Submit to Atmosphere Review for Atmosphere Propose a Special Issue

Journal Menu

Journal Browser

► Journal Browser

Atmospheric Aerosol Optical Properties

Print Special Issue Flyer
Special Issue Editors
Special Issue Information
Keywords
Related Special Issue
Published Papers

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Aerosols".

Deadline for manuscript submissions: closed (10 May 2022) | Viewed by 25795

Share This Special Issue

Special Issue Editors

Dr. Sandra Mogo

E-Mail Website
Guest Editor

Departamento de Física, Universidade da Beira Interior, 6201-001 Covilhã, Portugal
Interests: aerosol optical properties; absorption Ångström exponent; SEM/EDX; instrumentation; individual characterization of aerosol particles
Special Issues, Collections and Topics in MDPI journals

Dr. Edith Rodríguez

E-Mail Website
Guest Editor

Finnish Meteorological Institute, FI-00560 Helsinki, Finland
Interests: Remote sensing of Aerosols; climate change and aerosol clouds interactions

Dr. Natalia Prats

E-Mail Website
Guest Editor

Izaña Atmospheric Research Center, AEMET, 38001 Tenerife Island, Spain
Interests: aerosols; climatology; remote sensing; atmosphere; air quality; atmospheric pollution; aerosol science; atmospheric physics; air sampling; atmospheric sciences

Dr. Boris Barja

E-Mail Website
Guest Editor

Departamento de Matemática y Física, University of Magallanes, Av. Pdte. Manuel Bulnes 01855, Chile
Interests: meteorology; climatology; environmental chemistry; atmospheric pollution; atmospheric physics; optics; remote sensing; air quality; atmosphere; environment
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue aims to provide recent advances in the field of the optical properties of aerosols. The interaction of the solar radiation with these atmospheric particles plays an important role in determining the budget of the radiative forcing, as they can act both as absorbers of solar light, heating the atmosphere, or also, they can act as scatterers, preventing the solar radiation from reaching the ground. Thus, understanding aerosols' influence on the earth's climate is necessary to make anthropogenic-induced climate change predictions reliable. The direct effect of aerosols to scatter and absorb radiation in the atmosphere influences the amount of radiation reaching the earth's surface and the amount radiated back to space. Due to aerosols' indirect effect, the absorption of radiation in a polluted atmosphere may heat the atmosphere sufficiently to affect the formation of clouds and influence the lifetime of clouds by reducing the number of large cloud droplets and hence inhibit the precipitation formation process. Among other effects of aerosols, visibility is the easiest detectable effect of particles in the atmosphere. Due to the light absorption, particles' extinction coefficient can be substantial, leading to lower visibility.

Besides their contribution to climate change and visibility conditions, this topic is also relevant to those working with identifying potential sources of aerosols. Original results from laboratory and field measurements, both remote and in situ, are all welcome contributions. Authors are encouraged to include a section touching on future issues, opportunities, and/or concerns related to the next decade's horizons.

Topics of interest for the Special Issue include, but are not limited to:

- absorption and scattering coefficients;

- single scattering albedo and extinction coefficients;

- absorption and scattering Ångström exponents;

- effects of aerosols over climate: radiative forcing;

- other effects of aerosols: visibility.

Dr. Sandra Mogo
Dr. Edith Rodríguez
Dr. Natalia Prats
Dr. Boris Barja
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atmosphere is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

optical properties
absorption
scattering
single scattering albedo
Ångström exponent

Related Special Issue

Atmospheric Aerosol Optical Properties (2nd Edition) in Atmosphere

Published Papers (11 papers)

Download All Papers

Research

14 pages, 1738 KiB

Open AccessArticle

Mass Absorption Efficiency of PM₁ in Mexico City during ACU15

by Cristina Prieto, Harry Alvarez-Ospina, Dara Salcedo, Telma Castro and Oscar Peralta

Atmosphere 2023, 14(1), 100; https://doi.org/10.3390/atmos14010100 - 3 Jan 2023

Cited by 1 | Viewed by 1470

Abstract

From January to March 2015, an atmospheric aerosol measurement campaign, “Aerosoles en Ciudad Universitaria 2015” (ACU15), was carried out in Mexico City to determine the particles’ optical properties and chemical composition. Two photoacoustic spectrometers measured the scattering and absorption coefficient at two different wavelengths. The average absorption coefficient at 532 nm was 12.71 ± 9.48 Mm⁻¹ and at 870 nm was 10.35 ± 7.36 Mm⁻¹. The average scattering coefficient was 65.63 ± 47.12 Mm⁻¹ (532 nm) and 21.12 ± 14.24 Mm⁻¹ (870 nm). The chemical composition was determined via an aerosol chemical speciation monitor. The organic aerosol fraction represented 53% of the total PM₁ and was made up of 63% low volatile (4.64 µg m⁻³), 22% hydrogenated (1.90 µg m⁻³), and 15% semi-volatile organics (1.54 µg m⁻³). The correlation coefficient of chemical species (NO₃⁻, NH₄⁺, SO₄²⁻, low-volatile, and semi-volatile organics) and optical properties was 0.92. The multilinear regression showed a good agreement among chemical species and optical properties (r > 0.7). The mass absorption coefficient calculated for the measuring site at 870 nm was MAE₈₇₀ = 5.8 m² g⁻¹, instead of the default 4.74 m² g⁻¹. Furthermore, based on the median AAE, the 532 nm MAE₅₃₂ resulting from the multiple linear regression (MLR) showed the following coefficients: 7.70 m² g⁻¹ (eBC), 0.22 m² g⁻¹ (HOA), and 0.16 m² g⁻¹ (LV–OOA). The coefficients of MLR were: 7.08 m² g⁻¹ (eBC), 5.83 m² g⁻¹ (NO₃⁻), 5.69 m² g⁻¹ (low volatile organic aerosol), 2.78 m² g⁻¹ (SO₄²⁻), 2.40 m² g⁻¹ (hydrocarbon-like organic aerosol), and 1.04 m² g⁻¹ (semi volatile organic aerosol). Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

18 pages, 1316 KiB

Open AccessArticle

Controlled Laboratory Generation of Atmospheric Black Carbon Using Laser Excitation-Based Soot Generator: From Basic Principles to Application Perspectives: A Review

by Tibor Ajtai, Attila Kohut, Péter Raffai, Gábor Szabó and Zoltán Bozóki

Atmosphere 2022, 13(9), 1366; https://doi.org/10.3390/atmos13091366 - 26 Aug 2022

Cited by 2 | Viewed by 1626

Abstract

The mimicking of atmospheric soot with versatile chemophysical properties is a critical issue in many applications, starting from instrument calibration, through producing aerosol standards for academic research, and ending with the reduction of uncertainties associated to carbonaceous particulate matter in the atmosphere, just to name a few. The present study deals with laser ablation as a novel and interesting technique for the generation of soot with high elementary carbon (EC) content with microphysical features similar to diesel or atmospheric soot and for modelling biomass emission under well-controlled laboratory conditions. The operation of the laser-excitation-based soot generator and the characteristics of the produced particles are compared to the most widely used techniques like flame, spark discharge generators, and real combustion soot originating from diesel- and aircraft engines or from field measurement. The comparison shows that significant differences in the physicochemical features exist between the real combustion soot and the soot originating from different excitation mechanisms. Moreover, the soot produced by different techniques shown also significant differences. However, due to some inherent and favorable attributes of the laser ablation technique—such as the possibility of the independent variation of physical characteristics of the generated soot particles—the potential for modelling biomass burning or to produce soot particles even in the accumulation mode makes it a useful tool in many cases. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

23 pages, 14592 KiB

Open AccessFeature PaperArticle

Aerosol Distributions and Transport over Southern Morocco from Ground-Based and Satellite Observations (2004–2020)

by Tristan Millet, Hassan Bencherif, Aziza Bounhir, Nelson Bègue, Kévin Lamy, Marion Ranaivombola, Zouhair Benkhaldoun, Thierry Portafaix and Valentin Duflot

Atmosphere 2022, 13(6), 923; https://doi.org/10.3390/atmos13060923 - 6 Jun 2022

Cited by 5 | Viewed by 2071

Abstract

The present study investigates the optical properties of aerosols on daily and seasonal scales with the use of the aerosol optical depth (AOD) and Angström exponent (AE) data retrieved from AErosol RObotic NETwork (AERONET) and collected at four stations in Southern Morocco—Saada (31.63° N; 8.16° W), Ouarzazate (30.93° N; 6.91° W), Oukaïmeden (31.21° N; 7.86° W) and Ras-El-Aïn (31.67° N; 7.60° W). An evaluation of the aerosol volumetric size distribution (AVSD) is also obtained for Saada and Ouarzazate. An AOD inter-comparison is performed between AERONET data and satellite sensors (MODerate resolution Imaging Spectroradiometer—MODIS), as well as assimilation products (Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) and Copernicus Atmosphere Monitoring Service (CAMS)), by the means of a linear regression. Regardless of site location and elevation, the results show the prevalence of the annual cycle of AOD, with a maximum in summer and a minimum in winter. In association with this seasonal variation, the variations in AE and AVSD showed an increase in coarse mode over Ouarzazate and Saada during summer (July to August), underlining that Southern Morocco is prone to the regular transport of desert dust on a seasonal basis. The inter-comparison reveals that the MERRA-2 dataset is slightly more appropriate for the study region, since it shows correlation coefficients (r) ranging from 0.758 to 0.844 and intercepts ranging from 0.021 to 0.070, depending on the study site. The statistical analysis of the back-trajectories simulated by the HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model were consistent with the observations and confirmed the dominance of desert dust aerosols during the summer over the study region. On the other hand, the winter season reveals a predominance of anthropogenic and oceanic aerosols originating from the north and the west of the study site. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

20 pages, 2512 KiB

Open AccessEditor’s ChoiceArticle

Aerosol Optical Thickness Retrieval in Presence of Cloud: Application to S3A/SLSTR Observations

by Marta Luffarelli, Yves Govaerts and Lucio Franceschini

Atmosphere 2022, 13(5), 691; https://doi.org/10.3390/atmos13050691 - 26 Apr 2022

Cited by 3 | Viewed by 2745

Abstract

The Combined Inversion of Surface and AeRosols (CISAR) algorithm for the joint retrieval of surface and aerosol single scattering properties has been further developed in order to extend the retrieval to clouds and overcome the need for an external cloud mask. Pixels located in the transition zone between pure cloud and pure aerosol are often discarded by both aerosol and cloud algorithms, despite being essential for studying aerosol–cloud interactions, which still represent the largest source of uncertainty in climate predictions. The proposed approach aims at filling this gap and deepening the understanding of aerosol properties in cloudy environments. The new CISAR version is applied to Sentinel-3A/SLSTR observations and evaluated against different satellite products and ground measurements. The spatial coverage is greatly improved with respect to algorithms processing only pixels flagged as clear sky by the SLSTR cloud mask. The continuous retrieval of aerosol properties without any safety zone around clouds opens new possibilities for studying aerosol properties in cloudy environments. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

18 pages, 3545 KiB

Open AccessEditor’s ChoiceArticle

The Impact of the 2020 Oil Production Fluctuations on Methane Emissions over the Gulf Cooperation Council (GCC) Countries: A Satellite Approach

by Ashraf Farahat

Atmosphere 2022, 13(1), 11; https://doi.org/10.3390/atmos13010011 - 22 Dec 2021

Cited by 4 | Viewed by 3084

Abstract

The COVID-19 outbreak has significantly affected global industrial and transportation markets. Airlines, rails, and cars’ industries and their supporting energy sectors have been substantially disrupted by the pandemic. This has resulted in undermined energy demand around the world during 2019 and 2020. The organization of the Petroleum Exporting Countries (OPEC) led by Saudi Arabia failed to persuade Russia to cutback oil supplies to deal with the loss of demand from the COVID-19 pandemic. On 8 March 2020, Saudi Arabia announced a raise in its oil production and offered a large discount on its crude oil sales. By April 2020, Saudi Arabia increased its oil production to about 12 million-oil barrels/day. This rise in oil production has not only resulted in the biggest fall in oil prices since the 1991 Gulf War but also increased methane emissions over the Gulf Cooperation Council (GCC) regions. Here, we report 2019 and 2020 data set of average seasonal methane-mixing ratio retrieved from TROPOspheric Monitoring Instrument (TROPOMI) on board of S5P spacecraft over 19 refineries and oil fields in Saudi Arabia, Kuwait, Oman, United Arab Emirates, Qatar, and Bahrain. Low methane emissions were recorded over western and central Saudi Arabia compared to the eastern side of the country. In general, high methane emissions were observed in 2020 compared to 2019 around oil refineries and fields in western, central, and eastern regions of Saudi Arabia as well as over other GCC countries. This could be attributed to the oil high production associated with the oil prices fluctuation during 2020. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

14 pages, 3635 KiB

Open AccessArticle

Aerosol Light Absorption at 1064 nm: Pollution Sources, Meteorological Parameters and Gas Pollutants in Qingdao Coastal Area, China

by Jie Chen, Wenyue Zhu, Qiang Liu, Xianmei Qian, Xuebin Li, Jianjie Zheng, Tao Yang and Qiuyi Xu

Atmosphere 2021, 12(12), 1553; https://doi.org/10.3390/atmos12121553 - 24 Nov 2021

Cited by 1 | Viewed by 2036

Abstract

A two-month sampling campaign was carried out from 1 November to 30 December 2019, to investigate the light absorption of aerosols at coastal sites in Qingdao. The average values and standard deviations of the absorption coefficient (OAC) at λ = 1064 nm during the measurement period were 18.52 ± 13.31 Mm⁻¹. Combined with the backward trajectory model, the aerosol absorption coefficient and gas pollution concentration of six possible air mass trajectories were obtained and calculated. The maximum absorption coefficient of local air masses was approximately 20.4 Mm⁻¹ and anthropogenic pollution originated from mainly local sources in the Jiaozhou area. In our measurements at this site, the results also showed that there was a positive correlation between relative humidity (RH) and aerosol absorption. Without considering other factors, the size of aerosol particles grew with the increasing of RH, which changed the nonlinear relationship between the size and the absorption cross section of aerosol particles subsequently. In addition, the correlations between gas pollutants and OAC were calculated. The atmospheric environment is complex in sea–land intersection areas, especially in coastal cities. Analysis of various aerosol sources, meteorological conditions, and gas precursors enhances the study of aerosol optical absorption. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

18 pages, 2752 KiB

Open AccessArticle

A Novel Lidar Signal Denoising Method Based on Convolutional Autoencoding Deep Learning Neural Network

by Minghuan Hu, Jiandong Mao, Juan Li, Qiang Wang and Yi Zhang

Atmosphere 2021, 12(11), 1403; https://doi.org/10.3390/atmos12111403 - 26 Oct 2021

Cited by 13 | Viewed by 2877

Abstract

The lidar is susceptible to the dark current of the detector and the background light during the measuring process, which results in a significant amount of noise in the lidar return signal. To reduce noise, a novel denoising method based on the convolutional autoencoding deep-learning neural network is proposed. After the convolutional neural network was constructed to learn the deep features of lidar signal, the signal details were reconstructed by decoding part to obtain the denoised signal. To verify the feasibility of the proposed method, both the simulated signals and the actually measured signals by Mie-scattering lidar were denoised. Some comparisons with the wavelet threshold denoising method and the variational modal decomposition denoising method were performed. The results show the denoising effect of the proposed method was significantly better than the other two methods. The proposed method can eliminate complex noise in the lidar signal while retaining the complete details of the signal. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

13 pages, 24297 KiB

Open AccessArticle

Experimental Study on the Chemical Characterization of Atmospheric Aerosols in Wuhan, China

by Qianjun Mao, Fangyuan Cheng and Min Chen

Atmosphere 2021, 12(11), 1393; https://doi.org/10.3390/atmos12111393 - 25 Oct 2021

Cited by 5 | Viewed by 1316

Abstract

Air pollution has a significant impact on the use of solar energy. On the one hand, the polluted environment directly reduces the intensity of solar radiation, on the other hand, pollution of the environment will also reduce the life of the equipment. Therefore, mastering the dynamic characteristics of the atmospheric environment has certain guiding significance for the efficient utilization of solar energy. In this study, the concentrations of particulate matter, CO, SO₂ and NO₂ from Tianyun big data website are analyzed to obtain the general characteristics of particulate pollution in Wuhan. At the same time, a long-period sampling atmospheric particulate matter sampler in the Huangjiahu area of Wuhan has been used, and experimental analysis of the physical and chemical characteristics of the samples has been obtained. The results show that both PM2.5 and PM10 show obvious seasonal changes, and the concentration of the four anions during the sampling period is SO₄²⁻ > NO₃⁻ > Cl⁻ > F⁻. During the sampling period, atmospheric particulate matter is mainly composed of organic matter, inorganic anions and oxides of more than 20 elements. The results of the enrichment factor analysis show that elements such as Br, Pb, Sb and Zn are the main enriched elements during the sampling period. The enrichment factors of these elements are 246.43 ± 168.81, 133.28 ± 115.03, 403.305 ± 396.18 and 90.67 ± 67.01, respectively. The high enrichment of these elements also reflects the contribution of motor vehicle exhaust emission during the sampling period. Traffic source is the main emission source in the Huangjiahu area of Wuhan. This research has a certain guiding significance for many industries such as energy utilization, environmental monitoring, health care, transportation and so on. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

14 pages, 3533 KiB

Open AccessArticle

Analysis of Aerosol Optical Depth from Sun Photometer at Shouxian, China

by Lina Xun, Hui Lu, Congcong Qian, Yong Zhang, Shanshan Lyu and Xin Li

Atmosphere 2021, 12(9), 1226; https://doi.org/10.3390/atmos12091226 - 18 Sep 2021

Cited by 11 | Viewed by 2557

Abstract

We use two cloud screening methods—the clustering method and the multiplet method—to process the measurements of a sun photometer from March 2020 to April 2021 in Shouxian. The aerosol optical depth (AOD) and Angström parameters α and β are retrieved; variation characteristics and single scattering albedo are studied. The results show that: (1) The fitting coefficient of AOD retrieved by the two methods is 0.921, and the changing trend is consistent. The clustering method has fewer effective data points and days, reducing the overall average of AOD by 0.0542 (500 nm). (2) Diurnal variation of AOD can be divided into flat type, convex type, and concave type. Concave type and convex type occurred the most frequently, whereas flat type the least. (3) During observation, the overall average of AOD is 0.48, which is relatively high. Among them, AOD had a winter maximum (0.70), autumn and spring next (0.54 and 0.40), and a summer minimum (0.26). The variation trend of AOD and β is highly consistent, and the monthly mean of α is between 0.69 and 1.61, concerning mainly continental and urban aerosols. (4) Compared with others, the single scattering albedo in Shouxian is higher, reflecting strong scattering and weak aerosol absorption. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

17 pages, 2600 KiB

Open AccessArticle

Observation and Inversion of Aerosol Particle Size Distribution over Yinchuan Area

by Jiandong Mao, Yali Ren, Juan Li, Qiang Wang and Yi Zhang

Atmosphere 2021, 12(8), 992; https://doi.org/10.3390/atmos12080992 - 31 Jul 2021

Cited by 2 | Viewed by 2003

Abstract

Particle size distribution is one of the important microphysical parameters to characterize the aerosol properties. The aerosol optical depth is used as the function of wavelength to study the particle size distribution of whole atmospheric column. However, the inversion equation of the particle size distribution from the aerosol optical depth belongs to the Fredholm integral equation of the first kind, which is usually ill-conditioned. To overcome this drawback, the integral equation is first discretized directly by using the complex trapezoid formula. Then, the corresponding parameters are selected by the L curve method. Finally the truncated singular value decomposition regularization method is employed to regularize the discrete equation and retrieve the particle size distribution. To verify the feasibility of the algorithm, the aerosol optical depths taken by a sun photometer CE318 over Yinchuan area in four seasons, as well as hazy, sunny, floating dusty and blowing dusty days, were used to retrieve the particle size distribution. In order to verify the effect of truncated singular value decomposition algorithm, the Tikhonov regularization algorithm was also adopted to retrieve the aerosol PSD. By comparing the errors of the two regularizations, the truncated singular value decomposition regularization algorithm has a better retrieval effect. Moreover, to understand intuitively the sources of aerosol particles, the backward trajectory was used to track the source. The experiment results show that the truncated singular value decomposition regularization method is an effective method to retrieve the particle size distribution from aerosol optical depth. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

14 pages, 5059 KiB

Open AccessArticle

Aerosol Optical Properties around the East China Seas Based on AERONET Measurements

by Qianguang Tu, Zengzhou Hao, Yunwei Yan, Bangyi Tao, Chuyong Chung and Sumin Kim

Atmosphere 2021, 12(5), 642; https://doi.org/10.3390/atmos12050642 - 18 May 2021

Cited by 5 | Viewed by 2209

Abstract

Understanding aerosols optical properties over the oceans is vital for enhancing our knowledge of aerosol effects on climate and pollutant transport between continents. In this study, the characteristics of aerosol optical thickness (AOT) at 500 nm (

τ_{500 nm}

), Ångström exponent [...] Read more.

τ_{500 nm}

), Ångström exponent for the wavelength pair 440–870 nm (α) and volume size distribution (VSD), are presented and analyzed over the East China seas based on the observations at four AERONET sites during 1999–2019. The main results are: (1) the mean

τ_{500 nm}

(α) value ranged from 0.31 to 0.36 (1.17–1.31); (2) the distribution of

τ_{500 nm}

(α) is similar to a log-normal distribution with a right-skewed long tail larger than 0.5 (closer to the normal distribution); (3) large AOT (

τ_{500 nm} > 0.6

) was frequently observed in summer (June and July) and spring (March to May), followed by autumn and winter; (4) all aerosol types were observed, and urban/industrial aerosols and mixed types were dominant throughout the period. The atmospheric column aerosol was characterized by a bimodal lognormal size distribution with a fine mode at effective radius, Reff = 0.16 ± 0.01 μm, and coarse mode at Reff = 2.05 ± 0.1 μm. Full article

(This article belongs to the Special Issue Atmospheric Aerosol Optical Properties)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Atmospheric Aerosol Optical Properties

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Related Special Issue

Published Papers (11 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI