Aerosol Extinction Measurements Research Articles

Inference of stratospheric aerosol composition and size distribution from SAGE II satellite measurements

In this paper the authors present a method that can be used to infer stratospheric aerosol composition and size distribution, based on the water vapor concentration and aerosol extinction measurements from the satellite instrument of the Stratospheric Aerosol and Gas Experiment (SAGE II) and the associated temperatures provided by the National Meteorological Center (NMC). To infer the chemical composition, the aerosols are assumed to be sulfuric acid‐water droplets. The equilibrium acid weight percentage and refractive index at the SAGE II aerosol wavelengths can then be estimated by using the SAGE II‐observed water vapor and the associated temperatures. To infer the aerosol size distribution, a modified Levenberg‐Marquardt algorithm is adopted for determining model size distribution parameters in the least squares sense, based on the SAGE II‐observed multiwavelength aerosol extinctions. Both single‐mode lognormal and modified gamma representations are employed in the analysis. One of the most significant conclusions from this analysis is a determination of the information content of the SAGE II multiwavelength aerosol extinctions with respect to stratospheric aerosol size distributions. It is concluded that the best aerosol size information is contained in the aerosol radius range between approximately 0.25 and 0.80 μm.

SAGE II aerosol correlative observations: Profile measurements

Profiles of Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol extinction measurements are compared with dustsonde‐ and lidar‐derived aerosol extinction profiles during five correlative experiments between November 1984 and July 1986. Six‐channel dustsonde measurements of particle concentration are used to construct a size distribution, then converted to extinction using Mie theory. The two‐wavelength lidar backscatter data are converted to extinction, using model extinction to backscatter values constrained by the standard dustsonde two‐channel ratio. A set of wavelength‐dependent refractive indices is calculated and used in the conversion of both the dustsonde and lidar data to extinction. The November 30, 1984, intercomparison period provided near‐ideal conditions for SAGE II validation. A six‐channel dustsonde and two‐wavelength aircraft lidar system were nearly coincident with the SAGE II measurement. All four profiles of aerosol extinction at 1.02 μm agree very well from the tropopause to 28 km. Selected altitudes were also compared at all four SAGE II aerosol wavelengths: 1.02, 0.525, 0.453, and 0.385 μm. The remaining four intercomparisons vary in quality, but they are very good, considering the time and space gradients and other problems involved. Therefore the SAGE II lower stratospheric aerosol extinction measurements are consistent with dustsonde and lidar measurements for the conditions present during November 1984 to July 1986.

Extinction coefficient measurement of ambient aerosol particles using a ‘white cell’

It was possible to demonstrate in field experiments, that a ‘White Cell’ is a suitable instrument for ambient aerosol extinction measurements even under conditions of low mass concentration. Unsatisfactory agreement of measured and calculated extinction coefficients is due to insufficient information on particle bulk density. The margin within which the real and imaginary parts of the complex refractive index can be varied is sufficient to achieve agreement of measurement and calculation. Future measurements will include the explicit determination of the absorption and scattering coefficients. The additional absorption measurements will help to localize the limits of possible complex refractive index variations.

Antarctic springtime measurements of ozone, nitrogen dioxide, and aerosol extinction by Sam II, Sage, and Sage II

Simultaneous vertical profiles of O3, NO2 and aerosol extinction obtained with the Stratospheric Aerosol Measurement II (SAM II), Stratospheric Aerosol and Gas Experiment (SAGE), and SAGE II satellite instruments across the southern polar vortex show that significant differences exist at all altitudes. Both gaseous species display lower concentrations within the vortex over measurement altitudes ranging from the tropopause to 60 km and 20 to 40 km for O3 and NO2 respectively. Aerosol extinction above 15 ‐ 18 km and total aerosol stratospheric column are also lower inside the vortex than outside. Total column amounts of O3 and NO2 are found to be strongly coupled to spatial location within the vortex, with minimum total values located around the vortex center. Vertical profiles selected to emphasize the observed difference across the circumpolar vortex are presented for October 13, 1981, and October 13, 1985, near 70° and 68°S latitude, respectively.

Slant-Lidar Aerosol Extinction Measurements and their Relation to Measured and Calculated Albedo Changes

The slant-path (or zenith-angle scanning) lidar technique is used to measure boundary-layer optical depths for ten different times during a single day. For the range of optical depths encountered (0.03–0.14 at 0.69 μm wavelength), 1σ measurement uncertainties are about 0.03. The major source of uncertainty is daytime skylight background, effects of which are mitigated in this experiment by the low boundary-layer top height (<1.4 km above the lidar). Resulting particle column backscatter-to-extinction ratios vary between 0.010 and 0.053 sr−1. By assuming that these ratios are independent of height, vertical extinction profiles and the optical depth of a layer below a tower-mounted radiometer pair are derived. This radiometer pair is used to measure the change in surface plus layer albedo caused by the aerosol layer. The consistency of albedo and optical thickness measurements is tested by comparing measured albedo changes to those calculated from the optical thickness measurements. When reasonable values are assumed for particle refractive index and relative size distribution (not measured in this experiment), results agree to within the uncertainty arising from the 0.03 optical thickness measurement uncertainty.

A comparative study of aerosol extinction measurements made by the SAM II and SAGE satellite experiments

SAM II and SAGE are two satellite experiments designed to measure stratospheric aerosol extinction using the technique of solar occultation or limb extinction. Although each sensor is mounted aboard a different satellite, there are occasions when their measurement locations are nearly coincident, thereby providing opportunities for a measurement comparison. In this paper, the aerosol extinction profiles and daily contour plots for some of these events in 1979 are reported. The comparisons shown in this paper demonstrate that SAM II and SAGE are producing similar aerosol extinction profiles within their measurement errors and that since SAM II has been previously validated, these results show the validity of the SAGE aerosol measurements.

Particle size evaluations using multiwavelength extinction measurements

As the first phase of a program to develop a lidar method for remote evaluation of mean particle size of stationary source emissions, a data base was experimentally collected consisting of multiple-wavelength extinction coefficients and mean particle sizes of generated aerosols. Extinction data were collected using multi-wavelength (14) transmissometers and a 10-m long aerosol tunnel facility. Generated aerosols consisted of five size fractions of fly ash, three size fractions of silica, and single-size fractions of six other types of particulate material. Particle size evaluations were made by multistage impactor and by air permeability (Fisher) analysis of packed powder. The data base indicates that mean particle size smaller than l-microm diam could be estimated usefully from aerosol extinction measurements using a single-laser lidar system operating at 1.06- and 0.53-microm wavelengths. For larger mean particle sizes the extinction ratio is near unity, and longer wavelength systems are required. The data indicate that a two-laser lidar operating at 10.6 and 0.53 microm could provide estimates of mean particle size to diameters of at least 6 microm.

Relationships between extinction, absorption, backscattering, and mass content of sulfuric acid aerosols

Linear relationships between aerosol extinction, absorption, backscatter, and mass content are derived for polydispersions of sulfuric acid aerosols. These relationships are independent of the form of the size distribution and are a consequence of approximating the corresponding Mie efficiency factors (the extinction efficiency Qe, the absorption efficiency Qa, and the backscatter gain G) by linear functions of the particle size parameter x. The relationships are valid only at particular wavelengths that depend on the range of particle sizes present in a particular polydispersion. For example, at a wavelength λ = 0.694 μm the relation between aerosol backscatter coefficient σbs(m−1 sr−1) and mass content M (g m−3) is σbs = 0.048M for 75% sulfuric acid (25% water) aerosol, under the restriction that particles in the polydispersion have sizes not exceeding about 1.5 μm in radius. Possible applications of the relationships are (1) inference of path‐integrated mass content of sulfuric acid aerosol (for example, the clouds of Venus) from an infrared laser transmission measurement through the aerosol cloud, (2) determination of sulfuric acid aerosol mass content at a particular point in an aerosol cloud from aerosol absorption measurements at that point with a CO2 (λ = 10.6 μm) laser spectrophone, (3) inference of path‐integrated stratospheric aerosol mass from aerosol extinction measurements made by solar occultation for wavelengths λ = 0.55 and 1 μm, and (4) inference of vertical profiles of stratospheric aerosol mass from ruby lidar (λ = 0.694 μm) backscatter measurements.

Multiple scattering corrections for atmospheric aerosol extinction measurements

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text W. G. Tam, "Multiple scattering corrections for atmospheric aerosol extinction measurements," Appl. Opt. 19, 2090-2092 (1980) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Aerosol extinction and ozone measurements

The effect of aerosol extinction on Dobson measurements of total ozone is investigated, and several recent attempts to resolve this problem are reviewed. It is pointed out that the balloon measurements of Paetzold and his colleagues circumvent this problem: Solar-cycle and quasi-biennial effects can be clearly discerned in the balloon data. It is suggested that Paetzold's data would be ideal for testing stratospheric models and searching for man's effect on the stratospheric ozone layer.

Economical Multispectral Sun Photometer for Measurements of Aerosol Extinction from 044 μm to 16 μm and Precipitable Water

Economical Multispectral Sun Photometer for Measurements of Aerosol Extinction from 044 μm to 16 μm and Precipitable Water