AERONET Sun-photometer Measurements Research Articles

Aerosol Characterization with Long-Term AERONET Sun-Photometer Measurements in the Naples Mediterranean Area

We report on the characterization of columnar aerosol optical and microphysical properties in the Naples Mediterranean area over a period of five years by the ground-based sun–sky–lunar photometer operating at our observational station in the frame of the AERONET network. Statistical and climatological analyses of daily mean values of aerosol optical depth at 440 nm (AOD440) and Ångström exponent at 440/870 nm (α440/870) allowed for highlighting their typical seasonal behavior. In particular, we observe higher mean values of the AOD440 during summer or spring, which are consistent with an increased frequency of both Saharan dust transport events and biomass burning episodes affecting the measurement area in these periods of the year. Conversely, α440/870 does not show any typical seasonal trend. In order to gain information on the different aerosol contributions along the atmospheric column, the frequency distributions of AOD440 and α440/870 were analyzed and fitted by a superposition of Gaussian functions. The most populated modes are centered at α440/870 = 1.26 ± 0.07 and AOD440 = 0.16 ± 0.01. These values are associated with continental polluted aerosol mixed with sea salt aerosol and correspond to the background conditions typically observed in clear atmospheric conditions. Daily size distributions averaged over each month highlight that the fine aerosol component always prevails over the coarse fraction, except for the few months in which Saharan dust events are particularly frequent. Finally, the mean value of the SSA at 440 nm resulted as 0.94 ± 0.05, while the refractive index real and imaginary part were 1.47 ± 0.07 and (6.5 ± 0.2) × 10−3, respectively. These values are in agreement with those observed in other Mediterranean sites located in Southern Italy, evidencing a rather characteristic feature of the geographical region.

Characterization of forest fire and Saharan desert dust aerosols over south-western Europe using a multi-wavelength Raman lidar and Sun-photometer

In the morning of 21 July 2019, a dense forest fire smoke plume was detected over Évora (Portugal) in the lower troposphere. Around 13:00 UTC, a Sahara dust layer was detected by lidar between 3000 and 4000 m height above sea level. In this work results of these events using an EARLINET Raman lidar and AERONET Sun-photometer measurements are reported and discussed: the dense smoke layer, the mixing of smoke with dust and the lofted dust layer that crossed Évora. During the morning, in-situ hourly mean black carbon concentration reached a maximum of 6.28 ± 0.73 μgm−3. The AERONET fine mode aerosol optical depth at 500 nm reached 0.77 and the Ångström exponent at 440–870 nm varied between 1.45 and 1.82, indicating the presence of fine smoke particles in the atmospheric column. In the beginning of the afternoon, the lidar profiles indicated the presence of a smoke layer followed by two thin layers of pollution mixed with dust and a lofted dust layer. The smoke particles caused low particle linear depolarization ratios at 532 nm with mean value of 0.059 ± 0.002 in the smoke layer. In contrast, the lofted dust layer caused mean particle linear depolarization ratio at 532 nm of 0.26 ± 0.01. Mass concentrations were in the order of 22–29 μg m−3 in the smoke layer and 60–178 μg m−3 in the lofted dust layer. During the afternoon and at night, mixing dust layers were identified by using lidar data. In the afternoon, two aerosol layers exhibited mean particle linear depolarization ratios at 532 nm of 0.23 ± 0.01 and 0.25 ± 0.01 with the dust dominating the extinction and mass concentration in both aerosol layers. Mass concentrations of dust were in the order of 101–266 μg m−3 and 159–195 μg m−3. At night, the particle linear depolarization ratio presented low variability across the identified layer with mean value of 0.20 ± 0.01. The Ångström exponents were low, the mean lidar ratios were 50 ± 6 sr (355 nm) and 42 ± 4 sr (532 nm) and the aerosol optical depth was 0.32 (355 nm) and 0.30 (532 nm). Mass concentrations ranged in 10–28 μg m−3 for non-dust and in 77–186 μg m−3 for dust.

Multi-year analysis of aerosol optical properties and implications to radiative forcing over urban Pretoria, South Africa

The present study focused on investigating the aerosol optical properties and direct aerosol radiative forcing (DARF) using the AERONET Sunphotometer measurements conducted during 2011–2017 over an urban-industrial city, Pretoria (25.75° S, 28.28° E) located in the Northwest of South Africa (SA). Results revealed high aerosol optical depth (AOD440) and Angstrom exponent (AE440–870) during SON (0.28 ± 0.09, 1.46 ± 0.16) and DJF (0.24 ± 0.07, 1.48 ± 0.18) indicating the dominance of anthropogenic fine-mode aerosols from biomass burning. The single scattering albedo (SSA440) reached a maximum of 0.90 ± 0.05 in DJF and minimum (0.85 ± 0.04) during JJA. The source analysis from the concentration-weighted trajectory (CWT) model exhibited large heterogeneity in all seasons. However, the region is influenced by distinct aerosol types with the abundance of anthropogenic fine absorbing aerosols (86%) and the invisible ratio of dust particles. In addition, the aerosol volume size distribution (VSD) increased with an increasing AOD, exhibiting a bimodal lognormal structure, with a more pronounced peak in fine- relative to coarse-mode particles. Further, the inversion products showed a strong spectral dependence in SSA with substantial heterogeneity in all seasons. At last, the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model showed that the DARF within the atmosphere was more pronounced during SON (46.71 W m−2) and JJA (46.39 W m−2) due to significant differences in AOD and SSA, with an annual mean value of 33.16 W m−2, and the corresponding atmospheric heating rate of 0.96 K day−1. The study provides information on the existing aerosol distribution and their potential impact on climatic change over an urban city in the Northwest of SA and could form a basis for policymaking over the region.

Analysis of Radiative Properties and Direct Radiative Forcing Estimates of Dominant Aerosol Clusters over an Urban-Desert Region in West Africa

ABSTRACT The strategic location of the AERONET site in Ilorin, Nigeria, makes it possible to obtain information on several aerosol types and their radiative effects. The strong reversal of wind direction occasioned by the movement of the ITCZ during the West Africa Monsoon (WAM) plays a major role in the variability of aerosol nature at this site, which is confirmed by aerosol optical depth (AOD) (675 nm) and Angstrom exponent (AE) (440–870 nm) values with 1st and 99th percentile values of 0.08 and 2.16, and 0.11 and 1.47, respectively. The direct radiative forcing (DRF) and radiative forcing efficiency (RFE) of aerosol, as retrieved from the AERONET sun-photometer measurements, are estimated using radiative transfer calculations for the periods of 2005–2009 and 2011–2015. The DRF and RFE of the dominant aerosol classes—desert dust (DD), biomass burning (BB), urban (UB) and gas flaring (GF)—have been estimated. The median (± standard deviation) values of the DRF at the top of the atmosphere (TOA) for the DD, BB, UB and GF aerosol classes are –27.5 ± 13.2 Wm–2, –27.1 ± 8.3 Wm–2, –11.5 ± 13.2 Wm–2 and –9.6 ± 8.0 Wm–2, respectively, while those of the RFE are –26.2 ± 4.1 Wm–2 δ–1, –35.2 ± 4.6 Wm–2 δ–1, –31.0 ± 8.4 Wm–2 δ–1 and –37.0 ± 10.3 Wm–2 δ–1, respectively. Arguably due to its high SSA and assymetric values, the DD aerosol class shows the largest DRF but the smallest RFE. Its smallest AOD notwithstanding, the GF class can cause greater perturbation of the earth-atmosphere system in the sub-region both directly and indirectly, possibly due to the presence of black carbon and other co-emitted aerosol and the ageing of the GF aerosols. This study presents the first estimate of DRF for aerosols of gas flaring origin and shows that its radiative potential can be similar in magnitude to that of biomass burning and urban aerosol in West Africa.

Aerosol Properties over Southeastern China from Multi-Wavelength Raman and Depolarization Lidar Measurements

A dataset of particle optical properties of highly polluted urban aerosol over the Pearl River Delta, Guangzhou, China is presented. The data were derived from multi-wavelengths Raman and depolarization lidar Polly XT and AERONET sun photometer measurements. The measurement campaign was conducted from Nov 2011 to June 2012. High aerosol optical depth was observed in the polluted atmosphere over this megacity, with a mean value of 0.54 ± 0.33 and a peak value of even 1.9. For the particle characterization the lidar ratio and the linear particle depolarization ratio, both at 532 nm, were used. The mean values of these properties are 48.0 sr ± 10.7 sr for the lidar ratio and 4%+-4% for the particle depolarization ratio, which means most depolarization measurements stayed below 10%. So far, most of these results indicate urban pollution particles mixed with particles arisen from biomass and industrial burning.

Synergy of multispectral and multisensors satellite observations to evaluate desert aerosol transport and impact of dust deposition on inland waters: study case of Lake Garda

The capabilities of different Earth Observation multispectral satellites are employed for detecting and tracking of desert dust coming from North Africa toward the Northern Italy area and for evaluating the impact of Saharan dust deposition in inland waters, such as those of Lake Garda. Absorbing and scattering spectral optical properties of desert aerosol in the atmospheric windows in the ultraviolet, visible-near-infrared, and infrared spectral ranges are exploited in the dust retrieval performed by OMI/Aura, MODIS/Terra-Aqua, and SEVIRI/MSG satellite sensors. Therefore, the direct link between dust deposition and increase in phytoplankton abundance has been assessed retrieving MERIS-based chlorophyll-a (chl-a) concentration for the desert dust events. Estimates of the increased chl-a in the lake have been derived with values in concentration from 30% to 170%. AERONET sun-photometer measurements, gravimetric particulate matter samplings, <italic<in situ</italic< chl-a concentration and surface temperature are employed to select events and assess the presence of desert dust and recognize a corresponding increase of the phytoplankton abundance in the analyzed inland waters. The improved observational features that will be provided by the next European Sentinels missions, namely Sentinel-2, 3, 4, 5P, together with MTG-I (Imager) and MTG-S (Sounder) will allow better monitoring atmospheric constituents and studying the environmental impacts of desert dust transport.

Assessment of CALIPSO attenuated backscatter and aerosol retrievals with a combined ground-based multi-wavelength lidar and sunphotometer measurement

CALIPSO Level-1 attenuated backscatter and Level-2 aerosol products (Version-3.01) are evaluated with a combined ground-based lidar and AERONET-sunphotometer measurements in the daytime over the New York metropolitan area. To assess the CALIPSO Level-1 product, we combine the co-located ground-lidar and sunphotometer to derive aerosol extinction and backscatter profiles, and then simulate the CALIPSO equivalent attenuated backscatter coefficients. Direct statistical comparisons show a strong correlation (R = 0.92) and modest relative errors. Both dust and smoke plume events are focused to evaluate CALIPSO Level-2 aerosol layer products. The CALIPSO algorithms for cloud-aerosol discrimination and aerosol type classification are shown for the most part to work well, with a few exceptions in cases of aloft plumes with high aerosol loading. Small partitions of dense smoke are misclassified as the clouds or polluted dusts in the CALIPSO product. The aerosol extinction and backscatter coefficients are generally consistent between the CALIPSO and ground-based retrievals, but both geometric thickness and column optical depths of aerosol layers from CALIPSO products are underestimated. In addition, we find that some weakly scattering aerosol layers are clearly displayed by the ground-based lidar, but not identified by the current CALIPSO algorithm due to the detection sensitivity issue.

An update on polar aerosol optical properties using POLAR-AOD and other measurements performed during the International Polar Year

An updated set of time series of derived aerosol optical depth (AOD) and Ångström’s exponent α from a number of Arctic and Antarctic stations was analyzed to determine the long-term variations of these two parameters. The Arctic measurements were performed at Ny-Ålesund (1991–2010), Barrow (1977–2010) and some Siberian sites (1981–1991). The data were integrated with Level 2.0 AERONET sun-photometer measurements recorded at Hornsund, Svalbard, and Barrow for recent years, and at Tiksi for the summer 2010. The Antarctic data-set comprises sun-photometer measurements performed at Mirny (1982–2009), Neumayer (1991–2004), and Terra Nova Bay (1987–2005), and at South Pole (1977–2010). Analyses of daily mean AOD were made in the Arctic by (i) adjusting values to eliminate volcanic effects due to the El Chichón, Pinatubo, Kasatochi and Sarychev eruptions, and (ii) selecting the summer background aerosol data from those affected by forest fire smoke. Nearly null values of the long-term variation of summer background AOD were obtained at Ny-Ålesund (1991–2010) and at Barrow (1977–2010). No evidence of important variations in AOD was found when comparing the monthly mean values of AOD measured at Tiksi in summer 2010 with those derived from multi-filter actinometer measurements performed in the late 1980s at some Siberian sites. The long-term variations of seasonal mean AOD for Arctic Haze (AH) conditions and AH episode seasonal frequency were also evaluated, finding that these parameters underwent large fluctuations over the 35-year period at Ny-Ålesund and Barrow, without presenting well-defined long-term variations. A characterization of chemical composition, complex refractive index and single scattering albedo of ground-level aerosol polydispersions in summer and winter–spring is also presented, based on results mainly found in the literature. The long-term variation in Antarctic AOD was estimated to be stable, within ±0.10% per year, at the three coastal sites, and nearly null at South Pole, where a weak increase was only recently observed, associated with an appreciable decrease in α, plausibly due to the formation of thin stratospheric layers of ageing volcanic particles. The main characteristics of chemical composition, complex refractive index and single scattering albedo of Antarctic aerosols are also presented for coastal particles sampled at Neumayer and Terra Nova Bay, and continental particles at South Pole.

Observation operator for the assimilation of aerosol type resolving satellite measurements into a chemical transport model

Abstract. Modelling of aerosol particles with chemical transport models is still based mainly on static emission databases while episodic emissions cannot be treated sufficiently. To overcome this situation, a coupling of chemical mass concentration modelling with satellite-based measurements relying on physical and optical principles has been developed. This study deals with the observation operator for a component-wise assimilation of satellite measurements. It treats aerosol particles classified into water soluble, water insoluble, soot, sea salt and mineral dust containing aerosol particles in the atmospheric boundary layer as separately assimilated aerosol components. It builds on a mapping of aerosol classes used both in observation and model space taking their optical and chemical properties into account. Refractive indices for primary organic carbon particles, anthropogenic particles, and secondary organic species have been defined based on a literature review. Together with a treatment of different size distributions in observations and model state, this allows transforming the background from mass concentrations into aerosol optical depths. A two-dimensional, variational assimilation is applied for component-wise aerosol optical depths. Error covariance matrices are defined based on a validation against AERONET sun photometer measurements. Analysis fields are assessed threefold: (1) through validation against AERONET especially in Saharan dust outbreak situations, (2) through comparison with the British Black Smoke and Sulphur Dioxide Network for soot-containing particles, and (3) through comparison with measurements of the water soluble components SO4, NH4, and NO3 conducted by the EMEP (European Monitoring and Evaluation Programme) network. Separately, for the water soluble, the soot and the mineral dust aerosol components a bias reduction and subsequent a root mean square error reduction is observed in the analysis for a test period from July to November 2003. Additionally, examples of an improved analysis during wildfire and dust outbreak situations are shown.

Global evaluation of the Collection 5 MODIS dark-target aerosol products over land

Abstract. NASA's MODIS sensors have been observing the Earth from polar orbit, from Terra since early 2000 and from Aqua since mid 2002. We have applied a consistent retrieval and processing algorithm to both sensors to derive the Collection 5 (C005) dark-target aerosol products over land. Here, we validate the MODIS along-orbit Level 2 products by comparing to quality assured Level 2 AERONET sunphotometer measurements at over 300 sites. From 85 463 collocations, representing mutually cloud-free conditions, we find that &gt;66% (one standard deviation) of MODIS-retrieved aerosol optical depth (AOD) values compare to AERONET-observed values within an expected error (EE) envelope of ±(0.05 + 15%), with high correlation (R = 0.9). Thus, the MODIS AOD product is validated and quantitative. However, even though we can define EEs for MODIS-reported Ångström exponent and fine AOD over land, these products do not have similar physical validity. Although validated globally, MODIS-retrieved AOD does not fall within the EE envelope everywhere. We characterize some of the residual biases that are related to specific aerosol conditions, observation geometry, and/or surface properties, and relate them to situations where particular MODIS algorithm assumptions are violated. Both Terra's and Aqua's–retrieved AOD are similarly comparable to AERONET, however, Terra's global AOD bias changes with time, overestimating (by ~0.005) before 2004, and underestimating by similar magnitude after. This suggests how small calibration uncertainties of &lt;2% can lead to spurious conclusions about long-term aerosol trends.

Aerosol properties and associated radiative effects over Cairo (Egypt)

Cairo is one of the largest megacities in the World and the particle load of its atmosphere is known to be particularly important. In this work we aim at assessing the temporal variability of the aerosol's characteristics and the magnitude of its impacts on the transfer of solar radiation. For this we use the level 2 quality assured products obtained by inversion of the instantaneous AERONET sunphotometer measurements performed in Cairo during the Cairo Aerosol CHaracterization Experiment (CACHE), which lasted from the end of October 2004 to the end of March 2006. The analysis of the temporal variation of the aerosol's optical depth (AOD) and spectral dependence suggests that the aerosol is generally a mixture of at least 3 main components differing in composition and size. This is confirmed by the detailed analysis of the monthly-averaged size distributions and associated optical properties (single scattering albedo and asymmetry parameter). The components of the aerosol are found to be 1) a highly absorbing background aerosol produced by daily activities (traffic, industry), 2) an additional, ‘pollution’ component produced by the burning of agricultural wastes in the Nile delta, and 3) a coarse desert dust component. In July, an enhancement of the accumulation mode is observed due to the atmospheric stability favoring its building up and possibly to secondary aerosols being produced by active photochemistry. More generally, the time variability of the aerosol's characteristics is due to the combined effects of meteorological factors and seasonal production processes. Because of the large values of the AOD achieved during the desert dust and biomass burning episodes, the instantaneous aerosol radiative forcing (RF) at both the top (TOA) and bottom (BOA) of the atmosphere is maximal during these events. For instance, during the desert dust storm of April 8, 2005 RF BOA, RF TOA, and the corresponding atmospheric heating rate peaked at − 161.7 W/m 2, − 65.8 W/m 2, and 4.0 K/d, respectively. Outside these extreme events, the distributions of the radiative forcing values at BOA and TOA are Gaussian with means and standard deviations of − 58(± 27), and − 19(± 11)W/m 2, respectively. These two negative values indicate a cooling effect at the 2 atmospheric levels but the largest absolute value at BOA corresponds to a trapping of solar radiation inside the atmosphere. The averages of the instantaneous forcing efficiencies (FE) derived from measurements performed at solar zenith angles between 50 and 76° are − 195(± 42) and − 62(± 17)W/m 2.AOD 550 for BOA and TOA, respectively. The value at TOA is larger than in other urban environments, which could be due to the desert dust component backscattering more solar radiation to space than absorbing urban aerosols. The lower absorption of solar light by desert dust also explains qualitatively the lower than usual value of FE BOA. A more precise study of the effects of the desert dust and biomass burning aerosols shows that fluctuations of their monthly-averaged concentrations explain the departures of the TOA and BOA radiative forcings from the background situation. In April, the contributions of DD to the month averages of the instantaneous radiative forcing are as high as 53% at BOA, and 66% at TOA. In October, the biomass burning mode contributes 33 and 27% of these forcings, respectively. Noteworthy is that the contribution of DD to RF is never less than 17% (at BOA) and 27% (at TOA), emphasizing the importance of the mineral dust component on the transfer of solar radiation above Cairo, and this even in months when no major dust storm is observed.

Validation of the GRAPE single view aerosol retrieval for ATSR-2 and insights into the long term global AOD trend over the ocean

Abstract. The Global Retrieval of ATSR Cloud Parameters and Evaluation (GRAPE) project has produced a global data-set of cloud and aerosol properties from the Along Track Scanning Radiometer-2 (ATSR-2) instrument, covering the time period 1995–2001. This paper presents the validation of aerosol optical depths (AODs) over the ocean from this product against AERONET sun-photometer measurements, as well as a comparison to the Advanced Very High Resolution Radiometer (AVHRR) optical depth product produced by the Global Aerosol Climatology Project (GACP). The GRAPE AOD over ocean is found to be in good agreement with AERONET measurements, with a Pearson's correlation coefficient of 0.79 and a best-fit slope of 1.0±0.1, but with a positive bias of 0.08±0.04. Although the GRAPE and GACP datasets show reasonable agreement, there are significant differences. These discrepancies are explored, and suggest that the downward trend in AOD reported by GACP may arise from changes in sampling due to the orbital drift of the AVHRR instruments.

Modeling of Aerosol Vertical Profiles Using GIS and Remote Sensing

The use of Geographic Information Systems (GIS) and Remote Sensing (RS) by climatologists, environmentalists and urban planners for three dimensional modeling and visualization of the landscape is well established. However no previous study has implemented these techniques for 3D modeling of atmospheric aerosols because air quality data is traditionally measured at ground points, or from satellite images, with no vertical dimension. This study presents a prototype for modeling and visualizing aerosol vertical profiles over a 3D urban landscape in Hong Kong. The method uses a newly developed technique for the derivation of aerosol vertical profiles from AERONET sunphotometer measurements and surface visibility data, and links these to a 3D urban model. This permits automated modeling and visualization of aerosol concentrations at different atmospheric levels over the urban landscape in near-real time. Since the GIS platform permits presentation of the aerosol vertical distribution in 3D, it can be related to the built environment of the city. Examples are given of the applications of the model, including diagnosis of the relative contribution of vehicle emissions to pollution levels in the city, based on increased near-surface concentrations around weekday rush-hour times. The ability to model changes in air quality and visibility from ground level to the top of tall buildings is also demonstrated, and this has implications for energy use and environmental policies for the tall mega-cities of the future.

Saharan dust particle properties over the central Mediterranean

AERONET sun photometer measurements performed at five different sites of the Central Mediterranean during strong Saharan dust outbreaks are used to characterize optical and physical properties of dust particles. Sun photometer retrievals are combined at two of the five sites with lidar observations. It is shown that at low aerosol optical depths (AODs) the dust particle properties are quite dependent on dust load and monitoring site location. Differences on retrieved particle properties reduce with increasing dust load. AERONET retrievals at AOD (440 nm) ≥ 0.6 are then used in this paper to characterize dust particles over the central Mediterranean basin leading to columnar averaged values of the real refractive index < n > = 1.5 ± 0.1, the imaginary refractive index < k > = 0.004 ± 0.002, the single scattering albedo < SSA > = 0.89 ± 0.03, and the Angstrom exponent < Å > = 0.2 ± 0.1. It is shown that Å represents the best marker to trace the temporal evolution of dust events. Volume size distributions show a dominant coarse mode peaking at 1.7–3 μm. In particular, the average coarse mode that is centred at ≅ 2.2 μm at Lampedusa, which is ∼200 km away from the northwest Africa coast, gets peaked at ≅ 1.7 μm at Lecce, which is ∼800 km away. Lidar retrievals are used to characterize the vertical distribution of dust particles by the vertical profiles of the backscatter and extinction coefficients, the lidar ratio, and the depolarization ratio. Lidar retrievals show that over the Mediterranean basin, dust layers generally extend from 1 up to 6 km and that their vertical distribution can significantly change within a few hours. It is also shown that at high values of the AODs dust particles are characterized by lidar ratios spanning the 50–70 sr range and depolarization ratios larger than 30%.

Aerosol load characterization over South–East Italy for one year of AERONET sun-photometer measurements

Daily averaged retrievals of AERONET sun photometer measurements from March 2003 to March 2004 are used to provide preliminary results on the characterization of aerosol properties and changes over south–east Italy (40°20′N, 18°6′E). It is shown that aerosol optical and microphysical properties and the dominating aerosol types depend on seasons. Aerosol-parameter frequency distributions reveal the presence of individual modes that lead to the assumption that moderately absorbing urban–industrial and marine-polluted aerosols dominate in spring–summer and autumn–winter, respectively. It is shown that aerosol optical depths (AODs), single scattering albedos (SSAs), and Angstrom coefficients (Å) of urban–industrial (spring–summer) aerosols are characterized by lognormal distributions with peak values of 0.20±0.03, 0.94±0.01, and 1.58±0.03, respectively. On the contrary AOD, SSA and Å values of maritime-polluted (autumn–winter) aerosols are characterized by lognormal distributions with peak values of 0.049±0.008, 0.974±0.003, and 0.7±0.1, respectively. It is also shown that the frequency distribution of real n and imaginary k refractive indices permits inference of the dominant aerosol constituents: sea-salt, water soluble, soot, and mineral particles. Finally, it is shown that dust outbreaks do not significantly affect the seasonal evolution of aerosol parameters, and that sunphotometry retrievals along dust events are in satisfactory accord with experimental findings indicating that moderately-absorbing (0.005≤ k≤0.05) dust particles with a high content of illite are mainly advected over the Mediterranean basin during Sahara dust storms.

Aerosol properties from EP-TOMS near UV observations

A method of aerosol detection and characterization using satellite measured radiances in the near ultraviolet has recently been developed. The retrieval approach is based on the interaction between the processes of aerosol absorption and scattering and the strong near-UV Rayleigh scattering. That interaction produces spectral variations of the backscattered radiances that can be used to separate aerosol absorption from scattering effects. In this paper, we briefly discuss the physical basis of the near UV approach for aerosol sensing from space, and illustrate its application to specific aerosol events using data from the currently operational Total Ozone Mapping Spectrometer on the Earth Probe satellite (EP-TOMS). EP-TOMS derived optical depths of mineral, carbonaceous and sulfate aerosols are in good agreement with ground-based AERONET sun-photometer measurements.