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The space-borne CALIOP lidar data has been used to better understand the dust transport mechanism from the Mesopotamian region to the atmosphere of Zanjan, a city in the Northwest Iran Plateau. The level 2 aerosol profile data product of the CALIOP has been studied for 142 overpasses during 2006–2018. The mean values of aerosol optical depth (AOD) and particulate depolarization ratio (PDR) at 532 nm, extracted from 142 cases, are 0.23 and 0.17, respectively. Moreover, 32 dust events (23% of all) have been recorded. For these cases, the mean values of AOD and PDR reach 0.53 and 0.21, respectively. The monthly-mean values of AOD and PDR confirm previous studies that dust particles are the dominant type of aerosols in the atmosphere of Zanjan, and their concentrations are remarkably increased in dry and warm months, especially between April to August. Based on the vertical profiles of PDR and extinction coefficients, the altitude range of about 1–3.5 km AGL is the most probable range of dust layer distribution in the studied area. Also, some dust events have been studied in more detail using the CALIOP data, sunphotometer data, ECMWF and HYSPIT meteorological models, and AOD product of the MODIS. Based on the results, dust particles originated from the Tigris–Euphrates basin, rise from the surface of Mesopotamia, move eastward, pass above the Zagros Mountains (the barrier between Mesopotamia and Iran Plateau), and finally reach the atmosphere of the studied area and cause dust events. It seems that it is the most probable mechanism of dust transport to the Northwest Iran Plateau.

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) is unique in its ability to perform profiling measurements of aerosol and cloud layers globally. Detecting the layer boundaries of aerosols and clouds is a crucial step in CALIPSO data retrieval. The CALIPSO team uses the selective iterated boundary location (SIBYL) algorithm based on threshold arrays to find aerosol and cloud layers at different horizontal resolutions. However, threshold arrays could obstruct the detection of optically tenuous layers at a high resolution and may cause overestimation when averaging signals of layer and clear air at a low resolution. Here, a multiscale algorithm using a series of sliding window sizes without threshold setting is proposed based on a pre-defined probability. The results over land and marine areas show that the multiscale algorithm detected 37.41% and 16.36% more layer area than the SIBYL at 1–80 km resolutions at daytime and 1–5 km resolutions at night time, respectively. This indicates that the multiscale algorithm does not need a threshold array, allowing more tenuous layers to be detected, especially at low signal to noise ratios (SNRs). In contrast, the SIBYL detects 4.40% more layer area than the multiscale algorithm at 1–80 km resolutions at nighttime, mainly caused by the large proportion of layer area detected by SIBYL at 20 and 80 km resolutions. This implies possible noteworthy overestimation by the SIBYL at low resolutions. Additionally, the evaluation using the depolarization ratio of ice clouds shows that the extra detected layers by the multiscale algorithm are reliable. Besides, simulation tests show that the multiscale and SIBYL algorithms achieve a 100% true detection rate when SNR is approximately 2 and 4, respectively. The new multiscale algorithm could upgrade the resolution and accuracy of the layer detection of space lidars and reduce the underestimation of layer optical depth due to missing layers.

A remote sensing approach to retrieve the degree of nonsphericity of ice hydrometeors using scanning polarimetric Ka-band radar measurements from a U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program cloud radar operated in an alternate transmission–simultaneous reception mode is introduced. Nonsphericity is characterized by aspect ratios representing the ratios of particle minor-to-major dimensions. The approach is based on the use of a circular depolarization ratio (CDR) proxy reconstructed from differential reflectivity ZDR and copolar correlation coefficient ρhυ linear polarization measurements. Essentially combining information contained in ZDR and ρhυ, CDR-based retrievals of aspect ratios are fairly insensitive to hydrometeor orientation if measurements are performed at elevation angles of around 40°–50°. The suggested approach is applied to data collected using the third ARM Mobile Facility (AMF3), deployed to Oliktok Point, Alaska. Aspect ratio retrievals were also performed using ZDR measurements that are more strongly (compared to CDR) influenced by hydrometeor orientation. The results of radar-based retrievals are compared with in situ measurements from the tethered balloon system (TBS)-based video ice particle sampler and the ground-based multiangle snowflake camera. The observed ice hydrometeors were predominantly irregular-shaped ice crystals and aggregates, with aspect ratios varying between approximately 0.3 and 0.8. The retrievals assume that particle bulk density influencing (besides the particle shape) observed polarimetric variables can be deduced from the estimates of particle characteristic size. Uncertainties of CDR-based aspect ratio retrievals are estimated at about 0.1–0.15. Given these uncertainties, radar-based retrievals generally agreed with in situ measurements. The advantages of using the CDR proxy compared to the linear depolarization ratio are discussed.

Satellite recordings by CALIPSO and Aqua-MODIS, available data on the Aerosol Robotic Net-work (AERONET), and synoptic stations have been used to investigate dust storms over the Persian Gulf and the Oman Sea from January 2007 to December 2019. We found that the depo-larization of lidar signals by atmospheric dust particles is quite sensitive to their origins (deserts, or alluvial sediments). In the CALIPSO data set, the depolarization just over the thickness of an aerosol layer is called as the integrated depolarization ratio (IPDR). The IPDR and MODIS aerosol optical depth (AOD) over the mentioned waters are in correlation with the changes in the wind pattern over the region and activities of different dust sources in the neighborhoods of the waters. This investigation shows that the highest IPDR values belong to the dust particles which are originating from the Arabian Peninsula and impacting almost all regions in the south of the Iran Plateau from February to May. Also, these waters are under considerable influence of the Mesopotamian region and dust sources at the east side of the plateau. These sources are almost composed of alluvial sediments, and the IPDR for particles rising from them, is not high as those from the Arabian desert. Even though intense dust plumes raised from sources in the East of the Plateau impact these waters very frequently in summertime, but largest dust particles belong to the plumes originating from the Arabian desert in spring.

A polarization imaging lidar, employing a linearly polarized continuous-wave 450-nm laser diode and a polarization-sensitive image sensor has been proposed and demonstrated for atmospheric polarization studies. The polarization image sensor, fabricated with four-directional on-chip polarizers at 0°, 45°, 90° and 135°, is able to capture a four-directional polarized image of the laser beam that has been transmitted into the atmosphere, from which four polarized atmospheric backscattering signals with 0°, 45°, 90°, and 135° polarization angles can be simultaneously measured. A theoretical model has been established to retrieve the linear volume depolarization ratio (LVDR) as well as the misalignment (offset) angle between the polarization plane of the transmitted laser beam and the polarization plane of the 0°-directional on-chip polarizer of the image sensor, without employing additional optical components and sophisticated system adjustments. Atmospheric validation measurements have been carried out during a haze event. The promising results have shown a great potential of utilizing the proposed polarization imaging lidar technique for various atmospheric polarization studies.

To explore the vertical distribution of the aerosol optical parameters over Jinhua City, southeast China, a Dual-wavelength Mie Polarization Raman Lidar (DMPRL) system was operated to obtain the atmospheric backscattering signals from June 2013 to May 2014. Profiles of aerosol occurrence frequency and aerosol optical parameters, including backscattering ratio, particle depolarization ratio, and color ratio, were retrieved from the lidar signals. The cases with a cloud base below 6 km and profiles on rainy days were eliminated. The multi-layer vertical aerosol structure was found in Jinhua area and the altitude-resolved optical properties varies with seasons. In autumn, winter and spring, the aerosol layer occurrence frequencies were higher than summer at 3–6 km, especially in spring. The mean particle depolarization ratio at 4–6 km exceeded 0.1 in autumn, winter, and spring, whereas it was

We present final and quality-assured results of multiwavelength polarization/Raman lidar observations of the Saharan air layer (SAL) over the tropical Atlantic. Observations were performed aboard the German research vessel R/V Meteor during the 1-month transatlantic cruise from Guadeloupe to Cabo Verde over 4500 km from 61.5 to 20° W at 14–15° N in April–May 2013. First results of the shipborne lidar measurements, conducted in the framework of SALTRACE (Saharan Aerosol Long-range Transport and Aerosol–Cloud Interaction Experiment), were reported by Kanitz et al.(2014). Here, we present four observational cases representing key stages of the SAL evolution between Africa and the Caribbean in detail in terms of layering structures and optical properties of the mixture of predominantly dust and aged smoke in the SAL. We discuss to what extent the lidar results confirm the validity of the SAL conceptual model which describes the dust long-range transport and removal processes over the tropical Atlantic. Our observations of a clean marine aerosol layer (MAL, layer from the surface to the SAL base) confirm the conceptual model and suggest that the removal of dust from the MAL, below the SAL, is very efficient. However, the removal of dust from the SAL assumed in the conceptual model to be caused by gravitational settling in combination with large-scale subsidence is weaker than expected. To explain the observed homogenous (height-independent) dust optical properties from the SAL base to the SAL top, from the African coast to the Caribbean, we have to assume that the particle sedimentation strength is reduced and dust vertical mixing and upward transport mechanisms must be active in the SAL. Based on lidar observations on 20 nights at different longitudes in May 2013, we found, on average, MAL and SAL layer mean values (at 532 nm) of the extinction-to-backscatter ratio (lidar ratio) of 17±5 sr (MAL) and 43±8 sr (SAL), of the particle linear depolarization ratio of 0.025±0.015 (MAL) and 0.19±0.09 (SAL), and of the particle extinction coefficient of 67±45 Mm−1 (MAL) and 68±37 Mm−1 (SAL). The 532 nm optical depth of the lofted SAL was found to be, on average, 0.15±0.13 during the ship cruise. The comparably low values of the SAL mean lidar ratio and depolarization ratio (compared to typical pure dust values of 50–60 sr and 0.3, respectively) in combination with backward trajectories indicate a smoke contribution to light extinction of the order of 20 % during May 2013, at the end of the burning season in central-western Africa.

The aerosol color ratio, depolarization ratio and aerosol optical depth (AOD) were measured by a two-wavelength-depolarization lidar at Wuhan, China during the period from May 2015–July 2016. The annual average AOD at Wuhan was about 0.33 during the period 2015–2016. The seasonal average AOD is small (0.26 ± 0.25) during the winter (December–February) season and large (0.4 ± 0.1) during the summer (June–August) season. The monthly average color ratio is small (0.23 ± 0.09) in January and large (0.76 ± 0.21) in August with an annual average value 0.54. The maximum monthly mean depolarization ratio (0.2 ± 0.07) occurred in the month of October, while the minimum (0.06 ± 0.02) occurred in the month of September, and the annual mean depolarization ratio was about 0.17. An analysis of temporal variations of color ratio and depolarization ratio suggests the presence of coarse and non-spherical particles during the autumn. The aerosol color ratio between 0.3 and 2.0 km was large (0.65), suggesting a large number of coarse particles in this range. The vertical distribution of the depolarization ratio is uniform. Finally, the spatial aerosol distribution under different weather conditions and its relationship with the color ratio is investigated in detail. The color ratio value of 0.74 could be used as a threshold for distinguishing polluted weather from clean weather. The aerosol optical and physical properties are investigated to provide a comprehensive understanding of aerosol radiative forcing and environmental problems in this region.

The existing models predict that corner reflection (CR) of laser radiation by simple ice crystals of perfect shape, such as hexagonal columns or plates, can provide a significant contribution to the ice cloud backscattering. However in real clouds the CR effect may be suppressed due to crystal deformation and surface roughness. In contrast to the extinction coefficient, which is spectrally independent, consideration of diffraction associated with CR results in a spectral dependence of the backscattering coefficient. Thus measuring the spectral dependence of the cloud backscattering coefficient, the contribution of CR can be identified. The paper presents the results of profiling of backscattering coefficient (β) and particle depolarization ratio (δ) of ice and mixed-phase clouds over West Africa by means of a two-wavelength polarization Mie-Raman lidar operated at 355 nm and 532 nm during the SHADOW field campaign. The lidar observations were performed at a slant angle of 43 degree off zenith, thus CR from both randomly oriented crystals and oriented plates could be analyzed. For the most of the observations the cloud backscatter color ratio β355/β532 was close to 1.0, and no spectral features that might indicate the presence of CR of randomly oriented crystals were revealed. Still, in two measurement sessions we observed an increase of backscatter color ratio to a value of nearly 1.3 simultaneously with a decrease of the spectral depolarization ratio δ355/δ532 ratio from 1.0 to 0.8 inside the layers containing precipitating ice crystals. We attribute these changes in optical properties to corner reflections by horizontally oriented ice plates.

In this study, to understand the molecular self-organization in metal–organic charge-transfer nanowires, single gold-tetrathiafulvalene (Au–TTF) nanowires were analyzed using polarized Raman spectroscopy, combined with density functional theory (DFT) calculations. To verify the methodology, an investigation was done for neutral tetrathiafulvalene (TTF) bulk crystals with well-known structure. On the basis of the DFT calculation of the molecular Raman tensor and simulation of the angular-dependent depolarization ratio, the molecular orientation in single TTF crystals was verified. Thereon, the combined experimental and ab initio-simulation method was applied to study single Au–TTF nanowires. Our results clearly demonstrate, in contrast to the commonly accepted parallel molecular stacking model, that at least two molecules with different orientations are located in the unit cell of the nanowire’s crystal structure. The new tilted molecular column stacking wire model explains also the axial and radial growth...

A new methodology for estimating the depolarization ratio (DR) by dual-polarization radars with simultaneous transmission/reception of orthogonally polarized waves together with traditionally measured differential reflectivity ZDR, correlation coefficient ρhυ, and differential phase ΦDP in a single mode of operation is suggested. This depolarization ratio can serve as a proxy for circular depolarization ratio measured by radars with circular polarization. The suggested methodology implies the use of a high-power phase shifter to control the system differential phase on transmission and a special signal processing to eliminate the detrimental impact of differential phase on the estimate of DR. The feasibility of the suggested approach has been demonstrated by retrieving DR from the standard polarimetric variables and the raw in-phase I and quadrature Q components of radar signals and by implementing the scheme on a C-band radar with simultaneous transmission/reception of horizontally and vertically polarized waves. Possible practical implications of using DR include the detection of hail and the determination of its size above the melting layer, the discrimination between various habits of ice aloft, and the possible identification and quantification of riming, which is associated with the presence of supercooled cloud water. Some examples of these applications are presented.

The characteristics of springtime aerosols, including their optical and microphysical properties, were analyzed for the months of March to May of 2009 in Gwangju (35.23°N, 126.84°E), Korea. A high Light Detection and Ranging (LIDAR)-derived aerosol depolarization ratio (δ) of 0.25±0.04 was determined on dust particles during the observation period. The Angstrom exponent values of the 440-870nm wavelength pair (A440-870) and single-scattering albedo at 675nm (Ω675) measured by a CIMEL sun/sky radiometer were 0.77±0.19 and 0.95±0.01, respectively. The elevated dust layers reached a maximum elevation of 4km above sea level. Anthropogenic/smoke particles that originated from highly populated/industrialized regions could be distinguished by their relatively smaller particle size (A440-870 ranged between 1.33 and 1.36) and higher light-absorbing (Ω675 of 0.92±0.01) characteristics. These aerosols are mostly distributed at altitudes 100μg/m3). These results suggest that the accuracy of τLIDAR is influenced by specific atmospheric conditions, regardless of its uncertainty.

A dataset of particle optical properties of the highly polluted atmosphere over the Pearl River Delta, Guangzhou, China, is presented in this paper. The data were derived from the measurements of a multi-wavelengths Raman and depolarization lidar PollyXT and a co-located AERONET sun photometer. The measurement campaign was conducted from November 2011 to mid June 2012. These are the first Raman lidar measurements in the PRD that were lasting for several months. A mean value of aerosol optical depth observed by the sun photometer of 0.54 ± 0.33 was observed in the polluted atmosphere over this megacity for the whole measurement period. The lidar profiles frequently show lofted aerosol layers which reach up to altitudes of 2 to 3 km and especially in spring season up to even 5 km. These layers contain between 12 and 56 % of the total AOD, with the highest values in spring. The aerosol in these lofted layers were classified by their optical properties. The observed lidar ratio values are in the range from 30 to 80 sr with a mean value of 48.0 sr ± 10.7 sr. The linear particle depolarization ratio at 532 nm lied mostly below 5 % with a mean value of 3.6 ± 3.7. The majority of the Ångström exponents were observed between 1 and 1.5 indicating a coarse mode in addition to the fine mode in the particle size distribution. These results reveal that mainly urban pollution particles mixed with particles arisen from biomass and industrial burning are present in the atmosphere above the Pearl River Delta. Trajectory analyses show that these pollution mixtures arise mainly from local and regional sources.

A transition zone near cirrus lateral boundaries can be detected by CALIOP (cloud–aerosol lidar with orthogonal polarization). In the present study, for such transition zones over China, a number of optical properties, such as the backscatter coefficient and depolarization ratio, showed transitional characteristics between cirrus and clear sky. The stepped horizontal profile showed sharp changes in particle number and morphology between cirrus clouds and clear sky. The color ratio, however, was unable to show cirrus transition features because of the low signal-to-noise ratio. Typical ice particles presented a color ratio of 0.55–1.25 and a depolarization ratio of greater than 0.12, which were significantly higher than those of clear sky. Therefore, optical properties in transition took the form of stepwise horizontal profiles. The proportion of typical-featured particles also demonstrated a stepped horizontal profile similar to the optical characteristics, but the relationship between the proportion and the optical characteristics was not uniform in the cirrus clouds, transition zone, and clear sky. Therefore, the optical changes in the transition zone were caused by not only the change in particle concentration, but also the change in the particles themselves. The probability density distribution of the transition-zone widths showed a positive skewness distribution, and transition zones with widths of 3–5 km occurred most frequently. Overall, transition-zone width decreased with increasing temperature and increased with increasing vertical and horizontal wind speeds. This trend demonstrated independence with the direction of the vertical and horizontal winds. These observations implied that the transitional features were caused by material exchange, such as entrainment and turbulent transport, near the cirrus lateral boundaries, and by the phase transformation of particles, such as sublimation.

The linear particle depolarization ratios at 440, 675, 870, and 1020 nm were derived using data taken with the AERONET sun–sky radiometer at Seoul (37.45° N, 126.95° E), Kongju (36.47° N, 127.14° E), Gosan (33.29° N, 126.16° E), and Osaka (34.65° N, 135.59° E). The results are compared to the linear particle depolarization ratio measured by lidar at 532 nm. The correlation coefficient R2 between the linear particle depolarization ratio derived by AERONET data at 1020 nm and the linear particle depolarization ratio measured with lidar at 532 nm is 0.90, 0.92, 0.79, and 0.89 at Seoul, Kongju, Gosan, and Osaka, respectively. The correlation coefficients between the lidar-measured depolarization ratio at 532 nm and that retrieved by AERONET at 870 nm are 0.89, 0.92, 0.76, and 0.88 at Seoul, Kongju, Gosan, and Osaka, respectively. The correlation coefficients for the data taken at 675 nm are lower than the correlation coefficients at 870 and 1020 nm, respectively. Values are 0.81, 0.90, 0.64, and 0.81 at Seoul, Kongju, Gosan, and Osaka, respectively. The lowest correlation values are found for the AERONET-derived linear particle depolarization ratio at 440 nm, i.e., 0.38, 0.62, 0.26, and 0.28 at Seoul, Kongju, Gosan, and Osaka, respectively. We should expect a higher correlation between lidar-measured linear particle depolarization ratios at 532 nm and the ones derived from AERONET at 675 and 440 nm as the lidar wavelength is between the two AERONET wavelengths. We cannot currently explain why we find better correlation between lidar and AERONET linear particle depolarization ratios for the case that the AERONET wavelengths (675, 870, and 1020 nm) are significantly larger than the lidar measurement wavelength (532 nm). The linear particle depolarization ratio can be used as a parameter to obtain insight into the variation of optical and microphysical properties of dust when it is mixed with anthropogenic pollution particles. The single-scattering albedo increases with increasing measurement wavelength for low linear particle depolarization ratios, which indicates a high share of fine-mode anthropogenic pollution. In contrast, single-scattering albedo increases with increasing wavelength for high linear particle depolarization ratios, which indicated a high share of coarse-mode mineral dust particles. The retrieved volume particle size distributions are dominated by the fine-mode fraction if linear particle depolarization ratios are less than 0.15 at 532 nm. The fine-mode fraction of the size distributions decreases and the coarse-mode fraction of the size distribution increases for increasing linear particle depolarization ratio at 1020 nm. The dust ratio based on using the linear particle depolarization ratio derived from AERONET data is 0.12 to 0.17. These values are lower than the coarse-mode fraction derived from the volume concentrations of particle size distributions, in which case we can compute the coarse-mode fraction of dust.

Observations with lidars at Wuhan (30.5°N, 114.4°E), China from 2010 to 2013 captured nine cases of slowly-ascending humid aerosol/liquid water layers that occurred at altitudes of ~2 − 4 km in winter. Each of them was almost transparent initially with the backscatter ratio far less than 7.0 and depolarization ratio less than 0.03. With a slow ascent, the layer developed into a nearly opaque liquid cloud layer and then ice crystals abruptly formed at the upper edge of the cloud layer with very high liquid water content. The ice crystals likely came from water drop freezing. The freezing temperatures estimated from radiosonde measurements were −3 to −8 °C. For two available long-lived (>16 h) cases, the layer was observed to always lie just below an inversion layer. The ice development on the layer was followed by rainfall.

Determination of the molecular first hyperpolarizability by hyper-Rayleigh scattering (HRS) is usually significantly complicated by a presence of the multiphoton excited fluorescence which has to be separated from HRS to obtain a meaningful values of the hyperpolarizability. We show, by performing a spectrally-resolved measurement, that the intensity and spectral shape of the fluorescence can depend strongly on the fundamental laser wavelength. Consequently, a properly selected excitation wavelength can significantly simplify the process of separation of HRS from the detected signal. We tested the developed experimental setup with a polarization-insensitive detection by measuring HRS generated in water and in aqueous solutions of 2-aminopyrimidine (AMP) and its monocation (HAMP). The effective hyperpolarizability of AMP and HAMP was measured experimentally and compared with that obtained by quantum chemical calculations. The polarization-resolved HRS measurement was performed for AMP and the experimentally obtained depolarization ratio agrees well with that predicted theoretically, which confirms that routine density functional theory computations of static hyperpolarizability tensor components can be considered as a sufficient approach suitable for non-interacting molecules dissolved in water.

We present results of the vertical distribution variation of volcanic aerosol layers in the upper troposphere and lower stratosphere. The data were taken with our multiwavelength aerosol Raman lidar at Gwangju (35.10° N, 126.53° E), Korea. The volcanic ash particles and gases were released around 12 June 2011 during the eruption of the Nabro volcano (13.37° N, 41.7° E) in Eritrea, east Africa. Forward trajectory computations show that the volcanic aerosols were advected from North Africa to East Asia. The first measurement of the aerosol layer over Korea was on 19 June 2011. The aerosol layers appeared between 15 km and 17 km height asl (above sea level). The maximum value of the aerosol layer of the particle backscatter coefficient (1.5 ± 0.3 Mm−1 sr−1) and the linear particle depolarization ratio at 532 nm (2.2%) were observed at 16.4 km height asl. We continuously probed the upper troposphere and lower stratosphere for this volcanic aerosol layer during the following 6 months, until December 2011. The volcanic aerosol layer showed a single-peak of the particle backscatter coefficient and a comparably narrow vertical thickness at our observation site at the beginning of our observation period (i.e. comparably soon after the initial eruption period). After that initial period the vertical distribution of the plume changed. Multiple peaks and a comparably broad geometrical thickness developed with progressing observation time. The vertical thickness of the volcanic aerosol layer expanded up to 10 km by 3 August 2011. The linear particle depolarization ratios were larger in the lower part of the aerosol layer than the upper part of the aerosol layer. We observed a strong variation of the AOD (aerosol optical depth) in the first two months of our lidar observations. After these two months the AOD gradually decreased with time from September to December 20111 and the maximum particle backscatter coefficients consistently decreased. The corresponding e-folding decay time of the layer AOD was 117 days.

Backscatter ratios for two kinds of ice crystal models, an irregularly shaped Voronoi aggregates (VA) and a regularly shaped hexagonal columns (COL), are calculated using the geometrical-optics-integral-equation (GOIE) method for volume equivalent sphere radii (Req) ranging from 2.8 to 202.0μm. Ice crystals are assumed to be randomly oriented in three-dimensional (3D) space. Characteristics of the depolarization ratio (δ) and the lidar ratio (L) at a wavelength of 0.532μm and the color ratio (χ) at a wavelength pair of 1.064 and 0.532μm are investigated. The backscatter ratios calculated for VA are generally larger than those for COL. For example, L, δ, and χ for VA are approximately 50~60, 0.5~0.6, and 0.8~0.9, respectively, in the range of Req>10μm; 4~15, 0.2~0.3, and 0.45~0.5 for COL. Effects of deformation of COL on the backscatter ratios are examined by using hexagonal columns with hollowness. It is shown that the L, δ, and χ values significantly increase due to the hollowness. Furthermore, the degree of increase of the backscatter ratios is considerably sensitive to the crystal size and the depth of hollow. On the other hand, backscatter ratios calculated for VA show rather steady values with respect to the number and size of facets.

Agricultural biomass burning (ABB) has been of particular concern due to its influence on air quality and atmospheric radiation, as it produces large amounts of gaseous and aerosol emissions. This paper presents an integrated observation of a significant ABB episode in Nanjing, China, during early June 2011, using combined ground-based and satellite sensors (Moderate Resolution Imaging Spectroradiometer, Atmospheric Infrared Sounder, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and Ozone Monitoring Instrument products). The time-height distribution, optical properties, sources and transport of smoke, and its impacts on air quality are investigated. Lidar profiles indicate that the smoke aerosols are confined to the planetary boundary layer (PBL) and have a depolarization ratio of less than 0.08. The aerosol optical depths increase from 0.5 to 3.0 at 500 nm, while the extinction-related Angstrom exponent increases from 1.1 to 1.6 at the wavelength pair of 440–870 nm. The single-scattering albedo becomes lower at 670–1020 nm following the ABB intrusion and particularly shows a decreasing tendency between wavelengths of 440 to 1020 nm. The absorption Angstrom exponent (0.7) is smaller than 1.0, which may indicate the aged smoke particles mixed or coated with the urban aerosols. Surface particular matter PM10 and PM2.5 show a dramatic increase, reaching hourly mean of 800 µg/m3 and 485 µg/m3, respectively, which results in a heavy air pollution event. The stagnant and high-moisture weather provides favorable conditions for the aerosols to accumulate near the surface. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) also illustrate that the large-scale aerosols are primarily present in the PBL and transported to the ocean, but some dense smoke plumes are misclassified as cloud or polluted dust. By comparing with the observations, we found that the Weather Research and Forecasting–Chemistry model captured the accumulation and downwind transport of surface PM2.5 from 20:00 on 2 June to 10:00 on 3 June (phase 1) but showed a dramatic underestimate from 20:00 on 3–4 June (phase 2) when dense aerosols are present. Such a discrepancy in the model is associated with the improper vertical apportion of transported smoke and atmospheric diffusion conditions when comparing with the observed aerosol and wind profiles. In addition, the model simulations indicate that the transported smoke can contribute to 50–70% of the ground-level PM2.5 in Nanjing.

Mixing state of aerosols and optical properties including lidar ratio, particle depolarization ratio, and Angstrom exponent were investigated at Fukuoka in western Japan using a multi-wavelength Mie–Raman lidar (MMRL), various aerosol mass-concentration measurements, and a polarization optical particle counter during Winter–Spring 2015. Aerosol extinction coefficient, backscatter coefficient, and depolarization at 355 and 532 nm and attenuated backscatter coefficient at 1064 nm are obtained from the MMRL measurements. Ten aerosol episodes were classified into three categories (air pollution, mineral dust, and marine aerosol) based on aerosol mass-concentration measurements in the fine-mode (particle diameter Dp

We improved two-wavelength polarization Mie-scattering lidars at several main sites of the Asian dust and aerosol lidar observation network (AD-Net) by adding a nitrogen Raman scatter measurement channel at 607 nm and have conducted ground-based network observation with the improved Mie–Raman lidars (MRL) in East Asia since 2009. This MRL provides 1 α+ 2 β +1 δ data at nighttime: extinction coefficient ( α 532 ), backscatter coefficient ( β 532 ), and depolarization ratio ( δ 532 ) of particles at 532 nm and an attenuated backscatter coefficient at 1064 nm ( β at ,1064 ). Furthermore, we developed a Multi-wavelength Mie-Raman lidar (MMRL) providing 2 α +3 β +2 δ data ( α at 355 and 532 nm; β at 355 and 532; β at at 1064 nm; and δ at 355 and 532 nm) and constructed MMRLs at several main sites of the AD-Net. We identified an aerosol-rich layer and height of the planetary boundary layer (PBL) using β at ,1064 data, and derived aerosol optical properties (AOPs, for example, α a , β a , δ a , and lidar ratio ( S a )). We demonstrated that AOPs cloud be derived with appropriate accuracy. Seasonal means of AOPs in the PBL were evaluated for each MRL observation site using three-year data from 2010 through 2012; the AOPs changed according to each season and region. For example, S a ,532 at Fukue, Japan, were 44±15 sr in winter and 49±17 in summer; those at Seoul, Korea, were 56±18 sr in winter and 62±15 sr in summer. We developed an algorithm to estimate extinction coefficients at 532 nm for black carbon, dust, sea-salt, and air-pollution aerosols consisting of a mixture of sulfate, nitrate, and organic-carbon substances using the 1 α 532 +2 β 532 and 1064 +1 δ 532 data. With this method, we assume an external mixture of aerosol components and prescribe their size distributions, refractive indexes, and particle shapes. We applied the algorithm to the observed data to demonstrate the performance of the algorithm and determined the vertical structure for each aerosol component.

In this study, a multi-wavelength polarization lidar was developed at the Lidar Center for Atmosphere Remote Sensing, in Xi’an, China to study the vertical distribution of the optical and microphysical properties of smog aerosols. To better understand smog, two events with different haze conditions observed in January 2015 were analyzed in detail. Using these data, we performed a vertical characterization of smog evolution using the lidar range-squared-corrected signal and the aerosol depolarization ratio. Using inversion with regularization, we retrieved the vertical distribution of aerosol microphysical properties, including volume size distribution, volume concentration, number concentration and effective radius. We also used the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model to analyze aerosol sources during the two episodes. Our results show that the most polluted area in the lower troposphere during smog episodes is located below a height of 1 km above the ground level; under more severe smog conditions, it can be below 0.5 km. In the case of severe smog, we found a large number of spherical and fine particles concentrated in the very low troposphere, even below 0.5 km. Surprisingly, a dust layer with a slight depolarization ratio was observed above the smog layer.

This work reports on a combined experimental and theoretical investigation on the carotenoid Raman signal in several tomato fruits during their postharvest time evolution and ripening. Both resonant (180°) backscattering and polarized (90°) Raman scattering were used to monitor the most prominent bands of carotenoid (lycopene and β-carotene) evolution in different tomato varieties. Relevant findings of the present investigations were that while the depolarization ratio of the ν1 band hardly changed with time, the Raman ν1 band intensity did change showing a similar pattern for all tomatoes investigated. Indeed, all cases investigated revealed a rise of the carotenoid signal coincident with the onset of the turning stage of the fruit ripening, a pronounced maximum of the Raman signal followed by a post-maximum decline at the red ripening stage. A kinetic model has been developed to describe the time evolution of the observed Raman signatures based on the rate coefficient of the carotenoid synthesis and the time evolution of the scattering coefficient of the fruit. The model describes satisfactorily the tomato evolution through the distinct ripening stages providing new insight on the assessment of the postharvest fruit control and quality.

The irregular shape of mineral dust provides a strong signature on active and passive polarimetric remote sensing observations. Nowadays, advanced lidar systems operating in the framework of ACTRIS are capable of providing quality assured, calibrated multi-wavelength linear particle depolarization ratio measurements, while new developments will provide us more polarimetric measurements in the near future. Passive polarimeters are already part of ACTRIS and their integration in operational algorithms is expected in the near future. This wealth of new information combined with updated scattering databases and sophisticated inversion schemes provide the means towards an improved characterization of desert dust in the future. We present here some examples from the ACTRIS journey on dust research during the last decade, aiming to demonstrate the progress on issues such as: (a) the discrimination of desert dust in external mixtures, (b) the separation and estimation of the fine and coarse particle modes, (c) the synergy of passive and active remote sensing for the derivation of dust concentration profiles, (d) the provision of dust-related CCN and IN particle concentrations for aerosol-cloud interaction studies, (e) the development of new scattering databases based on realistic particle shapes, (e) the application of these techniques on spaceborne lidar retrievals for the provision of global and regional climatological datasets. Future plans within ACTRIS for the evaluation and advancement of the methodologies and retrievals are also discussed, combined with new developments within the framework of the D-TECT ERC Grant.

Studying the presence of aerosols in different atmospheric layers helps researchers understand their impacts on climate change, air quality, and human health. Therefore, in the present study, the optical and physical properties of aerosol layers over the Yellow River Basin (YERB) were investigated using the CALIPSO Level 2 aerosol layer products from January 2007 to December 2014. The Yellow River Basin was divided into three sub-regions i.e., YERB1 (the plain region downstream of the YERB), YERB2 (the Loess Plateau region in the middle reaches of the YERB), and YERB3 (the mountainous terrain in the upper reaches of the YERB). The results showed that the amount (number) of aerosol layers (N) was relatively large (&gt, 2 layers) in the lower part of the YERB (YERB1), which was mainly caused by atmospheric convection. The height of the highest aerosol layer top (HTH) and the height of the lowest aerosol layers base (HB1) varied significantly with respect to the topography of the YERB. High and low values of aerosol optical depth (AOD) were observed over the YERB1 (plain area) and YERB3 (elevated area) regions, respectively. Population, economy, and agricultural activities might be the possible reasons for spatial variations in AOD. AOD values for the lowest aerosol layer were high&mdash, between 0.7 and 1.0 throughout the year&mdash, indicating that aerosols were mainly concentrated at the bottom layer of the atmosphere. In addition, the integrated volume depolarization ratio (0.15&ndash, 0.2) and the integrated attenuated total color ratio (~0.1) were large during spring for the lowest aerosol layer due to the presence of dust aerosols. The thicknesses of the lowest aerosol layers (TL1) did not vary with respect to the topographic features of the YERB. Over the sub-regions of the YERB, a significant positive correlation between the AOD of the lowest aerosol layer (AOD1) and the thickness of the lowest aerosol layer (TL1) was found, which indicates that TL1 increases with the increase of AOD1. In the whole YERB, a positive linear correlation between the N and HTH was observed, whereas a negative correlation between N and the portion of AOD for the lowest aerosol layer (PAOD1) was found, which revealed that the large value of N leads to the small value of PAOD1. The results from the present study will be helpful to further investigate the aerosol behavior and their impacts on climate change, air quality, and human health over the YERB.

In this paper, we present aerosol retrieval results from the ACEPOL (Aerosol Characterization from Polarimeter and Lidar) campaign, which was a joint initiative between NASA and SRON – Netherlands Institute for Space Research. The campaign took place in October-November 2017 over the western part of the United States. During ACEPOL six different instruments were deployed on the NASA ER-2 high altitude aircraft, including four Multi-Angle Polarimeters (MAPs): SPEX airborne, the Airborne Hyper Angular Rainbow Polarimeter (AirHARP), the Airborne Multi-angle SpectroPolarimeter Imager (AirMSPI), and the Research Scanning Polarimeter (RSP). Also, two lidars participated: the High Spectral Resolution Lidar -2 (HSRL-2) and the Cloud Physics Lidar (CPL). Flights were conducted mainly for scenes with low aerosol load over land but also some cases with higher AOD were observed. We perform aerosol retrievals from SPEX airborne, RSP (410–865 nm range only), and AirMSPI using the SRON aerosol retrieval algorithm and compare the results against AERONET and HSRL-2 measurements (for SPEX airborne and RSP). All three MAPs compare well against AERONET for the Aerosol Optical Depth (AOD) (Mean Absolute Error (MAE) between 0.014–0.024 at 440 nm). For the fine mode effective radius the MAE ranges between 0.021–0.028 micron. For the comparison with HSRL-2 we focus on a day with low AOD (0.02–0.14 at 532 nm) over the California Central Valley, Arizona and Nevada (26 October) and a flight with high AOD (including measurements with AOD > 1.0 at 532 nm) over a prescribed forest fire in Arizona (9 November). For the day with low AOD the MAE in AOD (at 532 nm) with HSRL-2 are 0.014 and 0.022 for SPEX and RSP, respectively, showing the capability of MAPs to provide accurate AOD retrievals for the challenging case of low AOD over land. For the retrievals over the smoke plume also a reasonable agreement in AOD between the MAPs and HSRL-2 was found (MAE 0.088 and 0.079 for SPEX and RSP, respectively), despite the fact that the comparison is hampered by large spatial variability in AOD throughout the smoke plume. Also a good comparison is found between the MAPs and HSRL-2 for the aerosol depolarization ratio (a measure for particles sphericity) with MAE of 0.023 and 0.016 for SPEX and RSP, respectively. Finally, SPEX and RSP agree very well for the retrieved microphysical and optical properties of the smoke plume.