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 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 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.
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.
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.
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.
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.
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.
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