Radiative Effect and Mixing Processes of a Long-Lasting Dust Event over Athens, Greece, during the COVID-19 Period

We report on a long-lasting (10 days) Saharan dust event affecting large sections of South-Eastern Europe by using a synergy of lidar, satellite, in-situ observations and model simulations over Athens, Greece. The dust measurements (11–20 May 2020), performed during the confinement period due to the COVID-19 pandemic, revealed interesting features of the aerosol dust properties in the absence of important air pollution sources over the European continent. During the event, moderate aerosol optical depth (AOD) values (0.3–0.4) were observed inside the dust layer by the ground-based lidar measurements (at 532 nm). Vertical profiles of the lidar ratio and the particle linear depolarization ratio (at 355 nm) showed mean layer values of the order of 47 ± 9 sr and 28 ± 5%, respectively, revealing the coarse non-spherical mode of the probed plume. The values reported here are very close to pure dust measurements performed during dedicated campaigns in the African continent. By utilizing Libradtran simulations for two scenarios (one for typical midlatitude atmospheric conditions and one having reduced atmospheric pollutants due to COVID-19 restrictions, both affected by a free tropospheric dust layer), we revealed negligible differences in terms of radiative effect, of the order of +2.6% (SWBOA, cooling behavior) and +1.9% (LWBOA, heating behavior). Moreover, the net heating rate (HR) at the bottom of the atmosphere (BOA) was equal to +0.156 K/d and equal to +2.543 K/d within 1–6 km due to the presence of the dust layer at that height. On the contrary, the reduction in atmospheric pollutants could lead to a negative HR (−0.036 K/d) at the bottom of the atmosphere (BOA) if dust aerosols were absent, while typical atmospheric conditions are estimated to have an almost zero net HR value (+0.006 K/d). The NMMB-BSC forecast model provided the dust mass concentration over Athens, while the air mass advection from the African to the European continent was simulated by the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model.

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Airborne measurements of dust layer properties, particle size distribution and mixing state of Saharan dust during SAMUM 2006

Tellus B ◽

10.3402/tellusb.v61i1.16817 ◽

2009 ◽

Vol 61 (1) ◽

Cited By ~ 2

Author(s):

Bernadett Weinzierl ◽

Andreas Petzold ◽

Michael Esselborn ◽

Martin Wirth ◽

Katharina Rasp ◽

...

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Saharan Dust ◽

Mixing State ◽

Dust Layer ◽

Airborne Measurements

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An outstanding Saharan dust event at Mt. Cimone (2165 m a.s.l., Italy) in March 2004

Atmospheric Environment ◽

10.1016/j.atmosenv.2015.05.017 ◽

2015 ◽

Vol 113 ◽

pp. 223-235 ◽

Cited By ~ 11

Author(s):

Erika Brattich ◽

Angelo Riccio ◽

Laura Tositti ◽

Paolo Cristofanelli ◽

Paolo Bonasoni

Keyword(s):

Saharan Dust ◽

Dust Event

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WRF-chem sensitivity to vertical resolution during a saharan dust event

Physics and Chemistry of the Earth Parts A/B/C ◽

10.1016/j.pce.2015.04.002 ◽

2016 ◽

Vol 94 ◽

pp. 188-195 ◽

Cited By ~ 13

Author(s):

J.C. Teixeira ◽

A.C. Carvalho ◽

Paolo Tuccella ◽

Gabriele Curci ◽

A. Rocha

Keyword(s):

Saharan Dust ◽

Vertical Resolution ◽

Dust Event

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EARLINET dust observations vs. BSC-DREAM8b modeled profiles: 12-year-long systematic comparison at Potenza, Italy

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-8781-2014 ◽

2014 ◽

Vol 14 (16) ◽

pp. 8781-8793 ◽

Cited By ~ 39

Author(s):

L. Mona ◽

N. Papagiannopoulos ◽

S. Basart ◽

J. Baldasano ◽

I. Binietoglou ◽

...

Keyword(s):

Center Of Mass ◽

Saharan Dust ◽

Raman Lidar ◽

Dust Layer ◽

Systematic Comparison ◽

Dust Extinction ◽

Lidar Measurements ◽

Order Of Magnitude ◽

Lidar Ratio ◽

532 Nm

Abstract. In this paper, we report the first systematic comparison of 12-year modeled dust extinction profiles vs. Raman lidar measurements. We use the BSC-DREAM8b model, one of the most widely used dust regional models in the Mediterranean, and Potenza EARLINET lidar profiles for Saharan dust cases, the largest one-site database of dust extinction profiles. A total of 310 dust cases were compared for the May 2000–July 2012 period. The model reconstructs the measured layers well: profiles are correlated within 5% of significance for 60% of the cases and the dust layer center of mass as measured by lidar and modeled by BSC-DREAM8b differ on average 0.3 ± 1.0 km. Events with a dust optical depth lower than 0.1 account for 70% of uncorrelated profiles. Although there is good agreement in terms of profile shape and the order of magnitude of extinction values, the model overestimates the occurrence of dust layer top above 10 km. Comparison with extinction profiles measured by the Raman lidar shows that BSC-DREAM8b typically underestimates the dust extinction coefficient, in particular below 3 km. Lowest model–observation differences (below 17%) correspond to a lidar ratio at 532 nm and Ångström exponent at 355/532 nm of 60 ± 13 and 0.1 ± 0.6 sr, respectively. These are in agreement with values typically observed and modeled for pure desert dust. However, the highest differences (higher than 85%) are typically related to greater Ångström values (0.5 ± 0.6), denoting smaller particles. All these aspects indicate that the level of agreement decreases with an increase in mixing/modification processes.

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Observations of the spectral dependence of linear particle depolarization ratio of aerosols using NASA Langley airborne High Spectral Resolution Lidar

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-13453-2015 ◽

2015 ◽

Vol 15 (23) ◽

pp. 13453-13473 ◽

Cited By ~ 87

Author(s):

S. P. Burton ◽

J. W. Hair ◽

M. Kahnert ◽

R. A. Ferrare ◽

C. A. Hostetler ◽

...

Keyword(s):

Case Studies ◽

Spectral Resolution ◽

Spectral Dependence ◽

Saharan Dust ◽

Spherical Particles ◽

High Spectral Resolution ◽

Depolarization Ratio ◽

Dust Layer ◽

High Spectral Resolution Lidar ◽

532 Nm

Abstract. Linear particle depolarization ratio is presented for three case studies from the NASA Langley airborne High Spectral Resolution Lidar-2 HSRL-2). Particle depolarization ratio from lidar is an indicator of non-spherical particles and is sensitive to the fraction of non-spherical particles and their size. The HSRL-2 instrument measures depolarization at three wavelengths: 355, 532, and 1064 nm. The three measurement cases presented here include two cases of dust-dominated aerosol and one case of smoke aerosol. These cases have partial analogs in earlier HSRL-1 depolarization measurements at 532 and 1064 nm and in literature, but the availability of three wavelengths gives additional insight into different scenarios for non-spherical particles in the atmosphere. A case of transported Saharan dust has a spectral dependence with a peak of 0.30 at 532 nm with smaller particle depolarization ratios of 0.27 and 0.25 at 1064 and 355 nm, respectively. A case of aerosol containing locally generated wind-blown North American dust has a maximum of 0.38 at 1064 nm, decreasing to 0.37 and 0.24 at 532 and 355 nm, respectively. The cause of the maximum at 1064 nm is inferred to be very large particles that have not settled out of the dust layer. The smoke layer has the opposite spectral dependence, with the peak of 0.24 at 355 nm, decreasing to 0.09 and 0.02 at 532 and 1064 nm, respectively. The depolarization in the smoke case may be explained by the presence of coated soot aggregates. We note that in these specific case studies, the linear particle depolarization ratio for smoke and dust-dominated aerosol are more similar at 355 nm than at 532 nm, having possible implications for using the particle depolarization ratio at a single wavelength for aerosol typing.

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Identification of the Aerosol Types over Athens, Greece: The Influence of Air-Mass Transport

Advances in Meteorology ◽

10.1155/2010/168346 ◽

2010 ◽

Vol 2010 ◽

pp. 1-15 ◽

Cited By ~ 8

Author(s):

D. G. Kaskaoutis ◽

P. G. Kosmopoulos ◽

H. D. Kambezidis ◽

P. T. Nastos

Keyword(s):

Winter Season ◽

Saharan Dust ◽

Dust Particles ◽

Hysplit Model ◽

Air Mass ◽

Back Trajectories ◽

Air Masses ◽

Local Pollution ◽

Coarse Mode ◽

Aerosol Types

Aerosol optical depth at 550 nm () and fine-mode (FM) fraction data from Terra-MODIS were obtained over the Greater Athens Area covering the period February 2000–December 2005. Based on both and FM values three main aerosol types have been discriminated corresponding to urban/industrial aerosols, clean maritime conditions, and coarse-mode, probably desert dust, particles. Five main sectors were identified for the classification of the air-mass trajectories, which were further used in the analysis of the ( and FM data for the three aerosol types). The HYSPLIT model was used to compute back trajectories at three altitudes to investigate the relation between -FM and wind sector depending on the altitude. The accumulation of local pollution is favored in spring and corresponds to air masses at lower altitudes originating from Eastern Europe and the Balkan. Clean maritime conditions are rare over Athens, limited in the winter season and associated with air masses from the Western or Northwestern sector. The coarse-mode particles origin seems to be more complicated proportionally to the season. Thus, in summer the Northern sector dominates, while in the other seasons, and especially in spring, the air masses belong to the Southern sector enriched with Saharan dust aerosols.

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Saharan dust infrared optical depth and altitude retrieved from AIRS: a focus over North Atlantic – comparison to MODIS and CALIPSO

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-1953-2010 ◽

2010 ◽

Vol 10 (4) ◽

pp. 1953-1967 ◽

Cited By ~ 61

Author(s):

S. Peyridieu ◽

A. Chédin ◽

D. Tanré ◽

V. Capelle ◽

C. Pierangelo ◽

...

Keyword(s):

Optical Depth ◽

North Atlantic ◽

Western Indian Ocean ◽

Saharan Dust ◽

Orthogonal Polarization ◽

Dust Layer ◽

The North ◽

Moderate Resolution Imaging Spectroradiometer ◽

Good Agreement

Abstract. Monthly mean infrared (10 μm) dust layer aerosol optical depth (AOD) and mean altitude are simultaneously retrieved over the tropics (30° S–30° N) from almost seven years of Atmospheric Infrared Sounder (AIRS) observations covering the period January 2003 to September 2009. The method developed relies on the construction of look-up-tables computed for a large selection of atmospheric situations and follows two main steps: first, determination of the observed atmospheric thermodynamic situation and, second, determination of the dust properties. A very good agreement is found between AIRS-retrieved AODs and visible optical depths from the Moderate resolution Imaging Spectroradiometer (MODIS/Aqua) during the main (summer) dust season, in particular for three regions of the tropical North Atlantic and one region of the north-western Indian Ocean. Outside this season, differences are mostly due to the sensitivity of MODIS to aerosol species other than dust and to the more specific sensitivity of AIRS to the dust coarse mode. AIRS-retrieved dust layer mean altitudes are compared to the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP/CALIPSO) aerosol mean layer altitude for the period June 2006 to June 2009. Results for a region of the north tropical Atlantic downwind of the Sahara show a good agreement between the two products (σ≈360 m). Differences observed in the peak-to-trough seasonal amplitude, smaller from AIRS, are principally attributed to the large difference in spatial sampling of the two instruments. They also come from the intrinsic limit in sensitivity of the passive infrared sounders for low altitudes. These results demonstrate the capability of high resolution infrared sounders to measure not only dust aerosol AOD but also the mean dust layer altitude.

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Effect of Atmospheric Pollutants on the Air Quality in Tunisia

The Scientific World JOURNAL ◽

10.1100/2012/863528 ◽

2012 ◽

Vol 2012 ◽

pp. 1-8 ◽

Cited By ~ 6

Author(s):

Karim Bouchlaghem ◽

Blaise Nsom

Keyword(s):

Air Quality ◽

Atmospheric Pollutants ◽

Saharan Dust ◽

Aerodynamic Diameter ◽

Concentration Data ◽

Air Masses ◽

African Dust ◽

Yearly Average ◽

Daily Concentration

This paper presents the evolution of Saharan dust advection when the PM10 (particles with an aerodynamic diameter below 10 μm) concentration exceeds standard limits in different Tunisian sites. Meteorological and concentration data (from 2004 to 2010) obtained from several monitoring stations and in situ measurements were used to identify African dust change in seasonal occurrence, their source origin, and their impact on surface PM10 concentrations. We pointed out that the Saharan dust contribution caused frequently the surpassing of the maximum number of days in excess of EU standard limits as well as of the maximum yearly average in the Mediterranean Tunisian coasts. The maximum daily concentration reaches 439 μg/m3during the Saharan events. The decrease in particulate levels recorded at the end of each event is due to the injection of European air masses and rainfalls. Primary pollutants peaks were much higher in winter than in summer which can be explained on the basis of the lower ventilation and mixing.

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Experimental Investigation of Droplet Injections in the Vicinity of the Critical Point: A comparison of different model approaches

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems ◽

10.4995/ilass2017.2017.4635 ◽

2017 ◽

Cited By ~ 1

Author(s):

Christoph Steinhausen ◽

Grazia Lamanna ◽

Bernhard Weigand ◽

Rolf Stierle ◽

Joachim Groß ◽

...

Keyword(s):

Experimental Investigation ◽

Raman Scattering ◽

High Pressures ◽

Region Of Interest ◽

Theoretical Models ◽

Nitrogen Atmosphere ◽

Material Surface ◽

Atmospheric Conditions ◽

Mixing Processes ◽

Two Phase

The disintegration process of liquid fuel within combustion chambers is one of the most important parameters forefficient and stable combustion. Especially for high pressures exceeding the critical value of the injected fluids the mixing processes are not fully understood yet. Recently, different theoretical macroscopic models have been introduced to understand breakdown of the classical two phase regime and predict the transition from evaporation to a diffuse-mixing process. In order to gain deeper insight into the physical processes of this transition, a parametric study of free-falling n-pentane droplets in an inert nitrogen atmosphere is presented. Atmospheric conditions varied systematically from sub- to supercritical values with respect to the fluid properties. An overlay of a diffuse lighted image with a shadowgram directly in the optical setup (front lighted shadowgraphy) was applied to simultaneously detect the presence of a material surface of the droplet as well as changes in density gradients in the surrounding atmosphere. The experimental investigation illustrates, that the presence of a material surface cannot be shown by a direct shadowgram. However, reflections and refractions caused by diffuse ambient illumination are able to indicate the presence of a material surface. In case of the supercritical droplet injections in this study, front lighted shadowgraphy clearly revealed the presence of a material surface, even when the pre-heated droplets are released into a supercritical atmosphere. This detection of the droplet interface indicates, that the droplet remains subcritical in the region of interest, even though it is injected into a supercritical atmosphere. Based on the adiabatic mixing assumption recent Raman-scattering results in the wake of the droplet are re-evaluated to compute the temperature distribution. Presented experimental findings as well as the re-evaluation of recent Raman scattering results are compared to thermodynamic models to predict the onset of diffuse-mixing and supercritical disintegration of the droplet. Additionally, a one dimensional evaporation model is used to evaluate the validity of the adiabatic mixing assumption in the estimation of the droplet temperature. The presented findings contribute to the understanding of recent theoretical models for prediction of spray and droplet disintegration and the onset of diffuse-mixing processes.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4635

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Lidar Measuremnt on Dust Transport from the Saharan Desert to the Iran Plateau

EPJ Web of Conferences ◽

10.1051/epjconf/202023702020 ◽

2020 ◽

Vol 237 ◽

pp. 02020

Author(s):

Hossein Panahifar ◽

Ruhollah Moradhaseli ◽

Hadi Bourzoie ◽

Mahdi Gholami ◽

Hamid Reza Khalesifard

Keyword(s):

Trajectory Analysis ◽

Saharan Dust ◽

Dust Particles ◽

Raman Lidar ◽

Dust Layer ◽

Mean Values ◽

Dust Transport ◽

Lidar Ratio ◽

532 Nm ◽

Iran Plateau

Optical properties of long-range Saharan dust particles transported to the Iran Plateau have been investigated. The results were derived from the measurements of a dual-wavelength Depolarized backscatter/Raman lidar and a Cimel CE318-2 sunphotometer. Observations were performed in Zanjan, Northwest Iran. The backward trajectory analysis show that the lofted dust plumes come from the Saharan desert and travel along Mediterranean Sea and Turkey toward Iran. The lidar ratio within the lofted dust layer has been found with mean values of 50 sr at 532 nm. For the depolarization ratio, mean values of 25% have been found.

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