◽  
Author(s):  
F. Zhang ◽  
Z. Li ◽  
R. J. Li ◽  
L. Sun ◽  
C. Zhao ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Size Range ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
High Sensitivity ◽  
Condensation Nuclei ◽  
Long Term Observation ◽  
Aerosol Hygroscopicity ◽  
Ccn Activity ◽  
Aerosol Chemical Composition

Abstract. Aerosol hygroscopicity and cloud condensation nuclei (CCN) activity under clean conditions and polluted events are investigated based on size-resolved CCN and aerosol chemical composition observations during the Aerosol-CCN-Cloud Closure Experiment (AC3Exp) campaign conducted at Xianghe, China in summer 2013. About 14–22% of aerosol particles during the campaign are of externally mixed CCN-inactive particles that cannot serve as CCN under atmospheric typical supersaturation (SS) of ∼0.4%. A high sensitivity of Maximum activation fractions (MAF) to SS under polluted conditions has been observed. The pollutants can cause a maximum MAF decrease of 25–30% (at SS = 0.08%). Hygroscopicity parameter kappa (κ) are about 16–35% lower under polluted conditions than under clean conditions for particles in accumulation size range (80–180 nm); however, for particles in nucleation or Aitken size range (30–60 nm), κ is slightly higher under polluted conditions. A non-parallel observation (NPO) CCN closure study shows low correlation coefficient between estimated and observed CCN number concentrations (NCCN). About 30–40% uncertainties in NCCN prediction are associated with the changes of particle composition. A case study shows that CCN activation ratio (AR) increased with the increase of condensation nuclei (CN) number concentrations (NCN) in relatively clean days. In the case, AR exhibited good correlation with κchem, which is calculated from chemical volume fractions, due to particles mainly composed of soluble inorganics. On the contrary, AR declined with increase of NCN during polluted events when particles composed mostly of organics. Meanwhile, AR is closely related to f44, which is the fraction of total organic mass signal at m/z 44 and closely associated with particle organic oxidation level. Our study highlights the importance of aerosols chemical composition on determining the activation properties of aerosol particles, underlining the importance of long-term observation of CCN under different atmospheric environments, especially those with heavy pollution and high CN number concentrations.

scholarly journals Simulation study on the indirect effect of sulfate on the summer climate over the eastern China monsoon region

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Dongdong Wang ◽  
Bin Zhu ◽  
Hongbo Wang ◽  
Li Sun
Keyword(s):  
Radiative Forcing ◽  
Asian Summer Monsoon ◽  
Cloud Condensation Nuclei ◽  
Eastern China ◽  
Summer Precipitation ◽  
Cloud Droplet ◽  
Monsoon Region ◽  
Liquid Water Path ◽  
Surface Cooling ◽  
Community Atmosphere Model

AbstractIn this study, we designed a sensitivity test using the half number concentration of sulfate in the nucleation calculation process to study the aerosol-cloud interaction (ACI) of sulfate on clouds, precipitation, and monsoon intensity in the summer over the eastern China monsoon region (ECMR) with the National Center for Atmospheric Research Community Atmosphere Model version 5. Numerical experiments show that the ACI of sulfate led to an approximately 30% and 34% increase in the cloud condensation nuclei and cloud droplet number concentrations, respectively. Cloud droplet effective radius below 850 hPa decreased by approximately 4% in the southern ECMR, while the total liquid water path increased by 11%. The change in the indirect radiative forcing due to sulfate at the top of the atmosphere in the ECMR during summer was − 3.74 W·m−2. The decreased radiative forcing caused a surface cooling of 0.32 K and atmospheric cooling of approximately 0.3 K, as well as a 0.17 hPa increase in sea level pressure. These changes decreased the thermal difference between the land and sea and the gradient of the sea-land pressure, leading to a weakening in the East Asian summer monsoon (EASM) and a decrease in the total precipitation rate in the southern ECMR. The cloud lifetime effect has a relatively weaker contribution to summer precipitation, which is dominated by convection. The results show that the ACI of sulfate was one possible reason for the weakening of the EASM in the late 1970s.

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