Measurements of polarization scattering phase functions and spectral extinction coefficients were carried out in smoke aerosols formed as a result of thermal decomposition of wood materials, in a big aerosol chamber (BAC) of the IAO SB RAS. The results are presented of reconstructing of the parameters of the microstructure and the complex refractive index of smoke aerosols based on the developed algorithm for inverting optical measurements. Temporal variability of the microphysical characteristics of smoke is studied.
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 relationships between the aerosol extinction coefficients in the wavelength range from 0.45 to 3.9 micron, measured on a long horizontal path, and the angular light-scattering coefficients at an angle of 45°, are studied taking into account the mass concentration of the absorbing substance in aerosol particles obtained in a local volume. The role of air humidity in the change in the spectral structure of the components of aerosol extinction of radiation associated with the variability of submicron and coarse aerosols is revealed. The research was carried out within the framework of the state assignment of IAO SB RAS.
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.
A series of experiments in smokes of forest needle litter and pine wood in mixed combustion modes has been conducted in the Big Aerosol Chamber (BAC) of the Institute of Atmospheric Optics SB RAS. In the course of long (1-3 days) ageing of smokes, the correlations between the aerosol extinction coefficients in the wavelength range of 0.4 – 3.9 μm and directed scattering coefficients in the wavelength range of 0.46-0.63 μm were studied. The extinction and absorption Angstrom exponents are determined at different relative contributions of the smoldering/flaming modes.
The aerosol extinction coefficients in the wavelength range from 0.45 to 3.9 μm measured on a long horizontal path are compared with optical parameters measured in the visible wavelength range in a local air volume. The following parameters were analyzed: “dry” and “wet” angular scattering coefficients at an angle of 45°, as well as the mass concentration of the absorbing substance (“soot”) in aerosol particles. Round-the-clock measurements were carried out from March till November in 2000-2006. The comparison was carried out for three seasons: spring, summer, fall and four types of aerosol weather: “, background”, “haze”, “smog” and “smoke haze”. The role of each factor in extinction of optical radiation at different wavelengths is revealed.
The peculiarities of the aerosol microstructure in the near-ground layer and in the atmospheric column when smoke inflows into the atmosphere are studied. The parameters of aerosol microstructure were determined from the solution of the inverse problem for spectral aerosol extinction coefficients measured by the path method and the aerosol optical thickness measured by means of a sun-photometer in a clean atmosphere and when it was filled with smoke in the Tomsk region. The geometrical cross-section, volume concentration, and mean radius of particles of submicron and coarse aerosol fractions were calculated. Under background conditions, the coarse fraction prevails in the total aerosol volume. When air is filled with smoke, the submicron fraction of aerosol particles becomes dominant in the total aerosol volume. As a result, the particle radius averaged over the total ensemble decreases in a smoke-contaminated atmosphere. Also, when the atmosphere is filled with smoke, the nature of the regression relations between the microstructural parameters of different aerosol fractions and the spectral characteristics of the aerosol extinction of light significantly change.
The results of twenty-year-long round-the-clock measurements of the spectral transmittance of the atmosphere on a 1 km long horizontal near-ground path are discussed. The measurements were carried out in the suburb of Tomsk from March to October in 1997 - 2017. More than 10000 hourly average spectral aerosol extinction coefficients β(λ) were obtained in the wavelength range from 0.45 to 3.9 μm. The interannual and interseasonal variability of the components of the aerosol extinction is studied. The most probable values of the coefficients β(λ), which can be characterized as background for this region, are estimated. These values at the wavelengths of 0.45, 0.55, 1.06 and 3.9 μm are: 150, 100, 65 and 45 Mm-1, respectively. The interannual differences of the most probable and annual average values of the aerosol extinction coefficients are shown.
The time variation of microstructure of the near-surface aerosol in the summer period has been studied based on solving the inverse problem for spectral measurements of aerosol extinction coefficient. Experimental data were obtained in Tomsk on a horizontal path using the measurer of spectral transmittance of the atmosphere at 11 wavelengths in the range from 0.45 to 3.9 μm. The numerical algorithm, based on the method of integral distributions, was used to solve the inverse problem. The volume concentration and the mean radius of aerosol particles with separation into a submicron and coarse fraction are considered. Specific features of the aerosol microstructure during the smoke haze in the atmosphere are determined.
The paper analyzes the results of a ten-year long round-the-clock measurements of the atmospheric spectral transmittance of the atmosphere on a horizontal 1 km long near-surface path. Measurements were carried out in the suburb of Tomsk in 1997-2006 since March till October. More than 10,000 hourly average spectra of aerosol extinction coefficients were obtained in the wavelength range 0.45 to 3.9 μm. The role of coarse aerosol in the extinction of visible and IR radiation was estimated. It is shown that the most probable fraction of extinction by coarse aerosol at the wavelengths of 0.45, 0.55 and 1.06 μm, is 17, 22 and 50%, respectively.
An array of atmospheric aerosol optical characteristics is obtained from synchronous measurements on a long nearground path and in a local volume of air. The algorithm of statistical comparison of the data obtained is modernized. The spectral dependence of the single scattering albedo in the wavelength range 0.45 to 3.9 μm is calculated. Non-monotonic increase of albedo with wavelength is observed. Seasonal variations of albedo are estimated. Minimum values of albedo are observed in April and October, and maximum values are in July.
An array of spectral aerosol extinction coefficients is calculated from measurements of the spectral transparency of the atmosphere on a 1 km long horizontal path in 10 regions of the wavelength range 0.5 – 4 μm. An array of angular dependences of the aerosol scattering coefficients in the angular range 1.2 – 15° is obtained by means of an aureole photometer with closed scattering volume. Measurements were carried out under conditions of smoky atmosphere. Inverse problem was solved for two empirical data arrays obtained synchronously (200 realizations) and the aerosol particle cross section size distributions were calculated. It is shown that the results of two experiments are in quite good agreement in the particle size range from 0.18 to 1.8 μm. Objective. Determination of the aerosol particle size range, in which the results of aerosol monitoring by two instrumentation complexes are most representative. Method for solving the problem. The inverse problem was solved for two empirical data arrays: a) spectral aerosol extinction coefficients βext(λ) in the wavelength range 0.5 – 3.9 μm; b) angular dependences of the aerosol scattering coefficients βsct(φ) in the angular range Φ = 1.2 – 15° at the wavelength of 650 nm. The arrays βext(λ) and βsct(φ) were obtained in synchronous measurements by means of two independent instrumentation complexes [1,2]. In order to obtain the aerosol particle cross-section size distribution dS/dr, the inverse problem was solved using the algorithms [3-5]. The spectral dependence of the optical constants of aerosol particles was determined from the empirical data [6, 7]. Finally, two arrays of distributions dS/dr corresponding to the initial experiments data βext(λ) and βsct(φ) were calculated.
A technique is proposed for statistical estimation of the complex refractive index of absorbing aerosol using the data of field measurements of the optical characteristics of near-ground aerosol. The initial sub-array (165 realizations) of the refractive n(0.52) and absorption κ(0.52) indices of particulate matter is obtained from solution of the inverse problem for the wavelength of 0.52 μm. correlations of the obtained values n(0.52) and κ(0.52) with the optical parameters measured at the long atmospheric path and in the local volume are revealed. Iterative algorithm for estimation of the foregoing values separately for submicrometer and coarse aerosol is proposed. The errors in retrieval of the values n(0.52) and κ(0.52) are determined, they are δn=0,035 and δκ=0,016, respectively.
When solving the inverse problem for the data measured with nephelometer in the visible wavelength range, the complex refractive index of aerosol particles is determined with an accuracy up to n–κ. Joint analysis of the scattering and extinction coefficients allows to obtain n and κ separately and to extend the range of particle sizes where the size distribution function is retrieved reliably. Estimates of the errors in determining n and κ, as well as the sensitivity of the measured parameters and to particles of different sizes are presented.
Midges contribution estimates to extinction of optical radiation for background conditions of summer of Western Siberia are received. The midges represent live organisms the sizes some millimeters, and include a gnat, a midge, a wood louse, a mosquito and a gadfly. From July 24 to August 13, 2014 the coefficient extinction of midges changed from 0 to 0.14 km-1, and its average value made 0.065 km-1. The daily course extinction coefficient of midges of has the pronounced morning maximum falling on 8 hours and an indistinct evening minimum - for 19 hours. For the received data file, probability of difference of their average values at 8 and 19 hours by t-criterion of Student made 96%.
The paper presents the results of modeling of the aerosol optical characteristics taking into account the effect of relative humidity of air. Two algorithms were applied: humidification by the Hanel formula with the same parameter of condensation activity for all particles and introducing the dependence of aerosol hygroscopic properties on the particle size. The results of calculations are compared with the data of field measurements.
A comparison of the measured spectral aerosol extinction coefficients βa(λ) and scattering coefficients directed βS(θ). Coefficients βa(λ) were obtained from measurements of atmospheric transmission on horizontal path length of 1 km for wavelengths from 0.45 to 3.9 microns. Scattering coefficients βS (θ) were measured in the angular range from 1 to 15 ° at a wavelength of 0.53 μm. The data were obtained under conditions of forest fire smokes in July 2012 and in clean conditions in April 2013 (706 and 204 realizations, respectively). Under clean conditions, 82% of variations of the extinction of radiation in the whole wavelength range are caused by variability of coarse aerosol, and 98% of variations under smoke conditions are related to submicrometer particles.
Was compared to the measured spectral aerosol extinction coefficients βa(λ) (λ: 0.5 - 3.9 μm) with coefficients directional light scattering βS(θ) (λ = 0.53 μm, θ: 1-45 °) and with mass concentration of the absorbing material in aerosol particles MBC. Measurements of optical and meteorological parameters were performed under conditions of forest fire smokes in July 2012 (706 realizations). It is shown that the magnitude of the aerosol attenuation of visible and infrared radiation can be estimated with certain accuracy, by measuring the light scattering parameters in a local volume. For dense fumes βa (0.55)< 1 km -1 was estimated single scattering albedo, which amounted to 97 - 98% in the visible region of the spectrum.
The physical causes of diurnal variability of aerosol extinction of visible and infrared radiation in the surface layer of the atmosphere. It is shown that in the haze of Western Siberia important factors such variability are diurnal variations in relative humidity and temperature.
Correlation of variations of the aerosol extinction coefficients of optical radiation and the intensity of electric field under
haze and smoke conditions is analyzed on the basis of comprehensive field measurements. It is revealed that significant
(almost by an order of magnitude) decrease of the intensity of electric field is observed in smoke, when increasing the
atmospheric turbidity. It contradicts to the well-known electrooptical relationship and gives the reason to assume that the
quantity of charged particles significantly increases in smoke that dramatically changes the manner of electroptical
relations. At great number of fires on the Earth, one should take into account this fact in climatic models and to
remember it when considering the physical mechanisms of the effect of solar activity on weather and climate.
Analysis is carried out of the diurnal dynamics of the aerosol optical thickness of the atmosphere τA(λ) and the aerosol extinction coefficients in the near-ground layer α(λ) in the wavelength range λ = 0.44 - 1.06 μm, as well as of the vertical turbulent heat flux, measured simultaneously in June 2004 in the region of Tomsk. It is revealed that aerosol extinction in the near-ground layer in the range λ = 1.06 μm under conditions of small cloud fraction continuously increases during a day, but the aerosol optical thickness increases before 12-2 p.m., and then rapidly decreases. Probably, this fact is one of the factors of weak correlation between variations of the aerosol extinction of optical radiation on a near-ground path and in the atmospheric column. It is shown that the diurnal dynamics of τA(1.06) well correlates with the dynamics of the vertical turbulent heat flux.
The estimates of the “effective” height of the homogeneous aerosol atmosphere in wide wavelength range (0.44 to 3.9 μm) are obtained for the first time on the basis of simultaneous measurements of the spectral transparency of the atmosphere on near-ground long path and in the atmospheric column. This parameter qualitatively characterizes the height of the mixing layer for particles of different size. The spectral aerosol extinction coefficients in the near-ground layer of α(λ) and the optical thickness of the atmosphere τ(λ) were measured. The effective height of the homogeneous atmosphere was defined as H0(λ)=τ(λ)/α(λ).
A combined data array on diurnal variability of the spectral structure of the aerosol extinction coefficient on near-ground path and the aerosol optical thickness in the wavelength range 0.44 to 1.06 μm obtained in warm seasons 1995-2000 nearby Tomsk is considered. Temporal transformation of the spectral dependence of the effective height of the aerosol atmosphere H0(λ) in the period since 6 a.m. till 6 p.m. is analyzed. It is shown that the characteristics maximum centered at λ=0.52-0.56 μm is well pronounced in the spectral structure of the parameter H0(λ) near noon at minimum concentration of fine aerosol. The fact of existence of such a maximum is indirect confirmation of the hypothesis on the determining role of stratospheric intermediately dispersed particles in formation of rarely observed anomalous spectral dependence of the aerosol extinction in shortwave range.
The paper is devoted to consideration of the relative effect of random and regular geophysical factors on the mechanism of formation of the disperse composition of near-ground haze. More than one thousand realizations of the aerosol extinction spectra measured on a horizontal near-ground path nearby Tomsk were attracted to the analysis. The parameters of theoretical and experimental statistical ensembles were compared. Their properties were presented in the form of expansion in terms of orthonormalized system of eigenvectors of the autocorrelation matrix. The data are obtained which characterize the peculiarites fo the change of the fraction composition of the near-ground haze at passing from summer to autumn.
A rare case of anomalous spectral dependence of the aerosol extinction of radiation in visible wavelength range was observed near Tomsk in September 2002. It was formed in conditions of decay of smoke haze under the effect of arctic air mass coming. Maximum of the aerosol extinction which is usually located in the violet spectral range (λ ≤ 0.44 μm) has moved to the range λ≈ 0.8 - 1.4 μm. The results of solving the inverse problem have shown that when arctic air came, the content of the particles of accumulative fraction decreased, and the intermediately dispersed fraction moved to the range of smaller particles and became narrower.
Statistical characteristics of the variations of the spectral aerosol extinction coefficients α(λ) and meteorological parameters in near-ground atmospheric hazes are considered in this paper. To more adequately physically interpret the origin of variations, the total aerosol extinction coefficients are divided into components Δα1, Δα2 and Δα3 caused, respectively, by submicron (radius r≈0.05 to 0.45 μm), intermediately dispersed (r≈0.5 to 1.5 μm) and coarse (r>1.5 μm) particles. The relation of these characteristics with meterological parameters of the atmosphere are analyzed, and the role of different factors determining the variability of the aerosol extinction in visible and IR wavelength ranges is assessed.
This paper deals with the problem of interaction between the optical and electrical parameters of atmosphere. At present the interaction not investigated experimental enough. The results of several series of experiments are presented. The experiments in the artificial media camera; the experiments with the nephelometery installation; the experiments on the measurement of spectral transparency of natural atmosphere by the base method is considered as well. The experimental results allowed us to note the existence of the electro optic ratio. The special conditions for observing the above ratio are discussed.
Based on field data on spectral atmospheric transmission along the extended near-ground paths in an arid zone and in a region of West Siberia, excess continuous absorption of radiation in the 0.44-11.5 micrometers wavelength region has been revealed, which nonlinearly depends on the absolute air humidity. Its value, under assumption of quadratic dependence on absolute air humidity, is about 1000-1450 g -2cm5, far in excess of the continuous absorption by water vapor. The character of its spectral dependence suggests that it is related to the finely dispersed soot aerosol. The absorption coefficients obtained on the near-ground and slant paths are compared. The comparison made shows quite satisfactory agreement between them. The presence of the finely dispersed aerosol in the atmosphere is considered one of the important factors causing the anomalous absorption of optical radiation by clouds.
In this paper we discuss statistical properties of aerosol properties of aerosol extinction of visible and IR radiation from field measurements of spectral transmission of the atmosphere along a horizontal path. The measurements have been carried out in winter under three different types of optical weather (haze, ice mist, and snowfall). We also compare in this paper the spectral behavior of the aerosol extinction coefficients measured in Tomsk and near Moscow.
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