scholarly journals Advanced characterization of aerosol properties from measurements of spectral optical depth using the GRASP algorithm

2016 ◽  
Author(s):  
Benjamin Torres ◽  
Oleg Dubovik ◽  
David Fuertes ◽  
Gregory Schuster ◽  
Victoria Eugenia Cachorro ◽  
...  
Keyword(s):  
Optical Depth ◽  
Atmospheric Aerosols ◽  
A Priori ◽  
Advanced Characterization ◽  
Western Mediterranean ◽  
Coarse Mode ◽  
Fine Mode ◽  
Priori Information ◽  
Log Normal ◽  
Mode Volume

Abstract. This study evaluates the potential of using aerosol optical depth (τa) measurements to characterize the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP (Generalized Retrieval of Aerosol and Surface Properties) code for numerical testing of six different aerosol models with three different aerosol loads. We found that bimodal log-normal size distributions serve as useful input assumptions, especially when the measurements have inadequate spectral coverage and/or limited accuracy, such as lunar photometry. The direct numerical simulations indicate that the GRASP-AOD retrieval provides modal aerosol optical depths (fine and coarse) to within 0.01 of the input values. The retrieval of the fine mode radius, width, and volume concentration is stable and precise if the real part of the refractive index is known. The coarse mode properties are less accurate, but they are significantly improved when additional a priori information is available. In addition to these numerical studies, we used optical depth observations at six AERONET locations to validate our results with the standard AERONET inversion products. Differences in the fine mode volume median radii for the GRASP-AOD and AERONET inversions are less than 0.02 μm at sites dominated by the fine mode for all cases, although they are typically less than 0.01 μm when τa(440) > 0.3. The comparison of the coarse mode volume median radii shows larger differences than the fine mode at the same sites, with values typically between 0.2–0.3 μm. The comparison of coarse mode volume median radii between GRASP-AOD and AERONET improves for sites dominated by desert dust aerosol, with differences of less than 0.2 μm in most cases. The retrieved values of the fine-mode τa(500) using GRASP-AOD are generally between those values obtained by the standard AERONET inversion and the values obtained by the advance AERONET Spectral Deconvolution Algorithm (SDA), with differences typically lower than 0.02 between GRASP-AOD and both algorithms. Finally, we present some examples of application of GRASP-AOD inversion using moon-photometry and the airborne PLASMA sun-photometer during ChArMEx summer 2013 campaign in the western Mediterranean.

scholarly journals Advanced characterisation of aerosol size properties from measurements of spectral optical depth using the GRASP algorithm

2017 ◽  
Vol 10 (10) ◽  
pp. 3743-3781 ◽  
Author(s):  
Benjamin Torres ◽  
Oleg Dubovik ◽  
David Fuertes ◽  
Gregory Schuster ◽  
Victoria Eugenia Cachorro ◽  
...  
Keyword(s):  
Optical Depth ◽  
Atmospheric Aerosols ◽  
Volume Concentration ◽  
A Priori ◽  
Western Mediterranean ◽  
Dominant Mode ◽  
Coarse Mode ◽  
Fine Mode ◽  
The Difference ◽  
Log Normal

Abstract. This study evaluates the potential of using aerosol optical depth (τa) measurements to characterise the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP (Generalized Retrieval of Aerosol and Surface Properties) code for numerical testing of six different aerosol models with different aerosol loads. The direct numerical simulations (self-consistency tests) indicate that the GRASP-AOD retrieval provides modal aerosol optical depths (fine and coarse) to within 0.01 of the input values. The retrieval of the fine-mode radius, width and volume concentration are stable and precise if the real part of the refractive index is known. The coarse-mode properties are less accurate, but they are significantly improved when additional a priori information is available. The tests with random simulated errors show that the uncertainty in the bimodal log-normal size distribution parameters increases as the aerosol load decreases. Similarly, the reduction in the spectral range diminishes the stability of the retrieved parameters. In addition to these numerical studies, we used optical depth observations at eight AERONET locations to validate our results with the standard AERONET inversion products. We found that bimodal log-normal size distributions serve as useful input assumptions, especially when the measurements have inadequate spectral coverage and/or limited accuracy, such as moon photometry. Comparisons of the mode median radii between GRASP-AOD and AERONET indicate average differences of 0.013 µm for the fine mode and typical values of 0.2–0.3 µm for the coarse mode. The dominant mode (i.e. fine or coarse) indicates a 10 % difference in mode radii between the GRASP-AOD and AERONET inversions, and the average of the difference in volume concentration is around 17 % for both modes. The retrieved values of the fine-mode τa(500) using GRASP-AOD are generally between those values obtained by the standard AERONET inversion and the values obtained by the AERONET spectral deconvolution algorithm (SDA), with differences typically lower than 0.02 between GRASP-AOD and both algorithms. Finally, we present some examples of application of GRASP-AOD inversion using moon photometry and the airborne PLASMA sun photometer during the ChArMEx summer 2013 campaign in the western Mediterranean.

scholarly journals Characterisation of aerosol size properties from measurements of spectral optical depth: a global validation of the GRASP-AOD code using long-term AERONET data

2020 ◽  
Author(s):  
Benjamin Torres ◽  
David Fuertes
Keyword(s):  
Size Distribution ◽  
Optical Depth ◽  
Volume Concentration ◽  
Effective Radius ◽  
Aerosol Size Distribution ◽  
Retrieval Algorithm ◽  
Aerosol Retrieval ◽  
Coarse Mode ◽  
Fine Mode ◽  
Log Normal

Abstract. A validation study is conducted regarding aerosol optical size property retrievals from only measurements of the direct Sun beam (without the aid of diffuse radiation). The study focuses on testing with real data the new GRASP-AOD application which uses only spectral optical depth measurements to retrieve the total column aerosol size distributions, assumed as bimodal log-normal. In addition, a set of secondary integral parameters of aerosol size distribution and optical properties are provided: effective radius, total volume concentration and fine mode fraction of aerosol optical depth. The GRASP-AOD code is applied to almost three million observations acquired during twenty years (1997–2016) at thirty AERONET (Aerosol Robotic Network) sites. These validation sites have been selected based on known availability of an extensive data record, significant aerosol load variability along the year, wide worldwide coverage and divers aerosol types and source regions. The output parameters are compared to those coming from the operational AERONET retrievals. The retrieved fine mode fractions at 500 nm (τf(500)) obtained by GRASP-AOD application are compared to those retrieved by the Spectral Deconvolution Algorithm and by AERONET aerosol retrieval algorithm. The size distribution properties obtained by GRASP-AOD are compared to their equivalent values from the AERONET aerosol retrieval algorithm. The analysis showed the convincing capacity of GRASP-AOD approach to successfully discriminate between fine and coarse mode extinction to robustly retrieve τf(500). The comparisons of 2 million results of τf(500) retrieval by GRASP-AOD and SDA showed high correlation with a root-mean-square-error of 0.015. Also, the analysis showed that the τf(500) values computed by AERONET aerosol retrieval algorithm agree slightly better with GRASP-AOD (RMSE = 0.018, from 148526 comparisons) than with SDA (RMSE = 0.022, from 127203 comparisons). The comparisons of the size distribution retrieval showed the agreement for fine mode median radius between GRASP-AOD and AERONET aerosol retrieval algorithm results with RMSE of 0.032 μm (or 18.7 % in relative terms) for the situations when τ(440) > 0.2 that occurs for more than eighty thousand pairs of the study. For the cases where fine mode is dominant (i.e. α  0.2. The values of effective radius and total volume concentration computed from GRASP-AOD retrieval have been compared to those estimated by AERONET aerosol retrieval algorithm. The RMSE values of the correlations were of 30 % for the effective radius and 25 % for the total volume concentration when τ(440) > 0.2. Finally, the study discusses the importance of employing the assumption of bimodal log-normal size distribution. It also evaluates the potential of using ancillary data, in particular aureole measurements, for improving the characterization of the aerosol coarse mode properties.

scholarly journals Simplified aerosol modeling for variational data assimilation

2009 ◽  
Vol 2 (2) ◽  
pp. 213-229 ◽  
Author(s):  
N. Huneeus ◽  
O. Boucher ◽  
F. Chevallier
Keyword(s):  
Data Assimilation ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
General Circulation ◽  
Variational Data Assimilation ◽  
Sensitivity Analyses ◽  
Simplified Model ◽  
Desert Dust ◽  
Coarse Mode ◽  
Fine Mode

Abstract. We have developed a simplified aerosol model together with its tangent linear and adjoint versions for the ultimate aim of optimizing global aerosol and aerosol precursor emission using variational data assimilation. The model was derived from the general circulation model LMDz; it groups together the 24 aerosol species simulated in LMDz into 4 species, namely gaseous precursors, fine mode aerosols, coarse mode desert dust and coarse mode sea salt. The emissions have been kept as in the original model. Modifications, however, were introduced in the computation of aerosol optical depth and in the processes of sedimentation, dry and wet deposition and sulphur chemistry to ensure consistency with the new set of species and their composition. The simplified model successfully manages to reproduce the main features of the aerosol distribution in LMDz. The largest differences in aerosol load are observed for fine mode aerosols and gaseous precursors. Differences between the original and simplified models are mainly associated to the new deposition and sedimentation velocities consistent with the definition of species in the simplified model and the simplification of the sulphur chemistry. Furthermore, simulated aerosol optical depth remains within the variability of monthly AERONET observations for all aerosol types and all sites throughout most of the year. Largest differences are observed over sites with strong desert dust influence. In terms of the daily aerosol variability, the model is less able to reproduce the observed variability from the AERONET data with larger discrepancies in stations affected by industrial aerosols. The simplified model however, closely follows the daily simulation from LMDz. Sensitivity analyses with the tangent linear version show that the simplified sulphur chemistry is the dominant process responsible for the strong non-linearity of the model.

scholarly journals Assessment of cloud-related fine-mode AOD enhancements based on AERONET SDA product

2017 ◽  
Vol 17 (9) ◽  
pp. 5991-6001 ◽  
Author(s):  
Antti Arola ◽  
Thomas F. Eck ◽  
Harri Kokkola ◽  
Mikko R. A. Pitkänen ◽  
Sami Romakkaniemi
Keyword(s):  
Optical Depth ◽  
Relative Role ◽  
Hygroscopic Growth ◽  
Cloud Optical Depth ◽  
Cloud Processing ◽  
Clear Sky ◽  
Coarse Mode ◽  
Fine Mode ◽  
L1 And L2 ◽  
Sky Conditions

Abstract. AERONET (AErosol RObotic NETwork), which is a network of ground-based sun photometers, produces a data product called the aerosol spectral deconvolution algorithm (SDA) that utilizes spectral total aerosol optical depth (AOD) data to infer the component fine- and coarse-mode optical depths at 500 nm. Based on its assumptions, SDA identifies cloud optical depth as the coarse-mode AOD component and therefore effectively computes the fine-mode AOD also in mixed cloud–aerosol observations. Therefore, it can be argued that the more representative AOD for fine-mode fraction should be based on all direct sun measurements and not only on those cloud screened for clear-sky conditions, i.e., on those from level 1 (L1) instead of level 2 (L2) in AERONET. The objective of our study was to assess, including all the available AERONET sites, how the fine-mode AOD is enhanced in cloudy conditions, contrasting SDA L1 and L2 in our analysis. Assuming that the cloud screening correctly separates the cloudy and clear-sky conditions, then the increases in fine-mode AOD can be due to various cloud-related processes, mainly by the strong hygroscopic growth of particles in the vicinity of clouds and in-cloud processing leading to growth of accumulation mode particles. We estimated these cloud-related enhancements in fine-mode AOD seasonally and found, for instance, that in June–August season the average over all the AERONET sites was 0.011, when total fine-mode AOD from L2 data was 0.154; therefore, the relative enhancement was 7 %. The enhancements were largest, both absolutely and relatively, in East Asia; for example, in June–August season the absolute and relative differences in fine-mode AOD, between L1 and L2 measurements, were 0.022 and 10 %, respectively. Corresponding values in North America and Europe were about 0.01 and 6–7 %. In some highly polluted areas, the enhancement is greater than these regional averages, e.g., in Beijing region and in June–July–August (JJA) season the corresponding absolute values were about 0.1. It is difficult to separate the fine-mode AOD enhancements due to in-cloud processing and hygroscopic growth, but we attempted to get some understanding by conducting a similar analysis for SDA-based fine-mode Ångström exponent (AE) patterns. Moreover, we exploited a cloud parcel model, in order to understand in detail the relative role of different processes. We found that in marine conditions, were aerosol concentration are low and cloud scavenging is efficient, the AE changes in opposite direction than in the more polluted conditions, were hygroscopic growth of particles leads to a negative AE change.

scholarly journals Estimation of aerosol complex refractive indices for both fine and coarse modes simultaneously based on AERONET remote sensing products

2017 ◽  
Vol 10 (9) ◽  
pp. 3203-3213 ◽  
Author(s):  
Ying Zhang ◽  
Zhengqiang Li ◽  
Yuhuan Zhang ◽  
Donghui Li ◽  
Lili Qie ◽  
...  
Keyword(s):  
Imaginary Part ◽  
Atmospheric Aerosols ◽  
Fine Particles ◽  
Winter Season ◽  
Water Soluble ◽  
Refractive Indices ◽  
Coarse Mode ◽  
Seasonal Characteristics ◽  
Climate Change Assessment ◽  
Log Normal

Abstract. Climate change assessment, especially model evaluation, requires a better understanding of complex refractive indices (CRIs) of atmospheric aerosols – separately for both fine and coarse modes. However, the widely used aerosol CRI obtained by the global Aerosol Robotic Network (AERONET) corresponds to total-column aerosol particles without separation for fine and coarse modes. This paper establishes a method to separate CRIs of fine and coarse particles based on AERONET volume particle size distribution (VPSD), aerosol optical depth (AOD) and absorbing AOD (AAOD). The method consists of two steps. First a multimodal log-normal distribution that best approximates the AERONET VPSD is found. Then the fine and coarse mode CRIs are found by iterative fitting of AERONET AODs to Mie calculations. The numerical experiment shows good performance for typical water-soluble, biomass burning and dust aerosol types, and the estimated uncertainties on the retrieved sub-mode CRIs are about 0.11 (real part) and 78 % (imaginary part). The 1-year measurements at the AERONET Beijing site are processed, and we obtain CRIs of 1.48–0.010i (imaginary part at 440 nm is 0.012) for fine mode particles and 1.49–0.004i (imaginary part at 440 nm is 0.007) for coarse mode particles, for the period of 2014–2015. Our results also suggest that both fine and coarse aerosol mode CRIs have distinct seasonal characteristics; in particular, CRIs of fine particles in winter season are significantly higher than summer due to possible anthropogenic influences.

scholarly journals Aerosol optical, microphysical and radiative properties at three regional background insular sites in the western Mediterranean Basin

2016 ◽  
Author(s):  
M. Sicard ◽  
R. Barragan ◽  
F. Dulac ◽  
L. Alados-Arboledas ◽  
M. Mallet
Keyword(s):  
Radiative Forcing ◽  
Mediterranean Basin ◽  
Mineral Dust ◽  
Western Mediterranean ◽  
Radiative Properties ◽  
Annual Cycles ◽  
Regional Background ◽  
Coarse Mode ◽  
Western Mediterranean Basin ◽  
Mode Volume

Abstract. In the framework of the ChArMEx (the Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr/) program, the seasonal variability of the aerosol optical, microphysical and radiative properties is examined in two regional background insular sites in the western Mediterranean Basin (WMB): Ersa (Corsica Island, France) and Palma de Mallorca (Mallorca Island, Spain). A third site in Alborán (Alborán Island, Spain) with only a few months of data is considered for exploring the possible Northeast–Southwest (NE–SW) gradient of the aforementioned aerosol properties. The dataset is exclusively composed of AERONET (Aerosol Robotic Network; http://aeronet.gsfc.nasa.gov/) products during a four-year period (2011–2014). AERONET fluxes are validated with ground- and satellite-based flux measurements. To the best of our knowledge this is the first time that AERONET fluxes are validated at the top of the atmosphere. Products such as the aerosol optical depth (AOD), the fraction fine mode to total AOD, the particle size distribution, the sphericity, the radiative forcing and the radiative forcing efficiency show a clear annual cycle. The main drivers of the observed annual cycles are mineral dust outbreaks in summer and the transport of European continental aerosols in spring. A NE–SW gradient is observed on 6 parameters (3 extensive and 3 intensive) out of the 18 discussed in the paper. The NE–SW gradient of the AOD, the Ångström exponent, the coarse mode volume concentration, the sphericity and the radiative forcing at the surface are related to mineral dust outbreaks, while the NE–SW gradient of the coarse mode volume median radius is related to the decreasing influence of European continental aerosols along the NE–SW axis. The fact that two thirds of the parameters discussed in the paper do not present a NE–SW gradient is partly explained by two relevant findings: (1) a homogeneous spatial distribution of the fine particle loads over the three sites in spite of the distances between the sites and the differences in local sources, and (2) low values and the absence of spectral dependency of the absorption found in the southwesternmost site.

scholarly journals Aerosol retrieval experiments in the ESA Aerosol_cci project

2013 ◽  
Vol 6 (8) ◽  
pp. 1919-1957 ◽  
Author(s):  
T. Holzer-Popp ◽  
G. de Leeuw ◽  
J. Griesfeller ◽  
D. Martynenko ◽  
L. Klüser ◽  
...  
Keyword(s):  
A Priori ◽  
Round Robin ◽  
Aerosol Retrieval ◽  
Standard Product ◽  
Fine Mode ◽  
Sun Photometer ◽  
Priori Information ◽  
Cloud Mask ◽  
The Impact ◽  
Global Data

Abstract. Within the ESA Climate Change Initiative (CCI) project Aerosol_cci (2010–2013), algorithms for the production of long-term total column aerosol optical depth (AOD) datasets from European Earth Observation sensors are developed. Starting with eight existing pre-cursor algorithms three analysis steps are conducted to improve and qualify the algorithms: (1) a series of experiments applied to one month of global data to understand several major sensitivities to assumptions needed due to the ill-posed nature of the underlying inversion problem, (2) a round robin exercise of "best" versions of each of these algorithms (defined using the step 1 outcome) applied to four months of global data to identify mature algorithms, and (3) a comprehensive validation exercise applied to one complete year of global data produced by the algorithms selected as mature based on the round robin exercise. The algorithms tested included four using AATSR, three using MERIS and one using PARASOL. This paper summarizes the first step. Three experiments were conducted to assess the potential impact of major assumptions in the various aerosol retrieval algorithms. In the first experiment a common set of four aerosol components was used to provide all algorithms with the same assumptions. The second experiment introduced an aerosol property climatology, derived from a combination of model and sun photometer observations, as a priori information in the retrievals on the occurrence of the common aerosol components. The third experiment assessed the impact of using a common nadir cloud mask for AATSR and MERIS algorithms in order to characterize the sensitivity to remaining cloud contamination in the retrievals against the baseline dataset versions. The impact of the algorithm changes was assessed for one month (September 2008) of data: qualitatively by inspection of monthly mean AOD maps and quantitatively by comparing daily gridded satellite data against daily averaged AERONET sun photometer observations for the different versions of each algorithm globally (land and coastal) and for three regions with different aerosol regimes. The analysis allowed for an assessment of sensitivities of all algorithms, which helped define the best algorithm versions for the subsequent round robin exercise; all algorithms (except for MERIS) showed some, in parts significant, improvement. In particular, using common aerosol components and partly also a priori aerosol-type climatology is beneficial. On the other hand the use of an AATSR-based common cloud mask meant a clear improvement (though with significant reduction of coverage) for the MERIS standard product, but not for the algorithms using AATSR. It is noted that all these observations are mostly consistent for all five analyses (global land, global coastal, three regional), which can be understood well, since the set of aerosol components defined in Sect. 3.1 was explicitly designed to cover different global aerosol regimes (with low and high absorption fine mode, sea salt and dust).

scholarly journals Estimating aerosol emissions by assimilating observed aerosol optical depth in a global aerosol model

2012 ◽  
Vol 12 (1) ◽  
pp. 3075-3130 ◽  
Author(s):  
N. Huneeus ◽  
F. Chevallier ◽  
O. Boucher
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
A Priori ◽  
Global Scale ◽  
Aerosol Model ◽  
Initial Errors ◽  
Emission Fluxes ◽  
Independent Observations ◽  
Fine Mode ◽  
The Impact

Abstract. This study estimates the emission fluxes of a range of aerosol species and aerosol precursor at the global scale. These fluxes are estimated by assimilating daily total and fine mode aerosol optical depth (AOD) at 550 nm from the Moderate Resolution Imaging Spectroradiometer (MODIS) into a global aerosol model of intermediate complexity. Monthly emissions are fitted homogenously for each species over a set of predefined regions. The performance of the assimilation is evaluated by comparing the AOD after assimilation against the MODIS observations and against independent observations. The system is effective in forcing the model towards the observations, for both total and fine mode AOD. Significant improvements for the root mean square error and correlation coefficient against both the assimilated and independent datasets are observed as well as a significant decrease in the mean bias against the assimilated observations. The assimilation is more efficient over land than over ocean. The impact of the assimilation of fine mode AOD over ocean demonstrates potential for further improvement by including fine mode AOD observations over continents. The Angström exponent is also improved in African, European and dusty stations. The estimated emission flux for black carbon is 14.5 Tg yr−1, 119 Tg yr−1 for organic matter, 17 Pg yr−1 for sea salt, 82.7 TgS yr−1 for SO2 and 1383 Tg yr−1 for desert dust. They represent a difference of +45%, +40%, +26%, +13% and −39% respectively, with respect to the a priori values. The initial errors attributed to the emission fluxes are reduced for all estimated species.

scholarly journals Indirect estimation of absorption properties for fine aerosol particles using AATSR observations: a case study of wildfires in Russia in 2010

2015 ◽  
Vol 8 (8) ◽  
pp. 3075-3085 ◽  
Author(s):  
E. Rodríguez ◽  
P. Kolmonen ◽  
T. H. Virtanen ◽  
L. Sogacheva ◽  
A.-M. Sundström ◽  
...  
Keyword(s):  
Optical Depth ◽  
Continuous Variation ◽  
Radiative Transfer Model ◽  
Retrieval Algorithm ◽  
Transfer Model ◽  
Retrieval Process ◽  
Aerosol Model ◽  
Coarse Mode ◽  
Fine Mode ◽  
Aerosol Properties

Abstract. The Advanced Along-Track Scanning Radiometer (AATSR) on board the ENVISAT satellite is used to study aerosol properties. The retrieval of aerosol properties from satellite data is based on the optimized fit of simulated and measured reflectances at the top of the atmosphere (TOA). The simulations are made using a radiative transfer model with a variety of representative aerosol properties. The retrieval process utilizes a combination of four aerosol components, each of which is defined by their (lognormal) size distribution and a complex refractive index: a weakly and a strongly absorbing fine-mode component, coarse mode sea salt aerosol and coarse mode desert dust aerosol). These components are externally mixed to provide the aerosol model which in turn is used to calculate the aerosol optical depth (AOD). In the AATSR aerosol retrieval algorithm, the mixing of these components is decided by minimizing the error function given by the sum of the differences between measured and calculated path radiances at 3–4 wavelengths, where the path radiances are varied by varying the aerosol component mixing ratios. The continuous variation of the fine-mode components allows for the continuous variation of the fine-mode aerosol absorption. Assuming that the correct aerosol model (i.e. the correct mixing fractions of the four components) is selected during the retrieval process, also other aerosol properties could be computed such as the single scattering albedo (SSA). Implications of this assumption regarding the ratio of the weakly/strongly absorbing fine-mode fraction are investigated in this paper by evaluating the validity of the SSA thus obtained. The SSA is indirectly estimated for aerosol plumes with moderate-to-high AOD resulting from wildfires in Russia in the summer of 2010. Together with the AOD, the SSA provides the aerosol absorbing optical depth (AAOD). The results are compared with AERONET data, i.e. AOD level 2.0 and SSA and AAOD inversion products. The RMSE (root mean square error) is 0.03 for SSA and 0.02 for AAOD lower than 0.05. The SSA is further evaluated by comparison with the SSA retrieved from the Ozone Monitoring Instrument (OMI). The SSA retrieved from both instruments show similar features, with generally lower AATSR-estimated SSA values over areas affected by wildfires.

scholarly journals Sub-Mode Aerosol Volume Size Distribution and Complex Refractive Index from the Three-Year Ground-Based Measurements in Chengdu China

Atmosphere ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 46 ◽  
Author(s):  
Chi Zhang ◽  
Ying Zhang ◽  
Zhengqiang Li ◽  
Yongqian Wang ◽  
Hua Xu ◽  
...  
Keyword(s):  
Refractive Index ◽  
Size Distribution ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Complex Refractive Index ◽  
Observation Data ◽  
Aerosol Model ◽  
Coarse Mode ◽  
Fine Mode ◽  
Volume Size

Chengdu is a typical basin city of Southwest China with rare observations of remote sensing measurements. To assess the climate change and establish a region aerosol model, a deeper understanding of the separated volume size distribution (VSD) and complex refractive index (CRI) is required. In this study, we employed the sub-mode VSD and CRI in Chengdu based on the three years observation data to investigate the sub-mode characteristics and climate effects. The annual average fraction of the fine-mode aerosol optical depth (AODf) is 92%, which has the same monthly tendency as the total AOD. But the coarse-mode aerosol optical depth (AODc) has little variation in different months. There are four distinguishing modes of VSD in Chengdu; the median radii are 0.17 μm ± 0.05, 0.31 μm ± 0.12, 1.62 μm ± 0.45, 3.25 μm ± 0.99, respectively. The multi-year average and seasonal variations of fine- and coarse-mode VSD and CRI are also analyzed to characterize aerosols over this region. The fine-mode single scattering albedos (SSAs) are higher than the coarse-mode ones, which suggests that the coarse-mode aerosols have a stronger absorbing effect on solar light than the small-size aerosol particles in Chengdu.

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