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Jeffrey R. Pierce - One of the best experts on this subject based on the ideXlab platform.

  • analysis of feedbacks between nucleation rate survival probability and cloud Condensation Nuclei formation
    Atmospheric Chemistry and Physics, 2013
    Co-Authors: D M Westervelt, Jeffrey R. Pierce, Peter J. Adams
    Abstract:

    Abstract. Aerosol nucleation is an important source of particle number in the atmosphere. However, in order to become cloud Condensation Nuclei (CCN), freshly nucleated particles must undergo significant Condensational growth while avoiding coagulational scavenging. In an effort to quantify the contribution of nucleation to CCN, this work uses the GEOS-Chem-TOMAS global aerosol model to calculate changes in CCN concentrations against a broad range of nucleation rates and mechanisms. We then quantify the factors that control CCN formation from nucleation, including daily nucleation rates, growth rates, coagulation sinks, Condensation sinks, survival probabilities, and CCN formation rates, in order to examine feedbacks that may limit growth of nucleated particles to CCN. Nucleation rate parameterizations tested in GEOS-Chem-TOMAS include ternary nucleation (with multiple tuning factors), activation nucleation (with two pre-factors), binary nucleation, and ion-mediated nucleation. We find that nucleation makes a significant contribution to boundary layer CCN(0.2%), but this contribution is only modestly sensitive to the choice of nucleation scheme, ranging from 49 to 78% increase in concentrations over a control simulation with no nucleation. Moreover, a two order-of-magnitude increase in the globally averaged nucleation rate (via changes to tuning factors) results in small changes (less than 10%) to global CCN(0.2%) concentrations. To explain this, we present a simple theory showing that survival probability has an exponentially decreasing dependence on the square of the Condensation sink. This functional form stems from a negative correlation between Condensation sink and growth rate and a positive correlation between Condensation sink and coagulational scavenging. Conceptually, with a fixed condensable vapor budget (sulfuric acid and organics), any increase in CCN concentrations due to higher nucleation rates necessarily entails an increased aerosol surface area in the accumulation mode, resulting in a higher Condensation sink, which lowers vapor concentrations and growth rates. As a result, slowly growing Nuclei are exposed to a higher frequency of coagulational scavenging for a longer period of time, thus reducing their survival probabilities and closing a negative feedback loop that dampens the impact of nucleation on CCN. We confirm quantitatively that the decreases in survival probability predicted by GEOS-Chem-TOMAS due to higher nucleation rates are in accordance with this simple theory of survival probability.

  • analysis of feedbacks between nucleation rate survival probability and cloud Condensation Nuclei formation
    Atmospheric Chemistry and Physics, 2013
    Co-Authors: D M Westervelt, Jeffrey R. Pierce, Peter J. Adams
    Abstract:

    Abstract. Aerosol nucleation is an important source of particle number in the atmosphere. However, in order to become cloud Condensation Nuclei (CCN), freshly nucleated particles must undergo significant Condensational growth while avoiding coagulational scavenging. In an effort to quantify the contribution of nucleation to CCN, this work uses the GEOS-Chem-TOMAS global aerosol model to calculate changes in CCN concentrations against a broad range of nucleation rates and mechanisms. We then quantify the factors that control CCN formation from nucleation, including daily nucleation rates, growth rates, coagulation sinks, Condensation sinks, survival probabilities, and CCN formation rates, in order to examine feedbacks that may limit growth of nucleated particles to CCN. Nucleation rate parameterizations tested in GEOS-Chem-TOMAS include ternary nucleation (with multiple tuning factors), activation nucleation (with two pre-factors), binary nucleation, and ion-mediated nucleation. We find that nucleation makes a significant contribution to boundary layer CCN(0.2%), but this contribution is only modestly sensitive to the choice of nucleation scheme, ranging from 49 to 78% increase in concentrations over a control simulation with no nucleation. Moreover, a two order-of-magnitude increase in the globally averaged nucleation rate (via changes to tuning factors) results in small changes (less than 10%) to global CCN(0.2%) concentrations. To explain this, we present a simple theory showing that survival probability has an exponentially decreasing dependence on the square of the Condensation sink. This functional form stems from a negative correlation between Condensation sink and growth rate and a positive correlation between Condensation sink and coagulational scavenging. Conceptually, with a fixed condensable vapor budget (sulfuric acid and organics), any increase in CCN concentrations due to higher nucleation rates necessarily entails an increased aerosol surface area in the accumulation mode, resulting in a higher Condensation sink, which lowers vapor concentrations and growth rates. As a result, slowly growing Nuclei are exposed to a higher frequency of coagulational scavenging for a longer period of time, thus reducing their survival probabilities and closing a negative feedback loop that dampens the impact of nucleation on CCN. We confirm quantitatively that the decreases in survival probability predicted by GEOS-Chem-TOMAS due to higher nucleation rates are in accordance with this simple theory of survival probability.

  • the magnitude and causes of uncertainty in global model simulations of cloud Condensation Nuclei
    Atmospheric Chemistry and Physics, 2013
    Co-Authors: Lindsay Lee, Jeffrey R. Pierce, G W Mann, Philip Stier, K J Pringle, C L Reddington, D V Spracklen, K S Carslaw
    Abstract:

    Abstract. Aerosol–cloud interaction effects are a major source of uncertainty in climate models so it is important to quantify the sources of uncertainty and thereby direct research efforts. However, the computational expense of global aerosol models has prevented a full statistical analysis of their outputs. Here we perform a variance-based analysis of a global 3-D aerosol microphysics model to quantify the magnitude and leading causes of parametric uncertainty in model-estimated present-day concentrations of cloud Condensation Nuclei (CCN). Twenty-eight model parameters covering essentially all important aerosol processes, emissions and representation of aerosol size distributions were defined based on expert elicitation. An uncertainty analysis was then performed based on a Monte Carlo-type sampling of an emulator built for each model grid cell. The standard deviation around the mean CCN varies globally between about ±30% over some marine regions to ±40–100% over most land areas and high latitudes, implying that aerosol processes and emissions are likely to be a significant source of uncertainty in model simulations of aerosol–cloud effects on climate. Among the most important contributors to CCN uncertainty are the sizes of emitted primary particles, including carbonaceous combustion particles from wildfires, biomass burning and fossil fuel use, as well as sulfate particles formed on sub-grid scales. Emissions of carbonaceous combustion particles affect CCN uncertainty more than sulfur emissions. Aerosol emission-related parameters dominate the uncertainty close to sources, while uncertainty in aerosol microphysical processes becomes increasingly important in remote regions, being dominated by deposition and aerosol sulfate formation during cloud-processing. The results lead to several recommendations for research that would result in improved modelling of cloud–active aerosol on a global scale.

  • weak global sensitivity of cloud Condensation Nuclei and the aerosol indirect effect to criegee so 2 chemistry
    Atmospheric Chemistry and Physics, 2012
    Co-Authors: Jeffrey R. Pierce, M J Evans, Catherine E Scott, S D Dandrea, Delphine K Farmer, Erik Swietlicki, D V Spracklen
    Abstract:

    Abstract. H 2 SO 4 vapor is important for the nucleation of atmospheric aerosols and the growth of ultrafine particles to cloud Condensation Nuclei (CCN) sizes with important roles in the global aerosol budget and hence planetary radiative forcing. Recent studies have found that reactions of stabilized Criegee intermediates (CIs, formed from the ozonolysis of alkenes) with SO 2 may be an important source of H 2 SO 4 that has been missing from atmospheric aerosol models. For the first time in a global model, we investigate the impact of this new source of H 2 SO 4 in the atmosphere. We use the chemical transport model, GEOS-Chem, with the online aerosol microphysics module, TOMAS, to estimate the possible impact of CIs on present-day H 2 SO 4 , CCN, and the cloud-albedo aerosol indirect effect (AIE). We extend the standard GEOS-Chem chemistry with CI-forming reactions (ozonolysis of isoprene, methyl vinyl ketone, methacrolein, propene, and monoterpenes) from the Master Chemical Mechanism. Using a fast rate constant for CI+SO 2 , we find that the addition of this chemistry increases the global production of H 2 SO 4 by 4%. H 2 SO 4 concentrations increase by over 100% in forested tropical boundary layers and by over 10–25% in forested NH boundary layers (up to 100% in July) due to CI+SO 2 chemistry, but the change is generally negligible elsewhere. The predicted changes in CCN were strongly dampened to the CI+SO 2 changes in H 2 SO 4 in some regions: less than 15% in tropical forests and less than 2% in most mid-latitude locations. The global-mean CCN change was less than 1% both in the boundary layer and the free troposphere. The associated cloud-albedo AIE change was less than 0.03 W m −2 . The model global sensitivity of CCN and the AIE to CI+SO 2 chemistry is significantly (approximately one order-of-magnitude) smaller than the sensitivity of CCN and AIE to other uncertain model inputs, such as nucleation mechanisms, primary emissions, SOA (secondary organic aerosol) and deposition. Similarly, comparisons to size-distribution measurements show that uncertainties in other model parameters dominate model biases in the model-predicted size distributions. We conclude that improvement in the modeled CI+SO 2 chemistry would not likely lead to significant improvements in present-day CCN and AIE predictions.

  • can cosmic rays affect cloud Condensation Nuclei by altering new particle formation rates
    Geophysical Research Letters, 2009
    Co-Authors: Jeffrey R. Pierce, Peter J. Adams
    Abstract:

    [1] Although controversial, many observations have suggested that low-level cloud cover correlates with the cosmic ray flux. Because galactic cosmic rays have likely decreased in intensity over the last century, this hypothesis, if true, could partly explain 20th century warming, thereby upsetting the consensus view that greenhouse-gas forcing has caused most of the warming. The “ion-aerosol clear-air” hypothesis suggests that increased cosmic rays cause increases in new-particle formation, cloud Condensation Nuclei concentrations (CCN), and cloud cover. In this paper, we present the first calculations of the magnitude of the ion-aerosol clear-air mechanism using a general circulation model with online aerosol microphysics. In our simulations, changes in CCN from changes in cosmic rays during a solar cycle are two orders of magnitude too small to account for the observed changes in cloud properties; consequently, we conclude that the hypothesized effect is too small to play a significant role in current climate change.

Peter J. Adams - One of the best experts on this subject based on the ideXlab platform.

  • analysis of feedbacks between nucleation rate survival probability and cloud Condensation Nuclei formation
    Atmospheric Chemistry and Physics, 2013
    Co-Authors: D M Westervelt, Jeffrey R. Pierce, Peter J. Adams
    Abstract:

    Abstract. Aerosol nucleation is an important source of particle number in the atmosphere. However, in order to become cloud Condensation Nuclei (CCN), freshly nucleated particles must undergo significant Condensational growth while avoiding coagulational scavenging. In an effort to quantify the contribution of nucleation to CCN, this work uses the GEOS-Chem-TOMAS global aerosol model to calculate changes in CCN concentrations against a broad range of nucleation rates and mechanisms. We then quantify the factors that control CCN formation from nucleation, including daily nucleation rates, growth rates, coagulation sinks, Condensation sinks, survival probabilities, and CCN formation rates, in order to examine feedbacks that may limit growth of nucleated particles to CCN. Nucleation rate parameterizations tested in GEOS-Chem-TOMAS include ternary nucleation (with multiple tuning factors), activation nucleation (with two pre-factors), binary nucleation, and ion-mediated nucleation. We find that nucleation makes a significant contribution to boundary layer CCN(0.2%), but this contribution is only modestly sensitive to the choice of nucleation scheme, ranging from 49 to 78% increase in concentrations over a control simulation with no nucleation. Moreover, a two order-of-magnitude increase in the globally averaged nucleation rate (via changes to tuning factors) results in small changes (less than 10%) to global CCN(0.2%) concentrations. To explain this, we present a simple theory showing that survival probability has an exponentially decreasing dependence on the square of the Condensation sink. This functional form stems from a negative correlation between Condensation sink and growth rate and a positive correlation between Condensation sink and coagulational scavenging. Conceptually, with a fixed condensable vapor budget (sulfuric acid and organics), any increase in CCN concentrations due to higher nucleation rates necessarily entails an increased aerosol surface area in the accumulation mode, resulting in a higher Condensation sink, which lowers vapor concentrations and growth rates. As a result, slowly growing Nuclei are exposed to a higher frequency of coagulational scavenging for a longer period of time, thus reducing their survival probabilities and closing a negative feedback loop that dampens the impact of nucleation on CCN. We confirm quantitatively that the decreases in survival probability predicted by GEOS-Chem-TOMAS due to higher nucleation rates are in accordance with this simple theory of survival probability.

  • analysis of feedbacks between nucleation rate survival probability and cloud Condensation Nuclei formation
    Atmospheric Chemistry and Physics, 2013
    Co-Authors: D M Westervelt, Jeffrey R. Pierce, Peter J. Adams
    Abstract:

    Abstract. Aerosol nucleation is an important source of particle number in the atmosphere. However, in order to become cloud Condensation Nuclei (CCN), freshly nucleated particles must undergo significant Condensational growth while avoiding coagulational scavenging. In an effort to quantify the contribution of nucleation to CCN, this work uses the GEOS-Chem-TOMAS global aerosol model to calculate changes in CCN concentrations against a broad range of nucleation rates and mechanisms. We then quantify the factors that control CCN formation from nucleation, including daily nucleation rates, growth rates, coagulation sinks, Condensation sinks, survival probabilities, and CCN formation rates, in order to examine feedbacks that may limit growth of nucleated particles to CCN. Nucleation rate parameterizations tested in GEOS-Chem-TOMAS include ternary nucleation (with multiple tuning factors), activation nucleation (with two pre-factors), binary nucleation, and ion-mediated nucleation. We find that nucleation makes a significant contribution to boundary layer CCN(0.2%), but this contribution is only modestly sensitive to the choice of nucleation scheme, ranging from 49 to 78% increase in concentrations over a control simulation with no nucleation. Moreover, a two order-of-magnitude increase in the globally averaged nucleation rate (via changes to tuning factors) results in small changes (less than 10%) to global CCN(0.2%) concentrations. To explain this, we present a simple theory showing that survival probability has an exponentially decreasing dependence on the square of the Condensation sink. This functional form stems from a negative correlation between Condensation sink and growth rate and a positive correlation between Condensation sink and coagulational scavenging. Conceptually, with a fixed condensable vapor budget (sulfuric acid and organics), any increase in CCN concentrations due to higher nucleation rates necessarily entails an increased aerosol surface area in the accumulation mode, resulting in a higher Condensation sink, which lowers vapor concentrations and growth rates. As a result, slowly growing Nuclei are exposed to a higher frequency of coagulational scavenging for a longer period of time, thus reducing their survival probabilities and closing a negative feedback loop that dampens the impact of nucleation on CCN. We confirm quantitatively that the decreases in survival probability predicted by GEOS-Chem-TOMAS due to higher nucleation rates are in accordance with this simple theory of survival probability.

  • can cosmic rays affect cloud Condensation Nuclei by altering new particle formation rates
    Geophysical Research Letters, 2009
    Co-Authors: Jeffrey R. Pierce, Peter J. Adams
    Abstract:

    [1] Although controversial, many observations have suggested that low-level cloud cover correlates with the cosmic ray flux. Because galactic cosmic rays have likely decreased in intensity over the last century, this hypothesis, if true, could partly explain 20th century warming, thereby upsetting the consensus view that greenhouse-gas forcing has caused most of the warming. The “ion-aerosol clear-air” hypothesis suggests that increased cosmic rays cause increases in new-particle formation, cloud Condensation Nuclei concentrations (CCN), and cloud cover. In this paper, we present the first calculations of the magnitude of the ion-aerosol clear-air mechanism using a general circulation model with online aerosol microphysics. In our simulations, changes in CCN from changes in cosmic rays during a solar cycle are two orders of magnitude too small to account for the observed changes in cloud properties; consequently, we conclude that the hypothesized effect is too small to play a significant role in current climate change.

D M Westervelt - One of the best experts on this subject based on the ideXlab platform.

  • analysis of feedbacks between nucleation rate survival probability and cloud Condensation Nuclei formation
    Atmospheric Chemistry and Physics, 2013
    Co-Authors: D M Westervelt, Jeffrey R. Pierce, Peter J. Adams
    Abstract:

    Abstract. Aerosol nucleation is an important source of particle number in the atmosphere. However, in order to become cloud Condensation Nuclei (CCN), freshly nucleated particles must undergo significant Condensational growth while avoiding coagulational scavenging. In an effort to quantify the contribution of nucleation to CCN, this work uses the GEOS-Chem-TOMAS global aerosol model to calculate changes in CCN concentrations against a broad range of nucleation rates and mechanisms. We then quantify the factors that control CCN formation from nucleation, including daily nucleation rates, growth rates, coagulation sinks, Condensation sinks, survival probabilities, and CCN formation rates, in order to examine feedbacks that may limit growth of nucleated particles to CCN. Nucleation rate parameterizations tested in GEOS-Chem-TOMAS include ternary nucleation (with multiple tuning factors), activation nucleation (with two pre-factors), binary nucleation, and ion-mediated nucleation. We find that nucleation makes a significant contribution to boundary layer CCN(0.2%), but this contribution is only modestly sensitive to the choice of nucleation scheme, ranging from 49 to 78% increase in concentrations over a control simulation with no nucleation. Moreover, a two order-of-magnitude increase in the globally averaged nucleation rate (via changes to tuning factors) results in small changes (less than 10%) to global CCN(0.2%) concentrations. To explain this, we present a simple theory showing that survival probability has an exponentially decreasing dependence on the square of the Condensation sink. This functional form stems from a negative correlation between Condensation sink and growth rate and a positive correlation between Condensation sink and coagulational scavenging. Conceptually, with a fixed condensable vapor budget (sulfuric acid and organics), any increase in CCN concentrations due to higher nucleation rates necessarily entails an increased aerosol surface area in the accumulation mode, resulting in a higher Condensation sink, which lowers vapor concentrations and growth rates. As a result, slowly growing Nuclei are exposed to a higher frequency of coagulational scavenging for a longer period of time, thus reducing their survival probabilities and closing a negative feedback loop that dampens the impact of nucleation on CCN. We confirm quantitatively that the decreases in survival probability predicted by GEOS-Chem-TOMAS due to higher nucleation rates are in accordance with this simple theory of survival probability.

  • analysis of feedbacks between nucleation rate survival probability and cloud Condensation Nuclei formation
    Atmospheric Chemistry and Physics, 2013
    Co-Authors: D M Westervelt, Jeffrey R. Pierce, Peter J. Adams
    Abstract:

    Abstract. Aerosol nucleation is an important source of particle number in the atmosphere. However, in order to become cloud Condensation Nuclei (CCN), freshly nucleated particles must undergo significant Condensational growth while avoiding coagulational scavenging. In an effort to quantify the contribution of nucleation to CCN, this work uses the GEOS-Chem-TOMAS global aerosol model to calculate changes in CCN concentrations against a broad range of nucleation rates and mechanisms. We then quantify the factors that control CCN formation from nucleation, including daily nucleation rates, growth rates, coagulation sinks, Condensation sinks, survival probabilities, and CCN formation rates, in order to examine feedbacks that may limit growth of nucleated particles to CCN. Nucleation rate parameterizations tested in GEOS-Chem-TOMAS include ternary nucleation (with multiple tuning factors), activation nucleation (with two pre-factors), binary nucleation, and ion-mediated nucleation. We find that nucleation makes a significant contribution to boundary layer CCN(0.2%), but this contribution is only modestly sensitive to the choice of nucleation scheme, ranging from 49 to 78% increase in concentrations over a control simulation with no nucleation. Moreover, a two order-of-magnitude increase in the globally averaged nucleation rate (via changes to tuning factors) results in small changes (less than 10%) to global CCN(0.2%) concentrations. To explain this, we present a simple theory showing that survival probability has an exponentially decreasing dependence on the square of the Condensation sink. This functional form stems from a negative correlation between Condensation sink and growth rate and a positive correlation between Condensation sink and coagulational scavenging. Conceptually, with a fixed condensable vapor budget (sulfuric acid and organics), any increase in CCN concentrations due to higher nucleation rates necessarily entails an increased aerosol surface area in the accumulation mode, resulting in a higher Condensation sink, which lowers vapor concentrations and growth rates. As a result, slowly growing Nuclei are exposed to a higher frequency of coagulational scavenging for a longer period of time, thus reducing their survival probabilities and closing a negative feedback loop that dampens the impact of nucleation on CCN. We confirm quantitatively that the decreases in survival probability predicted by GEOS-Chem-TOMAS due to higher nucleation rates are in accordance with this simple theory of survival probability.

Markku Kulmala - One of the best experts on this subject based on the ideXlab platform.

  • comprehensive analysis of particle growth rates from nucleation mode to cloud Condensation Nuclei in boreal forest
    Atmospheric Chemistry and Physics, 2018
    Co-Authors: Pauli Paasonen, Markku Kulmala, Maija Peltola, Jenni Kontkanen, Heikki Junninen, Velimatti Kerminen
    Abstract:

    Abstract. Growth of aerosol particles to sizes at which they can act as cloud Condensation Nuclei (CCN) is a crucial factor in estimating the current and future impacts of aerosol–cloud–climate interactions. Growth rates (GRs) are typically determined for particles with diameters ( dP) smaller than 40 nm immediately after a regional new particle formation (NPF) event. These growth rates are often taken as representatives for the particle growth to CCN sizes ( dP  > 50–100 nm). In modelling frameworks, the concentration of the condensable vapours causing the growth is typically calculated with steady state assumptions, where the Condensation sink (CS) is the only loss term for the vapours. Additionally, the growth to CCN sizes is represented with the Condensation of extremely low-volatility vapours and gas–particle partitioning of semi-volatile vapours. Here, we use a novel automatic method to determine growth rates from below 10 nm to hundreds of nanometres from a 20-year-long particle size distribution (PSD) data set in boreal forest. With this method, we are able to detect growth rates also at times other than immediately after a NPF event. We show that the GR increases with an increasing oxidation rate of monoterpenes, which is closely coupled with the ambient temperature. Based on our analysis, the oxidation reactions of monoterpenes with ozone, hydroxyl radical and nitrate radical all are capable of producing vapours that contribute to the particle growth in the studied size ranges. We find that GR increases with particle diameter, resulting in up to 3-fold increases in GRs for particles with dP ∼  100 nm in comparison to those with dP ∼  10 nm. We use a single particle model to show that this increase in GR can be explained with aerosol-phase reactions, in which semi-volatile vapours form non-volatile dimers. Finally, our analysis reveals that the GR of particles with dP  < 100 nm is not limited by the Condensation sink, even though the GR of larger particles is. Our findings suggest that in the boreal continental environment, the formation of CCN from NPF or sub-100 nm emissions is more effective than previously thought and that the formation of CCN is not as strongly self-limiting a process as the previous estimates have suggested.

  • the analysis of size segregated cloud Condensation Nuclei counter ccnc data and its implications for cloud droplet activation
    Atmospheric Chemistry and Physics, 2013
    Co-Authors: Mikhail Paramonov, Markku Kulmala, V M Kerminen, Nonne L Prisle, P P Aalto, Ari Asmi, Tuukka Petaja
    Abstract:

    Abstract. Ambient aerosol, CCN (cloud Condensation Nuclei) and hygroscopic properties were measured with a size-segregated CCNC (cloud Condensation Nuclei counter) in a boreal environment of southern Finland at the SMEAR (Station for Measuring Ecosystem-Atmosphere Relations) II station. The instrumental setup operated at five levels of supersaturation S covering a range from 0.1–1% and measured particles with a size range of 20–300 nm; a total of 29 non-consecutive months of data are presented. The median critical diameter Dc ranged from 150 nm at S of 0.1% to 46 nm at S of 1.0%. The median aerosol hygroscopicity parameter κ ranged from 0.41 at S of 0.1% to 0.14 at S of 1.0%, indicating that ambient aerosol in Hyytiala is less hygroscopic than the global continental or European continental averages. It is, however, more hygroscopic than the ambient aerosol in an Amazon rainforest, a European high Alpine site or a forested mountainous site. A fairly low hygroscopicity in Hyytiala is likely a result of a large organic fraction present in the aerosol mass comparative to other locations within Europe. A considerable difference in particle hygroscopicity was found between particles smaller and larger than ~100 nm in diameter, possibly pointing out to the effect of cloud processing increasing κ of particles > 100 nm in diameter. The hygroscopicity of the smaller, ~50 nm particles did not change seasonally, whereas particles with a diameter of ~150 nm showed a decreased hygroscopicity in the summer, likely resulting from the increased VOC emissions of the surrounding boreal forest and secondary organic aerosol (SOA) formation. For the most part, no diurnal patterns of aerosol hygroscopic properties were found. Exceptions to this were the weak diurnal patterns of small, ~50 nm particles in the spring and summer, when a peak in hygroscopicity around noon was observed. No difference in CCN activation and hygroscopic properties was found on days with or without atmospheric new particle formation. During all seasons, except summer, a CCN-inactive fraction was found to be present, rendering the aerosol of 75–300 nm in diameter as internally mixed in the summer and not internally mixed for the rest of the year.

  • production of potential cloud Condensation Nuclei associated with atmospheric new particle formation in northern finland
    Journal of Geophysical Research, 2003
    Co-Authors: Heikki Lihavainen, Markku Kulmala, Mika Komppula, V M Kerminen, Juha Hatakka, V Aaltonen, Y Viisanen
    Abstract:

    [1] During a 33-month measurement period at a high-latitude background site in northern Finland, a total of 103 new particle formation events were observed. In 19 cases, movement of the air masses allowed the observation of particle formation and growth over a sufficiently long time to investigate the production of “potential” cloud Condensation Nuclei (CCN) resulting from new-particle formation. All the CCN formation events took place in relatively clean air that had traversed the Northern Atlantic/Arctic Ocean prior to arrival at our measurement site. The number of formed new, “potential” CCN varied significantly between the different events and correlated weakly with the number of new-particles formed during the same events. This is consistent with recent theoretical suggestions of some sort of decoupling between atmospheric new-particle formation and growth. The vapours responsible for the “potential” CCN production could not be identified but were mostly something else than sulfuric acid resulting from the oxidation of SO2 in the gas phase. Although atmospheric new-particle formation is likely to give only a minor contribution to the overall CCN budget at our measurement site, the situation may be different over areas where new-particle formation events are more common. At the very least, our results demonstrate that because of atmospheric new-particle formation, it may not be possible to find any universal relation between the aerosol mass and cloud droplet number concentration that is applicable to clean conditions.

Athanasios Nenes - One of the best experts on this subject based on the ideXlab platform.

  • Effects of film-forming compounds on the growth of giant cloud Condensation Nuclei: Implications for cloud microphysics and the aerosol indirect effect
    2020
    Co-Authors: Jeessy Medina, Athanasios Nenes
    Abstract:

    [ 1 ] The presence of giant cloud Condensation Nuclei (GCCN) within stratocumulus clouds can help the formation of drizzle by acting as collector drops. We propose that the presence of film-forming compounds (FFCs) on GCCN may decrease their growth enough to cease this drizzle formation mechanism. We systematically explore the accommodation properties and amount of FFCs necessary to have as ignificant impact on GCCN size under realistic conditions of growth inside typical stratocumulus clouds. It is found that even low mass fractions (as low as 0.2%) of FFCs with amodest effect on water vapor accommodation can significantly reduce GCCN size and their potential to act as collector drops. Our conclusions apply to both pristine and polluted aerosol conditions, which suggest that in the presence of FFCs, GCCN may be influencing the microphysical evolution of clouds to al esser extent than previously thought

  • on the effect of dust particles on global cloud Condensation Nuclei and cloud droplet number
    Journal of Geophysical Research, 2011
    Co-Authors: V A Karydis, Prashant Kumar, Donifan Barahona, Irina N Sokolik, Athanasios Nenes
    Abstract:

    [1] Aerosol-cloud interaction studies to date consider aerosol with a substantial fraction of soluble material as the sole source of cloud Condensation Nuclei (CCN). Emerging evidence suggests that mineral dust can act as good CCN through water adsorption onto the surface of particles. This study provides a first assessment of the contribution of insoluble dust to global CCN and cloud droplet number concentration (CDNC). Simulations are carried out with the NASA Global Modeling Initiative chemical transport model with an online aerosol simulation, considering emissions from fossil fuel, biomass burning, marine, and dust sources. CDNC is calculated online and explicitly considers the competition of soluble and insoluble CCN for water vapor. The predicted annual average contribution of insoluble mineral dust to CCN and CDNC in cloud-forming areas is up to 40 and 23.8%, respectively. Sensitivity tests suggest that uncertainties in dust size distribution and water adsorption parameters modulate the contribution of mineral dust to CDNC by 23 and 56%, respectively. Coating of dust by hygroscopic salts during the atmospheric aging causes a twofold enhancement of the dust contribution to CCN; the aged dust, however, can substantially deplete in-cloud supersaturation during the initial stages of cloud formation and can eventually reduce CDNC. Considering the hydrophilicity from adsorption and hygroscopicity from solute is required to comprehensively capture the dust-warm cloud interactions. The framework presented here addresses this need and can be easily integrated in atmospheric models.

  • measurements of cloud Condensation Nuclei activity and droplet activation kinetics of fresh unprocessed regional dust samples and minerals
    Atmospheric Chemistry and Physics, 2011
    Co-Authors: Prashant Kumar, Irina N Sokolik, Athanasios Nenes
    Abstract:

    Abstract. This study reports laboratory measurements of cloud Condensation Nuclei (CCN) activity and droplet activation kinetics of aerosols dry generated from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. Based on the observed dependence of critical supersaturation, sc, with particle dry diameter, Ddry, we found that FHH (Frenkel, Halsey and Hill) adsorption activation theory is a far more suitable framework for describing fresh dust CCN activity than Kohler theory. One set of FHH parameters (AFHH ∼ 2.25 ± 0.75, BFHH ∼ 1.20 ± 0.10) can adequately reproduce the measured CCN activity for all species considered, and also explains the large range of hygroscopicities reported in the literature. Based on a threshold droplet growth analysis, mineral dust aerosols were found to display retarded activation kinetics compared to ammonium sulfate. Comprehensive simulations of mineral dust activation and growth in the CCN instrument suggest that this retardation is equivalent to a reduction of the water vapor uptake coefficient (relative to that for calibration ammonium sulfate aerosol) by 30–80%. These results suggest that dust particles do not require deliquescent material to act as CCN in the atmosphere.

  • cloud Condensation Nuclei measurements in the marine boundary layer of the eastern mediterranean ccn closure and droplet growth kinetics
    Atmospheric Chemistry and Physics, 2009
    Co-Authors: A Bougiatioti, Christos Fountoukis, Nikos Kalivitis, Spyros N Pandis, Athanasios Nenes, Nikos Mihalopoulos
    Abstract:

    Abstract. Measurements of cloud Condensation Nuclei (CCN) concentrations (cm−3) between 0.2 and 1.0% supersaturation, aerosol size distribution and chemical composition were performed at a remote marine site in the eastern Mediterranean, from September to October 2007 during the FAME07 campaign. Most of the particles activate at ~0.6% supersaturation, characteristic of the aged nature of the aerosol sampled. Application of Kohler theory, using measurements of bulk composition, size distribution, and assuming that organics are insoluble resulted in agreement between predicted and measured CCN concentrations within 7±11% for all supersaturations, with a tendency for CCN underprediction (16±6%; r2=0.88) at the lowest supersaturations (0.21%). Including the effects of the water-soluble organic fraction (which represent around 70% of the total organic content) reduces the average underprediction bias at the low supersaturations, resulting in a total closure error of 0.6±6%. Using threshold droplet growth analysis, the growth kinetics of ambient CCN is consistent with NaCl calibration experiments; hence the presence of aged organics does not suppress the rate of water uptake in this environment. The knowledge of the soluble salt fraction is sufficient for the description of the CCN activity in this area.

  • cloud Condensation Nuclei activity closure and droplet growth kinetics of houston aerosol during the gulf of mexico atmospheric composition and climate study gomaccs
    Journal of Geophysical Research, 2009
    Co-Authors: S Lance, Athanasios Nenes, Claudio Mazzoleni, Manvendra K Dubey, Harmony Gates, Varuntida Varutbangkul, Tracey A Rissman, Shane M Murphy, Armin Sorooshian
    Abstract:

    In situ cloud Condensation Nuclei (CCN) measurements were obtained in the boundary layer over Houston, Texas, during the 2006 Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) campaign onboard the CIRPAS Twin Otter. Polluted air masses in and out of cloudy regions were sampled for a total of 22 flights, with CCN measurements obtained for 17 of these flights. In this paper, we focus on CCN closure during two flights, within and downwind of the Houston regional plume and over the Houston Ship Channel. During both flights, air was sampled with particle concentrations exceeding 25,000 cm^(−3) and CCN concentrations exceeding 10,000 cm^(−3). CCN closure is evaluated by comparing measured concentrations with those predicted on the basis of measured aerosol size distributions and aerosol mass spectrometer particle composition. Different assumptions concerning the internally mixed chemical composition result in average CCN overprediction ranging from 3% to 36% (based on a linear fit). It is hypothesized that the externally mixed fraction of the aerosol contributes much of the CCN closure scatter, while the internally mixed fraction largely controls the overprediction bias. On the basis of the droplet sizes of activated CCN, organics do not seem to impact, on average, the CCN activation kinetics.