scholarly journals A simple parameterization of the short-wave aerosol optical properties for surface direct and diffuse irradiances assessment in a numerical weather model

2014 ◽  
Vol 7 (1) ◽  
pp. 593-629
Author(s):  
J. A. Ruiz-Arias ◽  
J. Dudhia
Keyword(s):  
Optical Properties ◽  
Control Experiment ◽  
Weather Prediction ◽  
Single Scattering ◽  
Short Wave ◽  
Asymmetry Factor ◽  
Band Model ◽  
Aerosol Optical Properties ◽  
Numerical Weather ◽  
Clear Sky

Abstract. Broadband short-wave (SW) surface direct and diffuse irradiances are not typically within the set of output variables produced by numerical weather prediction (NWP) models. However, they are being more and more demanded in solar energy applications. A detailed representation of the aerosol optical properties is important to achieve an accurate assessment of these direct and diffuse irradiances. Nonetheless, NWP models typically oversimplify its representation or even neglect its effect. In this work, a flexible method to account for the SW aerosol optical properties in the computation of broadband SW surface direct and diffuse irradiances is presented. It only requires aerosol optical depth at 0.55 μm and the type of predominant aerosol. The rest of parameters needed to consider spectral aerosol extinction, namely, Angström exponent, aerosol single-scattering albedo and aerosol asymmetry factor, are parameterized. The parameterization has been tested in the RRTMG SW scheme of the Weather Research and Forecasting (WRF) NWP model. However, it can be adapted to any other SW radiative transfer band model. It has been verified against a control experiment along five radiometric stations in the contiguous US. The control experiment consisted of a clear-sky evaluation of the RRTMG solar radiation estimates obtained in WRF when RRTMG is driven with ground-observed aerosol optical properties. Overall, the verification has shown very satisfactory results for both broadband SW surface direct and diffuse irradiances. It has proven effective to significantly reduce the prediction error and constraint the seasonal bias in clear-sky conditions to within the typical observational error in well-maintained radiometers.

scholarly journals A simple parameterization of the short-wave aerosol optical properties for surface direct and diffuse irradiances assessment in a numerical weather model

2014 ◽  
Vol 7 (3) ◽  
pp. 1159-1174 ◽  
Author(s):  
J. A. Ruiz-Arias ◽  
J. Dudhia ◽  
C. A. Gueymard
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Control Experiment ◽  
Weather Prediction ◽  
Short Wave ◽  
Asymmetry Factor ◽  
Band Model ◽  
Aerosol Optical Properties ◽  
Numerical Weather ◽  
Clear Sky

Abstract. Broadband short-wave (SW) surface direct and diffuse irradiances are not typically within the set of output variables produced by numerical weather prediction (NWP) models. However, they are frequently requested for solar energy applications. In order to compute them, a detailed representation of the aerosol optical properties is important. Nonetheless, NWP models typically oversimplify aerosol representation or even neglect their effect. In this work, a flexible method to account for the SW aerosol optical properties in the computation of broadband SW surface direct and diffuse irradiances is presented. It only requires aerosol optical depth at 0.55 μm and knowledge of the type of predominant aerosol. Other parameters needed to consider spectral aerosol extinction, namely, Angström exponent, aerosol single-scattering albedo and aerosol asymmetry factor, are parameterized. The parameterization has been tested using the Rapid Radiative Transfer Model for climate and weather models (RRTMG) SW scheme of the Weather Research and Forecasting (WRF) NWP model for data over the continental US. In principle, it can be adapted to any other SW radiative transfer band model. It has been verified against a control experiment and using data from five radiometric stations in the contiguous US. The control experiment consisted of a clear-sky evaluation of the RRTMG solar radiation estimates obtained in WRF when RRTMG is driven with ground-observed aerosol optical properties. Overall, the verification has shown satisfactory results for both broadband SW surface direct and diffuse irradiances. The parameterization has proven effective in significantly reducing the prediction error and constraining the seasonal bias in clear-sky conditions to within the typical observational error expected in well maintained radiometers.

scholarly journals Effects of aerosols on clear-sky solar radiation in the ALADIN-HIRLAM NWP system

2016 ◽  
Vol 16 (9) ◽  
pp. 5933-5948 ◽  
Author(s):  
Emily Gleeson ◽  
Velle Toll ◽  
Kristian Pagh Nielsen ◽  
Laura Rontu ◽  
Ján Mašek
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Numerical Weather Prediction ◽  
Weather Prediction ◽  
Radiative Effect ◽  
Aerosol Optical Properties ◽  
Numerical Weather ◽  
Clear Sky ◽  
Radiation Scheme

Abstract. The direct shortwave radiative effect of aerosols under clear-sky conditions in the Aire Limitee Adaptation dynamique Developpement InterNational – High Resolution Limited Area Model (ALADIN-HIRLAM) numerical weather prediction system was investigated using three shortwave radiation schemes in diagnostic single-column experiments: the Integrated Forecast System (IFS), acraneb2 and the hlradia radiation schemes. The multi-band IFS scheme was formerly used operationally by the European Centre for Medium Range Weather Forecasts (ECMWF) whereas hlradia and acraneb2 are broadband schemes. The former is a new version of the HIRLAM radiation scheme while acraneb2 is the radiation scheme in the ALARO-1 physics package. The aim was to evaluate the strengths and weaknesses of the numerical weather prediction (NWP) system regarding aerosols and to prepare it for use of real-time aerosol information. The experiments were run with particular focus on the August 2010 Russian wildfire case. Each of the three radiation schemes accurately (within ±4 % at midday) simulates the direct shortwave aerosol effect when observed aerosol optical properties are used. When the aerosols were excluded from the simulations, errors of more than +15 % in global shortwave irradiance were found at midday, with the error reduced to +10 % when standard climatological aerosols were used. An error of −11 % was seen at midday if only observed aerosol optical depths at 550 nm, and not observation-based spectral dependence of aerosol optical depth, single scattering albedos and asymmetry factors, were included in the simulations. This demonstrates the importance of using the correct aerosol optical properties. The dependency of the direct radiative effect of aerosols on relative humidity was tested and shown to be within ±6 % in this case. By modifying the assumptions about the shape of the IFS climatological vertical aerosol profile, the inherent uncertainties associated with assuming fixed vertical profiles were investigated. The shortwave heating rates in the boundary layer changed by up to a factor of 2 in response to the aerosol vertical distribution without changing the total aerosol optical depth. Finally, we tested the radiative transfer approximations used in the three radiation schemes for typical aerosol optical properties compared to the accurate DISORT model. These approximations are found to be accurate to within ±13 % even for large aerosol loads.

scholarly journals Parametrizations of Liquid and Ice Clouds’ Optical Properties in Operational Numerical Weather Prediction Models

Atmosphere ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 89
Author(s):  
Harel. B. Muskatel ◽  
Ulrich Blahak ◽  
Pavel Khain ◽  
Yoav Levi ◽  
Qiang Fu
Keyword(s):  
Optical Properties ◽  
Numerical Weather Prediction ◽  
Radiation Transfer ◽  
Prediction Models ◽  
Weather Prediction ◽  
Effective Size ◽  
Asymmetry Factor ◽  
Numerical Weather ◽  
Numerical Weather Prediction Models ◽  
Spectral Averaging

Parametrization of radiation transfer through clouds is an important factor in the ability of Numerical Weather Prediction models to correctly describe the weather evolution. Here we present a practical parameterization of both liquid droplets and ice optical properties in the longwave and shortwave radiation. An advanced spectral averaging method is used to calculate the extinction coefficient, single scattering albedo, forward scattered fraction and asymmetry factor (bext, v, f, g), taking into account the nonlinear effects of light attenuation in the spectral averaging. An ensemble of particle size distributions was used for the ice optical properties calculations, which enables the effective size range to be extended up to 570 μm and thus be applicable for larger hydrometeor categories such as snow, graupel, and rain. The new parameterization was applied both in the COSMO limited-area model and in ICON global model and was evaluated by using the COSMO model to simulate stratiform ice and water clouds. Numerical weather prediction models usually determine the asymmetry factor as a function of effective size. For the first time in an operational numerical weather prediction (NWP) model, the asymmetry factor is parametrized as a function of aspect ratio. The method is generalized and is available on-line to be readily applied to any optical properties dataset and spectral intervals of a wide range of radiation transfer models and applications.

scholarly journals Aerosol optical properties and radiative effect determined from sky-radiometer over Loess Plateau of Northwest China

2011 ◽  
Vol 11 (22) ◽  
pp. 11455-11463 ◽  
Author(s):  
Y. Liu ◽  
J. Huang ◽  
G. Shi ◽  
T. Takamura ◽  
P. Khatri ◽  
...  
Keyword(s):  
Optical Properties ◽  
Northwest China ◽  
Single Scattering ◽  
Asymmetry Factor ◽  
Dust Event ◽  
Radiative Effects ◽  
Aerosol Optical Properties ◽  
Surface Solar Radiation ◽  
Outbreak Period ◽  
Dust Events

Abstract. The aerosol optical properties and their associated radiative effects are derived from sky-radiometer and surface solar radiation data collected over the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) for the period of March to May (MAM) 2009. The result shows that the seasonal mean aerosol optical depth (AOD) at 500 nm in MAM is 0.40. The single scattering albedo (SSA) at 500 nm in MAM at SACOL fluctuates significantly ranging from 0.82 to 0.98. The averaged value of SSA there for background aerosol is 0.90 in MAM, while it is smaller (0.87) during the dust event outbreak period. The smaller SSA can be interpreted as the result of larger particles during dust events. The averaged asymmetry factor (ASY) at 500 nm during dust event period is 0.73, which is larger than 0.70 of background aerosols. The averaged shortwave radiative effects of the aerosols during dust event period in MAM are 0.68, −70.02 and 70.70 W m−2, respectively, at the top of the atmosphere (TOA), surface and in the atmosphere. The aerosols heat the atmosphere during dust event period by up to about 2 K day−1 (daily averaged), which is 60 % larger than the heating (1.25 K day−1) of background aerosols. The significant heating effect in the atmosphere of the aerosols during dust event is determined by larger AOD and smaller SSA.

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.

scholarly journals Vertical profiles of aerosol optical properties and the solar heating rate estimated by combining sky radiometer and lidar measurements

2016 ◽  
Author(s):  
Rei Kudo ◽  
Tomoaki Nishizawa ◽  
Toshinori Aoyagi
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Heating Rate ◽  
Extinction Coefficient ◽  
Single Scattering ◽  
Solar Heating ◽  
Asymmetry Factor ◽  
Vertical Profiles ◽  
Aerosol Optical Properties ◽  
Lidar Measurements

Abstract. The SKYLIDAR algorithm was developed to estimate vertical profiles of aerosol optical properties from sky radiometer (SKYNET) and lidar (AD-Net) measurements. The solar heating rate was also estimated from the SKYLIDAR retrievals. The algorithm consists of two retrieval steps: (1) columnar properties are retrieved from the sky radiometer measurements and the vertically mean depolarization ratio obtained from the lidar measurements, and (2) vertical profiles are retrieved from the lidar measurements and the results of the first step. The derived parameters are the vertical profiles of the size distribution, refractive index (real and imaginary parts), extinction coefficient, single-scattering albedo, and asymmetry factor. Sensitivity tests were conducted by applying the SKYLIDAR algorithm to the simulated sky radiometer and lidar data for vertical profiles of three different aerosols, continental average, transported dust, and pollution aerosols. The vertical profiles of the size distribution, extinction coefficient, and asymmetry factor were well estimated in all cases. The vertical profiles of the refractive index and single-scattering albedo of transported dust were well estimated but not those of transported pollution aerosol. To demonstrate the performance and validity of the SKYLIDAR algorithm, we applied the SKYLIDAR algorithm to the actual measurements at Tsukuba, Japan. The detailed vertical structures of the aerosol optical properties and solar heating rate of transported dust and smoke were investigated. Examination of the relationship between the solar heating rate and the aerosol optical properties showed that the vertical profile of the asymmetry factor played an important role in creating vertical variation in the solar heating rate. We then compared the columnar optical properties between SKYLIDAR and SKYRAD.PACK retrievals, and the surface solar irradiance calculated from the SKYLIDAR retrievals was compared with pyranometer measurement. The results showed good agreements: The columnar values of the SKYLIDAR retrievals agreed with reliable SKYRAD.PACK retrievals, and the SKYLIDAR retrievals were sufficiently accurate to evaluate the surface solar irradiance.

scholarly journals Measurement-based climatology of aerosol direct radiative effect, its sensitivities, and uncertainties from a background southeast U.S. site

2017 ◽  
Author(s):  
James P. Sherman ◽  
Allison McComiskey
Keyword(s):  
Optical Properties ◽  
Ground Truth ◽  
Single Scattering ◽  
Surface Reflectance ◽  
Radiative Effect ◽  
Aerosol Optical Properties ◽  
Clear Sky ◽  
Aerosol Loading ◽  
Measurement Uncertainties ◽  
Seasonal Dependence

Abstract. Aerosol optical properties measured at Appalachian State University's co-located NASA AERONET and NOAA ESRL aerosol network monitoring sites over a nearly four-year period (June 2012 thru February 2016) are used, along with satellite-based surface reflectance measurements, to study the seasonal variability of diurnally averaged clear sky aerosol direct radiative effect (DRE) and radiative efficiency (RE) at the top-of-atmosphere (TOA) and at the surface. Aerosol chemistry and loading at the Appalachian State site are likely representative of the background southeast U.S. (SE U.S.), home to high summertime aerosol loading and one of only a few regions not to have warmed during the 20th century. This study is the first multi-year ground truth DRE study in the SE U.S., using aerosol network data products that are often used to validate satellite-based aerosol retrievals. The study is also the first in the SE U.S. to quantify DRE uncertainties and sensitivities to aerosol optical properties and surface reflectance, including their seasonal dependence. Median DRE for the study period is −2.9 W m−2 at the TOA and −6.1 Wm−2 at the surface. Monthly median and monthly mean DRE at the TOA (surface) are −1 to −2 W m−2 (−2 to −3 W m−2) during winter months and −5 to −6 W m−2 (−10 W m−2) during summer months. The DRE cycles follow the annual cycle of aerosol optical depth (AOD), which is 9 to 10 times larger in summer than in winter. Aerosol RE is anti-correlated with DRE, with winter values 1.5 to 2 times more negative than summer values. Due to the large seasonal dependence of aerosol DRE and RE, we quantify the sensitivity of DRE to aerosol optical properties and surface reflectance, using a calendar day representative of each season (21 December for winter; 21 March for spring, 21 June for summer, and 21 September for fall). We use these sensitivities along with measurement uncertainties of aerosol optical properties and surface reflectance to calculate DRE uncertainties. Aerosol DRE at both the TOA and surface is most sensitive to changes in AOD, followed (in order) by single-scattering albedo (ω0), scattering asymmetry parameter (g), and surface reflectance (R). One exception is under the high summertime aerosol loading conditions, when sensitivity of TOA DRE to ω0 is comparable to that of AOD. While DRE sensitivity to AOD varies by only ~ 25 to 30 % with season, DRE sensitivity to ω0, g, and R vary by factors of 10 to 20 with season. Since the measurement uncertainties of AOD, ω0, g, and R are comparable at Appalachian State, their relative contributions to DRE uncertainty are roughly proportional to their (seasonally dependent) DRE sensitivity values, which suggests that the seasonal dependence of DRE uncertainty must be accounted for. Clear sky aerosol DRE uncertainty at the TOA (surface) ranges from 0.44 W m−2 (0.73 W m−2) for December to 0.90 W m−2 (1.3 W m−2) for June. Expressed as a fraction of DRE computed using monthly median aerosol optical properties and surface reflectance, the DRE uncertainties at TOA (surface) are 16 to 20 % (12 to 20 %) for March, June, and September and 48 % (49 %) for December. The relatively low DRE uncertainties are largely due to the low uncertainty in AOD measured by AERONET. Use of satellite-based AOD measurements by MODIS in the DRE calculations increases DRE uncertainties by a factor of 2.5 to 5 and DRE uncertainties are dominated by AOD uncertainty for all seasons.

scholarly journals Vertical profiles of aerosol optical properties and the solar heating rate estimated by combining sky radiometer and lidar measurements

2016 ◽  
Vol 9 (7) ◽  
pp. 3223-3243 ◽  
Author(s):  
Rei Kudo ◽  
Tomoaki Nishizawa ◽  
Toshinori Aoyagi
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Heating Rate ◽  
Extinction Coefficient ◽  
Single Scattering ◽  
Solar Heating ◽  
Asymmetry Factor ◽  
Vertical Profiles ◽  
Aerosol Optical Properties ◽  
Lidar Measurements

Abstract. The SKYLIDAR algorithm was developed to estimate vertical profiles of aerosol optical properties from sky radiometer (SKYNET) and lidar (AD-Net) measurements. The solar heating rate was also estimated from the SKYLIDAR retrievals. The algorithm consists of two retrieval steps: (1) columnar properties are retrieved from the sky radiometer measurements and the vertically mean depolarization ratio obtained from the lidar measurements and (2) vertical profiles are retrieved from the lidar measurements and the results of the first step. The derived parameters are the vertical profiles of the size distribution, refractive index (real and imaginary parts), extinction coefficient, single-scattering albedo, and asymmetry factor. Sensitivity tests were conducted by applying the SKYLIDAR algorithm to the simulated sky radiometer and lidar data for vertical profiles of three different aerosols, continental average, transported dust, and pollution aerosols. The vertical profiles of the size distribution, extinction coefficient, and asymmetry factor were well estimated in all cases. The vertical profiles of the refractive index and single-scattering albedo of transported dust, but not those of transported pollution aerosol, were well estimated. To demonstrate the performance and validity of the SKYLIDAR algorithm, we applied the SKYLIDAR algorithm to the actual measurements at Tsukuba, Japan. The detailed vertical structures of the aerosol optical properties and solar heating rate of transported dust and smoke were investigated. Examination of the relationship between the solar heating rate and the aerosol optical properties showed that the vertical profile of the asymmetry factor played an important role in creating vertical variation in the solar heating rate. We then compared the columnar optical properties retrieved with the SKYLIDAR algorithm to those produced with the more established scheme SKYRAD.PACK, and the surface solar irradiance calculated from the SKYLIDAR retrievals was compared with pyranometer measurement. The results showed good agreements: the columnar values of the SKYLIDAR retrievals agreed with reliable SKYRAD.PACK retrievals, and the SKYLIDAR retrievals were sufficiently accurate to evaluate the surface solar irradiance.

scholarly journals Aerosol optical properties determined from sky-radiometer over Loess Plateau of Northwest China

2011 ◽  
Vol 11 (8) ◽  
pp. 23883-23910 ◽  
Author(s):  
Y. Liu ◽  
J. Huang ◽  
G. Shi ◽  
T. Takamura ◽  
P. Khatri ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Northwest China ◽  
Single Scattering ◽  
Asymmetry Factor ◽  
Dust Event ◽  
Aerosol Optical Properties ◽  
Surface Solar Radiation ◽  
Outbreak Period ◽  
Dust Events

Abstract. The aerosol optical properties and their associated radiative forcing are retrieved from sky-radiometer and surface solar radiation data collected over the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) for the period of March to May (MAM) 2009. The result shows that the seasonal mean aerosol optical depth (AOD) at 500 nm in MAM is 0.4. The single scattering albedo (SSA) at 500 nm in MAM at SACOL fluctuates significantly ranging from 0.82 to 0.97. The averaged value of SSA there for background aerosol is 0.92 in MAM, while it is smaller (0.89) during the dust event outbreak period. The smaller SSA can be interpreted as the result of larger particles during dust events. The averaged asymmetry factor (ASY) at 500 nm during dust event period is 0.81, which is much larger than 0.68 of background aerosols. The averaged shortwave radiative effect of the aerosols during dust event period in MAM is −6.25, −86.33 and 80.08 wm−2, respectively, at the top of the atmosphere (TOA), surface and in the atmosphere. The aerosols heat the atmosphere during dust event period by up to 2 K day−1 (daily averaged), which is 67 % larger than the heating (1.2 K day−1) of background aerosols. The significant heating effect in the atmosphere of the aerosols during dust event is determined by larger AOD and smaller SSA.

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

2006 ◽  
Vol 6 (3) ◽  
pp. 715-727 ◽  
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., 2006) 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 initialised 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 causes 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; long lasting BB aerosol episodes with large AOD are observed mainly in July and August, the driest months of the year, when the development of fires is frequent.

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