Public Health Aspects of Climate in Cities

the symposium have been published in two A better understanding of urban climatology volumes, with the assistance of WHO, as part would help public health authorities to devise ways of the WMO Technical Note Series.l of controlling air pollution and of improving environmental health in cities. The nature of the urban effect 'YHO is concerned with urban climatology The climatic conditions prevailing in cities ~amly from the point of view of air pollu­ may differ appreciably from those of the sur­ tiOn. The development of this aspect of rounding countryside and have important applied climatology depends on fundamental repercussions on health. Urban climatology investigations of urban climates to determine is therefore important to all those concerned the factors likely to be of importance in in­ with public health in cities. In particular, a creasing the level of any pollution or in miti­ study of urban climatology should enable gating its effects. planners to avoid past mistakes and thus As air moves across a city, the entire wind ensure that the cities of the future will be profile and turbulence spectrum are changed. healthier places to live in. In this context, This change is obviously important in de­ health must be understood in positive terms termining levels of air pollution, but its and not merely as the absence of disease. A effects are difficult to assess owing to the healthy city is not merely one in which the complexity of airflow patterns in urban areas. inhabitants are free from preventable disease· In general terms, the surface roughness that it is also one in which preventable nuisance~ air encounters when it reaches a city should such as pollution, noise, and objectionable lead to a reduction in average wind velocities and an increase in the number of days with ?dou~s are absent, whether or not they can be Identified as the causes of specific diseases. calm conditions. Both these factors tend to From the foregoing considerations, it is increase the severity of any pollution that may clear that certain aspects of urban climatology occur. are of direct concern to WHO and that the Conversely, air pollution itself may be one subject is of interest to other international of the factors responsible for the urban effect. bodies, primarily to theWorld Meteorological In highly polluted areas, gases and aerosols Organization and specifically its Commission may abso~b up to half the visible light and up for Climatology. In 1965, this Commission to two-thirds of the ultraviolet radiation. discussed the urgent need for meteorologists The temperature tends to be higher in and allied scientists, medical and health towns than in the surrounding countryside authorities, architects, engineers, town plan­ owing to changes in the thermal charac­ ners, etc., to be made aware of the "urban teristics of the surface (buildings and roads effect " on climate. Acting on recommenda­ instead ~f fields), changes in airflow patterns, tions of the Commission, WHO and WMO changes m evaporation rates and heat losses, jointly organized a symposium on urban and the heat added by human beings and their activities. A town thus constitutes what is cli~at~s and building climatology, which, at the mv1tation of the Belgian Government was called a " heat island ". held in Brussels in October 1968. 'The Finally, certain urban-induced changes in

135 participants included experts from 27 1 Urban climates. Proceedings of the WMO Symposium on countries and representatives of several inter­ Urban Climates and Building Climatology, Brussels, October 1968, Vols. I .and 11, 1970, Geneva, World Meteorological Organization national organizations. The proceedings of (Techmcal Notes Nos. 108 and 109).

161 precipitation are believed to exist. A number atmosphere. Pollution levels are the result of of cities have been found to have more rainy interaction between these two sets of factors, days, more thunderstorms, and more total both of which are extremely complex. precipitation than the surrounding rural For the purposes of urban public health areas. This is believed to be due to the pre­ and urban planning, some form of mathema­ sence of additional condensation nuclei, in­ tical model for the prediction of pollution creased turbulence resulting from increased levels would be of enormous value. Some surface roughness, and thermal convection progress has, in fact, been made in developing resulting from higher temperatures. models from which the pollution levels down­ wind from a single source of pollutants can Predicting pollution levels be predicted with a fair degree of accuracy, in spite of the numerous assumptions that Every city is unique in the types and have to be made. A single source of pollu­ quantities of pollutants emitted and the tion, however, constitutes a highly simplified meteorological conditions that determine the situation. In practice, urban areas contain dispersion of these pollutants in the urban numerous sources of pollutants, which are

Smog occurs in Los Angeles, USA, about 60 days a year. It is caused mainly by the exhaust gases of three million motor vehicles burning some 20 million litres offuel a day. The gases are frequently trapped close to ground level by temperature inversion layers in the atmosphere above the city.

162 randomly sized and spaced, vary in the lutants is the scarcity or absence of certain amount, temperature, and height of the types of data, including the character of emission, and are located in a complex urban emissions and meteorological measurements. topography that affects the meteorological For this reason the establishment of an variables involved in dispersion. It might adequate network of monitoring stations in seem, therefore, that there is little hope of urban areas is of vital importance, and such producing any kind of model of such a highly networks have been set up in many cities complex pollution pattern that could be of throughout the world. practical value. Experience in dealing with In the USSR, for example, monitoring sta­ other highly complex problems in meteoro­ tions are located at crossroads or squares logy has shown that this conclusion is unduly within areas of cities where air pollution is at pessimistic and that the development of a its greatest. Observations are made several comparatively simple model of urban pollu­ times a day of a number of meteorological tion can be considered a reasonable aim. factors and of the concentrations of the com­ Apart from its uses in urban public health monest pollutants. Motor vehicles are used and urban planning, such a model could be to measure ground-level concentrations along used to assess the effects of local changes in particular roads and in the vicinity of the the emission of pollutants and the results of chimneys of major industrial plants. Measure­ legislative measures. ments have also been made in both Hungary A model is being developed for the Los and the USSR of the vertical distribution of Angeles area that will enable carbon monox­ pollutants such as carbon monoxide by means ide concentrations to be predicted for any of helicopters and other aircraft. Such given day. It is based on the assumptions of: measurements are of obvious importance in horizontal transport of the pollutant by winds the construction of air intakes for the ventila­ of variable speed; time-dependent sources of tion systems of industrial premises. pollution of arbitrary distribution, configura­ A network of monitoring stations for sulfur tion, and strength; upper-level inversion of and smoke was set up in Belgium in January arbitrary height; ground-level absorption; 1968. It comprises 100 stations spread over chemical reactions with a net rate specified as the five main urban centres of Antwerp, an arbitrary function of time; and constant Brussels, Charleroi, Ghent, and Liege. A diffusion coefficients. Motor vehicle exhaust further 100 stations will gradually be added was the only source considered, since it is to the network. responsible for 97% of the carbon monoxide Two intensive surveys of air pollution were present in the air over Los Angeles. The carried out in the town of Reading, England, agreement found between the concentrations in recent years. It was concluded that even computed from the model and those measured the relatively high density of recording sta­ by monitoring stations was considered to be tions used in these surveys gave only a very encouraging in view of the crudity of generalized picture of the pollution pattern, some of the assumptions, e.g., that the diffu­ blurring the uneven character of pollution sion coefficients are constant. A more general due to irregular emissions from local sources. model is being developed that will take into For example, high concentrations of pol­ account such additional factors as chemical lutants may occur near low industrial chim­ reactions occurring simultaneously between neys under conditions of strong wind and various constituents of polluted air, diffusion much turbulence, when the smoke plume is coefficients that vary arbitrarily in time, wind quickly brought to the ground. movements in a vertical direction, and inver­ Reading was chosen for intensive investiga­ sion at variable height. tion because it was considered to be reason­ ably isolated from other pollution sources. The monitoring of air pollution The surveys showed, however, that some of One of the difficulties involved in any Reading's air pollution must have originated attempt to forecast the spread of urban pol- in the London area, the centre of which lies

163 64 km away. This emphasizes the need to assessed. When this potential is high, any monitor pollution for groups of towns as a new industries that are established will have whole and over distances of several dozens of to be of a type that does not generate pollu­ kilometres. Moreover, with the modern tion or else special precautions will have to be tendency for towns to expand and form taken to restrict effluents at source. conurbations, a danger is developing in many It is not only through their effect on air pol­ countries of the pollution of very large areas, lution that climatic factors influence health in stretching over hundreds of kilometres. urban areas. The heat-island effect may increase the heat stress on a city's population during the summer months. Radiation is also Climatology and city and regional planning important, especially in view of the current Most modern cities have developed in a fashion for buildings with large glass surfaces; haphazard manner, with little or no regard to many buildings are incorrectly oriented, with the climatic environment concerned. Climatic the result that their interior cooling system is factors are usually taken into account only inadequate in summer. in the construction of individual buildings. Noise is another urban nuisance that can In the past, an attempt has sometimes been adversely affect health. In general, noise made to minimize air pollution by confining levels in cities have risen in recent decades industrial establishments to areas downwind because of changes in the nature and amount from residential and commercial areas, ac­ of surface traffic and the introduction of jet cording to the prevailing wind direction. aircraft. Some medical authorities consider However, the less frequent conditions of light that existing noise levels are already detri­ winds and inversions, which are of greater mental to health. From this point of view importance from the point of view of pollu­ studies of the vertical structure of the atmos­ tion, have not generally been taken into phere are becoming of increasing importance account. because of its effect on sound propagation. Other possibilities are open to the town It has been claimed that tall hedges can planner and to public health authorities in filter out particulate pollutants from the air, minimizing pollution. These include control coniferous hedges being particularly effective of the types of fuel used for heating and power, and capable of removing as much as 80% of and design of urban areas in such a way as to the larger particles. In addition, the some­ reduce to a minimum those transportation what lower temperatures in parks and open services employing internal combustion en­ spaces compared with surrounding built-up gines. The development of new means of areas help to reduce the heat-island effect. transport and the reduction of manpower However, a study carried out in Liege, requirements through automation may Belgium, showed that the purifying effect of eventually make possible the location of all green spaces was limited. Their only useful heavy industry in places where meteorological effects appeared to be a slight modification of conditions are such as to favour the disper­ air turbulence, which facilitated the settling sion of effluents, and which are remote from of the larger dust particles, and the absorp­ areas where the emissions concerned might tion of noise. They were quite unable to endanger health or constitute a nuisance. remove toxic gases from the atmosphere. In the meantime, appropriate wind studies should be carried out before a location is Medical aspects of air pollution selected for any new industrial source of pol­ lution. These studies should include m01e The effects of air pollution on human than a simple determination of the prevailing health have been considered in a WHO wind direction; it is much more important to monograph 2 and at a symposium convened determine the frequency of general stagnation situations, from which the air pollution poten­ 'Heimann, H. (1961) Effects of air pollution on human health. In: Air pollution, by various authors, Geneva (World Health tial of individual locations and regions can be Organization: Monograph Series, No. 46), p. !59.

164 by WHO in Prague in 1967. 3 The effects of occur in subjects under stress or under the motor vehicle pollution in particular have influence of central nervous system depres­ been discussed by a WHO Expert Com­ sants. In addition, even small increases in mittee.4 carboxyhaemoglobin may be injurious to the Every city is confronted by the specific infirm. problems resulting from its own particular Lead is emitted in vehicle exhaust gases type of pollution. This can vary in character largely as an aerosol of inorganic lead salts from the smoky pollution of industrial cities and oxides. There appears to be no evidence to the pollution due largely to hydrocarbons that lead emitted in this way is producing and carbon monoxide in such heavily motor­ adverse effects at the present time. Exposure ized cities as Los Angeles. to lead, however, may result in storage of the A number of pollutants, such as sulfur pollutant in the body without measurable dioxide and ozone, are irritant gases. Such signs of toxicity, and it is known that stored gases, if highly soluble, dissolve in the pollutants can sometimes be released by aqueous fluids in the upper portion of the infection or biochemical stress. The intake of respiratory tract and therefore exert their lead resulting from air pollution must also be effects in that region. A gas that would not considered in relation to its intake in the diet normally be carried beyond the trachea and and from other sources. large bronchi may, however, in the presence Carcinogenic substances have been found of aerosols, be conveyed into the deeper parts in the air of many communities. Some may be of the lungs, and even as far as the alveolar derived from industrial sources, others, such walls. as the polycyclic organic compound 3,4 benz­ Of the irritant gases, sulfur dioxide, at low pyrene, from the incomplete combustion of concentrations, causes temporary spasm of hydrocarbons. Carcinogenic polycyclic com­ the smooth muscle of the bronchioles. At pounds have been found in some particulate somewhat higher concentrations, it causes emissions from diesel and petrol engines, but increased secretion of mucus, while at still numerous epidemiological studies have failed higher concentrations it causes severe inflam­ to show that motor vehicle exhaust is a cause mation of the mucous membranes with des­ of lung cancer. If it does contribute to the quamation of the surface epithelium. Its occurrence of this disease, its role must be effects are aggravated by cold air. It is not small in comparison with that of cigarette clear under what conditions a reduced level of smoking. Nevertheless, animal studies have reaction to sulfur dioxide occurs in man and shown that the inhalation of certain poly­ under what other conditions hypersensitivity cyclic hydrocarbons together with chemical occurs. irritants or adsorbed on inert particles can Ozone, which appears to be formed in the cause tumours of the lung. air by photochemical reactions, also has an irritant action in the respiratory tract, reach­ ing much deeper into the lungs than sulfur Legislative control of air pollution dioxide. Adequate control of air pollution cannot Carbon monoxide, a non-irritant gas, is an be achieved without suitable legislation. It is important pollutant emitted by motor vehi­ possible, in principle, to envisage legislation cles. Its presence in traffic exhaust fumes can over the control of air pollution that simply lead to blood carboxyhaemoglobin con­ prohibits all such pollution capable of causing centrations of 3-4%, but there is no un­ harmful effects or of constituting a nuisance. disputed evidence that such concentrations In practice, a more pragmatic approach is exert psychomotor effects. This lack of invariably adopted; that is, legislation aims to evidence does not necessarily mean that they ensure that the air is as clean as possible, are harmless, since synergistic effects may taking into account the cost of the various measures required and the resources avail­ ' See WHO Chronicle, 1969, 23, 264. Wld H/th Org. techn. Rep. Ser., 1961, 410, 30. able.

165 Examination of the legislation of a number sures taken by local authorities often involve of countries shows that the present tendency is the establishment of specially protected areas, to promulgate an enabling law giving the in which the air must be kept as clean as government power to monitor pollution and possible. Moreover, measures are often taken to take the necessary steps to prevent or con­ to deal with particularly dangerous sources of trol it. Such enabling laws often replace pollution. earlier legislation, which is fragmentary and The legislation of the countries mentioned applicable only to certain installations or pol­ above is concerned principally with sources lutants and is therefore no longer adequate of pollution, equipment for preventing or under present-day conditions. The enabling reducing pollution, the control of fuels and law is supplemented by orders or regulations chimneys, the establishment of town planning made under it, which deal in detail with standards, and the setting up of protected various pollution control measures. areas or areas subject to special supervision. This sequence of events has taken place in In general, inadequate attention is given to Belgium, the Federal Republic of Germany, protecting the public against the harmful France (where an enabling law was introduced effects of pollution by industrial establish­ as long ago as 1932), Italy, and the United ments. Such establishments should be re­ Kingdom, and similar laws are in course of quired to disclose the nature of the substances preparation in Luxembourg and the Nether­ used or produced in them, so that provision lands. Nevertheless, even in the United King­ can be made for the necessary measures to be dom, where the Clean Air Act has been in taken in the event of their accidental discharge force since 1956 and where the monitoring into the atmosphere. Legislation should also system is the best in western Europe, regula­ provide for special measures under certain tions for the implementation of the Act have climatic conditions that are liable to increase been few in number and inadequate in the hazards associated with pollution; such character. In Belgium, the enabling law of measures could include, for example, the 1964 has so far been followed by only one stopping of all road traffic and the use of fuels Crown Order for its implementation, and this less likely to cause pollution. Such provisions is concerned solely with the official approval have already been introduced in a number of of laboratories and agencies responsible for large cities in the USA. They are based on testing and research in the field of air pollu­ the continuous monitoring of pollution levels tion control. and the specification of stand-by and danger Part of the reason for this slow progress levels, at which the authorities are first lies in the difficulty of laying down standards alerted and then apply the appropriate for pollutant concentrations in effluents or for measures. the ground-level concentrations of pollutants. * * This difficulty has been avoided in certain * countries by the omission of all numerical The problems of urban climatology, and standards from the legislation. Where such the related ones of air pollution and its effects standards have been introduced they vary on human health, are of enormous complexity. from country to country; this is inevitable in Nevertheless, some progress is being made the absence of any adequate biological basis towards solving them. on which they can be established. In this A problem that deserves serious considera­ regard international organizations, including tion is that of increasing background pollu­ WHO, could have an important part to play. tion. Carbon dioxide concentrations in air Even in countries possessing a highly cen­ have increased substantially during this cen­ tralized administrative structure, local autho­ tury, and there is evidence of similar increases rities are given certain powers in the field of in the concentrations of other more serious air pollution control. This is because of the pollutants, such as carbon monoxide and the need to take account of local geographical, oxides of nitrogen. Studies are needed to industrial, and other conditions. The mea- determine whether these concentrations may

166 ultimately reach deleterious levels not only areas or on certain roads. Predictive models locally but regionally, or even on a global would be very useful in these situations. More scale. work is also required on the transport of pol­ Another problem is the lack of detailed lutants that are normally present in low con­ knowledge of the climatic factors capable of centrations, such as pollen, bacteria, and preventing the efficient dispersion of domestic asbestos dust. and industrial pollutants. A greater under­ Finally, there is an urgent need to define standing is also needed of the relationships much more rigorously the physical properties between pollutant concentrations outside and of the urban surface, particularly its thermal inside buildings and of the local factors and aerodynamic properties. Observation influencing pollution at various heights close sites must be selected more systematically so to tall buildings. More studies are needed on as to ensure that the results obtained in the beneficial effects of open spaces, parks, different investigations are comparable. Ana­ and hedges and on the possible effects of air lytical models based on field investigations pollution on vegetation. Warning systems and theoretical studies need to be developed must be established to forecast conditions for a variety of geographical locations, in (such as prolonged and localized inversions) order to study the influence of different that are likely to lead to disasters in industrial climatic variables.

Vaccination certificates Under the International Health Regulations a health authority may, in certain circumstances, require from travellers certificates of vaccination against cholera, smallpox, and yellow fever. The requirements of over 200 countries and territories in this respect, as on I January 1971, are listed in the latest edition of the WHO booklet Vaccination Certificate Requirements for International Travel (price £1, $3.00, or Sw. fr. 10.-). This booklet, which also contains information on yellow fever endemic zones, is a bilingual publication (English and French).

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