627 research outputs found
Methodologies to obtain aerosol property profiles from three-wavelength elastic lidar signals
No full textThe Lidar/Radiometer Inversion Code (LIRIC) and the Constrained Iterative Inversion (CII) procedure combined with a graphical aerosol classification framework (GF) have been used to analyse their ability in characterizing the altitude dependence of aerosol properties and evaluate their benefits and weaknesses. LIRIC and the CII technique rely on elastic lidar signals at 355, 532, and 1064 nm and collocated Aerosol Robotic Network (AERONET) Sun/sky photometer measurements to retrieve aerosol parameter profiles at the lidar wavelengths. The aerosol GF relies on the combined analysis of the Ångström exponent at the wavelength pairs 355 and 1064 nm (A(355, 1064)) and its spectral curvature (ΔA = A(355, 532) – A(532, 1064)) to estimate the fine-modal radius and the 532 nm fine-mode fraction. The application of the LIRIC and CII-GF techniques to three selected case studies representative of Central Mediterranean aerosol scenarios has revealed that the differences between the aerosol products from LIRIC and the corresponding ones from the CII-GF procedure varied with altitude, increased with the lidar wavelength decrease, and were significantly large when aerosol from different sources and/or from different advection routes was located at the altitudes sounded by the lidar. The plot on the aerosol GF of A(355, 1064) versus the spectral curvature has indicated that the LIRIC constraint that the fine-modal radius is height independent may represent a weakness if aerosol types and hence aerosol size distributions vary with altitude. The use of lidar ratios (LRs) constant with altitude could represent one of the main weaknesses of the CII-GF technique. The combined use of both techniques should allow obtaining a better characterization of the altitude dependence of aerosol properties from three-wavelength elastic lidar signals
Mediterranean aerosol typing by integrating three-wavelength lidar and sun photometer measurements
No full textBackscatter lidar measurements at 355, 532, and 1064 nm combined with aerosol optical thicknesses (AOTs) from sun photometer measurements collocated in space and time were used to retrieve the vertical profiles of intensive and extensive aerosol parameters. Then, the vertical profiles of the Ångström coefficients for different wavelength pairs (Å(λ1, λ2, z)), the color ratio (CR(z)), the fine mode fraction (η(z)) at 532 nm, and the fine modal radius (R f (z)), which represent aerosol characteristic properties independent from the aerosol load, were used for typing the aerosol over the Central Mediterranean. The ability of the Ångström coefficients to identify the main aerosol types affecting the Central Mediterranean with the support of the backward trajectory analysis was first demonstrated. Three main aerosol types, which were designed as continental-polluted (CP), marine-polluted (MP), and desert-polluted (DP), were identified. We found that both the variability range and the vertical profile structure of the tested aerosol intensive parameters varied with the aerosol type. The variability range and the altitude dependence of the aerosol extinction coefficients at 355, 532, and 1064 nm, respectively, also varied with the identified aerosol types even if they are extensive aerosol parameters. DP, MP, and CP aerosols were characterized by the Å(532, 1064 nm) mean values ± 1 standard deviation equal to 0.5 ± 0.2, 1.1 ± 0.2, 1.6 ± 0.2, respectively. η(%) mean values ± 1SD were equal to 50 ± 10, 73 ± 7, and 86 ± 6 for DP, MP, and CP aerosols, respectively. The R f and CR mean values ± 1SD were equal to 0.16 ± 0.05 μm and 1.3 ± 0.3, respectively, for DP aerosols; to 0.12 ± 0.03 μm and 1.8 ± 0.4, respectively, for MP aerosols; and to 0.11 ± 0.02 μm and 1.7 ± 0.4, respectively, for CP aerosols. CP and DP aerosols were on average responsible for greater AOT and LR values, but the LR and AOT dependence on wavelength was stronger for CP than for DP aerosols. The plots of the lidar ratio values at 355 nm versus the mean columnar values of the 532-1064 nm Ångström coefficient (Å c), the fine mode radius, the fine mode fraction at 532 nm (η c), and the color ratio, respectively, furthermore revealed the greater ability of the Å c and η c values to characterize different aerosol types
Lidar and in situ observations of aerosols, radiation fluxes, and meteorological parameters during the 20 March 2015 solar eclipse over southern Italy
No full textIrradiance Impact on Pollution by Integrating Nephelometer Measurements
No full textThree-wavelength integrating nephelometer measurements combined with short- (SW) and long-wave (LW) irradiance measurements were used to investigate the irradiance effects on the daily evolution of the particulate matter (PM) at the ground level, and contribute to the characterization of the land–atmosphere interaction in pollution dispersal. The integrating nephelometer measurements have allowed characterizing the daily changes of the PM optical and microphysical properties by the aerosol scattering coefficient (σp) and the scattering Ångström coefficient (å). We found that on a daily basis σp reached the minimum values when the irradiance reached the maximum values, since the convective motions, which favor the particle dispersion at the surface, increase with the irradiance. The å value, which is commonly used as qualitative indicator of the dominant particle size, has allowed evaluating the irradiance effects on the mean particle size distribution at the surface and revealed that the irradiance increase favors mainly the dispersion of the ground-level fine particles. Particle size-distribution measurements supported the last comment. Measurements were performed from 4 to 10 May 2015 when the study site was affected by a Saharan dust outbreak, to also evaluate the impact of long-range transported particles on the daily evolution of the ground-level particle’s properties and the SW and LW irradiance
Application of MODIS Products for Air Quality Studies Over Southeastern Italy
No full textAerosol optical thicknesses (AOTs) by the MODerate Resolution Imaging Spetroradiometer (MODIS) on-board Aqua and Terra satellites, and ground-based measurements of PM10 mass concentrations, collected over three years (2006–2008) at two suburban sites which are 20 km apart, are correlated to assess the use of satellite data for regional air quality studies over Southeastern Italy, in the central Mediterranean. Due to the geographical location, this area is affected by local and long-range transported marine, desert (from Sahara), and anthropogenic (from continental Europe) aerosols. 24-hour averaged PM10 mass concentrations span the 1.6–152 µg/m 3 range. Yearly means of PM10 mass concentrations decrease from 2006 to 2008 and vary within the 26–36 µg/m 3 range. Daily mean values of MODIS AOTs vary up to 0.8 at 550 nm, while yearly means span the 0.15–0.17 range. A first assessment of the regression relationship between daily averaged PM10 mass concentrations and MODIS-AOTs shows that linear correlation coefficients ( R ) vary within the 0.20–0.35 range and are affected by the sampling year and the site location. The PM10-AOT correlation becomes stronger (0.34 ≤ R ≤ 0.57) when the analysis is restricted to clear-sky MODIS measurements. The cloud screening procedure adopted within the AERONET network is used in this study to select clear-sky MODIS measurements, since it allows obtaining larger R values than the ones obtained using the cloud fraction MODIS product to select clear-sky MODIS measurements. Using three years of clear-sky measurements to estimate PM10 mass concentrations from MODIS-AOTs, the empirical relation we have found is: PM10 ( m g/m 3 ) = 25 ( m g/m 3 ) + 65 ( m g/m 3 ) × AOT. Over 80% of the differences between the measured and satellite estimated PM10 mass concentrations over the three years are within ±1 standard deviation of the yearly means. The differences between yearly means of calculated and measured mass concentrations that are close to zero in 2006, increase up to 4 m g/m 3 at one siteand 8 m g/m 3 at the other site in 2008. The PM10 mass concentration decrease from 2006 to 2008 contributes to this last result. Our results demonstrate the potential of MODIS data for deriving indirect estimates of PM10 over Southeastern Italy. It is also shown that a stronger relationship between PM10 and MODIS-AOTs is obtained when the AOT is divided by the product of the mixing layer height with the ground wind speed and the analysis restricted to clear sky MODIS measurements. However, we have found that the stronger correlation (0.52 ≤ R ≤ 0.66) does not allow a significant improvement of MODIS-based-estimates of PM10 mass concentrations
Experimental determination of short- and long-wave dust radiative effects in the Central Mediterranean and comparison with model results
No full textDownward and upward irradiance measurements, in the short-wave (SW) and long-wave (LW) spectral range, have been used in combination with simultaneous aerosol optical depths (AODs) to experimentally determine the instantaneous and clear-sky aerosol Direct Radiative Forcing (DRF) at the surface, during a desert dust outbreak which affected the Central Mediterranean from 9 to 13 July 2012. AODs were retrieved from AERONET (AErosol RObotic NETwork) sun/sky photometer measurements collocated in space and time. The importance of downward and upward radiative flux measurements to properly account for both the surface albedo dependence on the solar zenith angle, and the land surface temperature (T-Ls) has been highlighted. Measured radiative fluxes were in reasonable agreement with the CERES (Clouds and the Earth's Radiant Energy System) and AERONET corresponding ones collocated in space and time. SW and LW downward fluxes at the surface decreased up to 9% and increased up to 13%, respectively, as a consequence of a factor 5 increase of the AOD at 675 nm (AOD(675)). This is due to the cooling and warming effect of desert dust in the SW and LW spectral range, respectively. In fact, we have also found that the T-Ls increased at a rate of about 250 K per unit increase of the AOD(675). The aerosol DRF at the surface varied from -8 to -74 W m(-2) and from +1.2 to +9.6 W m(-2) in the SW and LW spectral domains, respectively. In particular, we have found that the LW-DRF on average offsets 14% of the related SW component. It is shown that a two-stream radiative transfer model can reproduce the experimental findings at the surface by replacing the refractive indices typical of dust particles with the ones obtained for a mixture made of dust and soot particles. The dust contamination by anthropogenic particles during its transport to the monitoring site located several hundred kilometers away from the source region was responsible for this last result. We have also found by model simulations that the LW-DRF increased linearly with T-Ls both at the surface and at the top of the atmosphere
Profiling of fine- and coarse-mode particles with LIRIC (LIdar/Radiometer Inversion Code)
No full textThe paper investigates numerical procedures that allow determining the dependence
on altitude of aerosol properties from multi wavelength elastic lidar signals. In particular,
the potential of the LIdar/Radiometer Inversion Code (LIRIC) to retrieve the ver-
5 tical profiles of fine and coarse-mode particles by combining 3-wavelength lidar measurements
and collocated AERONET (AErosol RObotic NETwork) sun/sky photometer
measurements is investigated
Aerosol Products by CALIOP at 532 nm and by a ground-based Raman lidar at 355 nm: Intercomparison methodology
No full textEstimation of mineral dust direct radiative forcing at the European Aerosol Research Lidar NETwork site of Lecce, Italy, during the ChArMEx/ADRIMED summer 2013 campaign: Impact of radiative transfer model spectral resolutions
No full textA field campaign took place in the western and central Mediterranean basin on June–July 2013 in the framework of the ChArMEx (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr/)/ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region, http://adrimed.sedoo.fr/) project to characterize the aerosol direct radiative forcing (DRF) over the Mediterranean. This work focuses on the aerosol DRF estimations at Lecce (40.33°N; 18.11°E; 30 m above sea level) during the Saharan dust outbreak that affected southern Italy from 20 to 24 June 2013. The Global Atmospheric Model (GAME) and the Two-Stream (TS) model were used to calculate the instantaneous aerosol DRF in the short-wave (SW) and long-wave (LW) spectral ranges, at the surface and at the top of the atmosphere (TOA). The main differences between the two models were due to the different numerical methods to solve the radiative transfer (RT) equations and to the more detailed spectral resolution of GAME compared to that of TS. 167 and 115 subbands were used by GAME in the 0.3–4 and 4–37 μm spectral ranges, respectively. Conversely, the TS model used 8 and 11 subbands in the same spectral ranges, respectively. We found on 22 June that the SW-DRFs from the two models were in good agreement, both at the TOA and at the surface. The instantaneous SW-DRFs at the surface and at the TOA varied from −50 to −34 W m−2 and from −6 to +8 W m−2, respectively, while the surface and TOA LW-DRFs ranged between +3.5 and +8.0 W m−2 and between +1.7 and +6.9 W m−2, respectively. In particular, both models provided positive TOA SW-DRFs at solar zenith angles smaller than 25° because of the mixing of the desert dust with anthropogenic pollution during its transport to the study site. In contrast, the TS model overestimated the GAME LW-DRF up to about 5 and 7.5 times at the surface and at the TOA, respectively, when the dust particle contribution was largest. The low spectral resolution of the real (n) and imaginary (k) refractive index values was mainly responsible for the LW-DRF overestimates of the TS model. However, we found that the “optimization” of the n and k values at 8.75 and 11.5 μm was sufficient in this study to obtain a satisfactory agreement between the LW-DRFs from the two models, both at the TOA and at the surface. The impact of the spectral dependence of the water vapor absorption coefficients on the estimation of the flux without aerosol has also been addressed. Paper results did not reveal any significant impact due to the different numerical methods used by the two models to solve the RT equations
Saharan dust impact on the chemical composition of PM10 and PM1 samples over south-eastern Italy
No full textAbstract Angström exponents (Å) and dust concentrations from the Barcelona Supercomputing Center-Dust REgional Atmospheric Model (BSC-DREAM) were used to infer the
impact of long-range transported desert dust particles at the ground level and evaluate their role on the chemical composition of PM1 and PM10 samples. Å values were calculated
from the scattering coefficients at 450 and 635 nm, retrieved from integrating nephelometer measurements. Nephelometer measurements were performed at a coastal site (Lecce, 40.33° N, 18.11° E) of south-eastern Italy from December 2011 till November 2012. Days characterized by Å daily mean values smaller than 0.95 and modelled daily dust concentrations larger than 0.1 μg m−3 at 86 m above the ground level were considered representative of days affected by African dust particles up to the ground level (dusty days). Both criteria have allowed identifying 86 dusty days during the investigated period. The analysis of 24-h simultaneously collected PM10 and PM1 samples revealed that the PM1 mass concentrations increased linearly with PM10 both in dusty and dustfree days, which were identified as the ones characterized by Å daily mean values larger than 1.3 and PM1/PM10 ratios larger than 0.35. These results suggested that the PM1 samples were also affected by desert particles on dusty days. In fact, chemical analyses revealed that the Al and Fe mean mass concentrations were larger in dusty day PM1 and PM10 samples. Then, we found that the crustal matter contribution was nearly twice and more than twice larger in dusty PM1 and PM10 samples, respectively, than in corresponding dust-free samples. Mass contributions of organic and elemental carbon, sulfates, and ammonium even if smaller in dusty samples than in dust-free PM1 and PM10 samples revealed the significant role of the anthropogenic pollution also on dusty days
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