scholarly journals Classifying Aerosols Based on Fuzzy Clustering and Their Optical and Microphysical Properties Study in Beijing, China

2017 ◽  
Vol 2017 ◽  
pp. 1-18 ◽  
Author(s):  
Wenhao Zhang ◽  
Hui Xu ◽  
Fengjie Zheng
Keyword(s):  
Optical Properties ◽  
Fuzzy Clustering ◽  
Fine Particle ◽  
Radiative Forcing ◽  
Clustering Algorithm ◽  
Temporal Variations ◽  
Global Scale ◽  
Dust Aerosol ◽  
Desert Dust ◽  
Aerosol Types

Classification of Beijing aerosol is carried out based on clustering optical properties obtained from three Aerosol Robotic Network (AERONET) sites. The fuzzy c-mean (FCM) clustering algorithm is used to classify fourteen-year (2001–2014) observations, totally of 6,732 records, into six aerosol types. They are identified as fine particle nonabsorbing, two kinds of fine particle moderately absorbing (fine-MA1 and fine-MA2), fine particle highly absorbing, polluted dust, and desert dust aerosol. These aerosol types exhibit obvious optical characteristics difference. While five of them show similarities with aerosol types identified elsewhere, the polluted dust aerosol has no comparable prototype. Then the membership degree, a significant parameter provided by fuzzy clustering, is used to analyze internal variation of optical properties of each aerosol type. Finally, temporal variations of aerosol types are investigated. The dominant aerosol types are polluted dust and desert dust in spring, fine particle nonabsorbing aerosol in summer, and fine particle highly absorbing aerosol in winter. The fine particle moderately absorbing aerosol occurs during the whole year. Optical properties of the six types can also be used for radiative forcing estimation and satellite aerosol retrieval. Additionally, methodology of this study can be applied to identify aerosol types on a global scale.

scholarly journals Retrieval of desert dust aerosol vertical profiles from IASI measurements in the TIR atmospheric window

2013 ◽  
Vol 6 (10) ◽  
pp. 2577-2591 ◽  
Author(s):  
S. Vandenbussche ◽  
S. Kochenova ◽  
A. C. Vandaele ◽  
N. Kumps ◽  
M. De Mazière
Keyword(s):  
Optical Depth ◽  
Radiative Forcing ◽  
Degrees Of Freedom ◽  
A Priori ◽  
Global Scale ◽  
Dust Aerosol ◽  
Vertical Profiles ◽  
Desert Dust ◽  
Dust Aerosols ◽  
Infrared Measurements

Abstract. Desert dust aerosols are the most prominent tropospheric aerosols, playing an important role in the earth's climate. However, their radiative forcing is currently not known with sufficient precision to even determine its sign. The sources of uncertainty are multiple, one of them being a poor characterisation of the dust aerosol's vertical profile on a global scale. In this work, we tackle this scientific issue by designing a method for retrieving dust aerosol vertical profiles from Thermal Infrared measurements by Infrared Atmospheric Sounding Interferometer (IASI) instruments onboard the Metop satellite series. IASI offers almost global coverage twice a day, and long (past and future) time series of radiances, therefore being extremely well suited for climate studies. Our retrieval follows Rodger's formalism and is based on a two-step approach, treating separately the issues of low altitude sensitivity and difficult a priori definition. We compare our results for a selected test case above the Atlantic Ocean and North Africa in June 2009, with optical depth data from MODIS, aerosol absorbing index from GOME-2 and OMI, and vertical profiles of extinction coefficients from CALIOP. We also use literature information on desert dust sources to interpret our results above land. Our retrievals provide perfectly reasonable results in terms of optical depth. The retrieved vertical profiles (with on average 1.5 degrees of freedom) show most of the time sensitivity down to the lowest layer, and agree well with CALIOP extinction profiles for medium to high dust optical depth. We conclude that this new method is extremely promising for improving the scientific knowledge about the 3-D distribution of desert dust aerosols in the atmosphere.

scholarly journals Retrieval of desert dust aerosol vertical profiles from IASI measurements in the TIR atmospheric window

2013 ◽  
Vol 6 (3) ◽  
pp. 4511-4550
Author(s):  
S. Vandenbussche ◽  
S. Kochenova ◽  
A. C. Vandaele ◽  
N. Kumps ◽  
M. De Mazière
Keyword(s):  
Optical Depth ◽  
Radiative Forcing ◽  
Degrees Of Freedom ◽  
A Priori ◽  
Global Scale ◽  
Test Case ◽  
Vertical Profiles ◽  
Desert Dust ◽  
Dust Aerosols ◽  
Infrared Measurements

Abstract. Desert dust aerosols are the most prominent tropospheric aerosols, playing an important role in the Earth's climate. However, their radiative forcing is currently not known with sufficient precision to even determine its sign. The sources of uncertainty are multiple, one of them being a poor characterisation of dust aerosols vertical profile on a global scale. In this work, we tackle this scientific issue by designing a method for retrieving dust aerosols vertical profiles from Thermal Infrared measurements by IASI instruments onboard the Metop satellite series. IASI offers almost global coverage twice a day, and long (past and future) time series of radiances, being therefore extremely well-suited for climate studies. Our retrieval follows Rodger's formalism and is based on a two-steps approach, treating separately the issues of low altitude sensitivity and of difficult a priori definition. We compare our results for a selected test-case, above the Atlantic Ocean and North Africa in June 2009, with optical depth data from MODIS, aerosol absorbing index from GOME-2 and OMI, and vertical profiles of extinction coefficients from CALIOP. We also use literature information on desert dust sources to interpret our results above land. Our retrievals provide perfectly reasonable results in terms of optical depth. The retrieved vertical profiles (with on average 1.5 degrees of freedom) show most of the time sensitivity down to the lowest layer, and agree well with CALIOP extinction profiles for medium to high dust optical depth. We conclude that this new method is extremely promising for improving the scientific knowledge about the 3-D distribution of desert dust aerosols in the atmosphere.

scholarly journals The surface aerosol optical properties in urban areas of Nanjing, west Yangtze River Delta of China

2016 ◽  
Author(s):  
B. L. Zhuang ◽  
T. J. Wang ◽  
J. Liu ◽  
S. Li ◽  
M. Xie ◽  
...  
Keyword(s):  
Optical Properties ◽  
Urban Areas ◽  
Radiative Forcing ◽  
Early Morning ◽  
Single Scattering ◽  
Temporal Variations ◽  
Yangtze River Delta ◽  
Aerosol Optical Properties ◽  
Growth Trend ◽  
Near Surface

Abstract. Observational studies of aerosol optical properties are useful to reducing uncertainties in estimating aerosol radiative forcing and forecasting visibility. In this study, the observed near-surface aerosol optical properties in urban Nanjing are analyzed from Mar 2014 to Feb 2016. Results show that near-surface urban aerosols in Nanjing are mainly from local emissions and the regions around. They have lower loadings but are more scattering than in most cities in China. The annual mean aerosol extinction coefficient (EC), single scattering albedo (SSA) and asymmetry parameter (ASP) at 550 nm are 381.96 Mm−1, 0.9 and 0.57, respectively. The aerosol absorption coefficient (AAC) is about one order of magnitude smaller than its scattering coefficient (SC). However, the absorbing aerosol has larger Ångström exponent (AAE) value, 1.58 at 470/660 nm, about 0.2 larger than the scattering aerosols' (SAE). All the aerosol optical properties followed a near unimodal pattern, the ranges around their averages accounting for more than 60 % of the total samplings. Additionally, they have substantial seasonality and diurnal variations. High levels of SC and AAC all appear in winter due to higher aerosol and trace gas emissions. AAE (ASP) is the smallest (largest) in summer because of high relative humidity (RH) which also causes considerably larger SC and smaller SAE, although intensive gas-to-particle transformation could produce a large number of finer scattering aerosols in this season. Seasonality of EC is different from the columnar aerosol optical depth. Larger AACs appear at the rush hours of the day while SC and Bsp only peak in the early morning. Aerosols are fresher at daytime than at nighttime, leading to their larger AE and smaller ASP. Different temporal variations between AAC and SC cause the aerosols more absorbing (smaller SSA) in autumn and around rush hours. ASP has a good quasi-LogNormal growth trend with increasing SC when RH is below 60 %. The correlation between AAC and SC at the site is close but a little smaller than that in suburban Nanjing in spring. Atmospheric visibility decreases exponentially with increasing EC or SC, more sharply in spring and summer. It could be further deteriorated with increasing SSA and ASP.

scholarly journals Spatiotemporal Spectral Variations of AOT in India’s EEZ over Arabian Sea: Validation of OCM-II

2012 ◽  
Vol 2012 ◽  
pp. 1-13
Author(s):  
C. P. Simha ◽  
P. C. S. Devara ◽  
S. K. Saha ◽  
K. N. Babu ◽  
A. K. Shukla
Keyword(s):  
Radiative Forcing ◽  
Arabian Sea ◽  
Indian Subcontinent ◽  
Anthropogenic Activities ◽  
Desert Dust ◽  
Range Transport ◽  
Color Monitor ◽  
Photometric Measurements ◽  
Aerosol Types

We report the results of sun-photometric measurements of Aerosol Optical Thickness (AOT) in India’s Exclusive Economic Zone (EEZ) over the Arabian Sea along with synchronous Ocean Color Monitor (OCM-II) derived AOT estimates during December 12, 2009–January 10, 2010. Relatively higher values of Angstrom exponent (α) around 1.2 near coast and 0.2–0.8 in the India’s EEZ, observed during the cruise period, indicate the presence of smaller particles near the coast due to anthropogenic activities; and larger particles in the India’s EEZ due to advection of pollutants from Indian subcontinent via long-range transport. Results related to α and its derivative reveal four different aerosol types (urban-industrial, desert-dust, clean-marine, and mixed-type) with varying fraction during the study period. Surface radiative forcing due to aerosols is found to be 20 W/m2 over India’s EEZ. OCM-derived AOTs showed good corroboration with in situ measurements with a correlation coefficient of about 0.95. A reasonably good correlation was also observed between AOT and wind speed (R = 0.6); AOT and relative humidity (R = 0.58). The concurrent MODIS AOT data also agree well with those observed by the OCEANSAT (OCM-II) satellite during the campaign period.

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.

scholarly journals Fine and coarse dust separation with polarization lidar

2014 ◽  
Vol 7 (5) ◽  
pp. 5173-5221 ◽  
Author(s):  
R. E. Mamouri ◽  
A. Ansmann
Keyword(s):  
Optical Properties ◽  
Case Studies ◽  
Mass Concentration ◽  
Dust Aerosol ◽  
Desert Dust ◽  
Coarse Mode ◽  
Integrated Optical ◽  
Fine Mode ◽  
Aerosol Backscatter

Abstract. The polarization-lidar photometer networking (POLIPHON) method for separating dust and non-dust aerosol backscatter and extinction, volume, and mass concentration is extended to allow for a height-resolved separation of fine-mode and coarse-mode dust properties in addition. The method is applied to a period with complex aerosol layering of fine-mode background dust from Turkey and Arabian desert dust from Syria. The observation was performed at the combined European Aerosol Research Lidar Network (EARLINET) and Aerosol Robotic Network (AERONET) site of Limassol (34.7° N, 33° E), Cyprus, in September 2011. The dust profiling methodology and case studies are presented. Consistency between the column-integrated optical properties obtained with sun/sky photometer and the respective results derived by means of the new lidar-based method corroborate the applicability of the extended POLIPHON version.

The impacts of optical properties on radiative forcing due to dust aerosol

2006 ◽  
Vol 23 (3) ◽  
pp. 431-441 ◽  
Author(s):  
Hong Wang ◽  
Guangyu Shi ◽  
Shuyan Li ◽  
Wei Li ◽  
Biao Wang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Dust Aerosol

scholarly journals Long-term multi-source data analysis about the characteristics of aerosol optical properties and types over Australia

2020 ◽  
Author(s):  
Xingchuan Yang ◽  
Chuanfeng Zhao ◽  
Yikun Yang
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Seasonal Variations ◽  
Dust Aerosol ◽  
Northern Australia ◽  
Aerosol Optical Properties ◽  
Austral Spring ◽  
Modis Aod ◽  
Central Australia ◽  
Aerosol Types

Abstract. The spatiotemporal distributions of aerosol optical properties and major aerosol types, along with the vertical distribution of major aerosol types over Australia, are investigated based on multi-year AERONET observations at nine sites, the Moderate Resolution Imaging Spectroradiometer (MODIS), Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and back-trajectory analysis from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT). The annual aerosol optical depth (AOD) at most sites showed increasing trends (0.002–0.028 yr−1) except for that at three sites of Canberra, Jabiru, and Lake Argyle, which showed decreasing trends (−0.004–−0.002 yr−1). In contrast, the annual Ångström exponent (AE) showed decreasing tendencies at most sites (−0.044–−0.005 yr−1). The results showed strong seasonal variations in AOD with high values in the austral spring and summer and relatively low values in the austral fall and winter, and weak seasonal variations in AE with the highest mean values in the austral spring at most sites. Spatially, the MODIS AOD showed obvious spatial heterogeneity with higher values appeared over the Australian tropical savanna regions, Lake Eyre Basin, and southeastern regions of Australia, while low values appeared over the arid regions in western Australia. Monthly averaged AOD increases from August to next austral spring peak (typically December–January), and decreases during the March–July. Classification of Australian aerosols revealed that the mixed type of aerosols (biomass burning and dust aerosol) are dominated in all seasons at nine sites, followed by biomass burning aerosol and dust aerosol. The MERRA-2 showed that carbonaceous over northern Australia, dust over central Australia, sulfate over densely populated northwestern and southeastern Australia, and sea salt over Australian coastal regions are the major types of atmospheric aerosols over Australia. The CALIPSO showed that polluted dust is the dominant aerosol type detected at heights 0.5–5 km during all seasons. Australian aerosol has similar source characteristics due to intercontinental transport of aerosols over Australia, especially for biomass burning and dust aerosols. However, the dust-prone characteristic of aerosol is more prominent over the central Australia, while the biomass burning-prone characteristic of aerosol is more prominent in northern Australia.

scholarly journals Lifecycle of light-absorbing carbonaceous aerosols in the atmosphere

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Dantong Liu ◽  
Cenlin He ◽  
Joshua P. Schwarz ◽  
Xuan Wang
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Water Solubility ◽  
Model Performance ◽  
Global Scale ◽  
Climate Impacts ◽  
Carbonaceous Aerosols ◽  
Earth System ◽  
The Earth ◽  
Improved Model

Abstract Light-absorbing carbonaceous aerosols (LACs), including black carbon and light-absorbing organic carbon (brown carbon, BrC), have an important role in the Earth system via heating the atmosphere, dimming the surface, modifying the dynamics, reducing snow/ice albedo, and exerting positive radiative forcing. The lifecycle of LACs, from emission to atmospheric evolution further to deposition, is key to their overall climate impacts and uncertainties in determining their hygroscopic and optical properties, atmospheric burden, interactions with clouds, and deposition on the snowpack. At present, direct observations constraining some key processes during the lifecycle of LACs (e.g., interactions between LACs and hydrometeors) are rather limited. Large inconsistencies between directly measured LAC properties and those used for model evaluations also exist. Modern models are starting to incorporate detailed aerosol microphysics to evaluate transformation rates of water solubility, chemical composition, optical properties, and phases of LACs, which have shown improved model performance. However, process-level understanding and modeling are still poor particularly for BrC, and yet to be sufficiently assessed due to lack of global-scale direct measurements. Appropriate treatments of size- and composition-resolved processes that influence both LAC microphysics and aerosol–cloud interactions are expected to advance the quantification of aerosol light absorption and climate impacts in the Earth system. This review summarizes recent advances and up-to-date knowledge on key processes during the lifecycle of LACs, highlighting the essential issues where measurements and modeling need improvement.

scholarly journals Aerosol optical properties at Lampedusa (Central Mediterranean) – 2. Determination of single scattering albedo at two wavelengths for different aerosol types

2005 ◽  
Vol 5 (4) ◽  
pp. 4971-5005 ◽  
Author(s):  
D. Meloni ◽  
A. di Sarra ◽  
G. Pace ◽  
F. Monteleone
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Biomass Burning ◽  
Surface Albedo ◽  
Single Scattering ◽  
Asymmetry Factor ◽  
Aerosol Optical Properties ◽  
Central Mediterranean ◽  
Desert Dust ◽  
Aerosol Types

Abstract. Aerosol optical properties were retrieved from direct and diffuse spectral irradiance measurements made by a multi-filter rotating shadowband radiometer (MFRSR) at the island of Lampedusa (35.5° N, 12.6° E), in the Central Mediterranean, in the period July 2001–September 2003. In a companion paper (Pace et al., 2005) the aerosol optical depth (AOD) and Ångström exponent were used together with airmass backward trajectories to identify and classify different aerosol types. The MFRSR diffuse-to-direct ratio (DDR) at 415.6 nm and 868.7 nm for aerosol classified as biomass burning-urban/industrial, originating primarily from the European continent, and desert dust, originating from the Sahara, is used in this study to estimate the aerosol single scattering albedo (SSA). A detailed radiative transfer model is initialized with the measured aerosol optical depth; calculations are performed at the two wavelengths varying the SSA values until the modelled DDR matches the MFRSR observations. Sensitivity studies are performed to estimate how uncertainties on AOD, DDR, asymmetry factor (g), and surface albedo influence the retrieved SSA values. The results show that a 3% variation of AOD or DDR produce a change of about 0.02 in the retrieved SSA value at 415.6 and 868.7 nm; a ±0.06 variation of the asymmetry factor g produces a change of the estimated SSA of <0.04 at 415.6 nm, and <0.06 at 868.7 nm; finally, an increase of the assumed surface albedo of 0.05 gives very small changes (0.01–0.02) in the retrieved SSA. The calculations show that the SSA of desert dust (DD) increases with wavelength, from 0.81±0.05 at 415.6 nm to 0.94±0.05 at 868.7 nm; on the contrary, the SSA of urban/industrial (UN) aerosols decreases from 0.96±0.02 at 415.6 nm to 0.87±0.07 at 868.7 nm; the SSA of biomass burning (BB) particles is 0.82±0.04 at 415.6 nm and 0.80±0.05 at 868.7 nm. Episodes of UN aerosols occur usually in June and July; BB aerosol episodes with large AOD and long duration are observed mainly in July and August, the driest months of the year, when the development of fires is favoured.

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