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DATE DUE DATE DUE DATE DUE 6/07 p:/CIRCIDateDue.indd-p.1 ‘TERIALS:{ .4» < drop tr. “ checkout n -” TNES w1' _‘|( is THE RELATIONSHIP OF MAN'S SETTLEMENT SYSTEM TO THE NATURAL SYSTEM ANOREU BARTON URBAN PLANNING BOO-PLAN 8 SCHOOL OF URBAN PLANNING and LANDSCAPE ARCHITECTURE MICHIGAN STATE UNIVERSITY MAY 29, 1972 TABLE or CONTENTS IN BACK OF 800K INTRODUCTION................................. ..... ..oage LAND physiography................. ..... ................bage soil..............................................page geology...........................................page NATER urban consumption................... ...... ......-.paqe urban impact......................................paoe water bollution.................... ........ .......page AIR urban impact on climate...........................page air pollution.....................................page effect of air pollution...........................page ENVIRONMENTAL USERS ivegetation........... ........ ...... ...... .........page functions of vegetation. ..... .....................page wildlife................... ...... . ........... .....paqe CUNCLUSIDN.. ......... ...............................page BIBLIOGRAPHY .......... 00.00.00.000...OOOOOCOOOOOOOICDEQB 1 3 9 12 15 16 17 22 25 28 29 29 3h 36 38 INTRODUCTION This paper will focus on the relationship between man's settlement system and the natural system. For the purposes of this discussion, man's settlement system is considered to be composed of man's processes, both physical and non-physical (cultural); the users, both direct and indirect, who are involved with the processes; the artifacts required by the processes and users; and the space which the which the processes, the users and the artifacts need to function. Anywhere from 32 to 52 percent of a city's land area is devoted to residential processes, 2 to A percent to commercial, 9 to 13 percent to industrial and trans- portation, and A to 1h percent to institutional, open space and' residential activities.1 The natural system is composed of land, water, air (as well as the processes which occur in each of these mediums), and the environmental users. These components can be further broken down. Land is composed of physiographic considerations, soils, and geology. water is composed of atmospheric, surface and sub- surface water. Air is a medium for a number of things, including the climatic processes: temperature, precipitation, humidity, air movement, and solar radiation. And finally, there are the environmental users: vegetation, animals (including man), birds, fish, and the lower life forms, who use the natural system. In the past, man’s ability to alter the environment has been limited by technology. As technology progresses and as population increases, man becomes more of an environmental agent. 1. A. woleman,-"Metabolism of Cities" Scientific American, (August, 1965), page 175. page 1 For this reason we can no longer rely on men's inadequacies as a protective control. It is this author's contention that pepple are basically good and, if they were aware of the consequences of their actions, they wouldn't abuse and destroy the natural system. Therefore, it is the purpose of this paper to examine this man-nature relationship, to assess how man uses the natural system and what impact his activities have on it, and also how the natural system influences, both positively and negatively, man and his processes. This set of relationships is graphically illustrated in the accompanying Environmental Planning Consider- ation Matrix. Both man‘s system and the natural system are broken down into their basic components and are displayed in a matrix form. This matrix can be used as a conceptual model in determining what and how the various components of the two Systems relate. The matrix can also be used to "score" (to determine how well a landuse or group of landuses "fit” a specific site) a given piece of land, water or air. It is hoped that the information generated in this paper will provide an information base and a systematic framework for making ecologically viable development decisions. page 2 LAND Man's relationship with the natural system is basically one of consumption: his activities and artifacts consume large amounts of land, air and water. For example, each addition of six persons to a city's population requires that one acre of non-urban land be converted to urban use.2 It is estimated that each year some 1,000,000 acres of farmland and other non-urban land is consumed by urbanization.3 Man's transportation system offers another good example of this consumption. In the United States, there are 3.6 million miles of roads and street, or about one mile of road for every square mile of land. About 2h,000 square miles of land is covered by roads and their rights-of—way. Freeways consume about 2h acres of land per mile of highway and some 80 acres for each interchange. Physiography, soils and geology comprise the land system component. Slope, perhaps, exerts the most limiting influence on man and his activities of all the physiographic components. Man's processes and their respective equipment, with the exception of some recreational activities, require relatively flat sites. Minimum slope (that slope which is great enough to ensure adequate surface drainage) is determine by the drainage capabilities of the various i surface materials. Maximum slopes are determined by the inherent limitations of the construction and operation of process equipment. For example, automobiles don't function ‘efficiently on slopes in excess of 8 percent. Eouipment limitations, 2. Guy-Harold Smith, Conservation of Natural Resources (New York: John wiley and Sons, 1971) page 615. 3. Time, February 2, 1970. page 3 erosion hazards, and increasing building costs generally limit construction to slopes of 20 percent or less. Structures can, however, be built on slopes as great as A0 percent, but the cost is excessive. Table #1 common SLOPE-LANOUSE REQUIREMENTS SLOPE USE MINIMUM SLOPE MAXIMUM SLOPE public paved streets 1 percent 8 percent private roads 1 percent 12 percent parking areas 1 percent 5 percent lawn areas 1.5 percent 15 percent agricultural uses 1 percent 12 percent (erosion) recreational (except hill sports) 1.5 percent 3 percent building construction 1 percent 10 to 20 percent industrial 1 percent just enough to drain general urban 1 percent 5 percent Physiographic features also influence the climatic processes. For example, slopes receive either more or less solar radiation, depending on their orientation, than a flat site. This has great impact on vegetation productivity, as well as being a phenomenon which can be used advantageously to modify temperature extremes in both over and underheated periods. page A SLOPE AND SOLAR RADIATION Landforms also influence air movement patterns. warm air flows up slope during the day and cold flows down slope at night. ‘- AIR MOVEMENT UP A SLOPE DURING THE DAY page 5 COLD AIR FLOWS DOWN THE SLOPE DURING THE NIGHT Observations by Geiger have shown that wind flow is diverted by a hill or mountain in both its horizontal and vertical stream patterns, causing higher speeds near the top on the windward side and less turbulent wind conditions on the lee slope. 5;: g. 0 I '0', . I ll‘: ' :':::::::.:'l-III: Ill:l:l:{.l:l:l:I:l:l:l:l:I:I:I:I:I:l'1:.:I}:I:l:l:l:I:I:I:l:$llfl:l:lll:l:I':l:fifi::::l:::::.}.::l:::$:'{-:S:I:JI::I£I‘I:JI::' 0.. ' ' '- '3’" - -'=31‘=--‘=+=- w“ --'~'::-‘-‘-' . :-' - ar- - :- :;.~:-:---:--+ 2- .- mar .;.-.-c-.~;;.::- a -.,., .-'=iE'-:=-.. 0.: O I 0:. I .:.:I:.. .::.:I:::O:I. e a 0.0.0.0...0.:..... .0. I I I I ‘1' l I l .... .............. ': ::::EE:.:::.:.:':::.'.:.' '.°. '.' '. e'e ' 2" ele':'e'e’e e'e':'e e'e e':. e'e e':.e'e e 0 -"0:0. e'e e'e'e':':.e e'e-l .".'.'.':'. e e'e 0'. . . : WIND.SHADOW EFFECT page 6 In many places mountainous landforms are partly responsible for the inversion layers over cities. Inversions, in the United States, happen anywhere from 10 to 50 percent of the time at elevations less than 500 feet. This phenomenon, however, can occur at almost any elevation where cold air flows down a mountain slope and is trapped under a warm air layer. ,.,\L,,y Inveasroe FAYFR .......................................................................... l' a ll- .I'Ielllll .-l-.-..1".".I.l.l::fll I. e I . I I l l a I I I II......"Iu'I‘.:.:e'l'e‘e-Iql‘ll’.".""':I.g:‘:l:.:':l:l:l'y.;'fi.¥'m'l'::W'l £32k::". lllllllllllllllllllll {I'l.":.: :_;‘:I'.. .............. t ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ““'““”‘*"~“vnm1£+wma+ -------------- ,anwfi+wxmmxnmvm+wwfios ................. , --------- 3 I e l I I e e e I I I e a l lll“:‘:l:l:I:l IIIIIII 'I‘II'.‘lll'.‘l'.:.'.:.'.:u:e'e:e:a:e e-‘e-I-Ile'lll'l I‘l'l.1-:I' :.',:.' :I:e:e-I e l I'a ll- .I‘lll-'.""':l:.:.:. IIIII :1I I """""" >‘-:-‘-:-:-§£‘ - ' - W-:<->:s:-:-:-:-:a+Awmmanfi+h+zim - am ' wax-Ath- COLD AIR FLOWING DOWN A SLOPE TO CAUSE AN INVERSION LAYER 8 These inversion layers usually dissipate in the afternoon as the sun begins to heat up the surrounding air enough to start it moving again. To alleviate these inversions, then, cities should be planned so that they are adequately ventilated and located away from potential inversion areas. Elevation is yet another physiographic limitation. Due to men's adaptation capabilities, elevation is not as much a limita- tion to him as it is to vegetation and the other environmental page 7 users. And finally, landforms function aesthetically as a sculptural medium. Landforms, whether natural or artificial, by their very presence, manipulate and articulate space. This is of course on a large scale. These masses form patterns and spaces which can and should be utilized by man when placing his processes and artifacts on the land. The aesthetic qualities (sense of place, enclosure, form, line, texture, color, mass, dominance, sequence, scale, diversity, symbolism, visual stim- ulation etc.) of natural landforms offer much aesthetic potential, especially to residential and recreational activities. page B SOILS “Our most valuable natural asset is the soil. The survival and prosperity of terrestrial biological communities, whether natural or artificial, depend on this layer. As in the earliest days, and in spite of the pragress of synthetic industries based on mineral products, man draws almost all his substance and most of the raw materials for his clothing and everyday needs from this source."h Soil affects, either positively or negatively, man's pro- cesses in several ways. First, soil is an agricultural medium. A soil's moieture content, drainage characteristics, and fertil- ity are all factors which determine its productivity. Soil is also an engineering variable which can affect the location, design, construction and maintenance of process equipment such as buildings and roads. A soil's workability will,to a large extent, determine how the soil can be worked as a sculptural medium. A stony soil, for example, will limit the effectiveness of earth moving equipment in sculpting the earth. A soil's shrink-swell movement from either freeze-thaw action or moisture changes must also be accounted for when designing structures on that soil. Associated with this is a a soil's bearing strength. Foundations of structures and roads must be designed according to the soil's load supporting capa- bilities. The depth and corrosiveness of a soil have an impact on the location and design of structure foundations and utility -systems. A soil, for example, which is too shallow makes h. J. Dorst, Pefore Nature Dies (Boston: Houghton Mifflin 00., 1970) page A5. page 9 subgrade construction extremely expensive for the reason that blasting is usually required. A soil's infiltration and drainage characteristics determine how fast and to.what extent a soil will dry out. A well drained soil is imperative to most landuses because both the soil structure and the vegetative cover suffer damage when they are subjected to use while the soil is too wet. This is especially critical in recreation. A soil's moisture content also influences the soil's bearing capacity and runoff charac- teristics. Also a soil's ability to absorb sewage effluent is dependent on that soil's drainage characteristics. A soil's fertility is one of the variables which determines the type, quantity and quality of vegetation (this of course includes agricultural products) which a given piece of land is able to produce and support. A soil can also be a significant mineral resource. These resource minerals include sand, gravel, peat and clay. Pollution is not limited only to the air and water. A soil can also become polluted as a result of pumping too much sewage effluent into it or from agricultural fertilizers, pesticides, or industrial and mining wastes. Since soils act as a filtering medium for water recharging the subsurface water system, it is imperative that soil's don't become polluted as the quality of the subsurface water can be no better than the soils above which .have filtered it. page 10 Soil erosion is natural; but usually occurs at a very slow rate. water and wind erosion reach a damaging degree when the natural groundcover is removed without substituting a substantial artificial equivalent. The impact of erosion is far reaching. Not only is the productive topsoil carried away, but once it finds its way into the surface waters, it seriously impairs the function- ing of fish, vegetation and the lower life forms. Eventually this sediment is carried downstream until it either stops at an obstruction, such as a dam (whereupon it piles up) or it runs on into larger water bodies creating major changes in the natural conditions. page 11 GEOLOGY Geology relates to man and his activities as both an engineering variable and as a resource material. As an engineering variable, geological characteristics, such as stability, earthquake activity, bearing strength, depth of the overburden, and pollution potential influence both the location and the design of the process equipment. The design of any structure, whether it is a bridge, a dam, road or a building, is, in part, determined by the site's stability. Foundations and underground structures and equipment, such as utilities, are influenced by the depth of the overburden as well as by the char- acteristics of the geological material itself. The characteristics of this material also determines whether subsurface water is present and also whether it can be extracted. And finally, gag- logical mineral resources offer a basic material for man to use in numerous ways. page 12 wwu>u uHmcgamo>I m:# an whqwd w __ ‘ A ..p.i~... J}. A . I. x... p... .4.¢ + a... . 4 .q. . ,.. e.-. a -I .. ¢ .. . a .. .. .T " 4... J a. .. M a” H. ‘9 . J. . . t. _ F . .. . ‘o . . . . . . . p u .. N .. o . .. .g . .. . _. 4 .. . . . . . . n . .h r : 75. if . . .1 TI“ I ell III I . a w+w ewh<3 ozsomu I :2... <¢oa<>w , _... , . .. ILL . . ... .. . .. E . +zo:<¢c.__._wr_.PLI ewe; .230 :1 s .. .... x7 /./ . . .. .. . _ \ / . v... - _ \7 \c. / l/ .. r ’3 u I.— — \ I / ._ _ . / / . . u T / / / . tease A... q / / . u I . _ . _ x /d , . I . a > o » . .t // z./P<¢ow mwx some zo.»<¢oeaxM/oz< zo_vmw\amzr mZOF OOP uo_xo zwoomh.z mZOP COP uo_xo_o «DUJam mzo» omp wh(J:o.hmFH0 squua>e a do >qo mwa 304w Paapao-»:a20 we wpqua \“u \ \‘I‘l’ I ’/ Wan“... \\\ Il/ .m. \WN..HU... .Iu.u...n..>.nv \\ // Icon...“ asEmma \ / sew. awmmwmwmmmmw \\ , mmwmflm swan coho: no mzo» 000.F Mmmwmwmwmwmww 1 , emmWWme m._._ o u 4...... same”mum“muwwwwwwfi , L .3 .. . A?p$cr5cta.~ .... .uxteot coon no mzo» 000 m mfi¢ww»fifiwa&& // \ Jfiafiflmqk , awmflwwmme. \ Juaww.e “mowm.Hnwwwwwwwfiw.” / \ .............H. .......... e we; .3 ma ca 000 . mmo mWHAFev M / \ mfiflwsa an // .\\\ aw . pagz. Aw I I I \I \I \ .\ coo-Io. lb page NATER Man has great impact on the hydrologic system. His settle- ment system not only consumes large quantities of water, as illustrated in Table #2, but also alters the water quality. This section will examine how men uses the hydrologic system and will also assess the potential value of the use of this system in the urban environment. Approximately 80 percent of the water consumed in the United States comes from surface sources while the remaining 20 percent comes from groundwater supplies. The following table points out that man's water consumption is growing with time. Table #2 DOMESTIC AND AGRICULTURAL HATER USE IN THE UNITED STATES in billion gallons per day...taken from water Facts, USDA, SCS, publication number PA-337. domestic agricultural year anglmunicipal industrial irrigation total 1900 3.0 15.0 22.2 A0.2 1920 6.0 27.0 58.h 91.6 1950 lh.0 77.0 79.0 170.0 1960 21.0 1h0.0 110.0 271.0 1980 29.0 363.0 161.0 553.0 Agriculture is the greatest water consumer fer the reason that only 50 percent of the water used in irrigation is actually returned to where it originally came from. Approximately 83 percent of the water taken for municipal use is returned to the ,the urban surface waters; and about 98 percent of the industrial water is returned. page 15 It is interesting to note that while the United States' population doubled between 1900 and 1950, the nation's total water needs increased four times. It is estimated that the potential water supoly available for direct human use is about two times that of our 1980 requirements. In other words, the potential water supply in the United States is about 1106 billion gallons per day. About 95 percent of this fresh water is being used at a greater rate than its precipitation replacement. The point to be made here is that the hydrologic system is indeed a closed and finite system. There are two principal effects of urbanization on water quality. First, the influx of waste materials from sewage plants tends to increase the dissolved- solids content and to decrease the oxygen content of the surface waters. Second, as flood peaks increase as the result of greater urban runoff, less water is available for the natural purification of ground- water recharging. Also, because more water flows downstream, less water recharges, and therefore less water is available between flood peaks for municipal supply and safe sewage dilution in the urban surface waters. 7 The Public Health Service estimates that approximately 20 percent of the nation's municipalities don‘t treat their sewage. About 30 percent use primary settling only, and about 60 percent use secondary treatment, which is the goal of the .1973 Federal watervguality standards. Primary treatment removes most of the trash and settles out about 30 percent of the effluent page 16 solids. In secondary treatment, bacteria reduces the Organic wastes into sludge. Approximately 90 percent of the pollutants are removed by the sedimentation process; but phosphates, ammonia, and some organic matter still remain. Teritary treatment further purifies the effluent by removing some of these remaining phos- phates. The following example is a typical illustration of the effects that cities have on the water which they use. A city of 100,000 people consumes approximately 70 million gallons of water each day, and adds the following quantities of foriegn materials to the water as result of this consumption: -17 tons of organic suspended solids -8 tons of dissolved organic solids -16 tons of dissolved solids‘ -1 ton of detergents -60 cubic feet of grit A city's treated effluent which is dumped into the urban rivers and streams is generally rich in nutrients and therefore causes rapid algae growth. This vegetation grows and dies and while doing so consumes oxygen which in turn threatens the fish life which is already experiencing a shortage of oxygen. It is estimated that the amount of urban runoff is about three times that of rural runoff. -Runoff volume is determined primarily by the infiltration characteristics of the surface material over which the water flows. It is also related to -slope of the land, the type of soil, and the type and extent of the vegetative cover. It is, therefore, directly related to the page 17 percentage of area covered by roofs, streets, parking lots and other impervious surfaces at the time of the precipitation. The following table illustrates the relationship between lot size, and therefore the residential density, and the percent of imper- vious surface and the amount of runoff to be expected. TABLE #3 LOT SIZE AND IMPERUIDUS SURFACE RELATIONSHIP...taken from "The Hydrologic Effects of Urban Landuse", L.8. Leopold, page 206, Man's Impact on Environment, T.R. Detwyler, ed. LUT SIZE in sggare feet IMPFRUIUUS SURFACE in percentage 6000 80 6000 to 15000 #0 15000 . 25 The articficially high amount of urban runoff allows less water to infiltrate into the ground.and therefore to recharge the groundwater supplies. This situation is often aggravated even further when urban development is allowed to cover over aquifer recharge areas. This is the primary reason for the rapid deple- tion of the uderground water reservoirs. The articficially large quantity of urban runoff is often responsible for erosion which lowers the water ouality by adding sediment to it. The principal effect of landuse on sediment comes from the exposure of the soil to storm runoff. This occurs primarily when the groundcover is stripped off, exposing the soil, as in the construction process. This sediment production is also a function of the slope of the land surface.. The greater the slope, page 18 the more severe the erosion and the sediment problem. The sediment yield in urban areas tends to be greater than in non- urbanized area even if there are only small and widely scattered units of unprotected soil in the urban areas. Sediment has damaging effects on such environmental users as fish, insects, and the vegetation. Mater quality can further be altered by what is referred to as thermal pollution. As the temperature of water increases, its ability to hold oxygen decreases. This is critical because the presence of dissolved oxygen is probably the single most critical factor in the biology of the aquatic environmental users and processes. The following graph illustrates this relationship between water temperature and its oxygen content. "As temperature BRAPH#1 MATER TEMPERATURE AND OXYGEN CONTENT...taken from Environment and Man, R.H. Magner, page 137. L.'b T +2 \ { ‘~\ 2‘ I21. \\ \ \\\ 21 \\\ In ‘~\\ § 6 P \‘ x ‘ A J E; 4. E t . . . 3 I6 Ex 39 gb TEMPE KATU RE °C page 19 increases, the quantity of dissolved oxygen decreases, but the respiration and oxidation rates double for every 100 0 increase."5 what this means, then, is that, in order for fish to survive in thermally polluted water, the water must have a higher oxygen content. This problem is aggravated in cities because the urban surface waters are already low in dissolved oxygen because of the fact that sewage effluent consumes oxygen. water temperature also interacts with other factors as well, For example, a fish's ability to withstand certain environmental impacts is directly related to water temperature. A higher water temperature normally lowers a fish’s immunity. A further consideration is that the life cycle of many aquatic organisms is delicately geared to the water temperature. Fish are often distributed, migrate, and spawn in response to temperature cues. when this natural temperature is artificially changed by thermal pollution, havoc inevitably results. The amenity value of the hydrological environment in the city is affected by three factors. The first factor deals with the stream channel. The urban stream channel which has gradually been enlarged due to increased floods caused by the high urban runoff tends to have unstable and bare banks, scoured and muddy channel beds, and a heavy accumulation of trash. The second factor is the usually ugly accumulation of urban artifacts in the channel and adjacent floodplain. More often than not, the least visually 5. R.H. Uagner, Environment and Man (New York: 0.0. Norton 00., 1971) page 139. page 20 pleasing and oldest structures are located near the urban streams and rivers. The third factor is the change brought about by the disposal of sewage effluent in the city's surface waters. The nutrients in the effluent promote the growth of plankton and algae. This can tranform a clear river or stream into one where the rocks and banks are covered with a foul-smelling slime. Also, as turbidity and 17122212723” fish give way to less desirable species which are able to tolerate the more polluted water; if the water quality becomes too low, nothing will live in it. "Streams flowing through cities, especially, could enhance the quality of urban life if they were properly managed and understood, although the variety and complexity of urban effects on hydrology appear to work against this."6 It is indeed sad to see the majority of our urban centers turn their backs on the potential of their surface waters and use them only for sewage dilution. If our water resources are to be available in the future for ALL the environmental users, we must rethink our traditional view that the water system is an infinite, free waste-disposal system, for it is this kind of thinking which perpetuates the all-to-tommon abuse of the whole natural system. 6. L.8. Leopold, "The Hydrologic Effects of Urban Landuse," Man's impact on Environment, ed. T.R. Detwyler, (New York: McGraw- Hill, 1971) page 214. page 21 AIR Man's processes and artifacts have-great effect on the atmospheric system. This sytem is composed of two things: air, which has both quality and quantity characteristics, and the climatic processes (temperature, precipitation, humidity, air movement, and solar radiation) which occur in this air medium. Cities are commonly referred to as "heat islands" for the reason that they usually tend to be warmer than the surrounding countryside. This phenomenon can be attributed to several things. First, the surface materials of an urban area and those of the more “natural“ surrounding area differ greatly. Because the materials of a city's buildings and streets conduct heat about three times as fast as wet sandy soil they are able to heat up faster and to a higher temperature than the countryside. Second, since city structures have a greater variety of shapes and orienta- tions than the natural landscape, there is more surface area in cities than in the country. This enables a city to heat up the air in it faster than the surrounding area. Third, cities and their processes generate heat. Fourth, a city tends to be warmer because of the manner in which it disposes of the precipitation which falls on it. Some of the precipitation which falls on the country runs off, but some is left to be evaporated. Since evaporation consumes heat, the temperature will drop. In a city, however, most of the precipitation runs off, leaving very little to be evaporated, whereby no heat energy is consumed, which -means that the temperature will not drop. Finally, the composition of city air tends to retard the escaping of city heat. ‘ Although little research on humidity has been done, the consensus of urban climatologists is that the average relative page 22 TABLE #u CLIMATIC CHANGES PRODUCED BY CITIES (after Landsberg, 1962)... taken from "Climate of the City," J.T. Peterson, Man's Impact on Environment, T.R. Detwyler ed., page 132. CLIMATIC ELEMENT Temperature annual mean winter minimum Relative Humidity annual mean winter summer Dust particles Cloudiness clouds fog-winter fog-summer Radiation total on flat ultraviolet-winter ultraviolet-summer wind speed annual mean extreme gusts calms Precipitation amounts days with less than .2 inch COMPARISON NITH THE RURAL ENVIRONS 1.0 to 1.5° F higher than the countryside 2.0 to 3.00 F higher than the countryside 6 percent lower 2 percent lower 8 percent lower 10 times more 5 to 10 percent more 100 percent more 30 percent more 15 to 20 percent less 30 percent less 5 percent less 20 to 30 percent lower 10 to 20 percent lower 5 to 20 percent more 5 to 10 percent more 10 percent more page 23 humidity in cities is several percent lower than that of nearby rural areas. The main reason for this difference is that the evaporation rate in a city is lower than that of the country because of the markedly different surfaces. Cities also tend to be cloudier and have more smog than the surrounding countryside because of the concentration of particulate matter which is found in city air. The blanket of particles over most large cities causes a significant reduction in the solar energy which reaches the city. The flow of air over a city differs in several ways from that over the surrounding natural landscape. Since the surfaces of a city are much rougher than those of the natural terrain, the air which passes through the city is slowed down due to the frictional drag. A city's "heat island" effect in conjunction with this friction also tends to produce more air turbulence over the city. A city also influences the occurrence and quantity of precipitation in its area. Typically, a city will recieve more precipitation than the surrounding area for the following reasons: 1. Combustion sources in the city add to the quantity of water vapor already in the atmosphere; 2. The higher temperatures of the city tend to intensify thermal convection; 3. A city's greater surface friction increases the atmosphere's mechanical turbulence; and A. The urban atmosphere contains large amounts of condensation concentrations. "Normal air" is composed primarily (99.99 percent) of four gases: nitrogen, oxygen, argon and carbon dioxide. These gases page 2A are not permanent features; each is the result of a delicate process where it is formed and removed. Oxygen, for example, is formed in the photosynthetic processes of vegetatiogflrs removed by animals (including man), by combustion and by slow oxidation of the minerals on the earth's surface. "All creatures live by a process of converting one form of energy into another. Man has raised himself above the animal level to the extent that he deliberately converts this energy by processes outside the limitations of his body. All extensions of the human senses, of the human frame, and of the human muscle, which is to say, our tools and the trippings of civilization, use this energy. Energy conversion has certain material by-products. when they become airborne, in sufficient concentrations to be troublesome to man, we call the resulting airborne material ”air pollution".7 According to the United States Health Service, approximately 192 million tons of pollutants are dumped into the atmosphere each year in the United States alone. Forest fires supply an additional 17 million tons. Table #5 illustrates the kinds and quantities of these air pollutants. As indicated, trans- portation accounts for the bulk of this pollution; autombiles account for the majority of transportation in the 0.5. Approxi- mately 99 percent of the 90 million motor vehicles in the 0.8. are powered by gasoline engines. These engines pollute from two sources: the gasoline looses.hydrocarbons and gasoline additives 7. Air Conservation Commission, "Air Conservation and the Kinds Air Pollutants," Man's Impact on Environment, ed. T.R. Detwyler, (New Vork: McGraw-Hill, 1971), page 86. page 25 .mo wcqa .moe.ou mwu>3eua .m.p .ezwzzom_>zw zo co<¢z. 0.2«2 .wmm 20.034400 m_< mo mhzcoz< 0% mum00 0.00m N.—m 0.09 0.pm 0.0m 0.—0p 44000 m.0p N.p N.N 0.0 N.0 mmm_w hmwmow 0.NOF m.pm m.mp 0.0m 0.FN ¢.m<20.0<0m 2. 20.0030200 uwnw .uhw m¢