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Measuring the distribution of atmospheric aerosol concentration is of great significance for accurately assessing the scale of explosions and fires, the evolution of atmospheric environment, and so on. Due to the effect of atmospheric diffusion and other complex meteorological conditions, the distribution of aerosol concentration will change significantly in a short period of time, which puts higher requirements on the speed of aerosol concentration measurement. The existing measurement technology mainly uses LIDAR for intensive sampling of aerosol in a region. Although lidar can achieve accurate measurement of the average concentration of atmospheric aerosol more conveniently, due to longer data processing time and more measurement sampling times, the timeliness of lidar remote sensing has decreased, resulting in the problem of difficult to capture the shape of atmospheric smoke and clouds in a timely manner. Therefore, this study proposes a fast reconstruction deep network model of aerosol extinction coefficient for lidar remote sensing from the perspective of sparse sampling-reconstruction. This model eliminates the feature distribution difference between lidar return signals under sparse sampling and conventional dense sampling by using unsupervised generative adversarial networks from the perspective of transfer learning. Then, the extinction coefficient reconstruction network with the encoding-decoding structure maps the low-dimensional abstract features of aerosol concentration distribution back to the high-dimensional extinction coefficient representation space. This model greatly reduces the sampling number of lidar, thereby reducing the total time required for aerosol extinction coefficient inversion. Experimental measurements of smoke and clouds above a thermal power plant show that the proposed deep network model can reduce more than 50% of the lidar sampling times within the allowable error range. This indicates that the model has the ability to significantly improve the remote sensing measurement efficiency of lidar for atmospheric aerosols.

Particle matter (PM) mass concentrations have an important influence on human and environmental health. Lidar plays an important role in the monitoring of PM concentrations. However, the accuracy of PM concentrations retrieved via lidar depends on the performance of the conversion model from the aerosol extinction coefficient (EC) to PM concentration. Therefore, surface PM concentrations, aerosol EC and five meteorological factors are used to build the conversion model that can also be applicable to lidar for retrieving PM concentrations. In this study, the traditional linear model (LM), random forest (RF) and artificial neural network (ANN) algorithms are used to estimate the mass concentrations of PM with aerodynamic diameters < 1 µm (PM1), 2.5 µm (PM2.5) and 10 µm (PM10). The influence of meteorological factors on the conversion model is analyzed. The results show that the meteorological parameters play a non-ignorable role in the model of PM retrieval based on EC, especially when retrieving PM10. Moreover, the performance of three models is investigated by comparing with the surface measurements. The results indicate that the RF and ANN models are more suitable to estimate PM than the LM model. The diurnal variations in mean relative error (MRE) from the three models are then analyzed. There is a diurnal pattern in MRE values, meaning that the maximum values occur in the afternoon and the minimum values occur at night. In addition, there are subtle differences in performance between two machine learning (ML) models. After analysis, it is found that for PM10, the RF method is superior to the ANN when the EC value is small, while the ANN method is superior to the RF when the EC value is relatively high, and the EC threshold is set to 0.6 km−1. For PM1 and PM2.5 estimation, the ANN is the most appropriate model. Finally, accurate diurnal variations in PM1 and PM2.5 based on the ANN model and PM10 based on the combined model of RF and ANN (named RA) are investigated. The results exhibit that the daily maximum values of PM1, PM2.5 and PM10 in the Wuhan area all occur at approximately 08:00–10:00 local time (LT), which is mainly due to the impact of commuter vehicle emissions and the impact of secondary photochemistry response aggravated by sufficient illumination and temperature rises after sunrise. These research results provide an important basis for particulate matter monitoring. [ABSTRACT FROM AUTHOR]

As a passive remote sensing technique, MAX-DOAS method was widely used to investigate the vertical profiles of aerosol and trace gases in the lower troposphere. However, the measurements for midlatitude marine boundary layer are rarely reported, especially during the storm weather system. In this study, the MAX-DOAS was used to retrieve the aerosol, HCHO and NO 2 vertical distribution at Huaniao Island of East China Sea in summer 2018, during which a strong tropical cyclone developed and passed through the measurement site. The observed aerosol optical depth (AOD), HCHO- and NO 2 - VCDs (Vertical Column Density) were in the range of 0.19-0.97, (2.57-12.27) × 1015 molec/cm2, (1.24-4.71) × 1015 molec/cm2, which is much higher than remote ocean area due to the short distance to continent. The vertically resolved aerosol extinction coefficient (AEC), HCHO and NO 2 presented the decline trend with the increase of height. After the typhoon passing through, the distribution of high levels of aerosol and HCHO stretched to about 1 km and the abundances of the bottom layer were found as double higher than before, reaching 0.51 km−1 and 2.44 ppbv, while NO 2 was still constrained within about 300 m with 2.59 ppbv in the bottom layer. The impacts of typhoon process forced air mass were also observed at the suburban site in Shanghai in view of both the aerosol extinction and chemical components. The different changes on air quality associated with typhoon and its mechanism in two different environments: coastal island and coastal city are worthy of further investigation as it frequent occurred in East Asia during summer and fall. [Display omitted] [ABSTRACT FROM AUTHOR]

Atmospheric boundary layer (ABL) structure was a crucial factor in altering the vertical aerosol distribution and modulating the impact of regional aerosol transport on the atmospheric environment in the receptor region. The long-term characteristics of ABL structures for different vertical aerosol distributions and the distinct influencing mechanisms between daytime and nighttime aerosol transport interacting with the diurnal ABL transition have rarely been studied in the receptor regions. Based on 9-year (2013–2021) satellite-retrieved profiles of aerosol extinction coefficients and meteorological sounding data, we targeted Wuhan, an urban city with noteworthy transport contribution in central China, to reveal the general wintertime transport height of ∼500 m and the corresponding unstable ABL structure during regional transport. By comparing typical daytime and nighttime aerosol transport with high-resolution Lidar observations, the aerosol transport near the ABL top coupled with intense mechanical mixing provided sufficient meteorological conditions for heavy aerosol pollution formation in the receptor regions, which was more favorable during nighttime transport followed by the adequate ABL development after sunrise. These findings enhance our comprehension of the ABL impact on air pollution in the receptor regions, which have implications for the precise prevention and control of the regional atmospheric environment. [Display omitted] • Aerosols were generally transported with unstable ABL structures in Wuhan. • Aerosol transport near ABL top with mechanical mixing accelerated aerosol pollution. • Nocturnal transport with daytime ABL development deteriorated aerosol pollution. [ABSTRACT FROM AUTHOR]

Copyright of Laser Technology is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Based on continuous observations of aerosol optical properties from sun-photometer and PM2.5 concentration, the variation of aerosol optical depth, single scattering albedo and asymmetry factor during a pollution episode in Beijing from 25 January to 28 January in 2018 are analyzed. Combined with Raman-Mie Lidar vertical detection, the vertical variation of aerosol extinction coefficient is analyzed in detail. Based on ground-based observations, using a shortwave radiative transfer model, the shortwave radiative heating rates under the clear sky background during the pollution episode are calculated. Results show that under clean condition (25 January 2018), the average daily PM2.5 concentration is 19.00 μg·m-3, aerosol optical depth at 440 nm is 0.13, single scattering albedo is 0.87, and the extinction coefficient of aerosol is less than 0.10 km-1. During the pollution episode (26-27 January 2018), the average daily PM2.5 concentration is 83.21 μg·m-3, aerosol optical depth is 2.48, single scattering albedo increases to 0.94, the main aerosol extinction layer height increases to 3.00 km and the mean extinction coefficient of the whole layer is 0.43 km-1. The aerosol layer can heat the atmosphere evidently, the magnitude of radiative heating rates by aerosol depends on distribution of the aerosol in the vertical direction, and the heating rate under the concentrated heating layer decreases rapidly. Under clean condition, extinction coefficient is less than 0.1 km-1 which causes the shortwave radiative heating rate of aerosol layer within 10.00 K·day-1. During the pollution episode, the strong heating effect in the middle and upper aerosol layers (1.50-3.00 km) where the average shortwave radiative heating rate reaches 13.89 K·day-1, while the lower aerosol layer (within 1.50 km) has a weak heating effect, and the average shortwave radiative heating rate within 1.50 km is only 0.99 K·day-1. Heating rate accuracy is affected by single scattering albedo, the increased aerosol scattering ability would weaken the heating effect on the atmosphere, and the heating rate in pollution condition is more sensitive to changes of aerosol scattering ability. With the mean extinction coefficient of the whole layer being 0.43 km-1, the increase of single scattering albedo from 0.87 to 0.94 cause the heating rate of the upper and middle aerosol layers decreases by 3.74 K·day-1, while the heating rate of the lower aerosol layer increases by 0.81 K·day-1 on 27 January 2018.

Abstract This study provides insights on the composition and variability of atmospheric aerosols over the United Arab Emirates (UAE) by analyzing the atmospheric conditions together with 14 years (2006–2019) of aerosol optical depth (AOD) retrieved from CALIPSO (Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite, and 7 years of AOD measured from the ground‐based Aerosol Robotic Network (AERONET). We found that mineral dust is the most prevailing aerosol subtype. In addition, polluted dust and polluted continental aerosols are observed mostly in the cold season. The AOD is higher in spring and summer, when the atmospheric conditions are more favorable to the occurrence of dust events. Moreover, there is another peak in winter associated with dust storms triggered by mid‐latitude baroclinic systems. In summer’s daytime, extinction coefficients in excess of 0.2 km−1 are observed up to 3–4 km above the surface, as a result of the warmer and windier conditions. In the cold season and at night, the dust layers are confined to the lower atmosphere below 2 km. On a climatological time scale, we found that the AOD over the UAE has been decreasing since 2009, possibly due to the increasing trend in precipitation and changes in land use. This study highlights the large contribution of dust aerosols to the total aerosol load over the UAE and stresses on the need to account for mineral dust aerosols in climate‐air pollution related studies as well as weather and air quality forecasts.

This study provides insights on the composition and variability of atmospheric aerosols over the United Arab Emirates (UAE) by analyzing the atmospheric conditions together with 14 years (2006–2019) of aerosol optical depth (AOD) retrieved from CALIPSO (Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite, and 7 years of AOD measured from the ground‐based Aerosol Robotic Network (AERONET). We found that mineral dust is the most prevailing aerosol subtype. In addition, polluted dust and polluted continental aerosols are observed mostly in the cold season. The AOD is higher in spring and summer, when the atmospheric conditions are more favorable to the occurrence of dust events. Moreover, there is another peak in winter associated with dust storms triggered by mid‐latitude baroclinic systems. In summer's daytime, extinction coefficients in excess of 0.2 km−1 are observed up to 3–4 km above the surface, as a result of the warmer and windier conditions. In the cold season and at night, the dust layers are confined to the lower atmosphere below 2 km. On a climatological time scale, we found that the AOD over the UAE has been decreasing since 2009, possibly due to the increasing trend in precipitation and changes in land use. This study highlights the large contribution of dust aerosols to the total aerosol load over the UAE and stresses on the need to account for mineral dust aerosols in climate‐air pollution related studies as well as weather and air quality forecasts. Key Points: Over the UAE, dust is the prevailing aerosol subtype, polluted dust and polluted continental aerosols are also observed mostly in winterIn summer, aerosols are observed up to 3–4 km above the surface, due to a deeper boundary layer. In winter they are confined below 2 kmAOD is higher in spring and summer and it has been decreasing since 2009 in correlation with positive precipitation trends [ABSTRACT FROM AUTHOR]

Default aerosol extinction coefficient profiles are commonly used instead of measured profiles in radiative transfer modeling, increasing the uncertainties in the simulations. The present study aimed to determine the magnitude of these uncertainties and contribute towards the understanding of the complex interactions between aerosols and solar radiation. Default, artificial and measured profiles of the aerosol extinction coefficient were used to simulate the profiles of different radiometric quantities in the atmosphere for different surface, atmospheric, and aerosol properties and for four spectral bands: ultraviolet-B, ultraviolet-A, visible, and near-infrared. Case studies were performed over different areas in Europe and North Africa. Analysis of the results showed that under cloudless skies, changing the altitude of an artificial aerosol layer has minor impact on the levels of shortwave radiation at the top and bottom of the atmosphere, even for high aerosol loads. Differences of up to 30% were, however, detected for individual spectral bands. Using measured instead of default profiles for the simulations led to more significant differences in the atmosphere, which became very large during dust episodes (10–60% for actinic flux at altitudes between 1 and 2 km, and up to 15 K/day for heating rates depending on the site and solar elevation).

An observation experiment on atmospheric aerosols based on Mie-Raman scattering lidar in northern suburb of Nanjing was introduced. To avoid the saturation effect of strong signals near the ground, the detection height of Raman scattering lidar was set high. For better inversion results, Mie-Raman scattering lidar's aerosol observational data were processed by wavelet denoising. Appropriate threshold was selected to denoise the experimental observed data. The atmospheric aerosol extinction coefficient profiles in the upper troposphere were retrieved by Raman scattering lidar. The atmospheric aerosol extinction coefficient profiles in the lower troposphere were retrieved by Mie scattering lidar. The retrieved upper tropospheric aerosol extinction coefficient profiles provided one boundary value for Fernald method. [ABSTRACT FROM AUTHOR]

Wuhan is a rapidly developing large city in central China. To analyze the aerosol characteristics over Wuhan, the optical properties of the nocturnal aerosol layers in the lower troposphere were observed using a ground-based LIDAR(Light Detection And Ranging) located in the Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing (LIESMARS) from Wuhan University, China (114°21′E, 30°32′N) in January 2013–January 2015. The vertical distribution and temporal variation of tropospheric aerosols over Wuhan were summarized. The atmospheric boundary layer height (ABLH) was mainly at an altitude of 1.5–2 km (~33.1% probability), with an annual average of 1.66 km. The ABLH was higher in spring–summer (~2 km) and lower in autumn–winter (~1.2 km). The aerosol optical depth (AOD) was higher in spring–autumn than in summer–winter. The highest AOD was about 0.79 in October and the lowest was about 0.08 in January. The annual average was about 0.3. To study the relationship between the AOD and the particulate matter ≤2.5 µm in the aerodynamic diameter (PM2.5) in the lower troposphere, a typical haze event from 9–14 October 2014 was investigated. The results showed a correlation coefficient of 0.5165 between these two variables.

The variability of the volume concentration and mean radius of particles of the fine and coarse fractions of surface aerosol in summer has been studied from the results of solution of the inverse problem for spectral measurements of the aerosol extinction coefficient. It has been shown that the main contribution (80%) to the total volume of near-surface aerosol is made by particles of the coarse fraction. The mean radius of fine particles varies from 0.08 to 0.25 μm. The variation range of the mean radius of coarse aerosol is 1.06–3 μm. The influence of atmosphere smokiness on variations in microstructure parameters is considered. The variability of retrieved microstructure parameters of near-surface aerosol is compared with similar results obtained from solar photometry data. [ABSTRACT FROM AUTHOR]

Results on retrieving parameters of the near-surface aerosol microstructure from spectral measurements of the coefficient of aerosol extinction of light in summer are presented. The experimental data have been obtained using an atmospheric transmittance meter at 11 wavelengths in the range 0.45–3.91 μm on a horizontal path near Tomsk. The inverse problem was solved using a numerical algorithm based on the integral distribution method. In the first part of the work, the variability of the geometrical cross section of particles from the fine fraction, coarse fraction, and total ensemble is analyzed. The effect of the smoke pollution of the atmosphere on variations in microstructure parameters has been considered. It has been shown that the main contribution (73–77%) to the total cross section of near-surface aerosol is made by particles of the fine fraction. Coefficients of variation in the cross sections of particles on monthly intervals without regard to the influence of smokes are high within 53–61% for the fine fraction and 53–69% for the coarse fraction of aerosol. The correlations between the aerosol extinction coefficients at different wavelengths and retrieved parameters of the aerosol microstructure have been studied. [ABSTRACT FROM AUTHOR]

Abstract Multi-AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were performed to remote sensing the aerosol vertical profiles in suburb area of Shanghai, China from April to December 2017. The retrieval of aerosol extinction was based on the optimal estimation method combing the measured oxygen dimer O 4 absorption with simulation of forward radiative transfer model. It suggests that the employment of O 4 correction factor (CF O4) for daily aerosol retrieval should be adjusted, which includes three typical cases that a fixed CF O4 , no usage of CF O4 and different CF O4 in the morning and afternoon. In cases of using CF O4 , elevation angle dependent CF O 4 (α) were further proposed. Moreover, the retrieval results can be improved if the local sounding data of atmospheric temperature and pressure profiles were introduced into the forward radiative transfer model without utilizing additional CF O4. Afterwards, the retrieved Aerosol Optical Depth (AOD) and the surface Aerosol Extinction Coefficient (AEC) was in a good agreement with the AOD obtained from sun photometer observations and in-suit PM 2.5 concentrations, with a correlation coefficient R of 0.866 and 0.833, respectively. Besides, the vertical AEC profiles retrieved by MAX-DOAS were also validated well by the co-located lidar measurement. It can be found that the particles were mainly distributed below 1 km, and the maximum AEC usually appeared in the lowest 300 m and decreased with the altitudes. The averaged AEC within 1 km varied from 0.20 to 0.75 km−1, 0.25 to 1.08 km−1, 0.55 to 2.45 km−1 and 0.70 to 2.75 km−1 under different air quality of Grade II, III, IV and V. The sounding meteorological parameters and backward trajectories of air masses were integrated to diagnose the influencing factor of AEC at different altitudes, which illustrated that the AEC levels at lowest layer were impacted by the long distance transportation of air pollutants from north-northwest and regional local air pollution nearby during the winter time. The study shows that ground-based MAX-DOAS observation is powerful remote sensing technique to provide better understanding of aerosol properties at both ground surface and higher altitudes. Highlights • Aerosol vertical distribution were obtained by MAX-DOAS measurements in Shanghai. • O 4 correction factor (CF O4) need to be adjusted in the aerosol retrieval scheme. • Using local temperature and pressure profiles can improve the aerosol retrieval. • MAX-DOAS remote sensing are well validated by other auxiliary datasets. • High aerosol extinction usually occurred at the lowest layer below 0.3 km in winter. [ABSTRACT FROM AUTHOR]

The aerosol optical characteristics in the East Asian cities of Fukuoka and Beijing were measured from 2010 to 2014. These long-term season-crossing data were compared to understand the differences between the aerosol characteristics at a source and a downstream region. Previously, few long-term, season-crossing observations have been reported. Using a method developed by one of the present authors, the measurement data were analyzed so that the retrieved optical properties can be more accurate than those obtained in previous studies. Using these data, the aerosol characteristics and their frequency distributions were reliably obtained. In Fukuoka, the annual means of the extinction, scattering, and absorption coefficients Cext (525 nm), Csca (525 nm), and Cabs (520 nm) were 74.6, 66.1, and 8.1 Mm-1, respectively, whereas those in Beijing were 412.1, 367.2, and 42.4 Mm-1, respectively. The coefficients in Fukuoka were approximately one-fifth of those in Beijing. The single-scattering albedos ω0 (525 nm) in Fukuoka and Beijing were 0.877 and 0.868, respectively. The asymmetry factors G (525 nm) in the two cities were 0.599 and 0.656, respectively. The extinction Ångström exponents αext in the two cities were 1.555 and 0.855, respectively. The absorption Ångström exponents αabs in the two cities were 1.106 and 0.977, respectively. The fine- and coarse-mode volume fractions in Fukuoka were approximately 80 % and 20 %, and those in Beijing were both approximately 50 %, except in summer. Cext, Csca, and Cabs showed a seasonal variation in both cities. Some other properties also showed a seasonal variation. In particular, the seasonal variation in α abs was clear in both cities; it tended to be small in summer and large in winter. The frequency distributions of various parameters were also investigated. The frequency of Cext > 500 Mm-1 in Fukuoka was very low, and large Cext values were recorded more frequently in spring than in other seasons. In Beijing, Cext > 1000 Mm-1 values were recorded more frequently, and the frequency of 10 Mm-1 £ Cabs £ 60 Mm-1 was high in spring and summer. Furthermore, αabs < 1.0 values were recorded frequently, which cannot be explained by the simple external mixture of absorbing aerosols. To demonstrate the usefulness of the data obtained in this study, the relationships among αabs, αext, the volume size distribution, the imaginary part of the refractive index, and ω0 were investigated, and two characteristic cases in Beijing (winter) and Fukuoka (spring) were preliminarily analyzed. [ABSTRACT FROM AUTHOR]

In this paper, we explore the horizontal extinction characteristics under different weather conditions on the ocean surface with on-site experiments on the Bo-hai and Huang-hai Seas in the summer of 2016. An experimental lidar system is designed to collect the on-site experimental data. By aiming at the inhomogeneity and uncertainty of the horizontal aerosol in practice, a joint retrieval method is proposed to retrieve the aerosol extinction coefficients (AEC) from the raw data along the optical path. The retrieval results of both the simulated and the real signals demonstrate that the joint retrieval method is practical. Finally, the sequence observation results of the on-site experiments under different weather conditions are reported and analyzed. These results can provide the attenuation information to analyze the atmospheric aerosol characteristics on the ocean surface. [ABSTRACT FROM AUTHOR]

A lidar detects atmospheric parameters by transmitting laser pulse to the atmosphere and receiving the backscattering signals from molecules and aerosol particles. Because of the small backscattering cross section, a lidar usually uses the high sensitive photomultiplier and avalanche photodiode as detector and uses photon counting technology for collection of weak backscatter signals. Photon Counting enables the capturing of extremely weak lidar return from long distance, throughout dark background, by a long time accumulation. Because of the strong solar background, the signal-to-noise ratio of lidar during daytime could be greatly restricted, especially for the lidar operating at visible wavelengths where solar background is prominent. Narrow band-pass filters must therefore be installed in order to isolate solar background noise at wavelengths close to that of the lidar receiving channel, whereas the background light in superposition with signal spectrum, limits an effective margin for signal-to-noise ratio (SNR) improvement. This work describes a lidar prototype operating at the Fraunhofer lines, the invisible band of solar spectrum, to achieve photon counting under intense solar background. The photon counting lidar prototype in Fraunhofer lines devised was used to observe the atmospheric boundary layer. The SNR was improved 2-3 times by operating the lidar at the wavelength in solar dark lines. The aerosol extinctions illustrate the vertical structures of aerosol in the atmospheric boundary over Qingdao suburban during summer 2011.

The horizontal and vertical distributions of aerosol extinction coefficient (AEC) and mass concentration over east China in October 2010 were investigated by using an online-coupled regional climate model and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) data. Model performance was evaluated comprehensively against ground observations of meteorological variables and PM 10 concentrations and CALIPSO retrieved AEC profiles, which demonstrated a good ability of the model in simulating spatial distribution and evolution of aerosol concentration and optical properties. Severe pollution episodes were found over wide areas of east China during the study period, with the maximum mean PM 10 concentration exceeding 200 μg m −3 in the Chongqing district and a part of the lower reaches of the Yellow River on 8–10 October. Both CALIPSO retrievals and model simulations revealed high AEC values (≥1 km −1 ) often occurred within 2 km above ground over most areas of east China. AEC vertical profile in or in the vicinity of China major cities along CALIPSO orbit track exhibited two typical features: one was AEC reached its maximum (∼4 km −1 ) near the surface (<200 m) and decreased rapidly to < 0.1 km −1 at altitudes above 1 km, another one was AEC peaked at higher altitudes of about 0.5–1 km with a maximum up to 3 km −1 . AEC vertical profile was strongly dependent on vertical distribution of both aerosol concentration, composition and relative humidity. The vertical cross sections over typical regions of east China exhibited a decreasing AEC in magnitude from the continent to the China seas. Over the continent, AEC was either maximum near the surface or peaked at higher altitudes (0.5–1.0 km) due to increases of relative humidity or aerosol concentration in those regions, whereas over the seas of China, AEC profile was characterized by peak values at an altitude around 1 km, mainly due to an elevated relative humidity there, which favored rapid aerosol hygroscopic growth and consequently AEC increase. [ABSTRACT FROM AUTHOR]

Due to a reliance on solar radiation, the aerosol optical depth (AOD) is observed only during the day by passive satellite-based instruments such as the MODerate resolution Imaging Spectroradiometer (MODIS). Research on urban air quality, atmospheric turbidity, and evolution of aerosols in the atmospheric boundary layer, however, requires 24-h measurement of aerosols. A lidar system is capable of detecting the vertical distribution of the aerosol extinction coefficient and calculating the AOD throughout the day, but routinely lidar observation is still quite limited and the results from MODIS and lidar sometimes are contradictory in China. In this study, long-term lidar observations from 2005 to 2009 over Hong Kong were analyzed with a focus on identification of the reasons for different seasonal variation in the AOD data obtained from MODIS and lidar. The lidar-retrieved AOD shows the lowest average level, but has the most significant diurnal variation during the summer. When considering only a 5-h period between 10:00 a.m. and 3:00 p.m. local time to match satellite passages, the average of the lidar-retrieved AOD doubles during the summer and exceeds that during the winter. This finding is consistent with the MODIS observation of a higher AOD during the summer and a lower AOD during the winter. The increase in the aerosol extinction coefficient in the upper level of the mixing layer makes the greatest contribution to the increase in the AOD at midday during the summer. These assessments suggest that large over-estimation may occur when long-term averages of AOD are estimated from passive satellite observations. [ABSTRACT FROM AUTHOR]

A comparative study on the vertical distributions of aerosol optical properties during haze and floating dust weather in Shanghai was conducted based on the data obtained from a micro pulse lidar. There was a distinct difference in layer thickness and extinction coefficient under the two types of weather conditions. Aerosols were concentrated below 1 km and the aerosol extinction coefficients ranged from 0.25 to 1.50 km on haze days. In contrast, aerosols with smaller extinction coefficients (0.20-0.35 km) accumulated mainly from the surface to 2 km on floating dust days. The seasonal variations of extinction and aerosol optical depth (AOD) for both haze and floating dust cases were similar-greatest in winter, smaller in spring, and smallest in autumn. More than 85% of the aerosols appeared in the atmosphere below 1 km during severe haze and floating dust weather. The diurnal variation of the extinction coefficient of haze exhibited a bimodal shape with two peaks in the morning or at noon, and at nightfall, respectively. The aerosol extinction coefficient gradually increased throughout the day during floating dust weather. Case studies showed that haze aerosols were generated from the surface and then lifted up, but floating dust aerosols were transported vertically from higher altitude to the surface. The AOD during floating dust weather was higher than that during haze. The boundary layer was more stable during haze than during floating dust weather. [ABSTRACT FROM AUTHOR]

Aerosol extinction coefficient profile is an essential parameter for atmospheric radiation model. It is difficult to get higher signal to noise ratio (SNR) of backscattering lidar from the ground to the tropopause especially in near range. Higher SNR problem can be solved by combining side-scattering and backscattering lidar. Using Raman-scattering lidar, aerosol extinction to backscatter ratio (lidar ratio) can be got. Based on side-scattering, backscattering and Raman-scattering lidar system, aerosol extinction coefficient is retrieved precisely from the earth’s surface to the tropopause. Case studies show this method is reasonable and feasible. [ABSTRACT FROM AUTHOR]

The method of retrieving atmospheric aerosol extinction coefficient from Raman lidar data is analysed. The logarithm for the ratio of nitrogen molecules density to distance correction signal is focused on and is discussed deeply. The weighted least squares method is used to lit the discrete signals. The weights are valued according to the kind of photomultiplier lube and its detecting mode. The profiles of the atmosphere aerosol's extinction coefficient are delectcd by Raman lidar at Wuhan. China. From the distribution of the aerosols, the structure and the change of atmospheric boundary layer are showed clearly. [ABSTRACT FROM AUTHOR]

Abstract: This article describes the design and performance of a cavity ring-down spectroscopic (CRDS) instrument for measuring extinction coefficients of laboratory and ambient atmospheric aerosols. Through averaging 1000 individual waveforms, a minimum detectable aerosol extinction coefficient of 6.1×10−7 m−1 is achieved. Tests with polystyrene spheres (PSS), we suggested this CRDS system could measure the extinction coefficient of aerosol with uncertainty <3% under laboratory controlled experimental conditions. The visual range measured with CRDS agrees well with visibility observations from Shanghai Meteorological Bureau. Combined with the TSI integrating nephelometer and NO x analyzer, CRDS was used to monitor the optical properties of ambient aerosols in the heavy pollution episode. The uncertainty for using the CRDS and TSI nephelometer to measure single scattering albedo (SSA) in an ambient measurement is estimated to be <12%. [Copyright &y& Elsevier]

Statistical processing is performed for data sets obtained at the Tomsk site in 2003–2005 on the boundary-layer spectral extinction coefficient β(λ) and the bulk-atmospheric aerosol optical depth τ(λ) in the wavelength range λ = 0.44–4.0 μ m. It is found that the maximal correlation between variations in β(λ) and τ(λ) is observed in the 2003 set under conditions of increased smoke content. It is shown that this can be related to an increase in the variability range of the aerosol extinction of radiation along both boundary-layer and in the atmospheric column at the time of arrival of smoke formations at the observation site. The correlation coefficients ρβτ(λ) for the cleaner conditions of 2004 and 2005 are much lower. The calculated eigenvectors of the joint autocorrelation matrix {β i(λ), τ i(λ)} showed that the decrease in correlation between variations in β(λ) and τ(λ) can be related to the process of particle transport out of the ground level by convective and turbulent flows. This leads to aerosol depletion in the ground level and accumulation in the atmospheric column. The inverse process related to aerosol sedimentation is also possible. [ABSTRACT FROM AUTHOR]

The phase function and extinction coefficient measured simultaneously are interpreted in terms of surface distribution function and mean effective aspect ratio of aerosol particles. All optical data were collected in the atmosphere of Vienna during field campaign in June 2005. It is shown that behavior of aspect ratio of Viennese aerosols has relation to relative humidity in such a way, that nearly spherical particles (with aspect ratio ε≈1) might became aspherical with ε≈1.3–1.6 under low relative humidity conditions. Typically, >80% of all Viennese aerosols have the aspect ratio <1.4, so the morphology of these particles behaves like perturbed spheres. The ε, exceptionally, can reach the value about 2, but these situations occur with probability <2%. Most typically, the aspect ratio peaks at ε≈1.2 in the atmosphere of Vienna. [Copyright &y& Elsevier]

Abstract: Aerosol optical data obtained by means of ground-based methods are applied to determine microphysical properties of aerosols in the atmosphere of Vienna-city. The measured aerosol extinction coefficient A serves as a source of information on the ambient aerosols. A large database of extinction efficiency factors for a set of irregularly shaped as well as the spherical particles of various sizes is pre-calculated and employed in the inversion procedure. The assumed particle models differ in chemical composition and are representative for most typical aerosol systems in the urban atmospheres. All database records are taken into a regularization scheme to solve the inverse problem for aerosol size distribution using measured extinction data. In addition, subsidiary data on spectral sky radiance are successfully incorporated into the mathematical model to retrieve the information on aerosol effective refractive index in the visible. As for Vienna, the aerosol extinction is a decreasing function of wavelength in visible spectrum—it indicates the predominance of sub-micrometer-sized particles in the atmosphere. The surface distribution function s(r)=dS/dr of aerosol particles customarily peaks at radii r≈0.2–0.3μm, while the volume distribution function v(r)=dV/dr∼rs(r) has a mode at radii about 0.3–0.4μm. Analysing size distributions dV/dlog(r) for irregularly shaped particles it is shown that the daily profile of this function is smoothly evolving and almost typically accounts for a first mode at radii between 0.8 and 0.9μm. [Copyright &y& Elsevier]

The paper presents a study of the sea-breeze transition periods performed using the relative volume extinction coefficient of the aerosol. The study is based on data acquired by a ground-based aerosol lidar and conventional meteorological instruments. The observations took place near Akhtopol in the southeastern corner of Bulgaria in the period 18–25 June 1993. The attention is focused on aerosol structure, and in particular on the distribution of aerosol extinction, in the lowest 700 m across shoreline during the transition periods and development of the breeze front. The lidar cross-sections from the transition periods reveal existence of three differing zones in the relative extinction distribution: a zone over the surface, which possesses the optical properties of the entire layer which develops subsequently; a second zone, which possesses the optical characteristics typical for the circulation before the transition; and a third zone, characterized by the lowest relative extinction and placed between the other two, which dissipates by the end of the transition. The estimated values of the extinction coefficient are significant for comparison only, i.e. relatively, rather than as absolute magnitudes, since no calibration using an independent mean was performed. The paper also discusses some peculiarities of the transition regime caused by the orography of the site. [Copyright &y& Elsevier]

Default aerosol extinction coefficient profiles are commonly used instead of measured profiles in radiative transfer modeling, increasing the uncertainties in the simulations. The present study aimed to determine the magnitude of these uncertainties and contribute towards the understanding of the complex interactions between aerosols and solar radiation. Default, artificial and measured profiles of the aerosol extinction coefficient were used to simulate the profiles of different radiometric quantities in the atmosphere for different surface, atmospheric, and aerosol properties and for four spectral bands: ultraviolet-B, ultraviolet-A, visible, and near-infrared. Case studies were performed over different areas in Europe and North Africa. Analysis of the results showed that under cloudless skies, changing the altitude of an artificial aerosol layer has minor impact on the levels of shortwave radiation at the top and bottom of the atmosphere, even for high aerosol loads. Differences of up to 30% were, however, detected for individual spectral bands. Using measured instead of default profiles for the simulations led to more significant differences in the atmosphere, which became very large during dust episodes (10–60% for actinic flux at altitudes between 1 and 2 km, and up to 15 K/day for heating rates depending on the site and solar elevation). [ABSTRACT FROM AUTHOR]