The volume depolarization ratio of the molecular backscatter signal detected with polarization lidar varies by a factor of nearly 4 depending on whether the rotational Raman bands are included in the detected signals of the individual system or not. If the rotational Raman spectrum is included partially in the signals, this calibration factor depends on the temperature of the atmosphere. This dependency is studied for different spectral widths of the receiving channels. In addition, the sensitivity to differences between the laser wavelength and the center wavelength of the receiver are discussed.

. Absolute calibrated signals at 532 and 1064 nm and the depolarization ratio from a multiwavelength lidar are used to categorize primary aerosol but also clouds in high temporal and spatial resolution. Automatically derived particle backscatter coefficient profiles in low temporal resolution (30 min) are applied to calibrate the lidar signals. From these calibrated lidar signals, new atmospheric parameters in temporally high resolution (quasi-particle-backscatter coefficients) are derived. By using thresholds obtained from multiyear, multisite EARLINET (European Aerosol Research Lidar Network) measurements, four aerosol classes (small; large, spherical; large, non-spherical; mixed, partly non-spherical) and several cloud classes (liquid, ice) are defined. Thus, particles are classified by their physical features (shape and size) instead of by source. The methodology is applied to 2 months of continuous observations (24 h a day, 7 days a week) with the multiwavelength-Raman-polarization lidar PollyXT during the High-Definition Clouds and Precipitation for advancing Climate Prediction (HD(CP)2) Observational Prototype Experiment (HOPE) in spring 2013. Cloudnet equipment was operated continuously directly next to the lidar and is used for comparison. By discussing three 24 h case studies, it is shown that the aerosol discrimination is very feasible and informative and gives a good complement to the Cloudnet target categorization. Performing the categorization for the 2-month data set of the entire HOPE campaign, almost 1 million pixel (5 min  ×  30 m) could be analysed with the newly developed tool. We find that the majority of the aerosol trapped in the planetary boundary layer (PBL) was composed of small particles as expected for a heavily populated and industrialized area. Large, spherical aerosol was observed mostly at the top of the PBL and close to the identified cloud bases, indicating the importance of hygroscopic growth of the particles at high relative humidity. Interestingly, it is found that on several days non-spherical particles were dispersed from the ground into the atmosphere.\n

. The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) on the NASA B200 aircraft has acquired extensive datasets of aerosol extinction (532 nm), aerosol optical depth (AOD) (532 nm), backscatter (532 and 1064 nm), and depolarization (532 and 1064 nm) profiles during 18 field missions that have been conducted over North America since 2006. The lidar measurements of aerosol intensive parameters (lidar ratio, depolarization, backscatter color ratio, and spectral depolarization ratio) are shown to vary with location and aerosol type. A methodology based on observations of known aerosol types is used to qualitatively classify the extensive set of HSRL aerosol measurements into eight separate types. Several examples are presented showing how the aerosol intensive parameters vary with aerosol type and how these aerosols are classified according to this new methodology. The HSRL-based classification reveals vertical variability of aerosol types during the NASA ARCTAS field experiment conducted over Alaska and northwest Canada during 2008. In two examples derived from flights conducted during ARCTAS, the HSRL classification of biomass burning smoke is shown to be consistent with aerosol types derived from coincident airborne in situ measurements of particle size and composition. The HSRL retrievals of AOD and inferences of aerosol types are used to apportion AOD to aerosol type; results of this analysis are shown for several experiments.\n

. The application of the POLIPHON (POlarization-LIdar PHOtometer Networking)\nmethod is presented for the first time in synergy with continuous\n24/7 polarized Micro-Pulse Lidar (P-MPL)\nmeasurements to derive the vertical separation of two or three particle\ncomponents in different aerosol mixtures, and the retrieval of their\nparticular optical properties. The procedure\nof extinction-to-mass conversion, together with an analysis of the mass extinction efficiency (MEE) parameter, is described, and the relative mass\ncontribution of each aerosol component is also derived in a further step. The\ngeneral POLIPHON algorithm is based on the specific particle linear\ndepolarization ratio given for different types of aerosols and can be run in\neither 1-step (POL-1) or 2 steps (POL-2) versions with dependence on either the\n2- or 3-component separation. In order to illustrate this procedure, aerosol\nmixing cases observed over Barcelona (NE Spain) are selected: a dust event\non 5 July 2016, smoke plumes detected on 23 May 2016 and a\npollination episode observed on 23 March 2016. In particular, the 3-component\nseparation is just applied for the dust case: a combined POL-1 with POL-2\nprocedure (POL-1/2) is used, and additionally the fine-dust contribution to\nthe total fine mode (fine dust plus non-dust aerosols) is estimated. The\nhigh dust impact before 12:00 UTC yields a mean mass loading of\n0.6±0.1 g m−2 due to the prevalence of Saharan coarse-dust\nparticles. After that time, the mean mass loading is reduced by two-thirds,\nshowing a rather weak dust incidence. In the smoke case, the arrival of fine\nbiomass-burning particles is detected at altitudes as high as 7 km.\nThe smoke particles, probably mixed with less depolarizing non-smoke\naerosols, are observed in air masses, having their origin from either North\nAmerican fires or the Arctic area, as reported by HYSPLIT back-trajectory\nanalysis. The particle linear depolarization ratio for smoke shows values in\nthe 0.10–0.15 range and even higher at given times, and the daily mean smoke\nmass loading is 0.017±0.008 g m−2, around 3 % of that found\nfor the dust event. Pollen particles are detected up to 1.5 km in height from\n10:00 UTC during an intense pollination event with a particle linear\ndepolarization ratio ranging between 0.10 and 0.15. The maximal mass loading\nof Platanus pollen particles is 0.011±0.003 g m−2,\nrepresenting around 2 % of the dust loading during the higher dust\nincidence. Regarding the MEE derived for each aerosol component, their values\nare in agreement with others referenced in the literature for the specific\naerosol types examined in this work: 0.5±0.1 and\n1.7±0.2 m2 g−1 are found for coarse and fine dust particles, 4.5±1.4 m2 g−1 is derived for smoke and\n2.4±0.5 m2 g−1 for non-smoke aerosols with Arctic origin, and a MEE of 2.4±0.8 m2 g−1 is obtained\nfor pollen particles, though it can reach higher or lower values depending on\npredominantly smaller or larger pollen grain sizes. Results reveal the high\npotential of the P-MPL system, a simple polarization-sensitive elastic\nbackscatter lidar working in a 24/7 operation mode, to retrieve the\nrelative optical and mass contributions of each aerosol component throughout\nthe day, reflecting the daily variability of their properties. In fact, this\nprocedure can be simply implemented in other P-MPLs that also operate within the\nworldwide Micro-Pulse Lidar Network (MPLNET), thus extending the aerosol\ndiscrimination at a global scale. Moreover, the method has the advantage of also\nbeing relatively easily applicable to space-borne lidars with an equivalent\nconfiguration such as the ongoing Cloud-Aerosol LIdar with Orthogonal\nPolarization (CALIOP) on board NASA CALIPSO (Cloud-Aerosol Lidar and Infrared\nPathfinder Satellite Observation) and the forthcoming Atmospheric\nLidar (ATLID) on board the ESA EarthCARE mission.\n

Accurately determining the atmospheric boundary layer height (ABLH) is needed when one is addressing the air quality-related issues in highly urbanized areas, as well as when one is investigating issues that are related to the emission and transport of dust aerosols over the source region. In this study, we propose a new ABLH retrieval method, which is named ADEILP (ABLH that is determined by polarization lidar); it is based on the short-term polarized lidar observation that took place during the intensive field campaign in July 2021 in Tazhong, the hinterland of Taklimakan Desert. Furthermore, we conducted comparisons between the ABLH that was identified using a radiosonde (ABLHsonde), the ABLH that was identified by ERA5 (ABLHERA5) and the ABHL that was identified by ADELIP (ABLHADELIP), and we discussed the implications of the dust events. The ADELIP method boasts remarkable advancements in two parts: (1) the lidar volume linear depolarization ratio (VLDR) that represented the aerosol type was adopted, which is very effective in distinguishing between the different types of boundary layers (e.g., mixing layer and residual layer); (2) the idea of breaking up the entire layer into sub-layers was applied on the basis of the continues wavelet transform (CWT) method, which is favorable when one is considering the effect of fine stratification in an aerosol layer. By combining the appropriate height limitations, these factors ensured that there was good robustness of the ADELIP method, thereby enabling it to deal with complex boundary layer structures. The comparisons revealed that ABLHADELIP shows good consistency with ABLHsonde and ABLHERA5 for non-dust events. Nevertheless, the ADELIP method overestimated the stable boundary layer and underestimated the heights of the mixing layer. The dust events seem to be a possible reason for the great difference between ABLHERA5 and ABLHsonde. Thus, it is worth suggesting that the influence that is caused by the differences of the vertical profile in the ERA5 product should be carefully considered when the issues on dust events are involved. Overall, these findings support the climatological analysis of the atmosphere boundary layer and the vertical distribution characteristics of aerosols over typical climatic zones.

Aerosols and clouds greatly affect the Earth’s radiation budget and global climate. Light detection and ranging (lidar) has been recognized as a promising active remote sensing technique for the vertical observations of aerosols and clouds. China launched its first space-borne aerosol-cloud high-spectral-resolution lidar (ACHSRL) on April 16, 2022, which is capable for high accuracy profiling of aerosols and clouds around the globe. This study presents a retrieval algorithm for aerosol and cloud optical properties from ACHSRL which were compared with the end-to-end Monte-Carlo simulations and validated with the data from an airborne flight with the ACHSRL prototype (A2P) instrument. Using imaging denoising, threshold discrimination, and iterative reconstruction methods, this algorithm was developed for calibration, feature detection, and extinction coefficient (EC) retrievals. The simulation results show that 95.4% of the backscatter coefficient (BSC) have an error less than 12% while 95.4% of EC have an error less than 24%. Cirrus and marine and urban aerosols were identified based on the airborne measurements over different surface types. Then, comparisons were made with U.S. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) profiles, Moderate-resolution Imaging Spectroradiometer (MODIS), and the ground-based sun photometers. High correlations (R > 0.79) were found between BSC (EC) profiles of A2P and CALIOP over forest and town cover, while the correlation coefficients are 0.57 for BSC and 0.58 for EC over ocean cover; the aerosol optical depth retrievals have correlation coefficient of 0.71 with MODIS data and show spatial variations consistent with those from the sun photometers. The algorithm developed for ACHSRL in this study can be directly employed for future space-borne high-spectral-resolution lidar (HSRL) and its data products will also supplement CALIOP data coverage for global observations of aerosol and cloud properties.

. The polarization-lidar photometer networking (POLIPHON) method for separating dust and non-dust aerosol backscatter and extinction, volume, and mass concentration is extended to allow for a height-resolved separation of fine-mode and coarse-mode dust properties in addition. The method is applied to a period with complex aerosol layering of fine-mode background dust from Turkey and Arabian desert dust from Syria. The observation was performed at the combined European Aerosol Research Lidar Network (EARLINET) and Aerosol Robotic Network (AERONET) site of Limassol (34.7° N, 33° E), Cyprus, in September 2011. The dust profiling methodology and case studies are presented. Consistency between the column-integrated optical properties obtained with sun/sky photometer and the respective results derived by means of the new lidar-based method corroborate the applicability of the extended POLIPHON version.\n

Descriptions are provided of the aerosol classification algorithms and the extinction-to-backscatter ratio (lidar ratio) selection schemes for the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) aerosol products. One year of CALIPSO level 2 version 2 data are analyzed to assess the veracity of the CALIPSO aerosol-type identification algorithm and generate vertically resolved distributions of aerosol types and their respective optical characteristics. To assess the robustness of the algorithm, the interannual variability is analyzed by using a fixed season (June–August) and aerosol type (polluted dust) over two consecutive years (2006 and 2007). The CALIPSO models define six aerosol types: clean continental, clean marine, dust, polluted continental, polluted dust, and smoke, with 532-nm (1064 nm) extinction-to-backscatter ratios Sa of 35 (30), 20 (45), 40 (55), 70 (30), 65 (30), and 70 (40) sr, respectively. This paper presents the global distributions of the CALIPSO aerosol types, the complementary distributions of integrated attenuated backscatter, and the volume depolarization ratio for each type. The aerosol-type distributions are further partitioned according to surface type (land/ocean) and detection resolution (5, 20, and 80 km) for optical and spatial context, because the optically thick layers are found most often at the smallest spatial resolution. Except for clean marine and polluted continental, all the aerosol types are found preferentially at the 80-km resolution. Nearly 80% of the smoke cases and 60% of the polluted dust cases are found over water, whereas dust and polluted continental cases are found over both land and water at comparable frequencies. Because the CALIPSO observables do not sufficiently constrain the determination of the aerosol, the surface type is used to augment the selection criteria. Distributions of the total attenuated color ratios show that the use of surface type in the typing algorithm does not result in abrupt and artificial changes in aerosol type or extinction.

Natural mineral dust and heavy anthropogenic pollution and its complex interactions cause significant environmental problems in East Asia. Due to restrictions of observing technique, real-time morphological change in Asian dust particles owing to coating process of anthropogenic pollutants is still statistically unclear. Here, we first used a newly developed, single-particle polarization detector and quantitatively investigate the evolution of the polarization property of backscattering light reflected from dust particle as they were mixing with anthropogenic pollutants in North China. The decrease in observed depolarization ratio is mainly attributed to the decrease of aspect ratio of the dust particles as a result of continuous coating processes. Hygroscopic growth of Calcium nitrate (Ca(NO3)(2)) on the surface of the dust particles played a vital role, particularly when they are stagnant in the polluted region with high RH conditions. Reliable statistics highlight the significant importance of internally mixed, 'quasi-spherical' Asian dust particles, which markedly act as cloud condensation nuclei and exert regional climate change.

An automatic system for detecting and counting sister chromatid exchanges in human chromosomes has been developed. Metaphase chromosomes from lymphocytes which had incorporated 5-bromodeoxyuridine for two replication cycles were treated with the dye 33258 Hoechst and photodegraded so that the sister chromatids exhibited differential Giemsa staining. A computer-controlled television-microscope system was used to acquire digitized metaphase spread images by direct scanning of microscope slides. Individual objects in the images were identified by a thresholding procedure. The probability that each object was a single, separate chromosome was estimated from size and shape measurements. An analysis of the spatial relationships of the dark-chromatid regions of each object yielded a set of possible exchange locations and estimated probabilities that such locations corresponded to sister chromatid exchanges. A normalized estimate of the sister chromatid exchange frequency was obtained by summing the joint probabilities that a location contained an exchange within a single, separate chromosome over the set of chromosomes from one or more cells and dividing by the expected value of the total chromosome area analyzed. Comparison with manual scoring of exchanges showed satisfactory agreement up to levels of approximately 30 sister chromatid exchanges/cell, or slightly more than twice control levels. The processing time for this automated sister chromatid exchange detection system was comparable to that of manual scoring.

Ground-based measurements were carried out during field campaigns in April–June of 2010, 2011 and 2012 over northwestern China at Minqin, the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) and Dunhuang. In this study, three dust cases were examined, and the statistical results of dust occurrence, along with physical and optical properties, were analyzed. The results show that both lofted dust layers and near-surface dust layers were characterized by extinction coefficients of 0.25–1.05 km−1 and high particle depolarization ratios (PDRs) of 0.25–0.40 at 527 nm wavelength. During the three campaigns, the frequencies of dust occurrence retrieved from the lidar observations were all higher than 88%, and the highest frequency was in April. The vertical distributions revealed that the maximum height of dust layers typically reached 7.8–9 km or higher. The high intensity of dust layers mostly occurred within the planetary boundary layer (PBL). The monthly averaged PDRs decreased from April to June, which implies a dust load reduction. A comparison of the relationship between the aerosol optical depth at 500 nm (AOD500) and the Angstrom exponent at 440–870 nm (AE440–870) confirms that there is a more complex mixture of dust aerosols with other types of aerosols when the effects of human activities become significant.