Realistic Aerosol Research Articles

The sensitivity of a coupled atmospheric‐oceanic model to variations in the albedo and absorptivity of a stratospheric aerosol layer

Considerable uncertainty exists regarding the precise physical parameters of a smoke or aerosol cloud that would be injected into the lower stratosphere by a catastrophic event such as a nuclear war, a major volcanic eruption, or an asteroid impact. In this paper, the sensitivity of the sea surface temperature of a one‐dimensional coupled atmospheric‐oceanic model to variations in the albedo and absorptivity of an aerosol cloud introduced into the lower stratosphere is examined. Zonally averaged results are produced for two latitudes in the southern hemisphere. The temperature response of the oceans to forcings by a cloud with realistic aerosol properties is examined, with particular emphasis on the impact on the surface climate on time scales of 6 months to 2 years.

A model for retrieval of surface spectral reflectance from satellite radiance measurements using realistic atmospheric aerosol profiles

Abstract An effort has been made to retrieve surface spectral reflectance from satellite radiance measurements. For this purpose, a simple cubic equation with surface reflectance as one of its roots has been derived. Besides satellite measured radiance, the other required quantities in the equation are calculated by using the actual solution of radiative transfer equation by a discrete ordinate method, taking into account the inhomogeneous aerosol distribution. The method has been tested for internal consistency by numerical simulations using realistic aerosol profiles. Finally, it has been tested with a Landsat image, giving good agreement with ground observations.

On a Petrov-Galerkin Finite Element Method for Evaporation of Polydisperse Aerosols

A Petrov-Galerkin finite element method is derived for evaporation of polydisperse aerosols. It is demonstrated that this numerical method is accurate and computationally efficient. Together with an appropriate grid system and upwinding factor, this method can reduce spurious oscillations to a negligible level and provide reliable results for a wide range of initial size distributions and evaporation rates. Its performance is superior to the upwind differencing method and the sectional method. It is also shown that analytical solutions are very useful in a priori design of grid systems for simulations of realistic aerosol systems, and evaporative cooling is a significant factor in modeling evaporation of polydisperse volatile aerosols.

Continuous Monitoring for Airborne Alpha Emitters in a Dusty Environment

Disposal of radioactive wastes in underground facilities requires continuous monitoring for airborne radioactive materials, both on the surface and underground. In addition to a natural background of nonradioactive and radioactive aerosols, there may be a sizeable dust contribution from ongoing work such as mining and vehicular traffic. In the monitoring of alpha-emitting radionuclides, these aerosols may lead to self-absorption in the source and a deterioration of the energy spectrum of the detected alpha particles. In this paper, the influence of a realistic background aerosol on the performance of an alpha monitoring system is evaluated theoretically. It is shown that depositing alpha emitters and background aerosol on a surface for counting leads rapidly to a considerable loss of counts, a deterioration of the alpha spectra, an eventual saturation of the count rates, and interference from the natural background of Rn daughters.

Aircraft observations of solar radiation in cloud-free atmospheres

Aircraft observations of solar radiative fluxes (including the downward diffuse component) made in cloud-free conditions in the lowest 8 km of the atmosphere, have been interpreted using simultaneous measurements of aerosol characteristics. Measured flux profiles have been compared with those derived from a two-stream model of radiative transfer which can incorporate both gaseous and aerosol effects. In one of the four cases examined, sufficient aerosol data were available to estimate the radiative properties of the aerosol which could then be included in the model calculations. The findings are shown to be broadly consistent with the observations when a realistic aerosol refractive index is used. The measurement of the downward diffuse radiation enabled the radiative properties of the aerosol to be calculated directly from the flux measurements. In particular, the average single-scattering albedo of aerosol within the boundary layer in continental air masses was estimated to be about 0.7.

An Explicit Form of the Mie Phase Matrix for Multiple Scattering Calculations in theI, Q, UandVRepresentation

Abstract An explicit expression is obtained for the phase matrix in the I, Q, U and V Stokes vector representation for a system containing a polydispersion of spherical particles. All of the symmetry relations derived by Hovenier using general arguments are established explicitly. Convenient algorithms are given for the computation of the phase matrix for a spherical polydispersion. Since this theory is so vitally important in radiative transfer, many researchers will need to compute these functions for realistic aerosol distributions. We have therefore presented results for a haze L distribution so that other researchers will have a way of checking their programs which compute these quantities.

A cyclone separator for aerosol sampling in the field.

SUMMARYTwo cyclones for sampling dilute aerosols in the field are described. Their advantages are their robustness and reliability, the high degree of concentration achieved, and the ease with which they will provide a long uninterrupted sequence of samples.Methods of correcting estimates of cloud concentration for transfer lag in the cyclone are derived.The cyclones were constructed by J. Nott. We are indebted to G. J. Harper and E. J. Morris for allowing us to make use of their observations, and to Dr J. S. Paterson (Superintendent, Allington Farm) for providing the realistic aerosol at our convenience.

Polarimetry of Mars

A summary of results of observations of the polarization of Mars shows that surface pressure determinations from these data have not yielded satisfactory results in spite of the extensive number of observations available. It is suggested that the difficulty lies mainly in the neglect of radiative components resulting from a combination of diffuse transmission and surface reflection, the effects of an unknown and variable aerosol component of the atmosphere, and the concentration of the observations in the longer visible wavelengths corresponding to very small atmospheric optical thicknesses. Computations of atmospheric effects to be expected from various Rayleigh and aerosol models of the atmosphere show that the polarizing effects of realistic aerosol models can vary widely, depending on particle parameters, and that polarization due to Rayleigh scattering by representative models of the Martian atmosphere can only serve to shift the position of the neutral point to smaller phase angles and to shift the polarization curve in the positive direction from its position for only the surface-reflected radiation. The extent to which the surface of Mars is composed of hydrated iron oxides is still an open question. Polarization measurements show that limonite is one, but by no means unique, possibility for a major constituent of the surface. Guidelines for polarization measurements from space probes are that emphasis be on uv wavelengths for atmospheric determinations, that intensity and polarization gradients be measured on center-to-limb scans of the planet, and that measurements of the position and magnitude of the maximum of the polarizationcurve, expected to be at phase angles of 90 degrees to 120 degrees , be given a high priority.