Atmospheric Extinction Coefficient Research Articles

Characteristics of Atmospheric PM2.5 Pollution and Its Influence on Visibility in Background Areas of Ji'nan

In order to study the seasonal variations in the chemical composition of atmospheric particulate matter with diameters less than 2.5 μm (PM2.5) and its influence on visibility in background areas, atmospheric PM2.5 samples were collected in spring, summer, autumn, and winter 2016 at Qixingtai in Ji'nan. The pollution characteristics of water-soluble ions components, organic carbon (OC), and elemental carbon (EC) were analyzed, and their regional transmission contributions were studied. The results show that NH4+, SO42-, and NO3- were the main components of water-soluble ions, accounting for 90.24% of the annual total ion concentration. The secondary water soluble inorganic ions were polluted severely. NO3-/SO42- presented obvious seasonal variations of high (low) levels in winter (summer). In each season, SO42- and NH4+ existed mainly in the form of (NH4)2SO4. The value of secondary OC (SOC)/OC ranged from 21.17% to 54.21%, indicating the presence of relatively severe secondary organic pollution in this area. The sulfur oxidation ratio (SOR) value in all seasons was greater than 0.1, indicating that the secondary generation of SO42- occurs in all seasons in this region, and the value of nitrogen oxidation ratio (NOR) in all seasons was higher than the SOR value. The secondary transformation of NO2 in the Qixingtai region was stronger than that of SO2. The range of atmospheric extinction coefficient (Bext) was 172.68-320.61 Mm-1, with an annual mean of 256.48 Mm-1. The atmospheric extinction coefficient showed an obvious seasonal trend of the lowest (highest) in summer (winter). The backward airflow trajectory shows that the Qixingtai was affected mainly by the long-distance transmission from Northwest China and the ocean in spring and summer and by local sources in autumn and winter. A comparison of the characteristics of atmospheric PM2.5 pollution in Ji'nan in 2008 revealed that the influence of motor vehicles on the atmospheric environment has been significantly improved.

Aerosol optical properties under different pollution levels in the Pearl River Delta (PRD) region of China

To clarify the aerosol hygroscopic growth and optical properties of the Pearl River Delta (PRD) region, integrated observations were conducted in Heshan City of Guangdong Province from October 19 to November 17, 2014. The concentrations and chemical compositions of PM2.5, aerosol optical properties and meteorological parameters were measured. The mean value of PM2.5 increased from less than 35 (excellent) to 35-75 μg/m3 (good) and then to greater than 75 μg/m3 (pollution), corresponding to mean PM2.5 values of 24.9, 51.2, and 93.3 μg/m3, respectively. The aerosol scattering hygroscopic growth factor (f(RH = 80%)) values were 2.0, 2.12, and 2.18 for the excellent, good, and pollution levels, respectively. The atmospheric extinction coefficient (σext) and the absorption coefficient of aerosols (σap) increased, and the single scattering albedo (SSA) decreased from the excellent to the pollution levels. For different air mass sources, under excellent and good levels, the land air mass from northern Heshan had lower f(RH) and σsp values. In addition, the mixed aerosol from the sea and coastal cities had lower f(RH) and showed that the local sources of coastal cities have higher scattering characteristics in pollution periods.

Single Image-Based Scene Visibility Estimation

This paper proposes a novel method to utilize a single daylight image of the observed scene to estimate the extinction coefficient of the observed atmosphere and obtain the scene visibility. The proposed method consists of three steps. First, based on the theory of atmospheric physics, we estimate the extinction coefficient of the clear atmosphere in an observed scene. Second, a method combining the dark channel prior and the edge collapse-based transmission refinement is employed to calculate the ratio between the extinction coefficient of the observed atmosphere and that of the clear atmosphere. This ratio indicates the increased degree of the extinction coefficient due to the increment of the atmospheric turbidity. Finally, by multiplying the extinction coefficient of the clear atmosphere and the ratio, the extinction coefficient of the observed atmosphere is calculated and the scene visibility is obtained. The numerous experiments on the proposed method suggest that it performs well in measuring the scene visibility in various types of scenes without additional assistance (e.g., geometric calibration of the camera, road marking extraction, and ground truth data collection).

MÉTODO ALTERNATIVO PARA LA EVALUACIÓN DE LA POLUCIÓN ATMOSFÉRICA CAUSADA POR LA QUEMA DE BIOMASA EN PLANTACIONES DE CAÑA DE AZUCAR

This paper describes an alternative method to assess atmospheric pollution levels caused by the burning of sugar cane fields during the harvest, affecting visibility in nearby residential areas. The samples of atmospheric dispersed material were taken on glass slides exposed to the environment on different periods of time. The scattered light by these samples is measured using a digital goniometric device that moves a CCD around each sample with 2,0 arc min resolution. Scattering measurements reveals that it is possible to differentiate between the samples of 12, 24, 36 and 48 hours of integration. This method is more sensitive because it integrates through time, even when the concentrations of contaminants are low. Based on Beer-Lambert scattering model, the scattered light on the samples is related to the atmospheric extinction coefficient and the meteorological visibility measured in the same days. A good linear correlation for the different time periods (R2 > 0.94)was obtained. Finally, measured scattering levels were compared to the intraocular scattering ones calculated from CIE equation, obtaining similar values to eyes of 80 years old people

Impact of Atmospheric Circulation and Meteorological Parameters on Wintertime Atmospheric Extinction in Chengdu and Chongqing of Southwest China during 2001–2016

ABSTRACT This study investigated the effect of atmospheric circulation and meteorological parameters on the surface atmospheric extinction coefficient (SEC) in Chengdu and Chongqing of southwest China during the winters of 2001–2016. Four predominant circulation types (CT) were first identified, representing a high-pressure system in the north (CT 1), a low-pressure system in the north (CT 2), a weak high-pressure system (CT 3) and a local low-pressure system (CT 4) at a geopotential height of 850 hPa. In Chengdu, variation in the SEC between the CTs was dominated by meteorological factors, such as wind, subsidence, inversion and planetary boundary layer height (PBLH), whereas the variation within each CT was mainly controlled by dispersion-related parameters (such as wind speed and PBLH for CTs 1, 2 and 4, which were associated with strong weather systems) or chemistry-related parameters (such as RH and T for CT 3, which was associated with a weak system). In Chongqing, dispersion and chemical processes were equally important due to the weaker impact of the atmospheric circulation. A new method for discriminating between synoptic and non-synoptic signals in SEC time series was proposed to estimate the effect of the circulation intensity by considering multiple influential meteorological parameters. Atmospheric circulation heightened the interannual SEC variations by ~23% in both Chengdu and Chongqing in more than half of the years but reduced them by 44.79% and 8.02% in Chengdu and Chongqing, respectively, in the remaining years. Synoptic changes were estimated to contribute 5–10% of the decreasing SEC trend but less than 1% of the increasing trend.

Accurate inversion of tropospheric aerosol extinction coefficient profile by Mie-Raman lidar

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.

Novel Lidar algorithm for horizontal visibility measurement and sea fog monitoring.

Traditionally, Klett and Fernald inversion estimates an initial value using the slope method for horizontal visibility, which causes inversion uncertainty. We proposed an algorithm to retrieve the extinction coefficient and visibility distribution information from scanning Lidar to overcome instability due to initial atmospheric extinction coefficient choice and assuming the Lidar ratio. Numerical simulations showed that extinction coefficient maximum relative was much larger for inhomogeneous atmosphere using the Klett method, reaching 0.31. In contrast, it is only 0.049 using the proposed algorithm. Experimental showed that the proposed algorithm and scanning Lidar system provide very high stability and accuracy, can work in different weather conditions and monitor sea fog evolution over real time, and is suitable for various situations with different visibility.

An RBF neural network approach for retrieving atmospheric extinction coefficients based on lidar measurements

Lidar is an effective remote sensing method for obtaining the optical properties of aerosols, such as the aerosol extinction coefficient (AEC), the aerosol optical depth (AOD), and the related atmospheric visibility. However, improving the accuracy and efficiency of lidar data retrieval remains challenging due to the uncertainties associated in determining the AEC boundary value (AEC-BV) and the aerosol extinction-to-backscatter ratio (AEBR), as well as the complex and time-consuming calculations required. In this paper, we propose a novel method, a feedback radial basis function (RBF-FB), for retrieving high-precision AEC profiles based on a radial basis function neural network. First, using the secant method, we determine accurate values for AEC-BV and AEBR, and generate the AEC profiles by the Fernald method. We then choose a set of lidar signals and their corresponding AEC profiles as learning samples for network training and establish an RBF network model for AEC retrieval. Next, we correct the network output by introducing a feedback mechanism that uses the AOD measured by a sun photometer as the error criterion. Tests on measured signals confirm that the outputs of the proposed RBF-FB model are consistent with the Fernald method and have the advantages of speed and robustness.

Interpolation for Aerosol Optical Depth at Four Wavelengths over Ilorin from Observed Aeronet Data

The Aerosol Optical Depth (AOD), which is the integral part of the atmospheric extinction coefficient from the surface to the top of the atmosphere, is an important parameter for observation of visibility degradation due to atmospheric pollution, solar radiation extinction and other climate effects. The wavelength dependence of Aerosol Optical Depth (AOD) varies between different aerosol types because of their different physical and chemical characteristic. This paper presents new data points using interpolation for Aerosol Optical Depth (AOD) at four spectral wavelengths (440-870nm. The data used consist of measurements collected at Ilorin AERONET site (8°32’N, 4°34’E) for AOD and Angstrom exponent at the four wavelengths (α440-870). Angstrom empirical formula was used to compute new data points by interpolation. A Regression analysis was then used to estimate the relationship between the interpolated AOD and the observed AOD at the different wavelengths of 440nm, 500nm, 670nm and 870nm. The coefficients of determination were found to be 0.978, 0.980, 0.999 and 0.997 respectively, indicating that the interpolated data agrees well with the measured data.

Multi-wavelength light-emitting diode light source radar system and near-ground atmospheric aerosol detection

Near-ground atmospheric aerosol has a direct effect on the living and production of human, and the research on its detection attracts substantial attention from engineers and scholars in the community of environment. Traditional monitoring instruments can accurately and continuously detect the aerosols above the ground, but it is difficult for them to obtain the information about vertical distribution of near-ground aerosols. As is well known, lidar can act as an efficient method to detect the aerosol's temporal and spatial distribution. However, this technique is restricted in the potential applications of the detection of aerosol at a certain wavelengths or near range. That is because it usually presents fixed wavelengths and a large blind area. In this work, a new multi-wavelength light-emitting diode (LED) light source radar system is designed and established for detecting the characteristics of atmospheric aerosol near ground. The paper is outlined as follows. Firstly, the composition and working principle of the LED light source radar system are introduced. Based on the structure of radar's transmitter and receiver, the geometric overlap factor is analyzed and calculated. The minimum detection height of the LED light source radar system is then determined to be 60 m. Secondly, the inversion method for the echo signal of LED light source radar is studied. In consideration of the suitability of near-range detection of LED light source radar, the Fernald forward integration method is used for inversing the aerosol extinction coefficient. The calibration value of aerosol extinction coefficient is further determined with the ground visibility data. Finally, by using the designed multi-wavelength LED light source radar system (475 nm, 530 nm, and 625 nm), near-ground aerosol observation at night in Xi'an city is carried out and three atmospheric conditions including light, moderate and severe pollution days are considered. The height distribution curves of atmospheric aerosol extinction coefficient of three wavelengths within a height of nearly 300 m are obtained. The characteristics of the distribution and change of near ground aerosols are accordingly discussed. The experimental results show that the multi-wavelength LED light source radar provides an efficient implementation for detecting the vertical distribution of atmospheric aerosol near the ground, and can make up for the inadequacy of lidar in near range detection.

Polarization lidar for atmospheric monitoring

Aerosol plays an important role in global climate and weather changes. Polarization lidar captures parallel and perpendicular signals from atmosphere to research aerosols. The lidar system we used has three emission wavelengths and could obtain the atmospheric aerosol extinction coefficient, backscattering coefficient and depolarization ratio. In this paper, the design of the lidar is described. The methods of data acquisition and inversion are given. Some recent results are presented.

A new method of measuring boundary value of atmospheric extinction coefficient

We construct a nonlinear equation between the return signal and the boundary value of extinction coefficient according to the lidar equation. And according to the nonlinear equation, we put forward a new method to solve the nonlinear equation by using Broyden algorithm. The Broyden algorithm is a concrete application of the quasi-Newton method. It has faster convergence and less iteration times, and does not need to calculate the derivative value. After choosing a suitable initial value, the boundary value can be obtained through the algorithm. A 532 nm single-band Mie scattering imaging lidar system is developed in Hefei, Southern China, for real-time atmospheric aerosol/particle remote sensing. Atmospheric measurement has been performed in Science Island during night time, and the time-range distribution of atmospheric backscattering signal was recorded on April 6, 2017, by employing the imaging lidar system. Then, the boundary values are achieved based on the Broyden algorithm and the least square algorithm. It adopts the Klett backward integration method to retrieve the horizontal distribution of extinction coefficients in a range of 1 km after the acquisition of the signal by changing the distance, then the horizontal atmospheric transmittance can be achieved based on the path integral. We also conduct a contrast experiment with the one-way transmission of the horizontal light near the ground within the range of 1 km at the same time. The initial site is situated in the experimental room besides the Dongpu reservoir and the end site is located on the second floor of our office building. The important things in this experiment are that the light reaching the target surface must be fully received and the laser power should be monitored at the double-end. Then we can obtain the transmittance by the direct method. By comparing the transmittance from the direct method with the transmittance from imaging lidar between the two different ways, i.e., Broyden algorithm and least square algorithm, then the correlation coefficients are obtained to be both over 0.95 in the period. And the method introduced in this paper is a little better than the least square algorithm with a value of 0.968. Besides, the average relative errors between the two inverse methods and the direct method are 4.66% and 9.10%, respectively. The average relative errors obtained by using the least square algorithm is about twice that by using the Broyden algorithm. It can be concluded that the algorithm introduced in this paper is effective and has certain advantages for the inverse problem.

Comparison of parameterizations for the atmospheric extinction coefficient in Lin'an, China

A more precise atmospheric extinction coefficient would be advantageous for improving air quality (visibility) forecasting. In this study, the size distribution, chemical composition and relative humidity were measured in Lin'an from January 9 to 31, 2015. The merits and weaknesses of three parameterization schemes are discussed in this paper, including the non-linear fitting scheme, the IMPROVE (Interagency Monitoring of Protected Visual Environment) algorithm and the κ-elemental carbon (EC)-Mie model. Comparing the three schemes mentioned above, we find that the non-linear fitting equation requires the least amount of data, and its calculation process is the simplest. However, its calculated values are significantly influenced by specific data and fitting formulas. The uncertainty of the variable coefficients makes it difficult to directly implement this method for other datasets. The calculated values of the three versions of the IMPROVE algorithm strongly correlate with the measured values, with slopes near 1.0 and statistical indexes (R2) of 0.848, 0.858 and 0.866. However, this method is affected by the chemical compositions of the particles in different regions; for example, when the quality of PM2.5 is reconstructed from the measured data, the coefficients of different components change, thus affecting the final results. The κ-EC-Mie model objectively reflects the changes in the law of visibility, as the model considers both the chemical composition and size distribution of particles, and its predominant merit is derived from the fact that it is calculated without an empirical formula, which may eliminate the computational errors caused by the uncertainties of coefficients.

Development and accuracy of a multipoint method for measuring visibility.

Accurate measurements of visibility are of great importance in many fields. This paper reports a multipoint visibility measurement (MVM) method to measure and calculate the atmospheric transmittance, extinction coefficient, and meteorological optical range (MOR). The relative errors of atmospheric transmittance and MOR measured by the MVM method and traditional transmissometer method are analyzed and compared. Experiments were conducted indoors, and the data were simultaneously processed. The results revealed that the MVM can effectively improve the accuracy under different visibility conditions. The greatest improvement of accuracy was 27%. The MVM can be used to calibrate and evaluate visibility meters.

Atmospheric Extinction Coefficients in the Ic Band for Several Major International Observatories: Results from the BiSON Telescopes, 1984–2016

Abstract Over 30 years of solar data have been acquired by the Birmingham Solar Oscillations Network (BiSON), an international network of telescopes used to study oscillations of the Sun. Five of the six BiSON telescopes are located at major observatories. The observational sites are, in order of increasing longitude: Mount Wilson (Hale) Observatory (MWO), California, USA; Las Campanas Observatory, Chile; Observatorio del Teide, Izaña, Tenerife, Canary Islands; the South African Astronomical Observatory, Sutherland, South Africa; Carnarvon, Western Australia; and the Paul Wild Observatory, Narrabri, New South Wales, Australia. The BiSON data may be used to measure atmospheric extinction coefficients in the band (approximately 700–900 nm), and presented here are the derived atmospheric extinction coefficients from each site over the years 1984–2016.

Pollution Characteristics and Light Extinction Contribution of Water-soluble Ions of PM2.5 in Hangzhou

The pollution characteristics and light extinction contribution of water-soluble ions of PM2.5 in Hangzhou were investigated by sampling and laboratory analysis of aerosol samplers in 2013. The water-soluble ions were dominant in PM2.5 and the total mass concentration was 37.5 μg·m-3, accounting for 44.4% of the PM2.5 mass concentration. Water-soluble ions were mainly composed of secondary ions(SO42-,NO3- and NH4+), which accounted for 83.4% of total ions. The highest mass concentrations of PM2.5 and major ions were observed in winter and the lowest in summer. The proportions of water-soluble ions in PM2.5 in summer and autumn were obviously higher than those in winter and spring and proportions of secondary ions in water-soluble ions were very close in each season. The contribution was the greatest to PM2.5 from secondary ions generation caused by fuel combustion and automobile exhaust. The annual average values of SOR and NOR were 0.27 and 0.15 respectively, the conversion rate of SO2 in atmosphere was greater than that of NOx. There was obvious positive correlation between SOR or NOR and humidity which indicated the important contribution of heterogeneous oxidation process to the generation of SO42- and NO3-. The annual average of[NO3-]/[SO42-] was 0.63, and the aerosol pollution was primarily affected by emissions from coal burning. In haze days, with the increase of haze pollution level, the mass concentrations of PM2.5, water-soluble ions, secondary ions as well as SOR and NOR all increased gradually, and the stable weather condition in haze days could efficiently promote the accumulation and secondary conversion of pollutants. There were obvious positive correlations between mass concentrations of PM2.5 and SNA and the atmospheric light extinction coefficient. The IMPROVE formula which was used to calculate the light extinction coefficients of different chemical components could efficiently indicate the tendency of aerosol scattering. The extinction contribution of SNA could reach 60.8%. The extinction coefficient of SNA was the highest in winter and lowest in summer, and its value and contribution proportion both increased gradually as the haze pollution level rose.

Atmospheric extinction coefficient retrieval and validation for the single-band Mie-scattering Scheimpflug lidar technique

An 808 nm single-band Mie scattering Scheimpflug lidar system is developed in Dalian, Northern China, for real-time, large-area atmospheric aerosol/particle remote sensing. Atmospheric measurement has been performed in urban area during a typical haze weather condition, and time-range distribution of atmospheric backscattering signal is recorded from March 18th to 22nd, 2017, by employing the Scheimpflug lidar system. Atmospheric extinction coefficient is then retrieved according to the Klett-inversion algorithm, while the boundary value is obtained by the slope-method in the far end where the atmosphere is homogeneous in a subinterval region. The correlation between the extinction coefficients retrieved from the Scheimpflug lidar technique and the PM10/PM2.5 concentrations measured by a conventional air pollution monitoring station is also studied. The good agreement between the measurement results, i.e., a correlation coefficient of 0.85, successfully demonstrates the feasibility and great potential of the Scheimpflug lidar technique for atmospheric studies and applications.

Expectation maximization and the retrieval of the atmospheric extinction coefficients by inversion of Raman lidar data.

We consider the problem of retrieving the aerosol extinction coefficient from Raman lidar measurements. This is an ill-posed inverse problem that needs regularization, and we propose to use the Expectation-Maximization (EM) algorithm to provide stable solutions. Indeed, EM is an iterative algorithm that imposes a positivity constraint on the solution, and provides regularization if iterations are stopped early enough. We describe the algorithm and propose a stopping criterion inspired by a statistical principle. We then discuss its properties concerning the spatial resolution. Finally, we validate the proposed approach by using both synthetic data and experimental measurements; we compare the reconstructions obtained by EM with those obtained by the Tikhonov method, by the Levenberg-Marquardt method, as well as those obtained by combining data smoothing and numerical derivation.

Effects of cloud and humidity on atmospheric extinction coefficient derived from visual range observations in Iranian major airports

ABSTRACTVisibility impairment, one of the restricting phenomena for aviation, results from light scattering and absorption. In this study, the historical visibility database for the period of 1981–2010 is used to obtain extinction coefficient according to the Koschmieder theory in the four busiest airports in Iran, including Tehran‐Mehrabad, Mashhad, Shiraz and Isfahan. The long‐term trend of extinction coefficient and its seasonal variations are investigated using 10th and 90th percentiles of extinction data to show the visual range in each airport. Correlation of the long‐term visibility trend with relative humidity (RH) and cloudiness is also examined. The comparison of seasonal mean extinctions shows the noticeable effect of local climate. The highest extinction coefficient value in each airport is seen during winter, while the lowest value occurs in summer. The seasonal mean extinction coefficient level in winter is about 0.1 km−1 higher than those of the other seasons. This is likely due to pollutants trapped by the stagnant cold air that partly obstruct visibility and increase the extinction in wintertime. There is not an outstanding variation of the tenth percentile of the extinction coefficient in the four airports. The low variation may relate to the definition of the upper threshold in visibility. Analysis shows that there is a positive correlation between extinction and humidity in all the airports that indicates the increase of scattering by hygroscopic particles with increasing humidity, such effect would be accentuated in high RH. The same result is seen for different percentages of cloudiness. To minimize the effects of humidity and cloudiness on the long‐term visibility trend, the days with the relative humidity values more than 70% and cloudiness of more than 5/8 of the sky are removed from the visibility trend analysis. The trends of the screened days are nearly parallel to the trends of raw data, but with a slight difference in each airport. The overall filtered long‐term trends show the increase of extinction coefficient at all the airports that emphasize the effect of pollution on the trend of light extinction within the whole period of this study. Eliminating the meteorological factors from the raw data does not change the overall increasing trend of extinction at Tehran and Isfahan airports. It suggests that the changes in air quality are responsible for the long‐term visibility degradation at these two stations that are located in the two most highly industrialized and polluted cities in Iran.

UBVI CCD Photometry of NGC 7790

UBVI CCD photometry of the intermediate age open cluster NGC 7790 has been obtained using AZT-22 1.5 m telescope (f/7.74) at the Maidanak Astronomical Observatory in Uzbekistan. NGC 7790 contains three δ Cep variable stars including CEa Cas, CEb Cas, and CF Cas. PSF photometry was carried out using IRAF/DAOPHOT for all observations. The total number of stars observed both in V and I filter was 1008 and the limiting magnitude was V≈22. To determine atmospheric extinction coefficients and photometric zero points, many blue and red standard stars as well as the standard stars in the celestial equator under various airmass were observed. Photometric data were transformed into the standard Johnson-Cousins' UBVI standard system. From the analysis of UBVI color-magnitude diagram and color-color diagram, the color excess in V and I filter (E(B−V )=0.58±0.02), the selective extinction ratio in V and I filter (RV ≡ AV/E(B−V ) =3.02±0.09) and distance modulus (V0−MV =12.65±0.10) of the cluster were determined. The age of the cluster was estimated to be log age=8.05±0.05 (yr) based on the position of these three Cepheid variables in the color-magnitude diagram, the isochrone of the Geneva group (Ekstrom et al., 2012-Z=0.019), and the isochrone of the Padova group (Bressan et al., 2012-Z=0.014) were used to compare each other. Of them, the Geneva models that considered stellar rotation well described the position of δ Cepheid variables in the blue loop. Although they were well consistent with standard period-luminosity relation of δ Cepheid variables, three Cepheid variables in NGC 7790 were, on average, brighter by about 0.5 mag than the absolute magnitude estimated from the mean period-luminosity relation at a given period.