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An aerosol generator and wind tunnel fumigation system designed for use in studies of aerosol deposition on leaf surfaces is described. Gross deposition on rough pubescent leaves was 10 times greater than on smooth, waxy leaves. Results suggest that aerosol deposition, on a per unit area basis, for single horizontal streamlining leaves, is similar to that for arrays of leaves under similar flow conditions. It is well-known that the primary source of lead in most communities is from the particulate emissions from automobiles. This lead is transported by the atmosphere from the highway and deposited on soil surfaces and/or directly on plant surfaces. The deposited lead may either enter plants through the roots in the soil (1-3) or through the leaf surfaces after aerosol deposition (3-5). This study will examine the deposition of lead aerosols on leaf surfaces.The deposition of P b on leaves is controlled by characteristics of the aerosol (size, chemical composition, cloud density), the leaf surface (roughness, pubescence, moisture), and the environment in which the plant lives (relative humidity, wind speed). Once a lead aerosol is deposited on a leaf surface it may gain entrance into the interior of the plant and be translocated throughout the plant to cause adverse effects on the plant's physiological processes. It is this possibility of physiological harm to the plant that forms the impetus for this study. By being able accurately to predict the extenr, of particle deposition on individual plant surfaces or arrays of leaves under various conditions, an estimation of the plant dosage of lead can be ascertained. This paper will address the questions concerning the correlation of the aerosol deposition rate for single and multiple leaf clusters. In order that the effects of surface roughness on aerosol leaf deposition might be bounded, two plant species representing extreme cases were examined. These were the tulip poplar and the sunflower leaf.Since the main objective of this investigation was to study the gross deposition of an aerosol on plant leaves in a well-defined flow field and not the resulting physiological response, it was proposed r,hat a uranine aerosol be used in place of a lead aerosol. The primary reason for this was the ease with which uranine particles can be analyzed as opposed to lead aerosols. To check the validity of this approach, an initial series of experiments was run to demonstrate the feasibility of substituting uranine parti-Present address, Engineering Research Center, Colorado State University, Fort Collins, Colo. 80521. cles for lead aerosols in the deposition studies. A second series of experiments compared particle deposition on smooth, waxy leaves with that of rough, pubescent leaves while a third set of results compared deposition on single leaves with that found on groups or assemblages of leaves. Experimental SystemA 0.929-m2 steel wind tunnel -7.315 meters in length was constructed as a transport system for the deposition studies (6). Air entering the tunnel passes through an ...

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The two-filter method described by Thomas and LeClare was used to investigate the effects of trace concentrations of nitric oxide and nitrogen dioxide in dry nitrogen on the diffusion coefficient of radium A (polonium-218). Charged radium A was neutralized in 10 parts per million (ppm) nitrogen dioxide in dry nitrogen, in 8.3 ppm nitric oxide in dry 92 percent nitrogen and 8 percent oxygen, and in nitrogen with 20 and 80 percent relative humidity. No neutralization was seen in dry nitrogen, dry oxygen, dry air, or 10 ppm nitric oxide in dry nitrogen. The diffusion coefficient of the neutral radium A species was found to be 0.079 square centimeters per second, regardless of the relative humidity of the nitrogen gas atmosphere. Lower values were observed for charged species.

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