scholarly journals Study on the role of Black Carbon aerosols in cloud droplets during the dissipation of a fog.

2021 ◽  
Author(s):  
Lea Al Asmar ◽  
Luc Musson-Genon ◽  
Eric Dupont ◽  
Karine Sartelet
Keyword(s):  
Black Carbon ◽  
Volume Fraction ◽  
Solar Heating ◽  
Urban Atmosphere ◽  
Radiative Properties ◽  
Solar Irradiation ◽  
Liquid Content ◽  
Cloud Droplets ◽  
The Impact

<p><span>Cloud condensation nuclei (CCN) are the subset of aerosol particles able to form cloud droplets.</span><span> CNN activation is influenced by the size distribution, chemical composition and number of particles. They consequently impact the cloud microstructure,</span><span> which affects the radiative properties of clouds, atmospheric circulation and thermodynamics, as well as radiative budgets. By influencing</span><span> the single scattering albedos of clouds, some particles lead to an increase of the solar irradiation absorption and solar heating in the cloud layers. A good example of these absorbing particles is those made of black carbon (</span><span>BC), which is emitted during the combustion of various types of fuel and non-exhaust traffic-related processes. </span><span>The present study deals with the role of BC in a solar radiative scheme and its interaction with clouds during a well-documented case of a fog that evolves into a low stratus cloud. To do so, the solar scheme of the computational fluid dynamic model </span><span><em>Code Saturne</em></span><span> is used for the estimation of fluxes and heating rates in the atmosphere</span><span><em>.</em></span><span> It is based on </span><span>the two-stream parameterization with calculations done in the ultraviolet-visible (UV-Vis) and solar infrared (SIR) bands. </span></p><p><span>A special attention is given on the impact of BC on the dissipation of the fog. As expected, </span><span>the introduction of BC in cloud droplets accentuates the heating in the layers at the top of the cloud where water liquid content is maximum. In the SIR band, there is an increase of approximatively 80 %. In the UV-Vis band, where absorption of solar irradiance by ozone is minor, the heating rate is now 10 times higher. The contribution of the UV-Vis band becomes more important. The augmentation of solar heating leads to a reduction of the liquid water content and, consecutively, to a faster dissipation of the fog and the stratus. Therefore, direct surface fluxes are also increased.</span></p><p><span>When increasing the volume fraction of black carbon in cloud droplets, the water liquid content is furthermore reduced leading to a faster dissipation of the fog. However, this impact is small, because the fog is formed in the morning. At this time, the cooling rate due to thermal radiation is higher than the solar heating at the top of the cloud. We expect the impact of black carbon in cloud droplets</span><span> to be higher for more persistent clouds or for a fog in the boundary layer of the urban atmosphere, where the fraction of BC in particles is higher.</span></p>

scholarly journals A light-driven burst of hydroxyl radicals dominates oxidation chemistry in newly activated cloud droplets

2019 ◽  
Vol 5 (5) ◽  
pp. eaav7689 ◽  
Author(s):  
Suzanne E. Paulson ◽  
Peter J. Gallimore ◽  
Xiaobi M. Kuang ◽  
Jie Rou Chen ◽  
Markus Kalberer ◽  
...  
Keyword(s):  
Hydroxyl Radicals ◽  
Uv Light ◽  
Aerosol Particles ◽  
Cloud Droplet ◽  
Radiative Properties ◽  
Size Distributions ◽  
Cloud Droplets ◽  
New Process ◽  
Oxidation Chemistry ◽  
The Impact

Aerosol particles and their interactions with clouds are one of the most uncertain aspects of the climate system. Aerosol processing by clouds contributes to this uncertainty, altering size distributions, chemical composition, and radiative properties. Many changes are limited by the availability of hydroxyl radicals in the droplets. We suggest an unrecognized potentially substantial source of OH formation in cloud droplets. During the first few minutes following cloud droplet formation, the material in aerosols produces a near-UV light–dependent burst of hydroxyl radicals, resulting in concentrations of 0.1 to 3.5 micromolar aqueous OH ([OH]aq). The source of this burst is previously unrecognized chemistry between iron(II) and peracids. The contribution of the “OH burst” to total OH in droplets varies widely, but it ranges up to a factor of 5 larger than previously known sources. Thus, this new process will substantially enhance the impact of clouds on aerosol properties.

scholarly journals Size-resolved observations of refractory black carbon particles in cloud droplets at a marine boundary layer site

2015 ◽  
Vol 15 (3) ◽  
pp. 1367-1383 ◽  
Author(s):  
J. C. Schroder ◽  
S. J. Hanna ◽  
R. L. Modini ◽  
A. L. Corrigan ◽  
S. M. Kreidenwies ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Marine Boundary Layer ◽  
Volume Fraction ◽  
Particle Diameter ◽  
Cloud Droplet ◽  
Cloud Droplets ◽  
Back Trajectories ◽  
Carbon Particles ◽  
La Jolla

Abstract. Size-resolved observations of aerosol particles and cloud droplet residuals were studied at a marine boundary layer site (251 m a.m.s.l.) in La Jolla, San Diego, California, during 2012. A counterflow virtual impactor (CVI) was used as the inlet to sample cloud residuals while a total inlet was used to sample both cloud residuals and interstitial particles. Two cloud events totaling 10 h of in-cloud sampling were analyzed. Based on bulk aerosol particle concentrations, mass concentrations of refractory black carbon (rBC), and back trajectories, the two air masses sampled were classified as polluted marine air. Since the fraction of cloud droplets sampled by the CVI was less than 100%, the measured activated fractions of rBC should be considered as lower limits to the total fraction of rBC activated during the two cloud events. Size distributions of rBC and a coating analysis showed that sub-100 nm rBC cores with relatively thick coatings were incorporated into the cloud droplets (i.e., 95 nm rBC cores with median coating thicknesses of at least 65 nm were incorporated into the cloud droplets). Measurements also show that the coating volume fraction of rBC cores is relatively large for sub-100 nm rBC cores. For example, the median coating volume fraction of 95 nm rBC cores incorporated into cloud droplets was at least 0.9, a result that is consistent with κ-Köhler theory. Measurements of the total diameter of the rBC-containing particles (rBC core and coating) suggest that the total diameter of rBC-containing particles needed to be at least 165 nm to be incorporated into cloud droplets when the core rBC diameter is ≥ 85 nm. This result is consistent with previous work that has shown that particle diameter is important for activation of non-rBC particles. The activated fractions of rBC determined from the measurements ranged from 0.01 to 0.1 for core rBC diameters ranging from 70 to 220 nm. This type of data is useful for constraining models used for predicting rBC concentrations in the atmosphere.

scholarly journals An algorithm for retrieving black carbon optical parameters from thermal-optical (OC/EC) instruments

2011 ◽  
Vol 4 (1) ◽  
pp. 1233-1254 ◽  
Author(s):  
A. Andersson ◽  
R. J. Sheesley ◽  
E. N. Kirillova ◽  
Ö. Gustafsson
Keyword(s):  
Black Carbon ◽  
Cross Sections ◽  
Global Climate ◽  
Light Attenuation ◽  
Radiative Properties ◽  
Optical Parameters ◽  
Carbon Detection ◽  
Recent Developments ◽  
The Common ◽  
The Impact

Abstract. Through absorption of sun light atmospheric black carbon (BC) is expected to influence regional/global climate by warming the atmosphere and dimming the surface. To evaluate the impact of these effects it is of interest to examine both the radiative properties of BC and the concentrations in air. Building on recent developments we present a novel application for combining these two aspects using the common thermal-optical (OC/EC) instrument. By correlating the OC/EC laser transmission with the FID-carbon detection non-carbon contributions to the light attenuation are detected. Such analysis allows the calculation of mass absorption cross-sections (MACs) for BC, corrected for certain in-organic components. This approach has been applied to data from two SS Asian and two SNS European sites, including a time series analysis for one of the SNS European sites. Taken together this study demonstrates broad applicability for this method while providing new insights into the optical properties of BC.

scholarly journals Theoretical and Experimental Characterization of the Ultrafast Aircraft Thermometer: Reduction of Aerodynamic Disturbances and Signal Processing

2005 ◽  
Vol 22 (7) ◽  
pp. 988-1003 ◽  
Author(s):  
Bogdan Rosa ◽  
Konrad Bajer ◽  
Krzysztof E. Haman ◽  
Tomasz Szoplik
Keyword(s):  
Boundary Layer ◽  
Electronic System ◽  
Reynolds Numbers ◽  
Aerodynamic Noise ◽  
Sensing Element ◽  
Cloud Droplets ◽  
Strong Shear ◽  
System Temperature ◽  
The Impact

Abstract The ultrafast aircraft thermometer, built for measuring temperature in clouds at flight speeds up to 100 m s−1, employs a 2.5-μm-thick platinum-coated tungsten wire as a sensing element. When temperature increases, the wire resistance increases. The changes are amplified by an electronic system. Temperature measurements made in a wind tunnel and during flights show noise that is related to the von Kármán vortex street generated behind the shield that protects the sensing element against the impact of cloud droplets. To reduce both the level of turbulence and the amount of water collected on the shield, suction is applied through the slits in its sides. The effect of suction on the flow field is twofold. First, at the Reynolds numbers that the thermometer is operated suction eliminates aerodynamic disturbances. Second, suction diverts the inner part of the boundary layer into the slit. This inner part is a region of strong shear and, therefore, a region where intensive viscous heating takes place. When the suction is on much of the air that is heated in the boundary layer in the front part of the shield is removed through the slits and never reaches the sensor. To study the role of the shield with suction and confirm its chosen shape, two-dimensional (2D) direct numerical simulations (DNSs) are performed of the airflow and of the trajectories of droplets of various sizes and initial positions. The influence on the temperature distribution of the irreversible dissipation of energy due to air viscosity is also examined. This is found to have a small but measurable effect. The effects associated with sampling and processing of the analog signal obtained from the sensing wire are discussed. The results herein quantitatively explain the nature of the measured aerodynamic noise.

scholarly journals Sensitivity of Radiative and Thermal Properties of Building Material in the Urban Atmosphere

2019 ◽  
Vol 11 (23) ◽  
pp. 6865 ◽  
Author(s):  
Marcos Vinicius Bueno de Morais ◽  
Viviana Vanesa Urbina Guerrero ◽  
Edmilson Dias de Freitas ◽  
Edson R. Marciotto ◽  
Hugo Valdés ◽  
...  
Keyword(s):  
Building Material ◽  
Urban Areas ◽  
Atmospheric Model ◽  
Sao Paulo ◽  
Urban Atmosphere ◽  
Radiative Properties ◽  
São Paulo ◽  
Cold Surface ◽  
Local Climate ◽  
The Impact

In the context of the impact of urbanization on climate change, this work aims to evaluate the sensitivity of the thermal and radiative properties of building surfaces in urban areas to the urban heat island intensity, a local scale meteorological phenomenon. For this, variations of albedo values, emissivity, thermal conductivity and heat capacity of roofs, streets and walls were simulated through an urban scheme coupled with the BRAMS mesoscale atmospheric model for the metropolitan area of São Paulo, considering two main urban types. The simulations show that, in general, looking for cold surface situations, the change of building material can contribute to a reduction of up to 3 °C for São Paulo. In addition, the role of orientation and the typological characteristics of constructions should be taken into account. In this sense, it is expected that this work guides civil engineers and builders to search for new materials in order to reduce the effects of urbanization on the local climate.

Intergroup Threat and Outgroup Attitudes

2013 ◽  
Vol 44 (5) ◽  
pp. 311-319 ◽  
Author(s):  
Marco Brambilla ◽  
David A. Butz
Keyword(s):  
Gay Men ◽  
Social Group ◽  
Welfare Recipients ◽  
Intergroup Attitudes ◽  
Social Policies ◽  
Intergroup Threat ◽  
Economic Threat ◽  
The Impact ◽  
General Climate

Two studies examined the impact of macrolevel symbolic threat on intergroup attitudes. In Study 1 (N = 71), participants exposed to a macrosymbolic threat (vs. nonsymbolic threat and neutral topic) reported less support toward social policies concerning gay men, an outgroup whose stereotypes implies a threat to values, but not toward welfare recipients, a social group whose stereotypes do not imply a threat to values. Study 2 (N = 78) showed that, whereas macrolevel symbolic threat led to less favorable attitudes toward gay men, macroeconomic threat led to less favorable attitudes toward Asians, an outgroup whose stereotypes imply an economic threat. These findings are discussed in terms of their implications for understanding the role of a general climate of threat in shaping intergroup attitudes.

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