The aerosol optical characteristics in the wavelength range of 0.46-0.87 μm were calculated on the basis of an empirical model of the aerosol optical characteristics in the summer background haze of Western Siberia. The Monte Carlo method was used to estimate the sensitivity of the model to uncertainties in measuring the input parameters: angular light scattering coefficient at a wavelength of 0.53 μm at an angle of 45°, mass concentration of the absorbing substance, and parameters of its lognormal size distribution, relative humidity of air. The relative errors in the reconstructed scattering, extinction, and absorption coefficients, single-scattering albedo, asymmetry factor, and lidar ratio are analyzed.
A series of simultaneous measurements of the spectral aerosol extinction coefficients at wavelengths of 0.45-3.9 μm, angular scattering and absorption in the wavelength range of 0.46-0.63 μm in pine combustion smokes was carried out in the Big Aerosol Chamber of IAO (BAC) in 2019-2021. Relationships between the aerosol optical characteristics at the initial stage of smoke formation are considered depending on: a) the value of the mass mixing parameter for open flame combustion (generation of black carbon microparticles) and smoldering combustion (brown carbon particles); b) the total mass of the combusted material. The spectral dependences of the aerosol scattering and absorption coefficients of pyrolysis (12 realizations) and mixed (28 realizations) smokes in the wavelength range from 0.45 to 3.9 μm were estimated.
The paper presents a complex refractive index in the model of the aerosol optical characteristics in the lower 5-km atmospheric layer of Western Siberia. The model is based on the data of long-term airborne sounding of the vertical profiles of angular scattering coefficients, atmospheric aerosol disperse composition, content of absorbing substance, and condensation activity of aerosol particles. Various algorithms for taking into account the absorbing substance and the aerosol condensation activity are considered.
The results of measurements of aerosol and absorbing substance vertical profiles from onboard of the TU-134 "Optic" laboratory aircraft during Arctic flights in the fall of 2020 are presented. The vertical distributions of mass concentrations of aerosol and absorbing matter over Arkhangelsk, Tiksi and Anadyr are analyzed. The aerosol optical characteristics over three cities in the north of Russia are reconstructed and compared with the measurement data.
When studying the condensation growth of atmospheric aerosol, many researchers note the dependence of the hygroscopic properties on the particle size. To change the aerosol size spectrum, we use diffusion selection, i.e. sequential removal of the finest fraction from the air flow. This makes it possible, on the one hand, to more accurately describe the distribution function in the size range r <0.2 μm, and, on the other hand, to increase the contribution of the intermediately dispersed fraction (r = 0.5 - 1 μm) to the formation of the optical signal. This work is devoted to the study of the sensitivity of the parameter of condensation activity of particles to changes in their size spectrum.
In the Large Aerosol Chamber of the IOA (LAC) in 2020, complex measurements were made of the spectral coefficients of aerosol attenuation at wavelengths 0.45-3.9 microns, angular scattering (nephelometer) and absorption (multi - wave aetalometry) - 0.46, 0.53, 0.59, 0.63 microns in pine combustion fumes. Investigated the variability of the optical and microphysical characteristics of aerosols at the stage of smoke formation, depending on the value of the mass mixing parameter for the modes of flame combustion (generation of black carbon microparticles) and smoldering combustion (brown carbon particles), the total mass of the material. The dynamics of the characteristics of fumes under 2-day aging under dark conditions and under the influence of ultraviolet radiation in the wavelength range of 300-400 nm is analyzed. Aerosol measurements were accompanied by sampling of particles on aerosol filters to determine the concentrations of elemental EC and organic carbon OS in the smoke aerosol by gas chromatography. For the studied pyrolysis and mixed combustion fumes, the spectral dependences of the aerosol attenuation and absorption coefficients, the mutual relationship of the aerosol attenuation, scattering and absorption coefficients are analyzed. Estimates of the variability of the adsorption parameters of Angstrom and the specific mass concentration of brown carbon in the combustion fumes of LGM are obtained, which are important for comparison with the data of satellite sounding of the fumes of Siberian forest fires.
The optical-microphysical characteristics of smokes from forest combustible materials with different contributions of flaming and smoldering combustion of biomass with 48-h ageing under dark conditions have been studied in the Big Aerosol Chamber of the Institute of Atmospheric Optics (IAO). The dynamics of spectral dependences of aerosol extinction coefficients at wavelengths of 0.45-3.9 µm, scattering and absorption coefficients at 0.46-0.63 µm, aerosol extinction, scattering, and absorption Angstrom exponents, Black Carbon (BC) mass concentration and relative BC content, and single scattering albedo was analyzed. Characteristics of model smokes have been compared with data for smoke plumes from remote Siberian wildfires to assess the mean values of the parameter of mixture of flaming/smoldering modes closest to the actual pattern of absorption properties of remote wildfires. A system for imitation of solar UV irradiation have been deployed in the Big Aerosol Chamber (BAC), and test experiments on generation of secondary organic aerosol under UV irradiation of the near-surface air pumped into BAC have been conducted.
The paper presents the results of one of the stages of development of the empirical model of the optical characteristics of tropospheric aerosol of Western Siberia. The model is based on classification by the types of aerosol weather constructed using the data of long-term measurements at the Aerosol station of IAO SB RAS. Here we discuss different variants of taking into account the aerosol absorbing and hygroscopic properties. The main feature of this paper is considering the size-resolved complex refractive index of particles. The results of model calculation are compared with the average experimental data on the angular scattering coefficient in the small-angle range and the spectral behavior of the aerosol extinction coefficients. It is shown that the most adequate reconstruction of the optical characteristics is reached in the case when the size distribution of absorbing substance has been described by a lognormal function and the dependence of the condensation growth factor on the particle size has been characterized by a maximum at a certain radius.
In the IOA SB RAS, a large aerosol chamber was used to perform 20 experiments on the burning of forest fuel materials (pine wood, coniferous litter) of two types in smoldering/flame combustion modes of different ratios. The chemical composition (PM, OC, EC) of fresh smokes (2 hours after substrate ignition) and of aged aerosol (on the 1st and 2nd days) was determined in dark conditions. The variability of the main characteristics of smoke aerosol during its aging was analyzed with different contributions of smoldering and flame combustion modes.
The work reports the results of the measurements of particulate matter (PM), organic (OC) and elemental (EC) carbon mass concentrations, and carbon isotope composition (δ13С) in atmospheric aerosol sampled along the route of the research vessel “Academician Mstislav Keldysh” (71 voyage). The measurements were carried out over the Baltic Sea – the North Sea – the North Atlantic – the Norwegian Sea – the Barents Sea from June to August 2018. The increased OC, EC concentrations and the high δ13С value in the samples collected off the coast of Greenland are shown to be not due to marine origin, but due to the transfer of atmospheric aerosol formed in Canada during biomass burning (forest fires).
We discuss the specific features of the spatial distribution of aerosol and black carbon concentrations in the near-ground atmospheric layer, as well as of aerosol optical depth (AOD) over the North Atlantic and Arctic Ocean according to measurements in two marine expeditions in 2018. On the average, the spatial distribution shows aerosol characteristics, decreasing with the growing latitude (from the Baltic to Barents Sea), and comparably low characteristics over Arctic seas, from the Barents to Eastern Siberian Sea. The average aerosol characteristics over the Arctic Ocean were: 4.8 cm-3 for number concentrations of particles (with diameters of 0.4 – 10 μm), 40 ng/m3 for black carbon mass concentration, and 0.048 for AOD (0.5 μm). The largest characteristics were obtained in the south of the Barents Sea (near Scandinavia), with values 11 cm-3 for particle concentration, 310 ng/m3 for black carbon concentration, and 0.164 for AOD (0.5 μm).
Based on data of seven expeditions, we considered the specific features of the spatial distribution of aerosol physicalchemical characteristics over Arctic seas in Russia. It is shown that the average aerosol and black carbon concentrations and aerosol optical depth of the atmosphere decrease by a factor of 2-2.5 in the direction from west to east. A more detailed analysis in the sectors of the Barents and Kara Seas revealed a tendency toward a decrease in aerosol characteristics in the northeast direction. We noted that the average ion concentrations in aerosol composition are close in value over the Barents and Kara Seas. Continental and maritime sources make nearly identical contributions to ion composition of aerosol over these seas.
Based on multiyear studies in the Russian Antarctic Expeditions (51st-62nd RAE), we discuss the specific features of the spatial distribution of atmospheric aerosol characteristics (aerosol optical depth and aerosol and black carbon concentrations) in the southern part of the World Ocean. It is shown that, with the growing separation (up to 170- 350 km) from Africa in the southern direction, a general regularity is a factor of 1.3-4.2 decrease in the average aerosol characteristics. At higher latitudes (40-55°S), the aerosol characteristics saturate to a quasi-constant level, followed by a decrease in the average values toward Antarctic coasts.
The results of measurements of the aerosol optical depth (AOD) of the atmosphere carried out in 66th and 67th cruises of RV “Akademik Mstislav Keldysh” (Kara and Barents Seas) and at Russian scientific center in Barentsburg (Svalbard) during polar summer of 2016 are analyzed. It is shown that the level of aerosol turbidity of the atmosphere was close to the long-term average data in arctic latitudes. The mean value of AOD(0.5 μm) obtained from shipborne measurements is 0.065±0.056 and analogous value in Barentsburg is 0.072±0.040. The smoke plumes of forest fires on the continent significantly affected the atmospheric turbidity during measurements. For example, the contribution of smoke aerosol in the mean value of AOD (0.5 μm) obtained onboard the ship is about 44%.
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