Aerosol Number Density Research Articles

The study on evaluation of atmospheric effect based on VTIR and MESSR of artificial satellite MOS-1

Abstract An attempt is made to retrieve aerosol number density based on the thermal infrared data obtained with VTIR (Visible and Thermal Infrared Radiometer) onboard MOS-1 (Marine Observation Satellite 1). It is found that in low moisture condition, aerosol number density can be retrieved from the thermal infrared remote sensing data as one of the maximum likelihood solutions of radiative transfer equation. The application of the method to MESSR data indicates a satisfactory result.

Some results of lidar aerosol measurements and their relationship with meteorological parameters

Vertical profile measurements of aerosol number density remotely in the lower atmosphere during night-time using a bistatic, continuous wave Argon ion laser radar (lidar) system have been in progress at the Indian Institute of Tropical Meteorology, Pune, India since September 1986. The observational programme includes the measurement of a minimum two and maximum seven vertical profiles of atmospheric aerosols in each month. This paper deals with the results of the analysis of lidar aerosol data archived for a period of one year (October 1986–September 1987) and presents the monthly variations in the height distribution of aerosol number density along with their deviations from the annual mean distribution. Also, presented in this paper are the results of (i) the temporal changes in the aerosol concentration at 30 m AGL and its relationship with surface wind and relative humidity, and (ii) the comparison of the aerosol profiles on some selected days with the near-simultaneously obtained vertical profiles of wind, temperature and relative humidity. The results suggest that variations of aerosol concentration exhibit a certain relationship with those of meteorological parameters, and the atmospheric stability conditions associate with the vertical gradients of concentration at the top of the aerosol layer.

Remote sounding of aerosols in the lower atmosphere using a bistatic CW helium-neon lidar

A bistatic, CW (continuous wave) lidar (light detection and ranging) system has been developed at the Indian Institute of Tropical Meteorology, Pune, India for remote sounding of atmospheric aerosols. The system comprises a Spectra-Physics Model 159, 5 mW helium-neon laser as transmitter and a 25 cm Newtonian telescope-photomultiplier assembly as receiver. The details of the experimental set-up and results of preliminary observations of aerosols carried out in the lowest layers (up to 300 m AGL) of the atmosphere are presented. The results were found to be in agreement with those of the model predicted aerosol number density profile obtained by other investigators in the height region of observations. The variations in the height distribution of aerosols are explained in the light of the atmospheric conditions prevailing over the measuring site.

Beam propagation through slab scattering media in the small angle approximation

A general solution to the radiative transfer equation applicable to beam propagation in scattering media in which scattering takes place principally in extreme forward direction was obtained by H. S. Snider and W. T. Scott [Phys. Rev. 76, 220 (1949)] and discussed by R. L. Fante [IEEE Trans. Antennas Propag. AP-21, 750 (1973)]. This solution is applicable to media in which the aerosol number densities are nonuniformly distributed in space. Subsequently, W. G. Tam and A. Zardecki [Appl. Opt. 21, 2405 (1982)] obtained a specific solution applicable to those cases in which the beam width and angular spread as well as the aerosol phase function can be approximated by a Gaussian. Their solution is restricted to uniform or step function shaped media in which the detector is in the scattering medium. The present work shows that the Tam and Zardecki approach can be applied to the inhomogeneous case. Specifically, a solution is obtained for a slab shaped scattering medium. The results are compared with those obtained by use of a Monte Carlo simulation and to experimental data.

Characterization of ICP nebulizer aerosols using near-forward angle Fraunhofer diffraction

Fraunhofer diffraction is utilized to characterize nebulizer aerosol parameters such as median size, size distribution, relative aerosol number density and aerosol transport efficiency. Parameters are measured for 6 different nebulizer designs, 4 different spray chamber configurations, and 3 different torch systems as a function of nebulizer operating pressure. Relative contributions of operating pressure and sample introduction component hardware toward aerosol conditioning are deduced. For the nebulization systems studied, selection appears to depend more on sample compatibility and convenience than on aerosol characteristics or analytical performance, since all produce similar results from solutions which are compatible with all nebulization systems tested.

A balloon-borne sun-tracking multichannel photometer for atmospheric aerosol measurements

A balloon borne multichannel photometer for measurement of atmospheric scattering in the near ultraviolet and the visible wavelength regions has been developed at the Physical Research Laboratory, Ahmedabad for study of the size distribution and number density of aerosols at tropospheric and lower stratospheric altitudes. The instrumentation involves tracking the sun in elevation and scanning in azimuth. The payload was recently flown on a 100 kg. balloon from the Hyderabad Balloon Facility on 18 April 1984. The balloon reached a float altitude of 35 km and good quality data has been obtained from an altitude of 6 km upto float altitude. Data analysis is still in progress. The present paper details the instrument design and presents a few illustrations of the instrument performance from this flight.

Yield of SO 2 and formation of aerosol in the photo-oxidation of DMS under atmospheric conditions

Photo-oxidation of DMS under atmospheric conditions was studied both in dry ( [H 2O] < 1 ppm ) and in humid air (relative humidity ~ 35%at 30°C). Yield of SO 2was 21 ± 5% at the early stage of reaction and finally increased to 29 ± 7%. Formation of aerosols were also measured. In dry air number concentration of aerosols was low (max. ~ 3.0 × 10 -3 cm −3 ). but geometrical mean diameter was large (~ 0.4 μm). In humid air number density of aerosols was high (max. ~ 3 × 10 5 cm -3 ), but geometrical mean diameter was small (~ 0.2 μm). Dimensionless parameter ( A/(N 1 3 V 2 3 ) ) was calculated to be 4.35 for the humid air system. Both methanesulfonic acid (CH 3SO 3H, MSA) and sulfuric acid were detected in sampled aerosols.

Comment on “Hy‐wire measurements of atmospheric potential” by R. H. Holzworth

Measurement of the temporal variation of the global electrical circuit is becoming of increasing interest to the scientific community. Holzworth (1983) suggests that a tethered balloon at about 500 m over Wallops Island may have recorded variations of the global electrical circuit. This note discussed the general problem of how meteorological processes in the lower atmosphere control the variation of atmospheric potential and thus mask the global signal. It is shown that the reported tethered balloon potential measurements occurred (1) when changes in aerosol number density spectrum would have been expected and (2) when changes in convection may have occurred. These meteorological processes modulate the atmospheric electric field intensity locally. There is no correlation when the curve determined by the UT hourly average of the tethered balloon potentials is correlated with the hourly UT variation of the global circuit as represented by the Carnegie curve. For the abrupt drops in potential that occurred coincident with the breakup of fog or discontinuation of the morning rise in temperature to be due to changes in the global circuit would require more than 50% of the several thousand global thunderstorms to stop abruptly; this is unlikely. Because of the occurrence of fog and convection of hazy air rich in space charge, a coastal region is particularly inappropriate for attempts to measure the global circuit variation. Aside from problems related to location, the excessive voltages reported in the tethered balloon data suggest some problem with the measuring technique itself. These data give potentials at 530 m which are 48% higher than comparable aircraft measurements. Extrapolated to the ionosphere, the tethered balloon potential profiles would generally give ionospheric potentials on the order of 500 kV, which is well beyond the values measured in any other program.

The Formation of Polar Stratospheric Clouds

Measurements of the stratospheric aerosol by SAM II during the northern and southern winters of 1979 showed a pronounced increase in extinction on occasions when the temperature fell to a low value (below 200 K). The correlation between extinction and temperature is evaluated on the basis of thermodynamic considerations. As the temperature falls, the hygroscopic aerosols absorb water vapor from the atmosphere, growing as they do so. The effect of the temperature on the size distribution and composition of the aerosol is determined, and the optical extinction at 1 micron wavelength is calculated using Mie scattering theory. The theoretical predictions of the change in extinction with temperature and humidity are compared with the SAM II results at 100 mb, and the water vapor mixing ratio and aerosol number density are inferred from these results. A best fit of the theoretical curves to the SAM II data gives a water vapor content of 5-6 ppmv, and a total particle number density of 6-7 particles/cu cm.

Observational Results On The Influence Of Surface Layer Stability And Inversion Entrainment On Surface Layer Marine Aerosol Number Density (1 Micrometer)

Wind speed and relative humidity have been the physical variables used in empirical expressions for equilibrium marine aerosol distributions. Recent formulations, which include the role of hydrostatic stability because it influences turbulent transport and entrainment of clear air from aloft, are examined on the basis of 1 um radius aerosol number density values. The aerosol data were collected along with a quite complete meteorological data set in the Northeast Atlantic during the international Joint Air Sea Interaction Experiment (JASIN-78). The 1 um number density values are normalized for generation and relative humidity influences, and analyses are performed to gain reasonable assurance that the aerosol were of sea salt origin. A stability influence was observed in the normalized number density results, but it was less than that predicted by a flux-profile relationship in which the only removal velocity was the gravitational fallout rate. Better agreement occurs when the entrainment rate of overlying air into the boundary layer is added as a removal velocity. This indicates that entrainment of clear air from aloft dilutes the near surface marine aerosol number densities a measurable amount.

Space-charge effects in aerosol charging and migration

Numerical calculations demonstrate the dominant effect of aerosol space charge in the ionic charging and electrostatic precipitation of a dense quiescent aerosol in an applied electric field. Alternative charging laws are used: one the sum of the field and diffusion charging currents, while the other, proposed by Liu and Yeh, includes an enhancement of the diffusion process by the applied field. Experiments are conducted in a parallel-plate geometry with 0.56-μm radius dioctylphthalate particles with number densities of 0.6 to 6 × 10 12 m −3 and applied fields of 0.23 × 10 5 to 1.05 × 10 5 V/m. Ions are injected using a “corona triode” arrangement which provides a uniform flux of ions and blocks the turbulent corona wind. The collected aerosol mass and ion current (which can be strongly suppressed by the aerosol) are recorded as functions of time. For the lower initial aerosol number densities, numerically determined deposition times predicted by the two charging models bracket the experimentally obtained time. Differences of factors of four or more between the experimentally obtained and numerically predicted deposition times at higher aerosol densities are attributed to observed fluid instability and convection driven by the charged aerosol.

Remote sensing of the middle atmospheric aerosol

Remote sensing of the middle atmospheric aerosol

Kinetic Model for Aerosol Formation in Rocket Contrails

A kinetic condensation model is presented for rocket contrail formation. The formulation treats condensation of water and acid species as a heterogeneous process occurring on soluble or insoluble nuclei particles in the rocket exhaust. The modeling objective is the prediction of condensate aerosol number densities and sizes in contrails. Numerical model results are presented for a HCI/H 2O exhausting rocket at several ambient conditions. It is found that plume condensate aerosol properties are affected by the loading and size distributions of the nuclei particles, especially at high altitudes. Nomenclature C = condensate mass concentration D = molecular diffusion coefficient e = saturated vapor pressure h = Harned coefficient A// = latent heat of vaporization or solution / = ionic strength of solution m = molality (moles solute/1000 g water) M2 - average acid molality of aerosol n = aerosol particle concentration P = pressure Pj, P2 = partial pressures R,z = radial and axial plume coordinates

The effect of surface characteristics on diffuse reflection radiation at ?=0.40 ?m

The diffuse radiation in the upward direction at the top and at an internal level of an inhomogeneous atmosphere is computed at λ=0.40 μm. The surface is assumed to reflect light in accordance with a hybrid mode of a diffuse and specular reflector. The objective is to estimate the effect of underlying surface characteristics in terms of the diffuse radiation field. By making use of these results, accuracy in monitoring the atmospheric aerosols would be increased for the use of remote sensing satellite techniques. Junge power lawv *=3 is adopted for the size distribution of aerosols (1963), while the data given by McClatchyet al. (1971) is used for the number density of aerosols with height distribution. It is noted from the computations that the diffuse reflection radiation is affected by the surface characteristics, even if the albedo of the surface is a fixed constant and very small.

Degree and Direction of Polarization of Multiple Scattered Light 2: Earth’s Atmosphere with Aerosols

The degree of polarization as well as the direction of the polarization are calculated by a Monte Carlo method for the reflected and transmitted photons from the earth's atmosphere. The solar photons are followed through multiple collisions with the aerosols and the Rayleigh scattering centers in the atmosphere. The aerosol number density as well as the ratio of aerosol to Rayleigh scattering vary with height. The aerosol index of refraction is assumed to be 1.55. The proportion of aerosol to Rayleigh scattering is appropriately chosen at each wavelength (lambda = 0.4 micro and 0.7 micro); ozone absorption is included where appropriate. Three different aerosol number densities are used to study the effects of aerosol variations. Results are given for a solar zenith angle of 81.37 degrees and various surface albedos. The radiance and polarization of the reflected and transmitted photons is particularly sensitive to the amount of aerosols in the atmosphere at certain angles of observation. The direction of pola ization shows little dependence on the surface albedo.

On size distributions of atmospheric aerosols

The question of the existence of asymptotic power laws, or more properly Pareto distributions, for atmospheric aerosols is examined. Present evidence that continental aerosols are asymptotically Paretian is not convincing. Improved tests for such an hypothesis are suggested. An analytical formulation of a model for the atmospheric aerosol, based on condensational growth for particles greater than a certain size, is shown to yield “characteristic” aerosol number densities whose forms are determined by the particular growth law assumed for condensation. The growth processes coupled to a reservoir of particles at the truncation point of the density, supplied by nucleation, condensation, and coagulation, cause the aerosol to “forget” its initial distribution and to approach with time the “characteristic” densities. When condensational growth proportional to particle mass is assumed, an exact Paretian density is obtained whose exponent is determined by the ratio of particle removal to growth rates. “Characteristic” densities arising from other condensational growth laws are summarized. It does not appear that these various “characteristic” densities can be resolved with present observational data for atmospheric aerosols.

Behavior of aerosols undergoing brownian coagulation and gravitational settling in closed systems

A generalized solution was obtained to an equation expressing the behavior of high number density aerosols undergoing Brownian motion and gravitational settling in a well stirred, closed system. Graphs are presented which show the variation with time of aerosol concentration and number density, and the geometric mean radius and geometric standard deviation of the aerosol size distribution.

Stratospheric aerosol measurements by optical radar

A laser radar is being used at Adelaide, South Australia (35°S) for routine studies of upper atmosphere densities and aerosol concentrations to an altitude of 60 km. The transmitter operates at a wavelength of 0.694 μ and generates pulses of 0.2 J energy and 0.5 μsec pulse length at a rate of 20 per min. The receiver is a 12 in. Newtonian telescope equipped with an interference filter of bandwidth 8 Å. The light is detected by a cooled photomultiplier, and the recording is carried out by integrating photon counts from selected height intervals. Results for the period February–June, 1969 show that, over the height range 10–60 km, the scattering can be considered as molecular with the exception of the region 13–24 km where enhanced scattering is attributed to aerosols. The maximum aerosol number density, averaged over the five months, is estimated as 1.3 × 10 6 m −3 and occurs at a height of 18.5 km.

Polarization of the Radiation Reflected and Transmitted by the Earth’s Atmosphere

The polarization of the reflected and transmitted radiation is calculated for a realistic model of the earth's atmosphere at five wavelengths ranging from 0.27 micro to 1.67 micro. The single scattering matrix is calculated from the Mie theory for an aerosol size distribution appropriate for our atmosphere. The solar photons are followed through multiple collisions with the aerosols and the Rayleigh scattering centers in the atmosphere by a Monte Carlo method. The aerosol number density as well as the ratio of aerosol to Rayleigh scattering varies with height. The proportion of aerosol to Rayleigh scattering is adjusted for each wavelength; ozone absorption is included where appropriate. The polarization is presented as a function of the zenith and azimuthal angle for six values of the earth's albedo, two values of the solar zenith angle, and four values of the total aerosol concentration. In general the polarization decreases as the wavelength increases and as the total aerosol concentration increases (because of the increasing importance of aerosol scattering). In most situations the polarization is much more sensitive than the radiance to changes in the parameters which specify the atmosphere.