Home – Home – Jornals – Atmospheric and Oceanic Optics 2023 number 12

A compact absorption spectrometer with a narrowband continuous tunable diode laser providing sensitivity in terms of the absorption coefficient on the order of 1 × 10^-6 cm^-1 is developed. The design of the spectrometer, the measurement technique, the scheme of ozone generation and maintenance are described. The spectrometer is used to record the absorption spectrum of the ozone molecule for a system of Wulf bands in the near infrared range 11900-12800 cm^-1 corresponding to the rovibronic transitions from the ground to the excited triplet electronic states above the main dissociation threshold of the molecule. The magnitude of the predissociation broadening is estimated from the simulation of the absorption coefficient in the measured spectral range. Ozone absorption cross sections in the considered range are recommended for atmospheric applications; they have been obtained using statistically weighted averaging of the new measurements and experimental laboratory data published in the literature.

Carbon dioxide absorption broadened by argon is studied on the basis of the asymptotic line wing theory. The line shape parameters concerned with the classical potential governing the center-of-mass motion and the quantum intermolecular interaction potential are found. The temperature dependence of the CO₂-Ar absorption beyond the 4.3 mm band edge is explained through changes in the classical potential describing the temperature behavior of the second virial coefficient in the temperature region under study.

Monitoring data on sulfates in atmospheric haze particles over Beijing in winter 2016 are considered. It has been established that the source of sulfates in humidified haze particles is the catalytic oxidation of sulfur dioxide (SO_2(газ)^Mn/Fe,O_2→SO^2-_4(aq)) proceeding in a branched mode. Concentration conditions of this process and the features of its dynamics in the atmosphere are discussed. The agreement between the calculated content of in particles and monitoring data indicates a branched mode of catalytic conversion of SO₂ in the atmosphere - a new source of sulfates. This fast non-photochemical channel should be taken into account in inventory system of sulfate sources in the global atmosphere.

Lichens are not only a bioindicator of air pollution, but they themselves, in turn, affect the chemical composition of the air. The results of studies of the qualitative composition of exometabolites in thalli of epiphytic lichens using the method of high-performance liquid chromatography are presented. A comparative analysis of the fractional composition of deposited aerosol matter in water washouts of lichens showed that it is characterized by a bimodal type of particle distribution. It is postulated that the appearance of the fine fraction is associated with the formation of secondary organic aerosols on the surface of epiphytic lichens. Their precursors are the products of photoactivated reactions between deposited aerosol matter and highly volatile organic compounds that arrive on the surface of lichens as a result of efflorescence. The mechanism of entry of secondary organic aerosols into the surface atmosphere under the influence of radiometric photophoresis is discussed.

The results of hyperspectral sounding of the atmosphere at the Ural Atmospheric Station in Kourovka from 2012-2022 are presented. It is shown that the average rate of CO₂ growth in the atmosphere of this region is about 2.5 ppm per year. The amount of carbon dioxide absorbed from the atmosphere by the forest ecosystem per unit area during the growing season (April-September) in the vicinity of the carbon landfill in Kourovka is estimated using two independent methods. One method is based on the data on the CO₂ total column obtained from sounding the atmosphere with a ground-based high-resolution infrared Fourier spectrometer. The second method is based on the use of an artificial neural network with data from spectral channels of the MODIS satellite sensor as injnit. The results obtained by both methods demonstrate good agreement. The estimates made show that the amount of CO₂ absorbed from the atmosphere by the forest ecosystem in the vicinity of the carbon landfill site during the growing season of 2022 is about 1.5 t/ha (the first method) and about 1.3 t/ha (the second method).

Study of the state of the Kerch Strait water area was carried out using data from a portable three-channel hyperspectrometer EMMA (Ecological Monitoring of Marine Areas), operating from board a moving vessel during daylight hours with a resolution of several meters along the route. Based on the measured spectra of the sea spectral radiance coefficient, the spectra of the light absorption index by water in the Kerch Strait were calculated. Verification of these data was carried out at the stations by measurements of Secchi disk visibility depth. The concentrations of the three main natural components averaged over the depth of light penetration into the water column were calculated from the spectra of total light absorption by water. They were compared with measurements in surface water samples taken along the route. The discrepancy in these estimates in some areas indicates a nonuniform depth distribution of the components, which was confirmed by vertical sounding at the stations; these areas are not used for calibration of remote sensing results. The EMMA data showed the distribution of the natural components in the water area of the Kerch Strait averaged over the depth of light penetration. It also made it possible to estimate some characteristics of the anthropogenic impact recorded by satellites.

One of the possible sources of carbon dioxide entering the atmosphere may be river ecosystems. The paper presents the results of measuring CO₂ fluxes from the surface of a number of rivers and lakes in the Tomsk region. It is shown that during the period of experiments the average carbon dioxide flows for the Ob River were 143.7 ± 21.7 (August 13-14, 2023), 53.3 ± 21.2 (August 19), and 80.4 ± 59.9 mgC × m^-2 × hour^-1 (August 20), respectively. On the river Ket: 66.1 ± 17.3, on the swamp lake Karasevoye 33.3 ± 17.3, on the Suiga River 50.2 ± 23.0, and the Iksa River 81.9 ± 11.5 mgC × m^-2 × hour^-1. Their magnitudes depended significantly not only on the object of study, but also on hydrometeorological conditions.

Cirrus clouds have a significant impact on the radiation balance of our planet and play a crucial role in climate formation. To study their optical properties, it is necessary to address the issue of light scattering by nonspherical ice particles. This article focuses on the numerical simulation of the characteristics of light backscattering for hollow hexagonal columns using the physical optics method. The study examines particles ranging in size from 10 to 316 mm, with wavelengths of 0.355, 0.532, and 1.064 mm. The findings reveal that as the cavity of hexagonal columns increases, the backscattering peak caused by corner reflection rapidly decreases, then several secondary maxima appear, which account for up to 10% of the main peak. At the same time, the position of these secondary maxima remains unaffected by particle size and incident wavelength but is significantly influenced by the particle's shape. These results are valuable for developing an optical model of cirrus clouds and for laser sounding of the atmosphere.

Methods of laser-induced fluorescence and their use in monitoring tools allow solving a number of key problems in the detection of algal blooms. The automated system developed by us makes it possible to process and analyze huge amount of fluorescent spectral characteristics of microalgae monocultures, to determine the dominant monocultures in the water area at the level of genus, and to estimate a possibility of their blooming. In addition, the system makes it possible to catalog reference optical characteristics of microalgae monocultures and to implement interactive algorithms for detecting dangerous microalgae species.

Efficiency of laser radiation harmonic generation in nonlinear crystals is among topical issues in applied nonlinear optics. This work theoretically studies the second harmonic generation (SHG) in a converging (focused into a crystal) laser beam. The influence of the amplitude profile (AP) of fundamental laser radiation beam (before a lens) on the SHG efficiency and on optimal focusing and wave detuning parameters is estimated for the first time. It is ascertained that the optimal values of focusing and especially wave detuning parameters vary in very wide ranges depending on the AP. Strong influence of the AP on the effective aperture length, which mainly limits the SHG efficiency, is shown. Optimization of the AP enables increasing the SHG efficiency by no more than ~ 10%.

The results of describing the spatial distribution of methane concentration in the surface water of Lake Baikal in the spring are presented. The basis was the measurements of CH₄ content which were first carried out in the round-the-clock continuous mode along the entire route of the passage of research vessel in the complex expeditions of LIN SB RAS in the spring seasons of 2013, 2016, 2017, 2018, 2021, and 2022. Based on the results of six expeditions, a data array was compiled; it included 12100 segments (with a step of 0.005° in latitude and 0.01° in longitude) which covered the total area 4466.7 km², or 14% of the Baikal mirror. For a more detailed description of the spatial distribution of methane concentrations in surface water throughout the Baikal water area, the statistical characteristics were calculated in four zones: between 0 and 100 m, 100 and 200 m, 200 and 400 m, and over 400 m isobaths. The comparison of the methane concentrations in the analyzed array with the data of other researchers obtained in different years in close regions of the water area made it possible to conclude that the results presented in the work adequately reflect the most stable features of the spatial distribution of methane concentration in surface water in spring seasons.