To establish spectro-structural correlations of practically important biologically active steroid phytohormones, namely, molecules (22S,23S)-24-epibrassinolide, (22S,23S)-28-homobrassinolide and homobrassinolide, a comparative analysis of experimental IR spectra and theoretical spectral absorption curves of these molecules with similar chemical structure has been done. This made it possible to evaluate the influence of structural features within the side chain of the studied molecules on the formation of IR spectra and to establish a connection between their structural differences and the observed changes in IR spectra in the range of 1500–950 cm^–1 . 

The results of a comparative analysis of spectral-luminescent properties of crystalline and glassy benzophenone are presented. The main spectral characteristics of glassy benzophenone (frequencies of pure electronic transitions in the phosphorescence spectra, band half-widths, relative quantum yields) have been found to possess a number of significant features in comparison with the crystalline phase in the temperature range of 4.2–220 K. Temperature-dependent structural changes in benzophenone have been studied by differential scanning calorimetry. The possibilities of phase transition appearance in benzophenone and their sequences have been shown to be different during cooling and heating the samples. The relationship between the spectral characteristics of various benzophenone phases and their transition temperatures has been demonstrated. To explain the experimental results, the model concepts describing the processes of charge carrier transport and transfer of electronic excitation energy in disordered amorphous and glassy molecular systems, as well as information on the structural features of glasses, have been used. 

It is shown that the S₁↔S₀ pure-electron transition frequencies of absorption and emission essentially differ. From this and known photophysical characteristics of biphenylene it follows that its fluorescence mechanism fits into model of specific C_2v symmetrical cis-azoalkane fluorescence having exchange-resonant nature. The model explains the reasons for the unusual intensity, half-width, polarization, and predominant manifestation of completely symmetric vibrations in the fluorescence spectrum.

The comparison of the fingerprint region of infrared and Raman spectra of aqueous solutions of acetic acid at concentrations of 0.3 and 0.8 mole fractions and pure solutions with the calculated data on terahertz spectroscopy was carried out. The molecular dynamics simulation of terahertz spectroscopy of aqueous solutions of acetic acid was presented. Terahertz spectroscopy was shown to be informative when comparing the structural reorganization of water molecules in aqueous solutions of acetic acid. Special attention was paid to the collective dynamics of water molecules depending on the concentration of acetic acid. 

The application of UV-VIS-NIR spectroscopy combined with multivariate analysis for the classification and identification of buckwheat groats was analyzed. Samples of buckwheat groats differing in harvest time, kernel size, roasting method and storage time were divided into groups using cluster analysis method. Method of principal components revealed absorption bands of the UV-VIS-NIR spectrum, corresponding to the functional groups of the components of the composition and making the greatest contribution to the differentiation of samples into the quality categories of buckwheat. The method of discriminant analysis confirmed the hypothesis on dividing the samples of buckwheat into groups, and a classification function for the identification and sorting of buckwheat was built. 

The technique of express-analysis of triethoxysilane (TES), which is the main intermediate product of chemical reactions occurring in the processes of silane synthesis, is described. The presented technique was developed on the basis of data obtained as a result of analytical studies of TES, using а MSD 5975C-GC 7890A chromato-mass spectrometer and an InViaRaman Spectrometer, which provide the construction of a calibration graph and a quantitative express-analysis TES using InVia Raman without standards

The photodissociation dynamics of oxalyl bromide is investigated near 265 and 234 nm using the velocity map ion imaging technique coupled with a state selective [2+1] resonance-enhanced multiphoton ionization scheme. The translational energy distribution and ² P_J, J = 3/2, 1/2 parameters of the Br atom formation process are extracted from two-dimensional ion images. The trimodal energy distribution of Br(² P_3/2) atoms is attributed to the primary C–Br bond fission as well as the secondary dissociation of brominecontaining C₂O₂Br radicals produced from the primary Br and Br* pathways. The conclusions are confirmed by the recoil anisotropy and the distribution width corresponding to the individual components. The branching ratio Br(² P_3/2)/Br(² P_1/2) confirms the excitation energy dependence. 

A spectroscopic method was proposed for studying the morphology of microsuspensions, based on the analysis of the scattering component of electromagnetic radiation passing through a sample (turbid medium), which makes it possible to determine the average size and distribution of scattering particles by size. By optical spectroscopy (UV, visible and IR spectral regions) and by an independent optical microscopy method suspensions of vaseline oil (VО) filled with mica and BaSO4 of various concentrations were investigated. Using these methods, the average sizes of scattering particles were determined and their size distribution curves were plotted for microsuspensions of VО/mica and VО/BaSO₄ with 4 and 5% filler content, respectively. The average sizes of filler particles for two suspensions determined by independent methods, practically coincided and amounted to 1.7 and 1.1 μm, respectively. It was found by the spectroscopic method that with an increase in the concentration of the filler due to the aggregation of particles, their average size becomes larger. 

The estimation of the applicability and the choice of the scale of quantitative one-parameter evaluation of the polarity of stationary liquid phases were carried out for gas-liquid chromatography. The absorption and luminescence spectra of five indicators including coumarin 153, coumarin 314, coronene, 4-dicyanomethylene-2-methyl-6-[4-(di-methylamino)-styryl]-4H-pyran (DCM), 3-aminophthalimide have been obtainned in solvents of different polarity at room temperature. The dependence of the wavelength of the fluorescence and absorption maxima on the polarity of the medium was evaluated. Various spectroscopic polarity scales are compared. The fluorescent coronene scale has been shown to be the most appropriate. This scale was used to assess the polarity of some widespread phases (squalane, polydimethylsiloxane liquid PMS-100, 3,3'-oxydipropionitrile, 2-ethyl-hexylsebacinate, etc.) for gas-liquid chromatography. This approach has been shown to be promising for preliminary selection of chromatographic stationary phases.

Using the Yb₂O₃ –YbCl₃–KCl oxide-chloride system as an example, an approach has been proposed and tested, which makes it possible to study the kinetics of dissolution of rare-earth metal oxides in hightemperature melted salt media by Raman spectroscopy. Evidence has been obtained for the chemical mechanism of dissolution of ytterbium oxide in the YbCl3–KCl melt and the irreversibility of the ongoing chemical reaction. It was found that the concentration of the reagent, namely, ytterbium oxide, decreases with time according to an exponential law. The reaction order with respect to Yb₂O₃ is the first. 

Two stages are distinguished, which are connected with evaporation and ignition of lignite, at impact of nanosecond laser pulses on lignite tablets with a density of 1 g/cm³  and particle size of 63 μm. At the first stage during the pulse, volatiles, evaporation, vaporization and nonlinear multiplication of luminescence centers are released. The ignition threshold at this stage is H⁽¹⁾_cr=0.2 J/cm² . The second stage includes the first and ignition of the coke residue with the ignition threshold of which is H⁽¹⁾_cr=3.5 J/cm². In the kinetics of glow at H ˃ H⁽¹⁾_cr , two components are distinguished, namely, a singlet glow with a duration of ~20 ns and the second glow component in the microsecond range, which decays in the second order kinetics. At H ˃ H⁽²⁾_cr in ~200 μs after the laser pulse, as a result of chemical reactions, the ignition and combustion of the coke residue occurs in the time interval of 200–1000 μs. The amplitude of the flame glow during the excitation pulse increases nonlinearly with increasing energy density, which testifies an avalanche nature of the process of formation of glow centers. 

With the COVID-19 outbreak, many challenges are posed before the scientific world to curb this pandemic. The diagnostic testing, treatment, and vaccine development for this infection caught the scientific community's immediate attention. Currently, despite the global proliferation of COVID-19 vaccination, the specific treatment for this disease is yet unknown. Meanwhile, COVID-19 detection or diagnosis using polymerase chain reaction (PCR)-based methods is expensive and less reliable. Moreover, this technique needs much time to furnish the results. Thus, the elaboration of a highly sensitive and fast method of COVID-19 diagnostics is of great importance. The spectroscopic approach is herein suggested as an efficient detection methodology for COVID-19 diagnosis, particularly Raman spectroscopy, infrared spectroscopy, and mass spectrometry. 

Two chemometric models drawing on diffuse reflectance near infrared spectroscopy and Raman scattering are proposed to predict caffeine content in tablets based on acetylsalicylic acid, dipyrone, and paracetamol contents. However, data mining from these analyses to create models generally requires a prior comparison between spectral data and the results from reference values obtained by analytical methodology. Therefore, the construction of a robust calibration model entails that both analytical methods are simultaneously employed on several samples, which represents a limiting factor for the widespread use of spectroscopy. In this case, grounded tablets of different brands, containing only the active principles acetylsalicylic acid, dipyrone, or paracetamol and their excipients, were doped with controlled amounts of pure caffeine ranging from 0 to 10%(w/w) and used as calibration samples. Thus, caffeine quantification with a reference method was not necessary. The prediction samples had at least one of the aforementioned active ingredients and caffeine in its original formulation. Hence, the %(w/w) values of caffeine used as reference for the prediction steps were calculated from the values described on the drug description leaflet and the tablet final mass. Partial least squares regression was used as a multivariate method to construct the models. The near infrared and Raman prediction models for caffeine, using four latent variables, presented the respective values of 0.79 and 0.78 of root mean square errors of cross validation, 0.74 and 1.00 of root mean square errors of prediction, and 0.97 and 0.97 of correlation coefficients.

The actual problems of using flax production waste for obtaining products which are necessary to produce cosmetics with sunscreen and antioxidant properties were studied. Preparations were obtained of ethanolignin from flax shives and raw materials that have subjected to alkaline pulping or biochemical modification. The bio-processing included the stage of enzymatic degradation of non-cellulosic polysaccharides with the generation of aldoses and stage of isothermal aging at 95^о С. Chemical transformations in the polymer were studied by Fourier-transform infrared spectroscopy (FTIR) with the decomposition of spectral curve into elementary vibration bands in the main atomic groups. The analysis of the spectra was carried out using the C-C stretching vibrations in the aromatic ring at 1510 сm^–1 as the internal standard. In spectra of hydrolyzed lignin an increase of absorption oxyaryl groups is combined with an increase in the band intensity of valence and deformation vibrations of C=C bond in alkene fragments. The enhancement of the auxochromic effect in double bonds adjoin to the aromatic ring is manifested as the increase of absorption in the nearultraviolet and visible light ranges. The biochemical preparation of the raw material provides the disappearance of the bands double bond in the carbonyl and alkene groups in the IR spectra. It is accompanied by strengthening in the absorption bands of alkyl hydroxyls by 1.5–2 times and hydroxyl group in the oxyaryl units by 3—4 times. The results are consistent with the data of analysis of biomodified preparation by the differential UV spectroscopy method and testify strengthening of photostabilizing ability of lignin in a combination with absolute transparency in the visible range. 

Human hemoglobin water solution was studied by a multi-angle static light scattering method. The sickle shape of erythrocytes was explained, in particular, by the ability of hemoglobin molecules to aggregation. The experimental data were processed by the methods of Debye, asymmetry, and Zimm. As a result of the work, the values of scattering particles weight were obtained and molecule size was estimated. It was assumed that the structure of the hemoglobin molecule had changed, and the molecule had acquired an elongated shape. The data obtained by the Zimm method are in the best agreement with the data obtained before. The large sizes of scattering particles obtained by the methods of asymmetry and Debye are possibly related to the fact that the dissociation of hemoglobin is a reversible dynamic process, the equilibrium of which depends on the protein concentration/

Due to the complications in the measurement of fine particulate matter (PM2.5), this paper proposes a method using lidar for assessing PM_2.5. By calculating the aerosol optical depth (AOD) for MODIS, CALIPSO, and ground-based lidar, the corrected PM_2.5 was predicted. The results showed that AOD and PM_2.5 had a linear relationship. The linear correlation coefficient between ground-based lidar AOD and PM_2.5 was 0.81, and the root mean square error (RMSE) and mean deviation (MD) were 24.43 and 18.41, respectively. The linear correlation coefficient between CALIPSO AOD and PM_2.5 was 0.8, and its RMSE and MD were 42.91 and 33.25, respectively. The linear correlation between AOD and PM_2.5 for VIIRS was approximately 0.7. This paper provides more possibilities for lidar observation and prediction of the environment

A numerical solution of the lidar equation for Raman scattering by hydrofluoride molecules is carried out with the purpose of selection of the wavelength of laser radiation, lidar parameters and obtaining the minimum measurement time for the Raman scattering signal that corresponds to the minimum concentration of molecules at TLV level. It is shown that the measurement time of the concentration of hydrofluoride molecules of 10¹⁴ cm^–3, which are studied by the considered lidar at a wavelength of laser radiation of 405 nm and height in the range of 100–1500 m, is within the interval of 0.04–14.4 s.

The transformation of phenol, resorcinol, catechol and hydroquinone in water in the concentration range of 10^–4—10^–6 M under conditions of short-term impact of ultraviolet radiation has been studied by the methods of fluorescence analysis and high-performance liquid chromatography. It was found that under the action of UV radiation, resorcinol is transformed easier than other compounds. It was shown that the main products of phenol photolysis are catechol and dihydroxybiphenyls. Resorcinol, catechol and hydroquinone form trihydroxybenzenes. 

A polarizing light beam splitter in a form of two Dove prisms of BK7 glass is created. А multilayer thinfilm coating made of two periodic structures is between the prisms. The number of Nb₂O₅ и SiO₂ layers in every structure and their thickness is selected in a way to ensure the reflection by them of the s-polarized and the transmission of p-polarized component of incident light in the entire specified operating spectral range of the splitter. It is achieved due to the partial overlap and complementation of the corresponding to the structures photon band-gap zones at the Brewster angle. The manufactured polarizing beam splitter at the full divergence angle of the input light beam up to 10° provided a degree of polarization of 0.99 in the operating wavelength range from 400 to 800 nm. Since the material for the manufacture of the polarizing beam splitter is optical glass, the size of the splitters of this design is limited only by the size of the working volume of the vacuum chambers for optical coatings.t beam up to 10° provided a degree of polarization of 0.99 in the operating wavelength range from 400 to 800 nm. Since the material for the manufacture of the polarizing beam splitter is optical glass,

Using luminescent spectroscopy of destruction products at excitation by monochromatic electrons with different energy in the gas phase, it was shown that studied electroactive molecules with approximately the same dimensions and different chemical structure have very different stability under interaction with electrons. All molecule spectra contain luminescence of hydrogen, С₂ and СН, as well as СО, CN, I, Al, Ir in molecules containing these elements or groups. Luminescence of decomposed molecules is observed at electron energy of about 40–50 eV (for the most typical components such as hydrogen in carbazole and aluminium in AlQ₃). This testifies that luminescence of fragments is the result of their excitation by electrons. The amount and luminescence intensity of decomposition products are increasing with a growth of temperature and electron energy. 

The temperature dependences of the refractive indices of the K₂SO₄ crystal with the copper impurity are studied. It is established that the introduction of the copper impurity leads to the appearance of isotropic points (intersection of the curves п_z(T) and п_x(Т) at a temperature of Т' ~ 612 K (∆n_y = 0), and п_z(T) and п_y(Т) at a temperature of T" ~ 689 K (∆n_x = 0)), as well as to the expansion of the temperature range of the intermediate phase and its shift towards lower temperatures. The critical index β of the phase transition order parameter is determined for the doped crystal within the phenomenological approach of the first fluctuation correction to the Landau theory (β ≈ 0.17 ± 0.05). A shift of the phase transition point towards low temperatures is established. The latter can be explained on the phenomenological level by the influence of internal stresses arising during the introduction of the impurity, similarly to the influence of uniaxial or hydrostatic pressures.

An inclusion complex was formed with methyl-β-cyclodextrin (Me-β-CD) and the smallest unit of the macrocyclic family of bathocuproine[Ed1], 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. With this newly formed fluorescent probe, the quenching effect of heavy metals was investigated. Spectral characterization of the complex was performed by UV-visible and fluorescence spectroscopy techniques. The complex formation constant (K_b), Gibbs free energy (ΔG⁰ ) and approximate quenching activation energy (E_a) values were calculated. Lifetime (τ), bimolecular quenching rate constant (k_q) values, and diffusion rate constant (k_d) calculations were made, and the mechanism of quenching by the effect of heavy metals was clarified.

The influence of aromatic antioxidants 2,6-di-tert-butyl-4-methylphenol (BHT) and diphenylamine (DPA) on the thermal–oxidative degradation of base oils 150N was studied by using the hot oil oxidation test (HOOT) with temperatures varying from 100 to 200^o C and times ranging from 1–24 h. Qualitative as well as quantitative analyses of the base oils and their fractions were done using gas chromatography-mass spectrometry (GC-MS) and spectroscopic (FTIR, UV–visible) techniques to gain a better understanding of their compositional and structural details. Oxidization processes were also studied and structural changes resulting from thermal oxidation were identified. The results indicate that the addition of antioxidants causes an obvious enhancement in the resistance of base oils to thermal–oxidative degradation. Moreover, the mixture of antioxidants shows better thermal–oxidative resistance than the phenolic or diphenylamine antioxidants alone. 

The solvent effects on C=O stretching vibrational frequency, ν(C=O), of ketoprofen (KETO) were studied experimentally using attenuated total reflection infrared spectroscopy (ATR-IR). The experimental ν(C=O) of KETO were correlated with empirical solvent parameters, including the Kirkwood–Bauer–Magat (KBM) equation, the acceptor numbers (ANs) of the solvents, the Swain equation, linear solvation energy relationships (LSERs), and the quadratic equation (QE). The solvent-induced ν(C=O) shifts of KETO displayed a better correlation with the LSER equation than with the KBM equation, ANs of the solvents, and the Swain equation. The linear effect of the solvent hydrogen-bond donor acidity (A_j) on ν(C=O) of KETO was found to be highly significant, whereas the hydrogen-bond acceptor basicity (Bj) and the interaction effect of A_j and B_j were not significant. It was also observed that the quadratic effects of A_j and B_j were slightly significant. Additionally, the linear effect of LSER parameters (π^*, δ, α , and β) and the interaction effect of π^* β on the ν(C=O) of KETO were highly significant.

We report the effect of the sintering temperature on the structure and valence states of Ru-Mn in Li₂Mn_0.9Ru_0.1O₃. These effects are explored by synchrotron X-ray diffraction patterns, Raman and X-ray absorption spectroscopy spectra (analysis of the Ru-M₄, Mn-L_2,3, and O-K edges). Ru doping at the Mn site in Li₂MnO₃ changes the lattice parameters of the parent Li₂MnO₃. Li₂Mn_0.9Ru_0.1O₃ sintered at 950^o C shows two peaks of the Ru-M₄ absorption edge. These peaks confirm the presence of mixed valence states Ru⁺⁴  and Ru+5 . The compound Li₂Mn_0.9Ru_0.1O₃ sintered at 1050^o C shows only one peak of the Ru-M4 absorption edge, which reveals the presence of the Ru⁺⁴  valence state. The Mn-L₃ absorption edge of Li₂Mn_0.9Ru_0.1O₃ shifts towards lower energy in comparison to the absorption edge of Li₂MnO₃. The O-K absorption edge of Li₂Mn_0.9Ru_0.1O₃ shows the origin of a new peak in comparison to the absorption edge of Li₂MnO₃ due to the presence of Mn⁺³  – O hybridization in Li₂Mn_0.9Ru_0.1O₃ sintered at 950^o C. The Raman spectrum of Li₂Mn_0.9Ru_0.1O₃ shows splitting and peak shifting with the change in the sintering conditions. The presence of mixed valences Mn⁺³, Mn⁺⁴ , Ru⁺⁴ , and Ru+5  in the lattice of Li₂Mn_0.9Ru_0.1O₃ sintered at 950o C may affect the charge–discharge properties of the Li₂Mn_0.9Ru_0.1O₃ cathode. 

This paper reports the red visible luminescence of ZnO nanofibers synthesized by electrospinning followed by thermal annealing. The ZnO nanofibers were prepared by electrospinning of the precursor mixture of zinc acetate/polyvinylpyrrolidone (PVP) by using different PVP concentrations, while thermal annealing was kept at 600°C. The ZnO nanofiber diameter was dependent on the PVP concentrations, which increased as PVP concentrations increased. Thermal annealing induced significant changes in ZnO nanofibers, which formed ZnO nanoparticle/nanofiber structures as a function of PVP concentrations. The ZnO nanofibers synthesized with PVP concentration of 20% induced homogeneous distribution of ZnO nanoparticles with highly visible luminescence intensities centering at ~650 nm. Results indicated that the use of electrospinning followed by thermal annealing could be an important method for the synthesis of ZnO nanoparticle/nanofiber structures, which could be used in advanced engineering such as optoelectronics and sensing. 

The multi-configuration Dirac–Hartree-Fock method is employed to calculate the energy levels, wavelengths, transition probabilities, and line strengths for electric dipole allowed (E1) and forbidden (M1, E2, M2) lines for the 4s² 4p and 4s4p²  configurations of Xe XXIV. From our radiative decay probabilities, we have also derived the radiative lifetimes of 10 fine-structure energy levels. The valence–valence and core– valence correlation effects, Breit interactions, as well as quantum electrodynamics (QED) effects are estimated in the subsequent relativistic configuration interaction (CI) calculations. The present results are compared with the experimental data and with the values from other calculations. In this paper, we predict new data for several radiative data where no other theoretical and/or experimental results are available. 

Two different simple, accurate, and precise UV spectrophotometric methods have been developed for the estimation of erlotinib hydrochloride in bulk and tablet forms by the zero-order (method I) and the zeroorder AUC (method II). The drug was dissolved in a phosphate buffer solution (pH 7.4), and at 228.20 nm the zero-order (method I) and at 224.20–230.20 nm the zero-order AUC (method II) were developed. For both methods, erlotinib has linearity in the concentration range 10–70 µg/mL, with a correlation coefficient R²  > 0.99. Both methods showed good reproducibility and recovery with %RSD less than 2 and an accuracy of 98.54–101.39 and 98.08–99.83%, respectively. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 1.16, 3.51, and 21.41, 64.90 µg/mL, respectively, for both methods. 

We propose an effective approach for determining the manufacturer of oxytetracycline based on terahertz time-domain spectroscopy and chemometrics. The applied method allowed detection and distinction of oxytetracycline tablets produced by four Chinese manufacturers. Absorption spectra within the frequency range of 0.2–1.6 THz were acquired for analysis, and principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE) were implemented for dimensionality reduction. The obtained data were input into different classifiers, namely, grid-search support vector machines (SVM), genetic algorithm-SVM, particle swarm optimizations (PSO-SVM), decision trees, and random forests. The results indicated that the absorption spectra of oxytetracycline produced by the four manufacturers could be differentiated, and that t-SNE outperformed PCA in terms of dimensionality reduction. The optimal classifier was obtained by combining t-SNE and PSO-SVM, and this approach demonstrated the highest cross validation accuracy (98.33%), an average training set accuracy of 97.72%, and an average test set accuracy of 94.25%. The novel approach described herein achieved rapid classification of oxytetracycline and allowed accurate tracing of the manufacturers. 

UV spectroscopy of tramadol (TRA) and paracetamol (PAR) shows substantial spectral overlap, which is a challenge for their simultaneous determination without preliminary separation. Three smart spectrophotometric methods based on the ratio spectra developed from the overlapping UV spectra of their binary mixture can be applied for a quantitative estimation of both drugs. The first derivative (DR1 ) of the ratio spectra was computed, and then the amplitudes were measured at 268.7 and 237.4 nm for TRA and PAR, respectively. The mean centered ratio (MCR) of the spectra was estimated by measuring the MCR spectra at 279 and 241.5 nm for TRA and PAR, respectively. Finally, the dual wavelength method (DW) was applied by measuring the difference in absorbance at 224.1 and 268.5 nm for TRA determination and at 248 and 285.4 nm for PAR determination without any interference. All the above-mentioned spectrophotometric methods can be used to estimate TRA in the linear range of 10–110 µg/mL. Furthermore, PAR can be estimated in the linear range of 1–25 µg/mL. These methods were successfully applied to the analysis of the combined dosage form and bulk powder of TRA and PAR. The methods were validated according to the International Conference on Harmonization (ICH) guidelines, and the obtained results were statistically compared with those obtained by previously reported methods. No significant difference with respect to accuracy and precision was observed. 

We report car-borne measurements of atmospheric NO₂ close to the ground by incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS). A compact IBBCEAS spectrometer with a blue light emitting diode (LED) having a central wavelength of 458 nm, a full width at half maximum of 25 nm, and a 50-cm-long cavity was developed for mobile measurements. The NO₂ detection limit of the spectrometer was calculated as 1.9 parts per billion by volume (ppbv) for a 30 s acquisition time by stabilizing the LED emitting spectrum, optimizing the NO₂ reference cross-sections, and by calibrating the reflectivity of the cavity mirrors. The accuracy of the spectrometer was verified by measuring NO₂ samples with various mixing ratios between 1–200 ppbv, which were produced by a gas dilution system in the laboratory. Three distinct journeys in Nanjing and the surrounding areas were selected as observation routes. The atmospheric NO₂ close to the ground was measured by the spectrometer from August 4 to 7, 2013. The mixing ratios of NO₂ ranged from 3 to 144 ppbv. These results were compared with the column density of NO₂ measured by a passive differential optical absorption spectroscopy (DOAS) instrument on the same car. Hence, we demonstrate the feasibility of using the spectrometer for car-borne measurements of atmospheric NO₂.