Search Results

You are looking at 1 - 10 of 11 items for

  • Author or Editor: A. J. Alkezweeny x
  • Refine by Access: All Content x
Clear All Modify Search
A. J. Alkezweeny

Abstract

Several experiments were conducted in St. Louis during the METROMEX program to determine the properties and formation of aerosol particles. It was found that the average of several distributions obtained during extended periods of time can be approximated by ΔNDD −4 for the optical size range. Furthermore, aerosol particles in the plume are growing by coagulation and chemical conversion. The conversion rate of SO2 to sulfate is about 11% h−1 and the sulfate is composed of mixture of a acid and neutralized salt aerosol.

Full access
A. J. Alkezweeny

Abstract

Full access
A. J. Alkezweeny

Abstract

Full access
A. J. Alkezweeny

Abstract

An investigation into the technique for measuring ice nuclei by the Millipore filter method is presented. It was found that the measured concentration is independent of the volume air sampled up to 1200 liters. Furthermore, the number of growing ice crystals on the filter surface increase with increase in the processing time up to 20 min. An increase in the concentration was also detected with increase of supersaturation.

Full access
A. J. Alkezweeny

Abstract

The authors measured aerosol and droplet size distributions in the range from 0.1 to 50 µm, concentrations and sizes of precipitation particles, concentrations of condensation nuclei, and state parameters in and in the vicinity of a towering summer cumulus cloud. The measurements show that the liquid water content, droplet concentration, and vertical velocity all peaked in the upper half of the cloud, but the droplet mean diameter increased with altitude. A large fraction of the aerosols (0.1–3.0 µm) remains in the haze state.

The vertical profiles of aerosols and condensation nuclei showed peaks between 5.0 and 7.0 km. The normalized aerosol size distribution shows a shift toward large aerosols. The peaks and the shift in the distribution were explained by chemical conversion of SO2 to sulfate in-cloud droplets.

Full access
A. J. Alkezweeny
and
N. S. Laulainen

Abstract

Clean and polluted air masses, advected over Lake Michigan, were studied using instrumented aircraft during the summers of 1976 and 1978. The results show that regardless of the degree of pollution, the particle size distribution is bimodal. The concentrations of sulfate, nitrate and trace metals in a clean air mass are more than an order of magnitude lower than those in polluted air masses. Furthermore, these concentrations are comparable with those measured in remote areas of the world. In clean air the ratio of the total light scattering to Rayleigh scattering is very close to one, indicating very low concentrations of particulates in the optically active size classes.

Full access
A. J. Alkezweeny
and
D. R. Drewes

Abstract

Results of urban pollutant measurements made during an aircraft flight downwind of St. Louis are presented. Decreases in the levels of SO2, NO x , and aerosol are noted, while O3 is observed to increase to more than 200 ppb at 150 km downwind. The influence of a power plant plume is also observed.

Full access
P. V. Hobbs
and
A. J. Alkezweeny

Abstract

The fragmentation of water droplets during freezing has not been previously established under conditions which resemble those in natural clouds. In laboratory experiments designed to investigate this phenomenon it is important that the droplets be close to the equilibrium state with their environment prior to nucleation. In this paper theoretical expressions are derived which may be used to calculate the degree to which a droplet is in equilibrium with its environment as it falls through a gas which has a vertical gradient of temperature.

Experiments are described in which the fragmentation of freezing droplets from 50–100 μ in diameter have been observed under conditions which are close to those in natural clouds. The fragmentation appeared to be independent of the nucleation temperature over the range investigated (−20 to −32C) and it also occurred for droplets nucleated at −8C by silver iodide in supension. Droplets from 20–50 μ in diameter were not observed to fragment during freezing.

Full access
J. K. S. Ching
and
A. J. Alkezweeny

Abstract

This paper examines the exchange of material by convective cloud processes between the mixed layer and the overlying free troposphere. It describes results of a field experiment that was conducted in Lexington, Kentucky, during the period from 20 July to 24 August 1983 to study the processes associated with the vertical transport of acidic pollutants by nonprecipitating cumulus convection. An aircraft released SF6 tracer either within or above the mixed layer, and it was sampled by another aircraft at various levels within or above the mixed layer in the active cumulus convective cloud zone, as well as on the ground. The results show that mixed layer pollutants are vented above the entrainment zone of its boundary layer into the overlying cloud layer by fields of active cumulus and that such active clouds may force cloud layer air downward into the mixed layer.

Full access
A. J. Alkezweeny
,
D. A. Burrows
, and
C. A. Grainger

Abstract

A number of cloud physics investigations were made within stratiform clouds in the areas around Denver, Colorado, and Kansas City, Missouri, during the winter months of 1989/90. There significant difference in the cloud-droplet-size distributions within the different cloud systems that appear to be associated with the urban plume of them metropolitan areas. This association has been made by looking at the trajectories of the air making up the cloud in different parts of the cloud and by concomitant measurements of NO2 within the cloud, using the presence or absence of NO2 as an indicator of an urbanization effect. In general the effect of the urban area is to significantly increase the number of droplets and decrease the median volume diameter (MVD) and the variance of the droplet diameters. In the clouds formed in unpolluted air, the MVD averaged 21.9 µm with a standard deviation of 7.4 µm, while the clouds formed in polluted air had an average MVD of 13.6 µm and a standard deviation of 1.9 µm.

Full access