scholarly journals Multi-Year Analyses of Columnar Aerosol Optical and Microphysical Properties in Xi’an, a Megacity in Northwestern China

2018 ◽  
Vol 10 (8) ◽  
pp. 1169 ◽  
Author(s):  
Xiaoli Su ◽  
Junji Cao ◽  
Zhengqiang Li ◽  
Kaitao Li ◽  
Hua Xu ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Single Scattering ◽  
Mean Value ◽  
Asymmetry Factor ◽  
Microphysical Properties ◽  
Sun Photometer ◽  
Spatio Temporal ◽  
The Impact ◽  
Aerosol Types

A thorough understanding of aerosol optical properties and their spatio-temporal variability are required to accurately evaluate aerosol effects in the climate system. In this study, a multi-year study of aerosol optical and microphysical properties was firstly performed in Xi’an based on three years of sun photometer remote sensing measurements from 2012 to 2015. The multi-year average of aerosol optical depth (AOD) at 440 nm was about 0.88 ± 0.24 (mean ± SD), while the averaged Ångström Exponent (AE) between 440 and 870 nm was 1.02 ± 0.15. The mean value of single scattering albedo (SSA) was around 0.89 ± 0.03. Aerosol optical depth and AE showed different seasonal variation patterns. Aerosol optical depth was slightly higher in winter (0.99 ± 0.36) than in other seasons (~0.85 ± 0.20), while AE showed its minimum in spring (0.85 ± 0.05) due to the impact of dust episodes. The seasonal variations of volume particle size distribution, spectral refractive index, SSA, and asymmetry factor were also analyzed to characterize aerosols over this region. Based on the aerosol products derived from sun photometer measurements, the classification of aerosol types was also conducted using two different methods in this region. Results show that the dominant aerosol types are absorbers in all seasons, especially in winter, demonstrating the strong absorptivity of aerosols in Xi’an.

scholarly journals Retrieval of aerosol single-scattering albedo and polarized phase function from polarized sun-photometer measurements for Zanjan's atmosphere

2013 ◽  
Vol 6 (10) ◽  
pp. 2659-2669 ◽  
Author(s):  
A. Bayat ◽  
H. R. Khalesifard ◽  
A. Masoumi
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Atmospheric Aerosols ◽  
Phase Function ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Sun Photometer ◽  
Ångstrom Exponent

Abstract. The polarized phase function of atmospheric aerosols has been investigated for the atmosphere of Zanjan, a city in northwest Iran. To do this, aerosol optical depth, Ångström exponent, single-scattering albedo, and polarized phase function have been retrieved from the measurements of a Cimel CE 318-2 polarized sun-photometer from February 2010 to December 2012. The results show that the maximum value of aerosol polarized phase function as well as the polarized phase function retrieved for a specific scattering angle (i.e., 60°) are strongly correlated (R = 0.95 and 0.95, respectively) with the Ångström exponent. The latter has a meaningful variation with respect to the changes in the complex refractive index of the atmospheric aerosols. Furthermore the polarized phase function shows a moderate negative correlation with respect to the atmospheric aerosol optical depth and single-scattering albedo (R = −0.76 and −0.33, respectively). Therefore the polarized phase function can be regarded as a key parameter to characterize the atmospheric particles of the region – a populated city in the semi-arid area and surrounded by some dust sources of the Earth's dust belt.

scholarly journals A Multi Linear Regression Model to Derive Dust PM10 in the Sahel Using AERONET Aerosol Optical Depth and CALIOP Aerosol Layer Products

2020 ◽  
Vol 12 (18) ◽  
pp. 3099
Author(s):  
Jean-François Léon ◽  
Nadège Martiny ◽  
Sébastien Merlet
Keyword(s):  
Linear Regression ◽  
Regression Model ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Linear Regression Model ◽  
Population Exposure ◽  
Aerosol Layer ◽  
Multi Linear Regression ◽  
Sun Photometer ◽  
The Impact

Due to a limited number of monitoring stations in Western Africa, the impact of mineral dust on PM10 surface concentrations is still poorly known. We propose a new method to retrieve PM10 dust surface concentrations from sun photometer aerosol optical depth (AOD) and CALIPSO/CALIOP Level 2 aerosol layer products. The method is based on a multi linear regression model that is trained using co-located PM10, AERONET and CALIOP observations at 3 different locations in the Sahel. In addition to the sun photometer AOD, the regression model uses the CALIOP-derived base and top altitude of the lowermost dust layer, its AOD, the columnar total and columnar dust AOD. Due to the low revisit period of the CALIPSO satellite, the monthly mean annual cycles of the parameters are used as predictor variables rather than instantaneous observations. The regression model improves the correlation coefficient between monthly mean PM10 and AOD from 0.15 (AERONET AOD only) to 0.75 (AERONET AOD and CALIOP parameters). The respective high and low PM10 concentration during the winter dry season and summer season are well produced. Days with surface PM10 above 100 μg/m3 are better identified when using the CALIOP parameters in the multi linear regression model. The number of true positives (actual and predicted concentrations above the threshold) is increased and leads to an improvement in the classification sensitivity (recall) by a factor 1.8. Our methodology can be extrapolated to the whole Sahel area provided that satellite derived AOD maps are used in order to create a new dataset on population exposure to dust events in this area.

scholarly journals Retrieval of aerosol optical depth over land based on a time series technique using MSG/SERIVI data

2012 ◽  
Vol 12 (2) ◽  
pp. 4031-4071 ◽  
Author(s):  
L. Mei ◽  
Y. Xue ◽  
G. de Leeuw ◽  
T. Holzer-Popp ◽  
J. Guang ◽  
...  
Keyword(s):  
Time Series ◽  
Detailed Analysis ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Optimal Solution ◽  
Single Scattering ◽  
Asymmetry Factor ◽  
Surface Reflectance ◽  
Deep Blue ◽  
Aerosol Type

Abstract. A novel approach for the joint retrieval of aerosol optical depth (AOD) and surface reflectance, using Meteosat Second Generation – Spinning Enhanced Visible and Infrared Imagers (MSG/SEVIRI) observations in two solar channels, is presented. The retrieval is based on a time series (TS) technique, which makes use of the two visible bands at 0.6 μm and 0.8 μm in three orderly scan times (15 min interval between two scans) to retrieve the AOD over land. Using the radiative transfer equation for plane-parallel atmospheres two coupled differential equations for the upward and downward fluxes are derived. The boundary conditions for the upward and downward fluxes at the top and at the bottom of the atmosphere are used in these equations to provide an analytic solution for the surface reflectance. To derive these fluxes, the aerosol single scattering albedo (SSA) and asymmetry factor are required to provide a solution. These are provided from a set of six pre-defined aerosol types with the SSA and asymmetry factor (g). We assume one aerosol type for a grid of 1° × 1° and the surface reflectance changes little between two consequent scans. A k approximation was used in the inversion to find the best solution of atmospheric properties and surface reflectance. The algorithm makes use of numerical minimisation routines to obtain the optimal solution of atmospheric properties and surface reflectance by selection of the most suitable aerosol type from pre-defined sets. Also, it is assumed that the surface reflectance is little influenced by aerosol scattering at 1.6 μm and therefore the ratio of surface reflectances in the solar band for two consequent scans can be well-approximated by the ratio of the reflectances at 1.6 μm. A further assumption is that the surface reflectance varies only slightly over a period of 30 min. A detailed analysis of the retrieval results show that it is suitable for AOD retrieval over land. Six Aerosol Robotic Network (AERONET) sites with different surface types were used for detailed analysis and 42 other AERONET sites were used for validation. From 445 collocations representing stable and homogeneous aerosol type, we found that >75% of MSG-retrieved AOD values compared to AERONET observed values with an error envelope of ±0.05 ± 0.15τ and a high correlation (R > 0.86). The AOD datasets derived using the TS method with SEVIRI data was also compared with collocated AOD products derived from the NASA TERRA and AQUA MODIS data using the dark dense vegetation (DDV) method and the Deep Blue algorithms. Using the TS method, AOD could be retrieved for more pixels than with the NASA Deep Blue algorithm. The AOD values derived compare favourably.

scholarly journals High temporal resolution estimates of columnar aerosol microphysical parameters from spectrum of aerosol optical depth by linear estimation: application to long-term AERONET and star-photometry measurements

2015 ◽  
Vol 8 (8) ◽  
pp. 3117-3133 ◽  
Author(s):  
D. Pérez-Ramírez ◽  
I. Veselovskii ◽  
D. N. Whiteman ◽  
A. Suvorina ◽  
M. Korenskiy ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Temporal Resolution ◽  
High Temporal Resolution ◽  
Linear Estimation ◽  
Night Time ◽  
Microphysical Properties ◽  
Fine Mode ◽  
Using Data ◽  
Aerosol Types

Abstract. This work deals with the applicability of the linear estimation technique (LE) to invert spectral measurements of aerosol optical depth (AOD) provided by AERONET CIMEL sun photometers. The inversion of particle properties using only direct-sun AODs allows the evaluation of parameters such as effective radius (reff) and columnar volume aerosol content (V) with significantly better temporal resolution than the operational AERONET algorithm which requires both direct sun and sky radiance measurements. Sensitivity studies performed demonstrate that the constraints on the range of the inversion are very important to minimize the uncertainties, and therefore estimates of reff can be obtained with uncertainties less than 30 % and of V with uncertainties below 40 %. The LE technique is applied to data acquired at five AERONET sites influenced by different aerosol types and the retrievals are compared with the results of the operational AERONET code. Good agreement between the two techniques is obtained when the fine mode predominates, while for coarse mode cases the LE results systematically underestimate both reff and V. The highest differences are found for cases where no mode predominates. To minimize these biases, correction functions are developed using the multi-year database of observations at selected sites, where the AERONET retrieval is used as the reference. The derived corrections are tested using data from 18 other AERONET stations offering a range of aerosol types. After correction, the LE retrievals provide better agreement with AERONET for all the sites considered. Finally, the LE approach developed here is applied to AERONET and star-photometry measurements in the city of Granada (Spain) to obtain day-to-night time evolution of columnar aerosol microphysical properties.

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

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1226
Author(s):  
Lina Xun ◽  
Hui Lu ◽  
Congcong Qian ◽  
Yong Zhang ◽  
Shanshan Lyu ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Screening Methods ◽  
Clustering Method ◽  
Flat Type ◽  
Variation Characteristics ◽  
Sun Photometer ◽  
Summer Minimum

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.

scholarly journals Increased aerosols content in the atmosphere over Ukraine during summer 2010

2017 ◽  
Author(s):  
Evgenia Galytska ◽  
Vassyl Danylevsky ◽  
René Hommel ◽  
John P. Burrows
Keyword(s):  
Forest Fires ◽  
Temporal Dynamics ◽  
Temporal Distribution ◽  
Single Scattering ◽  
Mean Value ◽  
Hysplit Model ◽  
Microphysical Properties ◽  
Modis Aod ◽  
Spatio Temporal ◽  
532 Nm

Abstract. In this paper we assess the influence of one of the most important sources of aerosols in the atmosphere, biomass burning, during summer 2010 on the abundance, dynamics, and properties of aerosols over Ukraine, also considering influences and effects over neighboring countries: ETR, Estonia, Belarus, Poland, Moldova, and Romania. MODIS satellite instrument data were used to study fires distribution. Ground-based remote measurements from the international sun photometers network AERONET and MODIS and CALIOP satellite instruments data were used to determine aerosols content and optical properties in the atmosphere over East Europe. HYSPLIT model was used to further investigate atmospheric dynamics and to simulate pathways of particles transport. We found that the highest air pollution was observed over Moscow in the first half of August 2010, apparently due to the proximity of the most active combustion centers. Significant temporal dynamics of the aerosols content with pronounced pollution peaks during August 7–17 was observed at Ukrainian (Kyiv, Sevastopol), Belarusian (Minsk), Estonian (Toravere) and Romanian (Bucharest) AERONET sites. Aerosols spatio-temporal distribution over Ukraine were constructed and analyzed using MODIS AOD 550 nm data validated by Kyiv AERONET site sunphotometer measurements, and CALIOP AOD 532 nm validated by MODIS AOD data. Vertical distribution of aerosols extinction at 532 nm, retrieved from the measurements by CALIOP, were constructed for the territory of Ukraine at locations where high AOD values were observed during intense wildfires. The influence of the fires on the optical and microphysical properties of aerosol particles, such as size distribution, spectral single-scattering albedo and refractive indices, was analyzed and estimated using Kyiv AERONET measurements, performed during summer 2010. In this study we show that the highest aerosols pollution over Ukraine recorded on summer 2010 was caused by particles transported from the forest fires in Russia. These fires caused the highest AOD 440 nm over Kyiv site, which for August 2010 exceeded the mean value for the same month for the entire observational period by factor of two. Also, the influence of fires resulted in a change of particles microphysical properties in the regions, where pollution was the highest.

scholarly journals Comparison of Columnar, Surface, and UAS Profiles of Absorbing Aerosol Optical Depth and Single-Scattering Albedo in South-East Poland

Atmosphere ◽  
2019 ◽  
Vol 10 (8) ◽  
pp. 446 ◽  
Author(s):  
Michał T. Chiliński ◽  
Krzysztof M. Markowicz ◽  
Olga Zawadzka ◽  
Iwona S. Stachlewska ◽  
Justyna Lisok ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Measurement Data ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Height Distribution ◽  
Vertical Profiles ◽  
Absorbing Aerosols ◽  
The Impact

The impact of absorbing aerosols on climate is complex, with their potential positive or negative forcing, depending on many factors, including their height distribution and reflective properties of the underlying background. Measurement data is very limited, due to insufficient remote sensing methods dedicated to the retrieval of their vertical distribution. Columnar values of absorbing aerosol optical depth (AAOD) and single scattering albedo (SSA) are retrieved by the Aerosol Robotic Network (AERONET). However, the number of available results is low due to sky condition and aerosol optical depth (AOD) limitation. Presented research describes results of field campaigns in Strzyżów (South-East Poland, Eastern Europe) dedicated to the comparison of the absorption coefficient and SSA measurements performed with on-ground in-situ devices (aethalomter, nephelometer), small unmanned aerial system (UAS) carrying micro-aethalometer, as well as with lidar/ceilometer. An important aspect is the comparison of measurement results with those delivered by AERONET. Correlation of absorption to scattering coefficients measured on ground (0.79) and correlation of extinction on ground to AOD measured by AERONET (0.77) was visibly higher than correlation between AOD and AAOD retrieved by AERONET (0.56). Columnar SSA was weakly correlated with ground SSA (higher values of columnar SSA), which were mainly explained by hygroscopic effects, increasing scattering coefficient in ambient (wet conditions), and partly high uncertainty of SSA retrieval. AAOD derived with the use of profiles from UAS up to PBL height, was estimated to contribute in average to 37% of the total AAOD. A method of AAOD estimation, in the whole troposphere, with use of measured vertical profiles of absorption coefficient and extinction coefficient profiles from lidars was proposed. AAOD measured with this method has poor correlation with AERONET data, however for some measurements, within PBL, AAOD was higher than reported by AERONET, suggesting potential underestimation in photometric measurement under particular conditions. Correlation of absorption coefficient in profile to on ground measurements decrease with altitude. Measurements of SSA from drones agree well with ground measurements and are lower than results from AERONET, which suggests a larger contribution of absorbing aerosols. As an alternative for AAOD estimation in case of lack of AERONET AAOD data simple models are proposed, which base on AOD scaling with SSA measured with different methods. Proposed solution increase potential of absorption coefficient measurements in vertical profiles and columns of the atmosphere. Presented solutions make measurements of absorption coefficients in vertical profiles more affordable and allow rough estimation of columnar values for the whole atmosphere.

scholarly journals Retrieval of aerosol single scattering albedo and polarized phase function from polarized sun-photometer measurements for Zanjan atmosphere

2013 ◽  
Vol 6 (2) ◽  
pp. 3317-3338 ◽  
Author(s):  
A. Bayat ◽  
H. R. Khalesifard ◽  
A. Masoumi
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Phase Function ◽  
Complex Refractive Index ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Sun Photometer ◽  
Ångstrom Exponent

Abstract. Aerosol optical depth, Ångström exponent, single scattering albedo, and polarized phase function have been retrieved from polarized sun-photometer measurements for atmosphere of Zanjan (36.70° N, 48.51° E, and 1800 m a.m.s.l.) from January 2010 to December 2012. The results show that the maximum value of aerosol polarized phase function as well as the polarized phase function retrieved for a specific scattering angle (i.e. 60°), are strongly correlated with the Ångström exponent. The latter one has a meaningful variations respect to the changes in the complex refractive index of the atmospheric aerosols. Furthermore the polarized phase function shows a moderate negative correlation respect to atmospheric aerosol optical depth and single scattering albedo. Therefore the polarized phase function can be regarded as a key parameter to characterize the atmospheric particles.

scholarly journals Aerosol optical depth and fine-mode fraction retrieval over East Asia using multi-angular total and polarized remote sensing

2012 ◽  
Vol 5 (3) ◽  
pp. 501-516 ◽  
Author(s):  
T. Cheng ◽  
X. Gu ◽  
D. Xie ◽  
Z. Li ◽  
T. Yu ◽  
...  
Keyword(s):  
East Asia ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Lookup Table ◽  
Retrieval Algorithm ◽  
Spatial And Temporal Variability ◽  
Aerosol Retrieval ◽  
Fine Mode ◽  
Sun Photometer ◽  
The Impact

Abstract. A new aerosol retrieval algorithm using multi-angular total and polarized measurements is presented. The algorithm retrieves aerosol optical depth (AOD), fine-mode fraction (FMF) for studying the impact of aerosol on climate change. The retrieval algorithm is based on a lookup table (LUT) method, which assumes that one fine and one coarse lognormal aerosol modes can be combined with proper weightings to represent the ambient aerosol properties. To reduce the ambiguity in retrieval algorithm, the key characteristics of aerosol model over East Asia are constrained using the cluster analysis technique based on the AERONET sun-photometer observation over East Asia, and the fine and coarse modes are not fixed but can vary. A mixing model of bare soil and green vegetation spectra and the Nadal and Breon model for the bidirectional polarized reflectance factor (BPDF) were used to simulate total and polarized surface reflectance of East Asia. By applying the present algorithm to POLDER measurements, three different aerosol cases of clear, polluted and dust are analyzed to test the algorithm. The comparison of retrieved aerosol optical depth (AOD) and fine-mode fraction (FMF) with those of AERONET sun-photometer observations show reliable results. Preliminary validation is encouraging. Using the new aerosol retrieval algorithm for multi-angular total and polarized measurements, the spatial and temporal variability of anthropogenic aerosol optical properties over East Asia, which were observed during a heavy polluted event, were analyzed. Exceptionally high values of aerosol optical depth contributed by fine mode of up to 0.5 (at 0.865 μm), and high values of fine-mode fraction of up to 0.9, were observed in this case study.

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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