Atmospheric Aerosol Extinction Research Articles

Novel Inversion Algorithm for the Atmospheric Aerosol Extinction Coefficient Based on an Improved Genetic Algorithm

As an important atmospheric component, aerosols play a very important role in the radiation budget balance of the earth–atmosphere system. To study the optical characteristics of aerosols, it is necessary to use an inversion algorithm to process the lidar return signal to obtain both the aerosol extinction coefficient and the backscattering coefficient. However, the lidar return power equation is ill-conditioned and contains two unknown parameters, meaning that traditional inversion algorithms must be solved by adopting certain assumptions (e.g., a uniform atmosphere and the lidar ratio), which to a certain extent can seriously affect the inversion accuracy. Here, to improve the accuracy of the aerosol extinction coefficient inversion, an inversion method based on an improved genetic algorithm is proposed. Using the U.S. Standard Atmosphere model and the return power equation, the aerosol extinction coefficient and the backscattering coefficient are independent variables that randomly provide initial values to simulate the theoretical lidar power. Then, the genetic algorithm is used to approximate the theoretical lidar power to the measured lidar return power with height; when the two are infinitely close, the values of the corresponding two independent variables (i.e., the extinction and backscattering coefficients) are inverted. Experiments performed to compare the different effects between a simple genetic algorithm and the improved genetic algorithm showed the proposed method capable of inverting the aerosol extinction coefficient without reliance on traditional inversion methods, representing a novel approach to the inversion of the aerosol extinction coefficient and the backscattering coefficient.

Long-term characterisation of the vertical structure of the Saharan Air Layer over the Canary Islands using lidar and radiosonde profiles: implications for radiative and cloud processes over the subtropical Atlantic Ocean

Abstract. Every year, large-scale African dust outbreaks frequently pass over the Canary Islands (Spain). Here we describe the seasonal evolution of atmospheric aerosol extinction and meteorological vertical profiles on Tenerife over the period 2007–2018 using long-term micropulse lidar (MPL-3) and radiosonde observations. These measurements are used to categorise the different patterns of dust transport over the subtropical North Atlantic and, for the first time, to robustly describe the dust vertical distribution in the Saharan Air Layer (SAL) over this region. Three atmospheric scenarios dominate the aerosol climatology: dust-free (clean) conditions, the Saharan summer scenario (summer-SAL) and the Saharan winter scenario (winter-SAL). A relatively well-mixed marine boundary layer (MBL) was observed in the case of clean (dust-free) conditions; it was associated with rather constant lidar extinction coefficients (α) below 0.036 km−1 with minimum α (< 0.022 km−1) in the free troposphere (FT). The summer-SAL has been characterised as a dust-laden layer strongly affecting both the MBL (Δα = +48 % relative to clean conditions) and the FT. The summer-SAL appears as a well-stratified layer, relatively dry at lower levels (Δr∼-44 % at the SAL’s base, where r is the water vapour mixing ratio) but more humid at higher levels compared with clean FT conditions (Δr∼+332 % at 5.3 km), with a peak of α> 0.066 km−1 at ∼ 2.5 km. Desert dust is present up to ∼ 6.0 km, the SAL top based on the altitude of SAL's temperature inversion. In the winter-SAL scenario, the dust layer is confined to lower levels below 2 km altitude. This layer is characterised by a dry anomaly at lower levels (Δr∼ −38 % in comparison to the clean scenario) and a dust peak at ∼ 1.3 km height. Clean FT conditions were found above 2.3 km. Our results reveal the important role that both dust and water vapour play in the radiative balance within the summer-SAL and winter-SAL. The dominant dust-induced shortwave (SW) radiative warming in summer (heating rates up to +0.7 K d−1) is found slightly below the dust maximum. However, the dominant contribution of water vapour was observed as a net SW warming observed within the SAL (from 2.1 to 5.7 km) and as a strong cold anomaly near the SAL's top (−0.6 K d−1). The higher water vapour content found to be carried on the summer-SAL, despite being very low, represents a high relative variation in comparison to the very dry clean free troposphere in the subtropics. This relevant aspect should be properly taken into account in atmospheric modelling processes. In the case of the winter-SAL, we observed a dust-induced radiative effect dominated by SW heating (maximum heating of +0.7 K d−1 at 1.5 km, near the dust peak); both dust and atmospheric water vapour impact heating in the atmospheric column. This is the case of the SW heating within the SAL (maximum near the r peak), the dry anomaly at lower levels (Δr∼ −38 % at 1 km) and the thermal cooling (∼ 0.3 K d−1) from the temperature inversion upwards. Finally, we hypothesise that the SAL can impact heterogeneous ice nucleation processes through the frequent occurrence of mid-level clouds observed near the SAL top at relatively warm temperatures. A dust event that affected Tenerife on August 2015 is simulated using the regional DREAM model to assess the role of dust and water vapour carried within SAL in the ice nucleation processes. The modelling results reproduce the arrival of the dust plume and its extension over the island and confirm the observed relationship between the summer-SAL conditions and the formation of mid- and high-level clouds.

Rapid mass growth and enhanced light extinction of atmospheric aerosols during the heating season haze episodes in Beijing revealed by aerosol–chemistry–radiation–boundary layer interaction

Abstract. Despite the numerous studies investigating haze formation mechanism in China, it is still puzzling that intensive haze episodes could form within hours directly following relatively clean periods. Haze has been suggested to be initiated by the variation of meteorological parameters and then to be substantially enhanced by aerosol–radiation–boundary layer feedback. However, knowledge on the detailed chemical processes and the driving factors for extensive aerosol mass accumulation during the feedback is still scarce. Here, the dependency of the aerosol number size distribution, mass concentration and chemical composition on the daytime mixing layer height (MLH) in urban Beijing is investigated. The size distribution and chemical composition-resolved dry aerosol light extinction is also explored. The results indicate that the aerosol mass concentration and fraction of nitrate increased dramatically when the MLH decreased from high to low conditions, corresponding to relatively clean and polluted conditions, respectively. Particles having their dry diameters in the size of ∼400–700 nm, and especially particle-phase ammonium nitrate and liquid water, contributed greatly to visibility degradation during the winter haze periods. The dependency of aerosol composition on the MLH revealed that ammonium nitrate and aerosol water content increased the most during low MLH conditions, which may have further triggered enhanced formation of sulfate and organic aerosol via heterogeneous reactions. As a result, more sulfate, nitrate and water-soluble organics were formed, leading to an enhanced water uptake ability and increased light extinction by the aerosols. The results of this study contribute towards a more detailed understanding of the aerosol–chemistry–radiation–boundary layer feedback that is likely to be responsible for explosive aerosol mass growth events in urban Beijing.

Ambient Atmospheric Aerosol Extinction Coefficient Reconstruction from PM2.5 Mass Concentrations and Application to Haze Identification in China

ABSTRACT This study developed a method of reconstructing the aerosol extinction coefficient based on hourly observations of the fine-particle (PM2.5) mass concentration, relative humidity (RH), and visibility at 9 stations in China between 2014 and 2015. First, we applied κ-Kӧhler theory to evaluate the number concentration distribution of the fine particles under ambient conditions from the PM2.5 mass and then used Mie theory to calculate the aerosol extinction coefficient. Second, we established the reconstruction model and identified reference values for the relevant parameters. After sensitivity tests confirmed good agreement between the extinction coefficients obtained through combinations of various values and those resulting from the reference values, linear regression was employed to reduce the discrepancy between the reconstructed and the observed coefficients. A closure study enabled us to determine the threshold of the extinction ratio (β/βObs) and identify haze and fog weather phenomena at the stations. Finally, we assessed the bias in the predicted number of hours with haze for 61 stations in China by comparing the estimates derived from different values for the model’s parameters with those derived from the reference values and found a relative bias of less than 15% for approximately 99.8% of the stations, indicating the feasibility of our approach for detecting haze.

Numerical and statistical modeling based investigation of the detection efficiency of high-spectral-resolution lidars at different laser radiation wavelengths

In the present work, a numerical and statistical modeling approach is developed for estimating the operation efficiency of high-spectral-resolution lidars (HSRLs), when determining the atmospheric aerosol extinction profiles along the lidar line of sight (LOS) at different sensing (laser) radiation wavelengths from the UV, VIS and NIR spectral ranges. The efficiency estimation is based on numerical modeling of the lidar signal profile along the LOS and the corresponding profile of the signal-to-noise ratio (SNR) of its measurement. The optimally efficient wavelength (at certain distances along the LOS) is that ensuring maximum signal strength and SNR and, consequently, brighter and clearer lidar images of specific aerosol objects and background. The results about the optimum wavelengths obtained under different atmospheric-turbidity conditions (clear or hazy atmosphere), in the presence of cirrus clouds, are proved by statistical modeling and processing of realistic (noisy) lidar profiles and recovering the atmospheric extinction profiles along the LOS. It is shown that up to certain characteristic altitudes (that are lower at higher turbidity) the UV wavelengths are advantageous in the above sense. Above the mentioned altitudes, successively, first the VIS and then the NIR wavelengths become more efficient compared to the UV wavelengths.

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.

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.

Aerosol extinction properties over coastal West Bengal Gangetic plain under inter-seasonal and sea breeze influenced transport processes

We analysed the atmospheric aerosol extinction properties under an influence of inter-seasonal and sea breeze (SB) transport processes over coastal West Bengal (WB) Gangetic plain (WBGP). The predominant frequency of airmass back trajectory path was through the Arabian Sea (AS) during southwest monsoon (SWmon) and that through the Indo-Gangetic plain (IGP) during transition to winter (Twin) season and the Bay of Bengal during transition to summer (Tsumm) season. Aerosol surface concentration (Sconc) and aerosol extinction exhibited heterogeneity in the seasonal variability over coastal WBGP with their highest seasonal mean being during winter and summer seasons respectively. Seasonal mean extinction was respectively 17% and 30% higher during winter and summer seasons than that during SWmon. While angstrom exponent (AE) was less than one during SWmon, Tsumm, and summer seasons, it was near to one during Twin and winter monsoon (Wmon), and was more than one during winter season. Relative contribution (%) of upper (at altitude above 1km) aerosol layer (UAL) to aerosol extinction during summer was four times of that during winter. Seasonally distinct vertical distribution of aerosol extinction associated with meteorological and SB influenced transport and that due to influence of high rise open burning emissions was inferred. Possible aerosol subtypes extracted during days in Tsumm were inferred to be mostly constituted of dust and polluted dust during daytime, in addition to polluted continental and smoke in UAL during nighttime. In contrast to that at nearby urban location (Kolkata, KOL), intensity of updraft of airmass evaluated during evening/SB activity hour (1730 local time, (LT)) at study site (Kharagpur, KGP) was as high as 3.5 times the intensity during near to noon hour (1130 LT); this intensity was the highest along coast of westBengal-Orissa. Enhanced Sconc and relative contribution of UAL to aerosol extinction (58% compared to 36% only at nearby urban location) was inferred associated with SB activity.

南京持续雾霾天气中亚微米细颗粒物化学组分及光学性质

A lasting haze pollution event occurred in the Central and East China in January 2013. In this study, Aerodyne Aerosol Chemical Speciation Monitor (ACSM), Photoacoustic Extinctiometer (PAX), and Aethalometer were deployed for real-time and lasting monitoring of non-refractory submicron aerosol (NR-PM1) components (i.e. organics, sulfate, nitrate, ammonium, and chloride), atmospheric aerosol extinction properties, and black carbon (BC) in Nanjing, respectively. During the measuring period, the contribution of PM1 (NR-PM1+BC) species, i.e., organics, nitrate, sulfate, ammonium, chloride, and BC were 32.3%, 26.0%, 17.9%, 13.2%, 2.8%, and 7.8%, respectively. Positive matrix factorization (PMF) analysis indicates that hydrocarbon-like (HOA), semi-volatile oxygenated organic aerosol (SV-OOA), low-volatile oxygenated organic aerosol (LV-OOA) were the major sources for PM1. HOA, SV-OOA, and LV-OOA on average accounted for 27.4%, 32.2%, and 40.4% of organic aerosol, respectively, which means that PM1 consisted mostly of the secondary species. Because of local cooking and traffic emissions, HOA loading dynamically increased at the nighttime, which resulted in a significant variation of organics. Generally, the mass concentrations, the mass fractions of secondary components (i.e. nitrate, sulfate, SV-OOA, and LV-OOA), as well as aerosol signal scattering albedo increased with increasing relative humidity (RH), respectively, implying that the increase in RH was beneficial to the continual formation of secondary aerosol. Furthermore, atmospheric visibility decreased with the increasing of RH and secondary species contents, indicating that there is a synergistic effect between the RH and the secondary species of PM1 on the atmospheric visibility during the haze period.

Measurement of aerosol optical extinction using diode laser cavity ringdown spectroscopy

Accurate measurement of optical extinction of atmospheric aerosols is important for quantifying the direct climate effects of aerosols. A portable cavity ringdown spectrometer utilizing a modulated multimode blue diode laser (linewidth ∼0.2 nm) is developed to measure the aerosol optical extinction. Laboratory generated ammonia sulfate particles (<1 μm in diameter) are characterized, with good agreements between the experimental measurements and Mie theory calculations. An optical extinction detection sensitivity of 0.24 Mm−1 (1σ) is achieved. Measurements of ambient aerosols are also carried out. This study demonstrates the feasibility of a compact, multimode diode laser cavity ringdown spectrometer for sensitive measurements of the optical extinction of atmospheric aerosols.

The Retrieval of Profiles of Particulate Extinction from Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Data: Uncertainty and Error Sensitivity Analyses

Abstract Profiles of atmospheric cloud and aerosol extinction coefficients are retrieved on a global scale from measurements made by the lidar on board the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission since mid-June 2006. This paper presents an analysis of how the uncertainties in the inputs to the extinction retrieval algorithm propagate as the retrieval proceeds downward to lower levels of the atmosphere. The mathematical analyses, which are being used to calculate the uncertainties reported in the current (version 3) data release, are supported by figures illustrating the retrieval uncertainties in both simulated and actual data. Equations are also derived that describe the sensitivity of the extinction retrieval algorithm to errors in profile calibration and in the lidar ratios used in the retrievals. Biases that could potentially result from low signal-to-noise ratios in the data are also examined. Using simulated data, the propagation of bias errors resulting from errors in profile calibration and lidar ratios is illustrated.

Lidar Measurements for Comparison of Atmospheric Aerosol Extinction and Scattering Properties over Lanzhou, China

The aerosol comparison experiment was conducted in the Semi-Arid Climate and Environment Observatory of Lanzhou University since March to April 2007 with the measurements of two micro-pulse lidars MPL-4B and CE370-2. In the paper, the differences of aerosol extinction coefficient and optical depth retrieved from the observations of MPL-4B and CE370-2 are analyzed, and the results show: the aerosol extinction coefficient retrieved from the observation of MPL-4B is in general smaller than that from CE370-2, and the difference mainly exists in the low layer, while their trends of vertical profiles agree well; the aerosol optical depths from the observations of MPL-4B and CE370-2 correlate linearly rather well with the coefficient of 0.71, and the aerosol optical depth retrieved from the measurement of MPL-4B is less than that from CE370-2 in whole.

Mie lidar observations of lower tropospheric aerosols and clouds

Mie lidar system is developed at Laser Science and Technology Centre, Delhi (28.38°N, 77.12°E) by using minimal number of commercially available off-the-shelf components. Neodymium Yttrium Aluminum Garnet (Nd:YAG) laser operating at 1064 nm with variable pulse energies between 25 and 400 mJ with 10 Hz repetition rate and 7 ns pulse duration is used as a transmitter and off-axis CASSEGRAIN telescope with 100 mm diameter as a receiver. Silicon avalanche photodiode (Si-APD) module with built-in preamplifier and front-end optics is used as detector. This system has been developed for the studies of lower tropospheric aerosols and clouds. Some experiments have been conducted using this set up and preliminary results are discussed. The characteristics of backscattered signals for various transmitter pulse energies are also studied. Atmospheric aerosol extinction coefficient values are calculated using Klett lidar inversion algorithm. The extinction coefficient, in general, falls with range in the lower troposphere and the values lie typically in the range 7.5 × 10 −5 m −1 to 1.12 × 10 −4 m −1 in the absence of any cloud whereas this value shoots maximum up to 1.267 × 10 −3 m −1 (peak extinction) in the presence of clouds.

A Real Time Inversion Method for Calculating Multi Laser Wavelengths’ Extinction Coefficients Profile of Atmospheric Aerosol

A new real time inversion method is proposed for calculating multi-wavelength laser atmospheric aerosol extinction coefficients’ profile. The real-time data of atmospheric aerosol extinction coefficients’ profile measured by 0.532μm lidar is utilized together with complex aerosol model of Fascode. The unique features of this method are discussed in detail. Atmospheric aerosol extinction coefficients inversely calculated by this method compared with real time measurements data. The results show that it is feasible to inversely calculate the infrared atmospheric propagation with reasonable accuracy. The real time atmospheric correcting model is established by the method for extinction coefficients at different wavelengths without absorption of water vapor.

A Real Time Evaluating Method of Aerosol Extinction Coefficients For Multi Laser Wavelengths

Abstract A new real-time evaluatting method is proposed for multi laser wavelengths’ extinction coefficients of atmospheric aerosol. The back scattered signal measured by single wavelength lidar is utilized together with complex aerosol model of Fascode. The unique features of this method are discussed in detail. Atmospheric aerosol extinction coefficients inversely calculated by this method are compared with real time measurements’ data. The results show that it is feasible to evaluate the signatures of infrared atmospheric propagation with reasonable accuracy. The real time atmospheric correcting model is established by the method for aerosol extinction coefficients at different wavelengths without absorption of water vapor. The profile of atmosperic aerosol extinction coefficients for many special wavelengths selected between the spectrum from visible to infrared is evaluated by using both the inversion methd and the data measured by 0.532 colon lidar. The results can be used for atmospheric correction for the laser applications from ground to high-level or vice versa.

New dust aerosol identification method for spaceborne lidar measurements

Classification is a critical step in the backscatter lidar data processing to accurately retrieve extinction and backscatter profiles of atmospheric aerosols and clouds. Different schemes, such as the probability distribution functions (PDFs) method, have been used in the cloud and aerosol classification. In this paper, we attempt to use the support vector machine (SVM) to discriminate aerosols from clouds, with a focus on dust aerosol classification in China. To demonstrate the feasibility of the SVM classifier, we chose dust storms that occurred in the Gobi and Taklimakan deserts and observed by the CALIPSO lidar in spring time 2007. The results show that the SVM can correctly identify the dust storms.

Remote sounding of atmospheric pressure profile from space, part 1: principle

The molecular oxygen absorption band near 0.762 µm can be used for remote sounding of atmospheric pressure profiles. Atmospheric O2 absorption, atmospheric molecular multi-scattering, extinction of atmospheric aerosols, bi-reflection at the earth surface, the atmospheric refractive effect and the global curvature are taken into account to establish an atmospheric radiation transfer equation. By means of an accurate O2 atmospheric transmittance model and a mean atmospheric transmittance model the remote sounding equation of surface pressure from space suitable to clear sky field of view is derived. At last, a pure physical retrieval method is given and the atmospheric pressure profile can be deduced.

Raman激光雷达探测气溶胶光学特性

The Raman multi-channels lidar developed by Wuhan University is described.The design principles of the whole system and main technical parameters are provided.The methods for retrieving aerosols' optical properties such as atmospheric aerosol extinction coefficient,backscattering coefficient and lidar ratio are presented in detail,and the key part of retrieving the aerosol extinction coefficient is discussed and analyzed.The real-time detections of optical properties for aerosol,cloud and boundary layer in the low-altitude atmosphere are done.The experiments show that the multi-channels Raman lidar system has good performance for detecting the vertical distribution of aerosols in the night and it is reliable.

Long optical cavities for open-path monitoring of atmospheric trace gases and aerosol extinction

An incoherent broadband cavity-enhanced absorption spectroscopy setup employing a 20 m long optical cavity is described for sensitive in situ measurements of light extinction between 630 and 690 nm. The setup was installed at the SAPHIR atmospheric simulation chamber during an intercomparison of instruments for nitrate (NO(3)) radical detection. The long cavity was stable for the entire duration of the two week campaign. A detection limit of approximately 2 pptv for NO(3) in an acquisition time of 5 s was established during that time. In addition to monitoring NO(3), nitrogen dioxide (NO(2)) concentrations were simultaneously retrieved and compared against concurrent measurements by a chemiluminescence detector. Some results from the campaign are presented to demonstrate the performance of the instrument in an atmosphere containing water vapor and inorganic aerosol. The spectral analysis of NO(3) and NO(2), the concentration dependence of the water absorption cross sections, and the retrieval of aerosol extinction are discussed. The first deployment of the setup in the field is also briefly described.