scholarly journals Ground-Based Remote Sensing of Aerosol Properties over a Coastal Megacity of Pakistan

2018 ◽  
Vol 2018 ◽  
pp. 1-12
Author(s):  
Salman Tariq ◽  
Zia Ul-Haq
Keyword(s):  
Atmospheric Aerosols ◽  
Global Climate ◽  
Single Scattering ◽  
Dust Particles ◽  
Fine Mode ◽  
Autumn And Winter ◽  
Coastal Megacity ◽  
Aerosol Properties ◽  
Peak Value

Atmospheric aerosols are considered to be an important constituent of Earth’s atmosphere because of their climatic, environmental, and health effects. Therefore, while studying the global climate change, investigation of aerosol concentrations and properties is essential both at local and regional levels. In this paper, we have used relatively long-term Aerosol Robotic Network (AERONET) data during September 2006–August 2014 to analyze aerosol properties such as aerosol optical depth at 500 nm (AOD), Ångström exponent (440–870 nm) (AE), refractive index (RI), and asymmetry parameter over Karachi, a coastal megacity of Pakistan. The average annual values of AOD and AE were found to be 0.48 ± 0.20 and 0.59 ± 0.29, respectively. The peak (0.88 ± 0.31) AOD was recorded in July with corresponding AE of 0.30 ± 0.22 representing reasonably higher concentration of coarse size particles over Karachi. The cluster analysis using the scatter plot between absorption AE and extinction AE revealed that desert dust prevailed in the atmosphere of Karachi in spring and summer, while biomass burning aerosols dominate in autumn and winter. The peak values of volume concentrations of coarse and fine-mode particulate matter were found in summer and autumn, respectively. Also, we found significant growing trend in single-scattering albedo with wavelength, indicating the domination of dust particles during summer and spring. The peak value of the real part of the RI was observed in spring (1.53) and modest in winter (1.50). On the contrary, the peak value of the imaginary part of the RI was observed to be constantly elevated in winter and lesser in spring.

scholarly journals Haze Optical Properties from Long-Term Ground-Based Remote Sensing over Beijing and Xuzhou, China

2018 ◽  
Vol 10 (4) ◽  
pp. 518 ◽  
Author(s):  
Kai Qin ◽  
Luyao Wang ◽  
Jian Xu ◽  
Husi Letu ◽  
Kefei Zhang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Fine Particles ◽  
Global Climate ◽  
Complex Refractive Index ◽  
Eastern China ◽  
Single Scattering ◽  
Dust Particles ◽  
Haze Pollution

Aerosol haze pollution has had a significant impact on both global climate and the regional air quality of Eastern China, which has a high proportion of high level pollution days. Statistical analyses of aerosol optical properties and direct radiative forcing at two AERONET sites (Beijing and Xuzhou) were conducted from 2013 to 2016. Results indicate: (1) Haze pollution days accounted for 26% and 20% of days from 2013 to 2016 in Beijing and Xuzhou, respectively, with the highest proportions in winter; (2) The averaged aerosol optical depth (AOD) at 550 nm on haze days were about 3.7 and 1.6 times greater than those on clean days in Beijing and Xuzhou, respectively. At both sites, the maximum AOD occurred in summer; (3) Hazes were dominated by fine particles at both sites. However, as compared to Xuzhou, Beijing had larger coarse mode AOD and higher percentage of small α. This data, together with an analysis of size distribution, suggests that the hazes in Beijing were more susceptible to coarse dust particles than Xuzhou; (4) During hazes in Beijing, the single scattering albedo (SSA) is significantly higher when compared to clean conditions (0.874 vs. 0.843 in SSA440 nm), an increase much less evident in Xuzhou. The most noticeable differences in both SSA and the imaginary part of the complex refractive index between Beijing and Xuzhou were found in winter; (5) In Beijing, the haze radiative forcing produced an averaged cooling effect of −113.6 ± 63.7 W/m2 at the surface, whereas the averaged heating effect of 77.5 ± 49.7 W/m2 within the atmosphere was at least twice as strong as clean days. In Xuzhou, such a radiative forcing effect appeared to be much smaller and the difference between haze and clean days was insignificant. Derived from long-term observation, these findings are more significant for the improvement of our understanding of haze formation in China and the assessment of its impacts on radiative forcing of climate change than previous short-term case studies.

scholarly journals Aerosol characterization at the Saharan AERONET site Tamanrasset

2014 ◽  
Vol 14 (21) ◽  
pp. 11753-11773 ◽  
Author(s):  
C. Guirado ◽  
E. Cuevas ◽  
V. E. Cachorro ◽  
C. Toledano ◽  
S. Alonso-Pérez ◽  
...  
Keyword(s):  
Precipitable Water ◽  
Saharan Dust ◽  
Dust Particles ◽  
Data Series ◽  
Precipitable Water Vapour ◽  
Convective Boundary ◽  
Air Masses ◽  
Fine Mode ◽  
Autumn And Winter ◽  
Sky Conditions

Abstract. More than 2 years of columnar atmospheric aerosol measurements (2006–2009) at the Tamanrasset site (22.79° N, 5.53° E, 1377 m a.s.l.), in the heart of the Sahara, are analysed. Aerosol Robotic Network (AERONET) level 2.0 data were used. The KCICLO (K is the name of a constant and ciclo means cycle in Spanish) method was applied to a part of the level 1.5 data series to improve the quality of the results. The annual variability of aerosol optical depth (AOD) and Ångström exponent (AE) has been found to be strongly linked to the convective boundary layer (CBL) thermodynamic features. The dry-cool season (autumn and winter) is characterized by a shallow CBL and very low mean turbidity (AOD ~ 0.09 at 440 nm, AE ~ 0.62). The wet-hot season (spring and summer) is dominated by high turbidity of coarse dust particles (AE ~ 0.28, AOD ~ 0.39 at 440 nm) and a deep CBL. The aerosol-type characterization shows desert mineral dust as the prevailing aerosol. Both pure Saharan dust and very clear sky conditions are observed depending on the season. However, several case studies indicate an anthropogenic fine mode contribution from the industrial areas in Libya and Algeria. The concentration weighted trajectory (CWT) source apportionment method was used to identify potential sources of air masses arriving at Tamanrasset at several heights for each season. Microphysical and optical properties and precipitable water vapour were also investigated.

scholarly journals Retrieval of aerosol microphysical and optical properties above liquid clouds from POLDER/PARASOL polarization measurements

2013 ◽  
Vol 6 (4) ◽  
pp. 991-1016 ◽  
Author(s):  
F. Waquet ◽  
C. Cornet ◽  
J.-L. Deuzé ◽  
O. Dubovik ◽  
F. Ducos ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Radiative Forcing ◽  
Mineral Dust ◽  
Spherical Particles ◽  
Dust Particles ◽  
Polarization Measurements ◽  
Microphysical Properties ◽  
Coarse Mode ◽  
Fine Mode ◽  
Aerosol Properties

Abstract. Most of the current aerosol retrievals from passive sensors are restricted to cloud-free scenes, which strongly reduces our ability to monitor the aerosol properties at a global scale and to estimate their radiative forcing. The presence of aerosol above clouds (AAC) affects the polarized light reflected by the cloud layer, as shown by the spaceborne measurements provided by the POlarization and Directionality of Earth Reflectances (POLDER) instrument on the PARASOL satellite. In a previous work, a first retrieval method was developed for AAC scenes and evaluated for biomass-burning aerosols transported over stratocumulus clouds. The method was restricted to the use of observations acquired at forward scattering angles (90–120°) where polarized measurements are highly sensitive to fine-mode particle scattering. Non-spherical particles in the coarse mode, such as mineral dust particles, do not much polarize light and cannot be handled with this method. In this paper, we present new developments that allow retrieving also the properties of mineral dust particles above clouds. These particles do not much polarize light but strongly reduce the polarized cloud bow generated by the liquid cloud layer beneath and observed for scattering angles around 140°. The spectral attenuation can be used to qualitatively identify the nature of the particles (i.e. accumulation mode versus coarse mode, i.e. mineral dust particles versus biomass-burning aerosols), whereas the magnitude of the attenuation is related to the optical thickness of the aerosol layer. We also use the polarized measurements acquired in the cloud bow to improve the retrieval of both the biomass-burning aerosol properties and the cloud microphysical properties. We provide accurate polarized radiance calculations for AAC scenes and evaluate the contribution of the POLDER polarization measurements for the simultaneous retrieval of the aerosol and cloud properties. We investigate various scenes with mineral dust particles and biomass-burning aerosols above clouds. For clouds, our results confirm that the droplet size distribution is narrow in high-latitude ocean regions and that the droplet effective radii retrieved from both polarization measurements and from total radiance measurements are generally close for AAC scenes (departures smaller than 2 μm). We found that the magnitude of the primary cloud bow cannot be accurately estimated with a plane parallel transfer radiative code. The errors for the modeling of the polarized cloud bow are between 4 and 8% for homogenous cloudy scenes, as shown by a 3-D radiative transfer code. These effects only weakly impact the retrieval of the Aerosol Optical Thickness (AOT) performed with a mineral dust particle model for which the microphysical properties are entirely known (relative error smaller than 6%). We show that the POLDER polarization measurements allow retrieving the AOT, the fine-mode particle size, the Ångström exponent and the fraction of spherical particles. However, the complex refractive index and the coarse-mode particle size cannot be accurately retrieved with the present polarization measurements. Our complete and accurate algorithm cannot be applied to process large amounts of data, so a simpler algorithm was developed to retrieve the AOT and the Ångström exponent above clouds in an operational way. Illustrations are provided for July–August 2008 near the African coast. Large mean AOTs above clouds at 0.865 μm (>0.3) are retrieved for oceanic regions near the coasts of South Africa that correspond to biomass-burning aerosols, whereas even larger mean AOTs above clouds for mineral dust particles (>0.6) are also retrieved near the coasts of Senegal. For these regions and time period, the direct AAC radiative forcing is likely to be significant. The final aim of this work is the global monitoring of the AAC properties and the estimation of the direct aerosol radiative forcing in cloudy scenes.

scholarly journals Advection patterns and aerosol optical and microphysical properties by AERONET over south-east Italy in the central Mediterranean

2007 ◽  
Vol 7 (6) ◽  
pp. 16071-16118
Author(s):  
M. Santese ◽  
F. De Tomasi ◽  
M. R. Perrone
Keyword(s):  
Single Scattering ◽  
Western Mediterranean ◽  
Water Soluble ◽  
Dust Particles ◽  
Asymmetry Factor ◽  
Central Mediterranean ◽  
Mass Source ◽  
Air Mass ◽  
Air Masses ◽  
Fine Mode

Abstract. Aerosol products by AERONET sun-sky radiometer measurements combined with air-mass backtrajectories were analyzed to identify source regions and pathways of air masses carrying aerosols to south-east Italy, and to determine the dependence of aerosol mean optical properties on advection patterns. Aerosol optical depth (AOD), fine mode fraction (η), single scattering albedo (SSA), asymmetry factor (g), and lidar ratio (Lr) at 440 nm were used to characterize aerosol properties. The analysis of 5-day-backtrajectories ending in Lecce on south-east Italy and referring to 240 measurement days of the 2003–2004 years revealed that 32% of the measurement days were characterized by air masses coming from Sector A, which includes all continental European sources with the exception of Spain. 3% of the measurement days were characterized by air masses coming from both the Sector B, which includes the Southern Mediterranean Sea and the Africa continent, and the Sector C, which includes the Western Mediterranean, the Iberian Peninsula, and the Atlantic Ocean. 62% of the measurement days were characterized by mixed advection patterns (Sector M). We found that AOD, SSA and g average values were not significantly dependent on air mass source Sector. In contrast, η and Lr average values were quite affected by the air mass source Sector. AOD, η, SSA, g, and Lr average values, which were equal to 0.29±0.15, 0.93±0.03, 0.93±0.03, 0.67±0.03, and 72±20 sr, respectively indicated that the Sector A aerosol could be considered representative of "continental average aerosol", mostly made of water soluble and a small amount of soot and insoluble components. Polluted-desert dust particles characterized by AOD=0.29±0.05, η=0.72±0.05, SSA=0.94±0.03, g=0.69±0.02, Lr=56±13 sr, were advected over south-east Italy from Sector B. Sector C was instead responsible for the advection of maritime-polluted particles, which were characterized by AOD=0.3±0.2, η=0.8±0.1, SSA=0.94±0.03, g=0.67±0.03, Lr=60±20 sr. Hence, we found that the aerosol load over south-east Italy was dominated by moderately-absorbing, fine-mode particles even if it was also affected by the minor contribution of desert and maritime type aerosol. The application of an aerosol mask to the Sector M data points supported last comment

scholarly journals Synergistic angular and spectral estimation of aerosol properties using CHRIS/PROBA-1 and simulated Sentinel-3 data

2014 ◽  
Vol 7 (6) ◽  
pp. 5381-5422
Author(s):  
W. H. Davies ◽  
P. R. J. North
Keyword(s):  
Physical Model ◽  
Spectral Estimation ◽  
Single Scattering ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Imaging Spectrometer ◽  
Fine Mode ◽  
Land Surfaces ◽  
General Physical ◽  
Aerosol Properties

Abstract. A method has been developed to estimate Aerosol Optical Depth (AOD), Fine Mode Fraction (FMF) and Single Scattering Albedo (SSA) over land surfaces using simulated Sentinel-3 data. The method uses inversion of a coupled surface/atmosphere radiative transfer model, and includes a general physical model of angular surface reflectance. An iterative process is used to determine the optimum value of the aerosol properties providing the best fit of the corrected reflectance values for a number of view angles and wavelengths with those provided by the physical model. A method of estimating AOD using only angular retrieval has previously been demonstrated on data from the ENVISAT and PROBA-1 satellite instruments, and is extended here to the synergistic spectral and angular sampling of Sentinel-3 and the additional aerosol properties. The method is tested using hyperspectral, multi-angle Compact High Resolution Imaging Spectrometer (CHRIS) images. The values obtained from these CHRIS observations are validated using ground based sun-photometer measurements. Results from 22 image sets using the synergistic retrieval and improved aerosol models show an RMSE of 0.06 in AOD, reduced to 0.03 over vegetated targets.

scholarly journals Aerosol characterization at the Saharan AERONET site Tamanrasset

2014 ◽  
Vol 14 (11) ◽  
pp. 16641-16690 ◽  
Author(s):  
C. Guirado ◽  
E. Cuevas ◽  
V. E. Cachorro ◽  
C. Toledano ◽  
S. Alonso-Pérez ◽  
...  
Keyword(s):  
Precipitable Water ◽  
Saharan Dust ◽  
Dust Particles ◽  
Data Series ◽  
Precipitable Water Vapour ◽  
Convective Boundary ◽  
Fine Mode ◽  
Winter Time ◽  
Summer Time ◽  
Autumn And Winter

Abstract. More than two years of columnar atmospheric aerosol measurements (2006–2009) at Tamanrasset site, in the heart of the Sahara desert, are analysed. AERONET level 2.0 data were used. The KCICLO method was applied to a part of level 1.5 data series to improve the quality of the results. The annual variability of aerosol optical depth (AOD) and Angstrom exponent (AE) has been found to be strongly linked to the Convective Boundary Layer (CBL) thermodynamic features. The dry-cool season (autumn and winter time) is characterized by a shallow CBL and very low mean turbidity (AOD ~ 0.09 at 440 nm, AE ~ 0.62). The wet-hot season (spring and summer time) is dominated by high turbidity of coarse dust particles (AE ~ 0.28, AOD ~ 0.39 at 440 nm) and a deep CBL. The aerosol-type characterization shows desert mineral dust as prevailing aerosol. Both pure Saharan dust and very clear sky conditions are observed depending on the season. However, several case studies indicate an anthropogenic fine mode contribution from Libya and Algeria's industrial areas. The Concentration Weighted Trajectory (CWT) source apportionment method was used to identify potential sources of air masses arriving at Tamanrasset at several heights for each season. Microphysical and optical properties and precipitable water vapour were also investigated.

scholarly journals TEMPORAL-SPATIAL CHANGES IN AEROSOLS DURING WINTER HAZE OF WUHAN： A TYPICAL HIGH-HUMID INLAND CITY IN CENTRAL CHINA

2020 ◽  
Vol XLIII-B3-2020 ◽  
pp. 807-812
Author(s):  
S. Jin ◽  
Y. Ma ◽  
W. Gong ◽  
M. Zhang
Keyword(s):  
Single Scattering ◽  
Central China ◽  
City Centre ◽  
Spatial Distributions ◽  
Suburban Areas ◽  
Microphysical Properties ◽  
Spatial Changes ◽  
Fine Mode ◽  
Temporal And Spatial ◽  
Peak Value

Abstract. Temporal and spatial changes of aerosols characteristics was investigated to improve understandings of haze in winters of Wuhan, based on measurements of a CIMEL sun-sky radiometer and a modified Dark Target (DT) method. A large increase in no-absorbing and fine-mode particle is the main characteristic of aerosol during winter haze periods. From no-haze to haze conditions, aerosol optical depth (AOD), fine-mode peak value of size distribution, and single scattering albedo increased respectively from 0.46, 0.47 µm3/µm2, and 0.84 to 0.93, 0.91 µm3/µm2, and 0.87. Based on above aerosol optical and microphysical properties, we re-calculated aerosol models and improved the DT method. Results showed that our improvement increased the expect error (%) from 17.9 to 70.9. Spatial distributions revealed that heavy aerosol loading often occurred in rural and suburban areas rather than city centre. With the haze developing, the AOD increased by ∼0.3 over north of Wuhan and showed a downward trend from north to south.

scholarly journals Comparing multiple model-derived aerosol optical properties to collocated ground-based and satellite measurements

2016 ◽  
Author(s):  
Ilissa B. Ocko ◽  
Paul A. Ginoux
Keyword(s):  
Climate Models ◽  
Climate Modeling ◽  
Global Climate ◽  
Measurement Techniques ◽  
Single Scattering ◽  
Global Climate Models ◽  
Multiple Model ◽  
Anthropogenic Aerosols ◽  
Earth’S Climate ◽  
Aerosol Properties

Abstract. Anthropogenic aerosols are a key factor governing Earth’s climate, and play a central role in human-caused climate change. However, because of aerosols’ complex physical, optical, and dynamical properties, aerosols are one of the most uncertain aspects of climate modeling. Fortunately, aerosol measurement networks over the past few decades have led to the establishment of long-term observations for numerous locations worldwide. Further, the availability of datasets from several different measurement techniques (such as ground-based and satellite instruments) can help scientists increasingly improve modeling efforts. This study explores the value of evaluating several model-simulated aerosol properties with data from collocated instruments. We compare optical depth (total, scattering, and absorption), single scattering albedo, Ångström exponent, and extinction vertical profiles in two prominent global climate models to seasonal observations from collocated instruments (AERONET and CALIOP) at seven polluted and biomass burning regions worldwide. We find that models may accurately reproduce one variable while totally failing at another; data from collocated instruments can reveal underlying aerosol-governing physics; column properties may wash out important vertical distinctions; and "improved" models does not mean all aspects are improved. We conclude that it is important to make use of all available data (parameters and instruments) when evaluating aerosol properties derived by models.

scholarly journals Classification and investigation of Asian aerosol absorptive properties

2013 ◽  
Vol 13 (4) ◽  
pp. 2253-2265 ◽  
Author(s):  
T. Logan ◽  
B. Xi ◽  
X. Dong ◽  
Z. Li ◽  
M. Cribb
Keyword(s):  
Mineral Dust ◽  
Winter Season ◽  
Chemical Properties ◽  
Single Scattering ◽  
Dust Particles ◽  
Mixed Complex ◽  
Complex Particle ◽  
Coarse Mode ◽  
Fine Mode ◽  
Biomass Particles

Abstract. Asian aerosols are among the most complex yet widely studied components of the atmosphere not only due to their seasonal variability but also their effects on climate change. Four Aerosol Robotic Network (AERONET) sites have been selected to represent aerosol properties dominated by pollution (Taihu), mixed complex particle types (Xianghe), desert-urban (SACOL), and biomass (Mukdahan) in East Asia during the 2001–2010 period. The volume size distribution, aerosol optical depth (τ and τabs), Ångström exponent (α and αabs), and the single scattering co-albedo (ωoabs) parameters over the four selected sites have been used to (a) illustrate seasonal changes in aerosol size and composition and (b) discern the absorptive characteristics of black carbon (BC), organic carbon (OC), mineral dust particles, and mixtures. A strongly absorbing mineral dust influence is seen at the Xianghe, Taihu, and SACOL sites during the spring months (MAM), as given by coarse mode dominance, mean α440–870 < 1, and mean αabs440–870 > 1.5. There is a shift towards weakly absorbing pollution (sulfate) and biomass (OC) aerosol dominance in the summer (JJA) and autumn (SON) months, as given by a strong fine mode influence, α440–870 > 1, and αabs440–870 < 1.5. A winter season (DJF) shift toward strongly fine mode, absorbing particles (BC and OC) is observed at Xianghe and Taihu (αabs440–870 > 1 and αabs440–870 > 1.5). At Mukdahan, a strong fine mode influence is evident year round, with weakly and strongly absorbing biomass particles dominant in the autumn and winter months, respectively, while particles exhibit variable absorption during the spring season. A classification method using α440–870 and ωoabs440 is developed in order to infer the seasonal physico-chemical properties of the aerosol types, such as fine and coarse mode, weak and strong absorption, at the four selected Asian sites.

scholarly journals Remote sensing of aerosol properties during intense smog events over Lahore (Pakistan)

2021 ◽  
Vol 48 (4) ◽  
Author(s):  
Salman Tariq ◽  
◽  
Sumayia Mehmood ◽  
Aiman Nisa ◽  
Zia ul-Haq ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Urban Areas ◽  
Climate Changes ◽  
Single Scattering ◽  
Atmospheric Pollutants ◽  
Hysplit Model ◽  
Fine Mode ◽  
Main Component ◽  
Aerosol Types ◽  
Aerosol Properties

In recent years, smog has been one of the main concerns in heavily populated urban areas like Lahore (Pakistan) and Kanpur (India). Atmospheric pollutants like aerosols play an important role in smog. In this paper, aerosol types are identified in smog episodes, based on Aerosol Robotic Network (AERONET) data, during 4-year period i.e., 2015-2018. Aerosols are classified based on fine mode fraction (FMF) and single scattering albedo (SSA). One of the main aerosol types which are abundant in every smog episode is Black Carbon (BC) aerosol while dust is present throughout the year. BC is responsible for radiation imbalance and is considered the main component in climate changes at regional and global levels. Furthermore, time series of aerosol optical depth (AOD) during smog episodes is used to identify the variability of aerosol burden in the atmosphere. Backward trajectories from the HYSPLIT model are used to trace the origin of aerosols during the days of maximum AOD.

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