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R. E. Munn

The topic is approached from the viewpoint of community air-pollution programs and control. After a brief discussion of the economic costs of atmospheric pollution in an industrial area, a skeleton outline of the important factors in weathering by pollutants is presented. A few of the factors are considered in detail under the general headings of soiling, erosion, and corrosion.

Significant differences in weathering are found for industrial, rural, marine, and very dry climates. Most community surveys include routine tests of the dirtiness of the air but exclude corrosion tests, although this factor is of great economic importance.

Methods of corrosion testing are considered, and it is concluded that they are not feasible yet for community surveys. Increasing interest in corrosion, however, is undoubtedly leading to a broader understanding of the problem.

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R. E. Munn

Abstract

A theoretical expression is derived for the root-mean-square vertical-eddy fluctuation in terms of the friction velocity, the height and Monin and Obukhov's function ϕ. Steady-state conditions and constant shearing stress are assumed.

It is shown that increases with height under superadiabatic conditions, is constant with height when the lapse rate is adiabatic and decreases with height during inversions. Indirect evidence suggests that the height variation of can be approximated by a power law.

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R. E. Munn

Many of the atmospheric anomalies that occur around built-up areas were described qualitatively in the last century. Stimulated no doubt by the 1968 WMO Brussels Symposium on Urban Climates and by the present widespread interest in the environment of “human settlements,” there has been a recent quantum jump in the number of published papers on urban meteorology, including many attempts to model and quantify the anomalies.

This short paper, which is not intended to be a survey, contains some thoughts on a few selected topics. The importance of monitoring beyond the suburban limits is stressed, in view of the interactions between the urban and regional fields of motion. Despite the fact that cities are usually located in irregular terrain, the value of searching for universal results is stressed both on the micro- and mesoscales within and near cities.

As part of the design of new studies, inventories of existing data should be made. In many cases, the data banks deserve reexamination from time to time as new models and points of view emerge.

Finally, some comments on observing requirements are made, including the need for at least one first-order meteorological and air quality reference station in each large metropolitan area.

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R. E. Munn

Abstract

The standard deviations of azimuth and elevation angle have been determined at Douglas Point, Ontario (at a height of 82 ft), and at Paisley, ten miles distant (at a height of 50 ft), on about 500 occasions during the early summer of 1962. The data have been classified according to wind speed, wind direction and time of day. Individual standard deviations may be affected by intermittency and non-stationarity. However, median values display well-defined trends. Since the trends are similar at two locations with differing terrains, the results may have qualitative applicability to other areas.

There is a diurnal cycle with largest median standard deviations during the day. As the wind speed increases, the direction becomes steadier with one exception; at night, the median standard deviations for short pre-smoothing times increase when the wind rises above 10 mph. Because of local obstructions, wind direction has a large effect on the magnitude of the standard deviations.

A sample of about 80 concurrent observations shows no close association between standard deviations at Douglas Point and at Paisley.

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R. E. Munn

Abstract

From dimensional arguments Sutton in 1932 proposed a power law form for the Lagrangian autocorrelation, R(ξ). The resulting diffusion equations have been widely used.

There have been very few experimental determinations of R(ξ) in the last 30 years. However, an examination of available data suggests that Sutton's proposal may be a satisfactory approximation for a usefully broad range. Extrapolation to long travel distances is not justified on the basis of published curves for R(ξ) and on theoretical grounds (largely because the Lagrangian integral scale of turbulence becomes infinite).

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R. J. Polavarapu and R. E. Munn

Abstract

An instrument for direct measurement of vapor pressure and vapor pressure gradient (and similarly for temperature) has been designed and constructed. Thermistors are used as wet-and dry-bulb thermometers in the adjacent arms of a resistance bridge network. The resistance arms and the thermistors in the bridge circuit are theoretically determined by relating the differential equation of the output voltage with the psychrometric differential equation. The output voltage varies linearly with vapor pressure in the range 5–40 mb. Field measurements show fast fluctuations in temperature and vapor pressure gradients. The accuracy of the instrument in the measurement of vapor pressure is about ±1.2% in the working range 0–32C.

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R. E. Munn and Morris Katz

During the period 27 to 29 December 1958, the Detroit-Windsor area experienced a prolonged inversion. Winds were light, visibility was poor, and air pollution levels were high. The circumstances surrounding the event are described on both the synoptic and the meso scales.

The broad features, a stationary ridge of high pressure and a light southeast gradient of stable air, fit the classical inversion picture. However, there are interesting small-scale details. In particular, a cooling at 300 ft on the morning of December 29th is described and is shown to be consistent with other available data including observations from a 100-ft tower at Lagoona Beach, Michigan.

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R. E. Munn, M. S. Hirt, and B. F. Findlay

Abstract

Metropolitan Toronto (population of about 2,160,000 and area of 2282 km2) is on the north shore of Lake Ontario (area of 19,400 km2). The interaction between the daytime urban heat island and the lake circulation is studied using several years of records of daily maximum temperatures from a network of about 23 observing stations, pre-stratifying the data according to the regional wind patterns at the geostrophic level and according to the daily sunshine total. The results show that the heat island exists and is detectable during the time of maximum heating in Toronto. Further, the position of the heat island, although a result of urban influence (automobile traffic, industry, home heating units, etc.), is displaced in response to regional and lake breeze wind patterns and the modification of the lake breeze as it moves across the built-up area.

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