scholarly journals Atmospheric radiative effects of an in-situ measured Saharan dust plume and the role of large particles

2007 ◽  
Vol 7 (3) ◽  
pp. 7767-7817 ◽  
Author(s):  
S. Otto ◽  
M. de Reus ◽  
T. Trautmann ◽  
A. Thomas ◽  
M. Wendisch ◽  
...  
Keyword(s):  
Complex Refractive Index ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Saharan Dust ◽  
Dust Particles ◽  
Modal Parameters ◽  
Size Distributions ◽  
Radiative Effects ◽  
Enhanced Absorption ◽  
Large Particles

Abstract. This work will present aerosol size distributions measured in a Saharan dust plume between 0.9 and 12 km altitude during the ACE-2 campaign 1997. The distributions contain a significant fraction of large particles of diameters from 4 to 30 μm. Radiative transfer calculations have been performed using these data as input. Shortwave, longwave as well as total atmospheric radiative effects (AREs) of the dust plume are investigated over ocean and desert within the scope of sensitivity studies considering varied input parameters like solar zenith angle, scaled total dust optical depth, tropospheric standard aerosol profiles and particle complex refractive index. The results indicate that the large particle fraction has a predominant impact on the optical properties of the dust. A single scattering albedo of ωo=0.75–0.96 at 550 nm was simulated in the entire dust column as well as 0.76 within the Saharan dust layer at ~4 km altitude indicating enhanced absorption. The measured dust leads to cooling over the ocean but warming over the desert due to differences in their spectral surface albedo and surface temperature. The large particles absorb strongly and they contribute at least 20% to the ARE in the dusty atmosphere. From the measured size distributions modal parameters of a bimodal lognormal column volume size distribution were deduced, resulting in a coarse median diameter of ~9 μm and a column single scattering albedo of 0.78 at 550 nm. A sensitivity study demonstrates that variabilities in the modal parameters can cause completely different AREs and emphasises the warming effect of the large mineral dust particles.

scholarly journals Atmospheric radiative effects of an in situ measured Saharan dust plume and the role of large particles

2007 ◽  
Vol 7 (18) ◽  
pp. 4887-4903 ◽  
Author(s):  
S. Otto ◽  
M. de Reus ◽  
T. Trautmann ◽  
A. Thomas ◽  
M. Wendisch ◽  
...  
Keyword(s):  
Complex Refractive Index ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Saharan Dust ◽  
Dust Particles ◽  
Modal Parameters ◽  
Size Distributions ◽  
Radiative Effects ◽  
Enhanced Absorption ◽  
Large Particles

Abstract. This work will present aerosol size distributions measured in a Saharan dust plume between 0.9 and 12 km altitude during the ACE-2 campaign 1997. The distributions contain a significant fraction of large particles of diameters from 4 to 30 μm. Radiative transfer calculations have been performed using these data as input. Shortwave, longwave as well as total atmospheric radiative effects (AREs) of the dust plume are investigated over ocean and desert within the scope of sensitivity studies considering varied input parameters like solar zenith angle, scaled total dust optical depth, tropospheric standard aerosol profiles and particle complex refractive index. The results indicate that the large particle fraction has a predominant impact on the optical properties of the dust. A single scattering albedo of ωo=0.75–0.96 at 550 nm was simulated in the entire dust column as well as 0.76 within the Saharan dust layer at ~4 km altitude indicating enhanced absorption. The measured dust leads to cooling over the ocean but warming over the desert due to differences in their spectral surface albedo and surface temperature. The large particles absorb strongly and they contribute at least 20% to the ARE in the dusty atmosphere. From the measured size distributions modal parameters of a bimodal lognormal column volume size distribution were deduced, resulting in a coarse median diameter of ~9 μm and a column single scattering albedo of 0.78 at 550 nm. A sensitivity study demonstrates that variabilities in the modal parameters can cause completely different AREs and emphasises the warming effect of the large mineral dust particles.

scholarly journals Observations of Saharan dust microphysical and optical properties from the Eastern Atlantic during NAMMA airborne field campaign

2011 ◽  
Vol 11 (2) ◽  
pp. 723-740 ◽  
Author(s):  
G. Chen ◽  
L. D. Ziemba ◽  
D. A. Chu ◽  
K. L. Thornhill ◽  
G. L. Schuster ◽  
...  
Keyword(s):  
Particle Size ◽  
Optical Properties ◽  
Dust Particle ◽  
Saharan Dust ◽  
Dust Particles ◽  
Small Range ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Field Campaign ◽  
Sahara Dust

Abstract. As part of the international project entitled "African Monsoon Multidisciplinary Analysis (AMMA)", NAMMA (NASA AMMA) aimed to gain a better understanding of the relationship between the African Easterly Waves (AEWs), the Sahara Air Layer (SAL), and tropical cyclogenesis. The NAMMA airborne field campaign was based out of the Cape Verde Islands during the peak of the hurricane season, i.e., August and September 2006. Multiple Sahara dust layers were sampled during 62 encounters in the eastern portion of the hurricane main development region, covering both the eastern North Atlantic Ocean and the western Saharan desert (i.e., 5–22° N and 10–35° W). The centers of these layers were located at altitudes between 1.5 and 3.3 km and the layer thickness ranged from 0.5 to 3 km. Detailed dust microphysical and optical properties were characterized using a suite of in-situ instruments aboard the NASA DC-8 that included a particle counter, an Ultra-High Sensitivity Aerosol Spectrometer, an Aerodynamic Particle Sizer, a nephelometer, and a Particle Soot Absorption Photometer. The NAAMA sampling inlet has a size cut (i.e., 50% transmission efficiency size) of approximately 4 μm in diameter for dust particles, which limits the representativeness of the NAMMA observational findings. The NAMMA dust observations showed relatively low particle number densities, ranging from 268 to 461 cm−3, but highly elevated volume density with an average at 45 μm3 cm−3. NAMMA dust particle size distributions can be well represented by tri-modal lognormal regressions. The estimated volume median diameter (VMD) is averaged at 2.1 μm with a small range of variation regardless of the vertical and geographical sampling locations. The Ångström Exponent assessments exhibited strong wavelength dependence for absorption but a weak one for scattering. The single scattering albedo was estimated at 0.97 ± 0.02. The imaginary part of the refractive index for Sahara dust was estimated at 0.0022, with a range from 0.0015 to 0.0044. Closure analysis showed that observed scattering coefficients are highly correlated with those calculated from spherical Mie-Theory and observed dust particle size distributions. These values are generally consistent with literature values reported from studies with similar particle sampling size range.

scholarly journals Modeling of Aerosol Radiation-Relevant Parameters in the Troposphere of Siberia on the Basis of Empirical Data

Atmosphere ◽  
2018 ◽  
Vol 9 (11) ◽  
pp. 414 ◽  
Author(s):  
Mikhail Panchenko ◽  
Svetlana Terpugova ◽  
Victor Pol’kin ◽  
Valerii Kozlov ◽  
Dmitry Chernov
Keyword(s):  
Complex Refractive Index ◽  
West Siberia ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Optical Characteristics ◽  
Asymmetry Factor ◽  
Size Spectrum ◽  
Scattering Phase ◽  
Scattering Phase Function ◽  
Modal Radius

The paper presents the generalized empirical model of the aerosol optical characteristics in the lower 5-km layer of the atmosphere of West Siberia. The model is based on the data of long-term airborne sensing of the vertical profiles of the angular scattering coefficient, aerosol disperse composition, as well as the content of absorbing particles. The model provides for retrieval of the aerosol optical characteristics in visible and near IR wavelength ranges (complex refractive index, scattering and absorption coefficients, optical depth, single scattering albedo, and asymmetry factor of the scattering phase function). The main attention in the presented version of the model is given to two aspects: The study of the effect of the size spectrum of the absorbing substance in the composition of aerosol particles on radiative-relevant parameters (the single scattering albedo (SSA) and the asymmetry factor (AF)) and the consideration of different algorithms for taking into account the relative humidity of air. The ranges of uncertainty of SSA and AF at variations in the modal radius of the absorbing fraction at different altitudes in the troposphere are estimated.

scholarly journals Optical properties of atmospheric fine particles near Beijing during the HOPE-J<sup>3</sup>A Campaign

2015 ◽  
Vol 15 (22) ◽  
pp. 33675-33730
Author(s):  
X. Xu ◽  
W. Zhao ◽  
Q. Zhang ◽  
S. Wang ◽  
B. Fang ◽  
...  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Fine Particles ◽  
Complex Refractive Index ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Organic Mass ◽  
Absorption Coefficients ◽  
Aerosol Composition ◽  
Inorganic Species

Abstract. The optical properties and chemical composition of PM1.0 (particulate with an aerodynamic diameter of less than 1.0 μm) particles in a suburban environment (Huairou) near the mega-city Beijing were measured during the HOPE-J3A (Haze Observation Project Especially for Jing-Jin-Ji Area) field campaign. The campaign covered the period November 2014 to January 2015 during the winter coal heating season. The average and standard deviations for the extinction, scattering, absorption coefficients, and the aerosol single scattering albedo (SSA) at λ = 470 nm during the measurement period were 201 ± 240, 164 ± 202, 37 ± 43 Mm-1, and 0.80 ± 0.08, respectively. The mean mass scattering (MSE) and absorption (MAE) efficiencies were 4.77 ± 0.01 and 0.87 ± 0.03 m2g-1, respectively. Highly time-resolved air pollution episodes clearly show the dramatic evolution of the PM1.0 size distribution, extensive optical properties (extinction, scattering, and absorption coefficients) and intensive optical properties (single scattering albedo and complex refractive index) during haze formation, development and decline. Time periods were classified into three different pollution levels (clear, slightly polluted, and polluted) for further analysis. It was found that: (1) The diurnal patterns of the aerosol extinction, scattering, absorption coefficients, and SSA differed for the three pollution classes. (2) The real and imaginary part of complex refractive index (CRI) increased, while the SSA decreased from clear to polluted days. (3) The relative contributions of organic and inorganic species to observed aerosol composition changed significantly from clear to polluted days: the organic mass fraction decreased (50 to 43 %) while the proportion of sulfates, nitrates, and ammonium increased strongly (34 to 44 %). (4) The fractional contribution of chemical components to extinction coefficients was calculated by using the modified IMPROVE algorithm. Organic mass was the largest contributor (58 %) to the total extinction of PM1.0. When the air quality deteriorated, the change of the relative contribution of sulfate aerosol to the total extinction was small, but the contribution of nitrate aerosol increased significantly (from 17 % on clear days to 23 % on polluted days). (5) The observed mass scattering efficiencies increased consistently with the pollution extent, however, the observed mass absorption efficiencies increased consistently with increasing mass concentration in slightly pollution conditions, but decreased under polluted conditions.

Research on the single scattering albedo of spheroids

2014 ◽  
Vol 24 (8) ◽  
pp. 1762-1768 ◽  
Author(s):  
Hong Tang ◽  
Xian-Xia Li
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Complex Refractive Index ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Scattering Cross Section ◽  
Nonspherical Particles ◽  
Incident Wavelength ◽  
Content Type ◽  
Scattering Cross

Purpose – The purpose of this paper is to discuss the light scattering of nonspherical particles that is very important for the research on the aerosol optical properties. Design/methodology/approach – In this paper, the authors use the spheroid model as the characteristic particle shape to study the single scattering albedo of real nonspherical particles. Meanwhile, the extinction and scattering cross section of spheroids are calculated with the T matrix method combined with the improved geometric optics approximation method (IGOM). Findings – Through this combination, the extinction and scattering cross section of spheroids can be obtained in the larger size range and aspect ratio range. Furthermore, the comparison of the single scattering albedo for the spheroids and their equivalent spheres is conducted in order to investigate the difference of the spherical and nonspherical particles. Originality/value – Simulation experiments indicate that the single scattering albedo of spheroids can be calculated well with this combination, and it has some obvious influence on the variation of the aspect ratio, incident wavelength, and complex refractive index of spheroid particles.

scholarly journals Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and first climatology analysis

2004 ◽  
Vol 4 (11/12) ◽  
pp. 2465-2480 ◽  
Author(s):  
M. Collaud Coen ◽  
E. Weingartner ◽  
D. Schaub ◽  
C. Hueglin ◽  
C. Corrigan ◽  
...  
Keyword(s):  
Wavelength Dependence ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Saharan Dust ◽  
Back Trajectories ◽  
Suspended Particulate ◽  
Dust Events ◽  
Source Countries ◽  
Average Contribution ◽  
North Western

Abstract. Scattering and absorption coefficients have been measured continuously at several wavelengths since March 2001 at the high altitude site Jungfraujoch (3580ma.s.l.). From these data, the wavelength dependences of the Ångström exponent and particularly of the single scattering albedo are determined. While the exponent of the single scattering albedo usually increases with wavelength, it decreases with wavelength during Saharan dust events (SDE) due to the greater size of the mineral aerosol particles and their different chemical composition. This change in the sign of the single scattering exponent turns out to be a sensitive means for detecting Saharan dust events. The occurrence of SDE detected by this new method was confirmed by visual inspection of filter colors and by studying long-range back-trajectories. An examination of SDE over a 22-month period shows that SDE are more frequent during the March-June period as well as during October and November. The trajectory analysis indicated a mean traveling time of 96.5h, with the most important source countries situated in the northern and north-western part of the Saharan desert. Most of the SDE do not lead to a detectable increase of the 48-h total suspended particulate matter (TSP) concentration at the Jungfraujoch. During Saharan dust events, the average contribution of this dust to hourly TSP at the Jungfraujoch is 16µg/m3, which corresponds to an annual mean of 0.8µg/m3 or 24% of TSP.

scholarly journals Complex refractive indices of Saharan dust samples at visible and near UV wavelengths: a laboratory study

2011 ◽  
Vol 11 (7) ◽  
pp. 21363-21427 ◽  
Author(s):  
R. Wagner ◽  
T. Ajtai ◽  
K. Kandler ◽  
K. Lieke ◽  
C. Linke ◽  
...  
Keyword(s):  
Refractive Index ◽  
Complex Refractive Index ◽  
Mineralogical Composition ◽  
Sensitivity Study ◽  
Saharan Dust ◽  
Dust Particles ◽  
Particle Analysis ◽  
Refractive Indices ◽  
Aerosol Chamber ◽  
Electron Microscopical

Abstract. We have retrieved the wavelength-dependent imaginary parts of the complex refractive index for five different Saharan dust aerosol particles of variable mineralogical composition at wavelengths between 305 and 955 nm. The dust particles were generated by re-dispersing soil samples into a laboratory aerosol chamber, typically yielding particle sizes with mean diameters ranging from 0.3 to 0.4 μm and maximum diameters from 2 to 4 μm. The extinction and absorption coefficients as well as the number size distribution of the dust particles were simultaneously measured by various established techniques. An inversion scheme based on a spheroidal dust model was employed to deduce the refractive indices. The retrieved imaginary parts of the complex refractive index were in the range from 0.003 to 0.005, 0.005 to 0.011, and 0.016 to 0.050 at the wavelengths 955, 505, and 305 nm. The hematite content of the dust particles was determined by electron-microscopical single particle analysis. Hematite volume fractions in the range from 1.1 to 2.7 % were found for the different dusts, a range typical for atmospheric mineral dust. We have performed a sensitivity study to assess how accurately the retrieved imaginary refractive indices could be reproduced by calculations with mixing rule approximations using the experimentally determined hematite contents as input.

scholarly journals Physical and optical properties of atmospheric aerosol by in-situ and radiometric measurements

2009 ◽  
Vol 9 (6) ◽  
pp. 25565-25597
Author(s):  
M. Calvello ◽  
F. Esposito ◽  
G. Pavese ◽  
C. Serio
Keyword(s):  
Optical Properties ◽  
Atmospheric Aerosols ◽  
Saharan Dust ◽  
Dust Particles ◽  
Rural Site ◽  
Size Distributions ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Observation Methods

Abstract. Physical and optical properties of atmospheric aerosols collected by using a high resolution (1.5 nm) spectroradiometer (spectral range 400–800 nm), a 13 stages Dekati Low Pressure Impactor (size range 30 nm–10 μm), and an AE31 Aethalometer (7 wavelenghts from 370 nm to 950 nm), have been examined in a semi-rural site in Southwest Italy (Tito Scalo, 40°35´ N, 15°41´ E, 750 m a.s.l.). In particular, daily averaged values of AOD and Ångström turbidity parameters from radiometric data together with mass-size distributions from impactor data and Black Carbon (BC) concentrations have been analyzed from May to October 2008. Furthermore, by inverting direct solar radiances, aerosol columnar number and volume size distributions have been obtained for the same period. Comparison of different observation methods, allowed to verify if, and in what conditions, changes in aerosol properties measured at ground are representative of columnar properties variations. Agreement between columnar and in-situ measurements has been obtained in case of anthropogenic aerosol loading, while in case of Saharan dust intrusions some discrepancies have been found when dust particles were located at high layers in the atmosphere (4–8 km) thus affecting columnar properties more than surface ones. For anthropogenic aerosols, a good correlation has been confirmed through the comparison of fine aerosol fraction contribution as measured by radiometer, impactor and aethalometer, suggesting that in this case particles are more homogeneously distributed over the lower layers of atmosphere and columnar aerosol optical properties are dominated by surface measured component.

scholarly journals Characterisation of episodic aerosol types over the Australian continent

2009 ◽  
Vol 9 (6) ◽  
pp. 1943-1956 ◽  
Author(s):  
Y. Qin ◽  
R. M. Mitchell
Keyword(s):  
Cluster Analysis ◽  
Optical Properties ◽  
Radiative Forcing ◽  
Climate Models ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Back Trajectory ◽  
Enhanced Absorption ◽  
Australian Continent ◽  
Aerosol Types

Abstract. Classification of Australian continental aerosol types resulting from episodes of enhanced source activity, such as smoke plumes and dust outbreaks, is carried out via cluster analysis of optical properties obtained from inversion of sky radiance distributions at Australian aerosol ground stations using data obtained over the last decade. The cluster analysis distinguishes four significant classes, which are identified on the basis of their optical properties and provenance as determined by satellite imagery and back-trajectory analysis. The four classes are identified respectively as aged smoke, fresh smoke, coarse dust and a super-absorptive aerosol. While the first three classes show similarities with comparable aerosol types identified elsewhere, the super-absorptive aerosol has no obvious foreign prototype. The class identified as coarse dust shows a prominent depression in single scattering albedo in the blue spectral region due to absorption by hematite, which is shown to be more abundant in central Australian dust relative to the "dust belt"of the Northern Hemisphere. The super-absorptive class is distinctive in view of its very low single scattering albedo (~0.7 at 500 nm) and variable enhanced absorption at 440 nm. The strong absorption by this aerosol requires a high black carbon content while the enhanced blue-band absorption may derive from organic compounds emitted during the burning of specific vegetation types. This aerosol exerts a positive radiative forcing at the top of atmosphere (TOA), with a large deposition of energy in the atmosphere per unit aerosol optical depth. This contrasts to the other three classes where the TOA forcing is negative. Optical properties of the four types will be used to improve the representation of Australian continental aerosol in climate models, and to enhance the accuracy of satellite-based aerosol retrievals over Australia.

Urban aerosol in Moscow megacity and its radiative effects according to the AeroRadCity experiment and COSMO-ART modelling

2020 ◽  
Author(s):  
Nataly Chubarova ◽  
Elizaveta Androsova ◽  
Elena Volpert ◽  
Alexander Kirsanov ◽  
Bernhard Vogel ◽  
...  
Keyword(s):  
Numerical Experiments ◽  
Urban Pollution ◽  
Pollutant Dispersion ◽  
Single Scattering ◽  
Insoluble Fraction ◽  
Particle Dispersion ◽  
Single Scattering Albedo ◽  
Urban Aerosol ◽  
Radiative Effects ◽  
Russian Science

&lt;p&gt;The AeroRadCity urban aerosol experiment over Moscow megacity have been carried out during spring 2018 and 2019. The experiment included measurement campaign at the Moscow MSU MO and numerical experiments using COSMO-ART model (Vogel et al., 2010, Vilfand et al., 2017). We examined the dynamic of aerosol properties and their radiative effects under various meteorological conditions using both columnar and surface aerosol measurements (AERONET dataset, mass concentration of PM10, black carbon (BC), different aerosol gas-precursors, etc.). For qualifying urban pollution special attention was given to the analysis of columnar and surface Angstrom absorption coefficients, low values of which indicated the BC dominance as a result of high-temperature combustion of natural fuel in transport engines. We obtained a positive statistically significant dependence of AOD on PM and BC concentrations with a pronounced bifurcation point around PM10=0.04 mgm&lt;sup&gt;-3&lt;/sup&gt;. Model and experimental data demonstrated positive BC relationships with PM10, NO&lt;sub&gt;2&lt;/sub&gt; and SO&lt;sub&gt;2&lt;/sub&gt; at Moscow megacity (Chubarova et al., 2019). The analysis of radiative effects of aerosol in clear sky conditions has revealed up to 30% loss for UV irradiance and 15% - for shortwave irradiance at high AOD. Much intensive radiation attenuation is observed in the afternoon, when remote pollution sources affected solar fluxes at elevated boundary layer conditions. Negative (cooling) RF effect at TOA varied from -20 Wm&lt;sup&gt;-2&lt;/sup&gt; to -1 Wm&lt;sup&gt;-2&lt;/sup&gt; with average of -8 Wm&lt;sup&gt;-&lt;/sup&gt;2. The minimum (absolute) RF effect corresponded to the lowest AOT and single scattering albedo. A statistically significant regression dependence of the single scattering albedo on BC/PM10 fraction was obtained at high level of particle dispersion intensity.&lt;/p&gt;&lt;p&gt;The urban AOT550 calculations in COSMO-ART model were compared with the results of measurements in Moscow and Zvenigorod at the A. M. Oboukhov IFA RAS institute. They showed a satisfactory agreement between model and measured values of city aerosol pollution (respectively, dAOT= 0.017&amp;#160; and dAOT= 0.013). In some days the difference increased up to 0.05 in conditions with low intensity of pollutant dispersion.&lt;/p&gt;&lt;p&gt;During the experiment a high correlation (R&lt;sup&gt;2&lt;/sup&gt;=0.95) was revealed between the insoluble component and the total mineralization of rain precipitation, which indicates that 70% of aerosol deposition occurs as the insoluble fraction. We show that at the initial concentration of C&lt;sub&gt;0&lt;/sub&gt;(PM)&gt;10 &amp;#956;gm&lt;sup&gt;-3&lt;/sup&gt; exponential washout coefficients are significant for PM (alfa (PM)=0.17+-0.09 hour&lt;sup&gt;-1&lt;/sup&gt;) and insignificant for BC (alfa (BC) =0.07+-0.10 hour&lt;sup&gt;-1&lt;/sup&gt;). At C&lt;sub&gt;0&lt;/sub&gt;(PM) &lt;10 &amp;#956;gm&lt;sup&gt;-3&lt;/sup&gt;, the alfa values both for PM and BC are close to zero. According to the numerical experiments with and without account of wet deposition the alfa value was estimated to be 0.08 hour&lt;sup&gt;-1&lt;/sup&gt;, which fits the confidence interval obtained from the measurements. The work was supported by the Russian Science Foundation, grant # 18-17-00149.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Chubarova N.E. et al. (2019). &lt;em&gt;GEOGRAPHY, ENVIRONMENT, SUSTAINABILITY&lt;/em&gt;. 2019;12(4):114-131. &lt;/p&gt;&lt;p&gt;Vogel et al., (2010). In Integrated Systems of Meso-meteorological and Chemical Transport Models, Springer, pp. 75-80.&lt;/p&gt;&lt;p&gt;Vilfand et al. (2017). Russian Meteorology and Hydrology, vol. 42, &amp;#8470; 5, pp. 292&amp;#8211;298. DOI:10.3103/S106837391705003X.&lt;/p&gt;

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