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Highlights • A fluorescence-Mie lidar for observing fluorescent aerosols was developed in Beijing. • The spatio-temporal variability of fluorescent aerosols in the lower atmosphere was investigated. • The LIF results was validated by backward trajectories and local pollutants emission data. • The mean ratio of LIF-to-Mie is good correlated with PM2.5 concentration. Abstract An integrated fluorescence-Mie lidar was built to observe fluorescent aerosol at the altitude below 1.5 km. It was constructed with the third harmonic of Nd:YAG laser (355 nm), a Newtonian telescope and two single-channel photomultiplier tubes. Based on the Mie scattering theory and laser-induced fluorescence (LIF) theory, the vertical distribution of fluorescent aerosol was retrieved by the LIF-to-Mie signal ratio. As a common factor, the geometric form factor of the system was cancelled out when dividing LIF signal by Mie signal, therefore the high-precision of the LIF-to-Mie signal ratio was obtained in the lower atmosphere. After continuous observations under different air quality conditions, the time-height indications of fluorescent aerosol were obtained. The fluorescence efficiency was preliminary estimated. By combining the backward trajectories analysis and the local emission data of SO 2 and NO 2 , the time-height indications were analyzed for investigating the sources of fluorescent aerosol. The correlation between PM2.5 concentration and the mean value of LIF-to-Mie signal ratio was also studied. The good agreement between the results indicate that the above mentioned method can be employed to analyze the spatio-temporal distribution of fluorescent aerosol and has a great potential in meteorological application. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dual-wavelength-excitation fluorescence spectra detection of aerosol stream. • Fluorescence signals from two bands received by bifurcated fiber bundle. • Self-developed combined spectrometer with time-sharing detection. • A 32-channel PMT as the detector, resolution of 6 nm/channel for both bands. • Detection of two band fluorescence spectra of six kinds of samples. We developed a dual-wavelength-excitation aerosol fluorescence spectra detection device prototype. In our system, the 263 nm and 355 nm lasers are used to sequentially excite the fluorescence of aerosol stream, which is located spatially and temporally by two crossed infrared lasers; a bifurcated fiber bundle is applied to receive the fluorescence spectra of 274–463 nm and 374–565 nm. Besides, with a 32-channel photomultiplier tube as detector, a self-developed combined spectrometer with Czerny-Turner design is employed to detect the two band spectra in a preset timing sequence. Experiments show that the system can detect the fluorescence spectra, after dual-wavelength-excitation, of three intrinsic fluorophore samples and three bioaerosol samples. [ABSTRACT FROM AUTHOR]

An iterative method, based on a derived inverse relationship between atmospheric backscatter coefficient and aerosol lidar ratio, is proposed to invert the lidar ratio profile and aerosol extinction coefficient. The feasibility of this method is investigated theoretically and experimentally. Simulation results show the inversion accuracy of aerosol optical properties for iterative method can be improved in the near-surface aerosol layer and the optical thick layer. Experimentally, as a result of the reduced insufficiency error and incoherence error, the aerosol optical properties with higher accuracy can be obtained in the near-surface region and the region of numerical derivative distortion. In addition, the particle component can be distinguished roughly based on this improved lidar ratio profile. [ABSTRACT FROM AUTHOR]

Complexly distributed aerosol particles have significant impacts on climate and environmental changes. As one of the vital atmospheric power sources, the wind field deeply affects the distribution and transport of aerosol particles. For a more comprehensive investigation of the aerosols flux and transport mechanism, two retrieval methods of aerosol optical properties (backscatter coefficient and extinction coefficient at 1550 nm) from coherent Doppler lidar (CDL) observation are proposed in this paper. The first method utilizes the calculated aerosol backscatter coefficient (532 nm) from Mie-scattering lidar datasets and the iterative Fernald method to retrieve aerosol optical property profiles during joint measurements with CDL and Mie-scattering lidar. After verifying the correctness of the first method compared with AERONET datasets, we proposed the second retrieval method. Using the forward integral Fernald method with near-ground reference aerosol extinction coefficient calculated by atmospheric visibility, aerosol optical properties at 1550 nm could be obtained. Thirty-six-day joint measurements with two lidars were specially designed and conducted to verify the correctness of these retrieval methods. The validation results of these two methods indicate great performances, where the mean relative errors are 0.0272 and 0.1656, and the correlation coefficients are 0.9306 and 0.9197, respectively. In conclusion, the feasibility of these two retrieval methods extends the capability of CDL to detect aerosol optical properties and also provides a possibility to observe the aerosol distribution and transport process comprehensively, which is a great promotion of aerosol transport studies development. [ABSTRACT FROM AUTHOR]

The types of aerosols are essential for estimating radiative forcing effects, improving the lidar retrieval algorithms, and identifying aerosol sources. However, it is difficult to categorize the aerosols with similar optical properties based on lidar techniques. In this study, an approach was proposed to distinguish desert dust (DD), mineral dust (MD), air pollution aerosols (APA), and their mixtures (DD&MD, DD&APA, MD&APA, DD&MD&APA). We established the fluorescence–Mie​ polarization lidar (FMPL) system to categorize three types of main aerosols using the customized fluorescence-to-Mie ratio (FMR) and volume depolarization ratio (VDR) in the experiments from September 2017 to December 2018. Then, the mixture of the aerosols was classified by combining backward trajectory analysis. The feasibility of this method was verified through five typical cases in the paper, and it is proved that the method could be employed to study air pollution issues based on FMPL, which could provide references for the meteorological investigation. • We established a fluorescence–Mie polarization lidar system. • We defined Fluorescence-to-Mie ratio (FMR). • Aerosols were divided into seven types according to their FMR and VDR. [ABSTRACT FROM AUTHOR]

• A simple de-noising operation is implemented to increase the signal-to-noise ratio. • The operation avoids the subjectivity of the iterative number of iteration method. • The more accurate aerosol backscatter coefficient could be obtained in the near ground (< 2 km). • A higher effective detection altitude is obtained with the simple de-noising operation. The de-noising of lidar signal, especially for the range-dependent systematic noise, always affects the signal-to-noise ratio of lidar signal and the inversion accuracy of aerosol backscatter coefficient. To avoid this issue, a simple de-noising operation is implemented to increase the signal-to-noise ratio and obtain a more accurate aerosol backscatter coefficient. Theoretically, the subjectivity of the iterative number of iteration method can be avoided by the simple de-noising operation. And the feasibility of the simple de-noising operation is investigated by simulation and the routine lidar experimental data. In the near ground, the aerosol backscatter coefficient with higher accuracy of about 4–10 times could be obtained with the simple de-noising operation, compared with the traditional de-noising operation. Moreover, the long-term stability of the range-dependent systematic noise can be found by the experimental results, which avoids the frequent measurement of the systematic noise. In addition, a higher effective detection altitude is obtained with the simple de-noising operation. [ABSTRACT FROM AUTHOR]