Guidelines for Air Quality, WHO, Geneva, 1999 GUIDELINES FOR AIR QUALITY
This WHO document on the Guidelines for Air Quality is the outcome of the WHO Expert Task Forcemeeting held in Geneva, Switzerland, in December 1997. It bases on the document entitled “Air QualityGuidelines for Europe” that was prepared by the WHO Regional Office for Europe and regionalbackground papers.
Note to the user:The electronic form of this document is available on the CD ROM of the Healthy Cities Air ManagementInformation System AMIS and, in part, from the Web site of the World Health Organization(
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Guidelines for Air Quality, WHO, Geneva, 1999 TABLE OF CONTENTS
Executive Summary
Physico-chemical aspects of air pollution and units used to describe concentrations ofair pollutants Factors affecting the concentrations of air pollutants Air pollutant concentrations, and factors affecting susceptibility Concentrations of classical pollutants in ambient air Concentrations and factors affecting susceptibility to indoor air pollution Effects of differing levels of disease in the population Specific differences in prevalent levels of air pollutants Exposure to air pollutantsSulphur dioxideNitrogen dioxideCarbon monoxideOzoneParticulate matterLeadOther air pollutants The 1987 WHO Air Quality Guidelines for Europe Development of the guideline setting process Factors to be considered in setting air quality standards Cost-benefit analysis and other factorsReferences Short-period exposures (less than 24-h)Exposure over a 24-h periodLong-term exposure Guidelines for Air Quality, WHO, Geneva, 1999 Long-term exposure effects
Other air pollutantsGuidelines based on non-carcinogenic health endpointsGuidelines based on carcinogenic health endpoints Classical air pollutants: Applicability of the WHO Air Quality Guideline for Europe Studies of effects of air pollutants on health in WHO regionsSulphur dioxide LatinMediterranean RegionWestern Pacific RegionSouth East AsiaAfrica LatinWestern Pacific RegionSouth East Asia Mediterranean RegionWestern Pacific Region LatinWestern Pacific RegionSouth East Asia LatinMediterranean RegionWestern Pacific RegionSouth East Asia Indoor air pollution in developed countries Important Indoor air pollutants and their sources Indoor air quality in less developed countries Guidelines for Air Quality, WHO, Geneva, 1999 Ambient Air Quality Monitoring and Assessment Quality assurance and quality control (QA/QC) Instrumental issuesPassive samplesActive samplersAutomatic analysersRemote sensorsGeneral advice on instrument selection Key pollutants and measurement methodsSulphur dioxide Passive samplersActive samplersAutomatic analysersRemote sensors Passive samplersActive samplersAutomatic analysersRemote sensors Passive samplersActive samplersAutomatic analysersRemote sensors Passive samplersActive samplersAutomatic analysersRemote sensors Air Quality ManagementBasic principles in air quality managementAir quality management strategy Strategies for ambient air quality management Stages in the development of ambient air quality management Guidelines for Air Quality, WHO, Geneva, 1999 Emissions control approachesCommand-and-controlEconomic instrumentsCo-regulationSelf-regulation Evaluation of control optionsTechnicalFinancialSocialHealth and environmentEffect-oriented and source-oriented principles Control of point sourcesSiting and planningSource emissions reductionManagement and operational changesProcess optimisationCombustion modificationFuel modificationsEmissions control International air quality managementReferences Strategies for indoor air quality management in developed countries Strategies for indoor air quality control and improvement SiteBuilding envelope designVentilationCommissioningMaterial selectionCombustion appliances Management of pollutants sourcesOperation and maintenance of ventilation systemsAir cleaning Addressing occupant complaints and symptomsBuilding diagnostic procedures Guidance/educationResearch supportProblem assessment and surveysStandard/protocol development Management of indoor air quality in developing countries Guidelines for Air Quality, WHO, Geneva, 1999 Priority setting in Air Quality Management Enforcement of air quality standards: Clean air implementation plans Guidelines for Air Quality, WHO, Geneva, 1999 Foreword
Achievements in air quality management underlie increased economic and social welfare in manydeveloping countries. Sound air quality management is also a proven way of enhancing public health,since air pollution is associated with increases in outpatient visits due to respiratory and cardiovasculardiseases, in hospital admissions and in daily mortality. Recent estimates of the increase in daily mortalityshow that on a global scale 4-8% of premature deaths are due to exposure to particulate matter in theambient and indoor environment. Moreover, around 20-30% of all respiratory diseases appear to becaused by ambient and indoor air pollution, with emphasis on the latter. It is suggested that without cleanair, a sound economic development becomes virtually impossible and social conflicts inevitable.
Although enormous progress has been made in developing clean air implementation plans for urban areas,especially in developed countries, a substantial number of people living in urban areas - around 1.5billion, or 25 per cent of the global population - are still exposed to enhanced concentrations of gaseousand particle compounds in the air they breathe. And the use of open fires for indoor cooking and heatingcurrently exposes about 2 billion people to quite substantial concentrations of suspended particulatematter, 10-20 times higher than ambient concentrations according to the limited measurements available.
Other sources of air pollution include industrial and vehicular emissions, as well as vegetation fires. Furthermore, the rate of population growth continues to increase and is likely to peak around the year2000, leading to a doubling of the global population by the middle of the 21st century. Most populationgrowth will occur in low-income countries and will stress already inadequate infrastructures and technicaland financial capacities. In parallel, the process of urbanisation will continue, such that the proportionof the global population living in cities will increase from around 45% to around 62% by the year 2025,creating dense centres of anthropogenic emissions.
The primary aim of the WHO Guidelines for Air Quality is to protect public health from theeffects of air pollution, and to eliminate or minimize exposure to hazardous pollutants. Airquality guidelines are set up to help governments derive legally enforceable air quality standards,and to guide the environmental health authorities and professionals who are trying to protectpeople from the harmful effects of environmental air pollution. Agenda 21 states in Chapter 6 on human health and environmental pollution: Nationally determined action programmes in this area, with international assistance, supportand coordination where necessary, should include: Develop appropriate pollution control technology on the basis of risk assessment and epidemiological research for the introduction of environmentally sound productionprocesses and suitable safe mass transport. Develop air pollution control capacities in large cities, emphasizing enforcement programmes and using monitoring networks, as appropriate. Guidelines for Air Quality, WHO, Geneva, 1999 Support research and develop programmes for applying prevention and control methods to reducing indoor air pollution, including the provision of economic incentivesfor the installation of appropriate technology. Develop and implement health education campaigns, particularly in developing countries, to reduce the health impact of domestic use of biomass and coal. The WHO Guidelines for Air Quality should help to greatly reduce the burden of excessmortality and preventable disability suffered by the poor. It should also help counter potentialhealth threats resulting from economic crises, unhealthy environments and risky behaviour. Inthis sense, the Guidelines contribute to meeting two of the key challenges that were highlightedin the 1999 World Health Report and, thus, they contribute to making health a fundamentalhuman right.
Dr Richard HelmerDirector, Department for Protection of the Environment Guidelines for Air Quality, WHO, Geneva, 1999 The risks posed to human health by air pollution have been evaluated since the 1950s andguideline values were derived in 1958. In 1987, the WHO Regional Office for Europe EUROpublished the Air Quality Guidelines for Europe. Since 1993, these guidelines have been revisedand updated. In a recent Expert Task Force Meeting convened in December 1997 in Geneva,Switzerland, the Guidelines for Air Quality was extended to provide global coverage andapplicability, and the issues of air quality assessment and control were addressed in more detail.
The WHO Guidelines for Air Quality document is the outcome of the consensus deliberationsof the WHO Expert Task Force.
The WHO Guidelines for Air Quality provides a basis for protecting public health from the adverseeffects of environmental pollutants and for eliminating ,or reducing to a minimum, contaminants that areknown or likely hazards to human health and well-being. The Guidelines does so by providingbackground information and guidance to governments for making risk management decisions, particularlyin setting standards. It also helps governments carry out local air quality control measures.
The WHO Guidelines for Air Quality values are levels of air pollution below which lifetime exposure,or exposure for a given averaging time, does not constitute a significant health risk. If these limits areexceeded in the short-term it does not mean that adverse effects automatically occur; however the risk ofsuch effects increases. Although the Guidelines for Air Quality values are health- or environment-basedlevels, they are not standards per se. Air quality standards are air quality guidelines promulgated bygovernments, for which additional factors may be considered. For example, the prevailing exposurelevels, the natural background contamination, environmental conditions such as temperature, humidityand altitude, and socio-economic factors. When proceeding from the Guidelines for Air Quality to standards, policy options include such questionsas what proportion of the general population, and which susceptible groups, should be protected. Severaladditional items must also be considered: the legal aspects; a definition of what constitutes adverseeffects; a description of the population at risk; the exposure-response relationship; the characterisationof exposure; an assessment of risks and their acceptability; and the financial costs of air pollution controlsand their benefits.
The Air Quality Guideline has been prepared as a practical response to the need for action with respectto air pollution at the local level, and for improved legislation, management and guidance at the nationaland regional levels. WHO will be pleased to see that these Guidelines are used widely. Continuingefforts will be made to improve its content and structure. It would be appreciated if users of theGuidelines would provide feedback and their own experiences. Please send your comments andsuggestions on the WHO Guidelines for Air Quality – Guideline document directly to the Department ofProtection of the Human Environment, Occupational and Environmental Health, World HealthOrganization, Geneva, Switzerland (Fax: +41 22-791 4123, e-mail: [email protected]).
Guidelines for Air Quality, WHO, Geneva, 1999 The WHO thanks all individuals who contributed to the preparation of the Guidelines for Air Quality.
The international, multidisciplinary group of contributors and reviewers are listed in the “Participant list”in Annex 5. Special thanks are due to the chairpersons of the meeting and workgroups of the WHOexpert task force meeting, held in Geneva, Switzerland in December 1997: Dr Robert Maynard, who actedas the chairperson of the meeting; Professor Morton Lippmann and Professor Bernd Seifert, who chairedthe three workgroups. Thanks are also due to Dr Frank Murray for acting as rapporteur of the meeting andreviewing the draft document. Contributions from those who provided the background papers and whocontributed to the success of the WHO expert meeting are gratefully acknowledged: Prof. Dr Ursula Ackermann-Liebrich, University of Basel, Switzerland;Dr Amrit Aggarwal, National Environmental Engineering Research Institute, Nagpur, India;Mr Jonathan Bower, AEA Technology, Culham, United Kingdom;Dr Bingheng Chen, World Health Organization, Geneva, Switzerland;Dr Mostafa El-Desouky, Ministry of Health, KuwaitDr Ruth Etzel, Centres for Disease Control and Prevention, Atlanta, GA, USA;Dr Hidekazu Fujimaki, National Institute for Environmental Studies, Ibaraki, Japan;Dr Kersten Gutschmidt, World Health Organization, Geneva, Switzerland;Dr Richard Helmer, World Health Organization, Geneva, Switzerland;Dr Michal Krzyzanowski, WHO European Centre for Environment & Health (ECEH), De Bilt, Netherlands;Dr Rolaf van Leeuwen, WHO European Centre for Environment & Health (ECEH), De Bilt, Netherlands;Mr Gerhard Leutert, Federal Office of Environment, Forests and Landscape, Bern, Switzerland;Professor Morton Lippmann, New York University Medical Centre, Tuxedo, NY, USA;Ms Angela Mathee, Eastern Metropolitan Substructure (Johannesburg), Sandton, South Africa; Dr RobertL. Maynard, Department of Health, London, United Kingdom;Professor Frank Murray, Murdoch University, Murdoch, Australia;Professor Mahmood Nasralla, National Research Centre, Dokki, Cairo, Egypt; Dr Roberto Romano, Pan American Health Organization/WHO Regional Office for the Americas,Washington, DC, USA;Dr Isabelle Romieu, Centres for Disease Control and Prevention, Atlanta, GA, USA;Dr Dieter Schwela, World Health Organization, Geneva, Switzerland;Professor Bernd Seifert, Institute for Water, Soil & Air Hygiene, Federal Environmental AgencyBerlin, Germany;Dr Bimala Shrestha, WHO Representative’s Office, Kathmandu, Nepal;Professor Kirk Smith,University of California, Berkeley, CA, USA;Dr Yasmin von Schirnding, World Health Organization, Geneva, Switzerland;Professor Gerhard Winneke, Univerität Düsserldorf, Germany;Dr Ruqiu Ye, National Environmental Protection Agency, Beijing, People’s Republic of China;Dr Maged Younes, World Health Organization, Geneva, Switzerland.
Particular thanks are due to the Ministry of Environment, Bonn, Germany; and the Federal Officeof Environment, Forests and Landscape, Bern, Switzerland. They provided funding to convenethe WHO expert task force meeting in Geneva, Switzerland, in December 1997, to produce theGuidelines.
Guidelines for Air Quality, WHO, Geneva, 1999 Executive Summary
Air pollution is a major environmental health problem, affecting developed and developing countriesaround the world. Increasing amounts of potentially harmful gases and particles are being emitted intothe atmosphere on a global scale, resulting in damage to human health and the environment. It isdamaging the resources needed for the long-term sustainable development of the planet. There are three broad sources of air pollution from human activities: Stationary sources, Mobile sources,and Indoor sources. In developing countries, indoor air pollution from using open fires for cooking andheating may be a serious problem. It has been estimated that about 1.9 million people die annually dueto exposure to high concentrations of suspended particulate matter in the indoor air environment, whilethe excess mortality due to suspended particulate matter and sulphur dioxide in the ambient air amountsto about 500 000 people annually. Although the indoor air database is weak due to the scarcity ofmonitoring results, these estimates indicate that a serious indoor air problem may exist in developingcountries.
Air pollutants are usually classified into suspended particulate matter (dusts, fumes, mists, smokes),gaseous pollutants (gases and vapours) and odours. Current techniques used to measure the massconcentration of particles in air make use of size-specific sampling devices. Thus the mass of particles lessthan 10 µm diameter may be determined (PM10 ) as an index of the mass concentration of particles that canpenetrate into the human thorax. The mass concentration of particles of less than 2.5 µm diameter (PM2.5)is a means of measuring the total gravimetric concentration of several chemically distinct classes of particlesthat are emitted into, or formed within, the ambient air as very small particles. Fine and coarse particles generally have distinct sources and formation mechanisms, although there may besome overlap. Biological material such as bacteria, pollen and spores may also be found in the coarse mode.
Fine and coarse particles typically exhibit different behaviour in the atmosphere and these differences mustbe taken into consideration when interpreting central-site monitored values, as well as the behaviour ofparticles after they penetrate homes and buildings, where people spend most of their time. Fineaccumulation-mode particles typically have longer atmospheric lifetimes (days to weeks) than coarseparticles, and tend to be more uniformly dispersed across an urban area or large geographic region. Largerparticles generally deposit more rapidly than small particles; as a result, total coarse particle mass is lessuniform in concentration across a region than that of fine particles. This publication is focused on those gases and particulate matter that have been accepted as posing a threatto health. The relative health threat of different pollutant gases and particles varies with their concentrationsover time and distance, implying that the effects of air pollutants on health may vary from country-to-country.
Consequently, careful monitoring of the concentrations of polluting gases, as well as of the particle sizedistribution, concentration and composition, is needed before an acceptable estimate of the effects can beproduced. The picture is further complicated because some pollutant combinations act in an additive mannerand some perhaps synergistically.
WHO’s air quality guidelines were first published as Air Quality Guidelines for Europe in 1987 (WHO1987). Since 1993 the Air Quality Guidelines for Europe has been revised and updated, incorporatinga review of the literature published since 1987 (WHO 1999a). Also, the following additional compoundswere considered in the review procedure: 1,3 butadiene, environmental tobacco smoke (ETS), fluoride,man-made vitreous fibres and platinum. Parallel to the review of the air quality guidelines for Europe,the Environmental Health Criteria series of the International Programme on Chemical Safety has Guidelines for Air Quality, WHO, Geneva, 1999 continued and the health risks of more than 120 chemical compound and mixtures were assessed between1987 and 1998.
The WHO Air Quality Guidelines for Europe (WHO 1987) were based on evidence from theepidemiological and toxicological literature published in Europe and North America. They did notconsider the effects of exposure to the different ambient air particle concentrations in developingcountries, as well as the different conditions in these countries. However, these guidelines were usedintensively throughout the world. In view of the different conditions in developing countries, the literalapplication of the WHO Air Quality Guidelines for Europe could be misleading. Factors such as highand low temperature, humidity, altitude, background concentrations and nutritional status could influencethe health outcomes after the population has been exposed to air pollution. To make the WHO AirQuality Guidelines for Europe globally applicable, a task force group meeting was convened at WHOHeadquarters from 2-5 December 1997. The outcome of that meeting is this publication of globallyapplicable air quality guidelines.
The objective of WHO’s Guidelines For Air Quality is to help countries derive their own national airquality standards. The guidelines are technologically feasible and consider socio-economic and culturalconstraints. They provide a basis for protecting public health from the adverse effects of air pollution andfor eliminating, or reducing to a minimum, those air pollutants that are likely hazardous to human health.
Consequently, the instruments of air quality management are also addressed in this publication.
Factors affecting the concentrations of air pollutants
Local concentrations of air pollutants depend upon the strength of their sources and the efficiency of theirdispersion. Day to day variations in concentrations are more affected by meteorological conditions than bychanges in source strengths. Wind is of key importance in dispersing air pollutants and for ground levelsources pollutant concentrations are inversely related to wind speed. Turbulence is also important: a "rough"terrain, as produced for example by buildings, tends to lead to increased turbulence and better dispersion ofpollutants.
Exposure to air pollutants
The total daily exposure of an individual to air pollution is the sum of the separate contacts to air pollutionexperienced by that individual as he/she passes through a series of environments (also called micro-environments) during the course of the day (e.g. at home, while commuting, in the streets, etc.). Exposuresin each of these environments can be estimated as the product of the concentration of the pollutant in questionand the time spent in the environment.
There are many factors that can account for the substantial differences between the concentrations ofpollutants measured at central sites and those in the breathing zone of residents of the community. Manyof these factors can be modelled and such models have been used for estimating dose distributionsassociated with ambient air concentrations.
Health significance of air pollution
A new database of epidemiological studies emerged in the late 1980s and 1990s. This database of time-seriesstudies was developed first in the United States and later in Europe and other areas. In essence the time seriesapproach takes the day as the unit of analysis and relates the daily occurrence of events such as deaths oradmissions to hospital to daily average concentrations of pollutants whilst taking careful account ofconfounding factors such as season, temperature and day of the week. Powerful statistical techniques havebeen applied and coefficients have been produced that relate the daily average concentrations of pollutantsto their effects. Associations have been demonstrated between daily average concentrations of particles,ozone, sulphur dioxide, airborne acidity, nitrogen dioxide, and carbon monoxide. Although the associations Guidelines for Air Quality, WHO, Geneva, 1999 for each of these pollutants were not significant in all studies, taking the body of evidence as a whole theconsistency is striking. For particles and ozone it has been accepted by many that the studies provide noindication of any threshold of effect.
Air pollutant concentrations and factors affecting susceptibility
The concentrations of classical pollutants in ambient air of European countries and of the UnitedStates have been extensively discussed in the Air Quality Guidelines for Europe (WHO 1999a). Indeveloping countries, by contrast, the concentrations of pollution levels in ambient air are higherby an order of magnitude, according to the main source of information on air pollution indeveloping countries, the Air Management Information System (AMIS).
Indoor air pollutants usually differ in type and concentration from outdoor air pollutants. Indoorpollutants include environmental tobacco smoke, biological particles, non-biological particles, volatileorganic compounds, nitrogen oxides, lead, radon, carbon monoxide, asbestos, various synthetic chemicalsand others. Degradation of indoor air quality has been associated with a range of health effects, fromdiscomfort and irritation to chronic pathologies and cancers.
On a global scale, biomass fuels are used daily in about half the world’s households as energy for cookingand/or heating. Biomass smoke contains significant amounts of several important pollutants: carbonmonoxide, particulate matter, hydrocarbons and to a lesser extent, nitrogen oxides. However, biomasssmoke also contains many organic compounds, including PAH that are thought to be toxic, carcinogenic,mutagenic or otherwise of concern. In China, coal burning is a major source of indoor air pollution andcoal smoke contains all of these pollutants as well as additional ones, e.g. sulphur oxides and heavymetals such as lead.
An unknown, but significant, proportion of biomass fuel burning takes place in conditions wheremuch of the air-borne effluent is released into poorly ventilated living areas. Therefore, someof the highest concentrations of particulate matter and other pollutants occur in rural, indoorenvironments in developing countries. Due to the high pollutant concentrations and the largepopulations involved, the total human exposure to many important air pollutants can be muchhigher in homes of the poor in developing countries than in the outdoor air of cities in thedeveloped world.
Altitude, temperature and humidity vary significantly across the globe. At increased altitude the partialpressure of oxygen falls and inhalation increases in compensation. For particles, this increased inhalation willlead to an increased intake of airborne particles. On the other hand, for gaseous pollutants no increase ineffects over those experienced at sea level would be expected. Temperature has a very significant effect onhealth, whereas humidity is unlikely to have a significant effect on the toxicity of gaseous pollutants.
The age structure of populations differs markedly from country to country. Old people tend to showincreased susceptibility to air pollution. Very young children may also be at increased risk. People with apoor standard of living suffer from nutritional deficiencies, infectious disease due to poor sanitation andovercrowding, and tend to be provided with a poor standard of medical care. Each of these factors mayrender individuals more susceptible to the effects of air pollution. Diseases which produce narrowing of theairways, a reduction in the area of the gas-exchange surface of the lung and an increased alteration ofinhalation-perfusion ratios are likely to make the subject more susceptible to the effects of a range of airpollutants.
Guidelines for Air Quality, WHO, Geneva, 1999 Role of guidelines and standards
The purpose of the Guidelines for Air Quality is to provide a basis for protecting public health from adverseeffects of air pollution and for eliminating, or reducing to a minimum, those contaminants that are known tobe, or likely to be, hazardous to human health and well being. The Guidelines should provide backgroundinformation for nations engaged in setting air quality standards, although their use is not restricted to this.
These Guidelines are not intended as standards. In moving from guidelines to standards, prevailing exposurelevels and environmental, social, economic and cultural conditions in a nation or region should be taken intoaccount. In certain circumstances there may be valid reasons to pursue policies which will result in pollutantconcentrations above or below the guideline values.
In the updated version of the Air Quality Guidelines for Europe, a similar approach to that in the 1987air quality guidelines was used. However, total tolerable intakes were calculated for multimediapollutants first, and then adequately partitioned among the different exposure routes. The term"protection factor" used in the 1987 guidelines was abandoned. Instead, uncertainty factors were usedto account for the extrapolation from animal to man (alternatively, human equivalent concentrations werecalculated), and to account for individual variability. Wherever information on inter- and intraspeciesdifferences in pharmacokinetics was available, data-derived uncertainty factors were employed. Additional uncertainty factors were applied whenever necessary to account for the nature and severity ofthe observed effects and for the adequacy of the database. For most of the compounds considered,information on the dose/exposure response relationship was provided, to give policymakers clearguidelines on the possible impact of the pollutant at different exposure levels and to permit an informeddecision making process to take place. For some compounds, e.g. platinum, a guideline value wasconsidered unnecessary as exposure through ambient air levels was considerably below the lowest levelat which effects were seen. For other compounds, for example particulate matter (PM10), no thresholdof effect(s) could be found and therefore no guideline value could be derived. Instead, exposure-effectinformation highlighting the public health impact of different pollutant levels was provided.
In the updating process for carcinogens, a more flexible approach than in the 1987 air qualityguidelines was applied. As a default approach, low-dose risk extrapolation was conducted forthe IARC groups 1 (proven human carcinogen) and 2A (probable human carcinogen, limitedevidence), and an uncertainty factor was applied for agents in IARC groups 2B (probable humancarcinogen, inadequate evidence) and 3 (unclassified chemicals). However, the mechanism ofaction of the carcinogen was the determining factor for the method of assessment. Hence, it wasdecided that compounds classified under 1 or 2A could be assessed using uncertainty factors, ifevidence for a non-threshold mechanism of carcinogenicity existed. By way of contrast,compounds classified under 2B could be assessed by low-dose extrapolation methods, if a non-threshold mechanism of carcinogenicity in animals was proven. Flexibility was also given in thechoice of the extrapolation model, depending on the available data (including data for PBPKmodelling). The linearized multistage model was used as a default approach. Besides providingunit risk estimates in cases where low dose risk extrapolation was conducted, levels associatedwith excess cancer risk of 1 : 10000, 1 : 100 000 and 1 : 1000 000 were calculated.
Exposure-response relationships
These guidelines place some emphasis on epidemiological data. Epidemiological studies are sometimespreferable to controlled exposure studies in that they provide information on responses in populations andon the effects of real exposures to pollutants and pollutant mixtures. However, the results of epidemiologicalstudies are less easy to use than the results of controlled exposure studies in defining guidelines.
For both particles and ozone an assumption of linearity was made when defining the exposure-responserelationships included in the revised guidelines. Extrapolation beyond the available data is dangerous; Guidelines for Air Quality, WHO, Geneva, 1999 however, as there is evidence to suggest that the exposure-response relationship may become less steep asambient levels of particles rise. For ozone, the relationship at low concentrations may be concave upwards.
These are important points to be considered if the guidelines are to be used in countries with levels ofpollution different from the range covered by the guidelines.
Moving from guidelines to standards
An air quality standard is a description of a level of air quality, adopted by a regulatory authority asenforceable. At its simplest, an air quality standard should be defined in terms of one or moreconcentrations and averaging times. Further information on the form of exposure (e.g. outdoor), onmonitoring to assess compliance with the standard, and on methods of data analysis and QualityAssurance and Quality Control requirements should be added. Other factors to be considered in settingan air quality standard include the nature of the pollution effects and whether they represent adverse healtheffects; and whether special populations are at risk.
The development of air quality standards is only a part of an adequate air quality management strategy.
Legislation, identification of authorities responsible for enforcement of emission standards and penaltiesfor exceeding standards are also necessary. Emission standards may play an important role in themanagement strategy especially if exceeding air quality standards is used as a trigger for abatementmeasures. These may be needed at both the national and the local level. Air quality standards are alsoimportant in informing the public about air quality. Used in this way they are a double edged weapon asthe public commonly assumes that once a standard is exceeded adverse effects on health will occur. Thismay not be the case.
The transfer of the dose-response relationships to other parts of the world, especially for particulatematter, should be conducted with caution for several reasons. These include:1.
The chemical composition of the particles.
The responsiveness of the population.
The limitations of the established relationships.
Cost-benefit analysis and other factors
Cost-benefit analysis is one way of formally weighing the costs of reducing air pollution against the benefitsproduced. The concept is that emissions are reduced until the marginal costs and benefits are equal. Whilethe cost of abatement measures may be relatively easy to quantify, this may not be the case when non-technical measures are employed. In any case, it is likely to be more difficult to assign monetary values tothe benefits obtained. Some aspects of reduced morbidity, such as the reduced use of hospital facilities anddrugs are comparatively easy to cost; others, such as reductions in premature deaths and symptoms, are not.
Applying monetary values based on a "willingness to pay" basis has been suggested, and has been acceptedas appropriate by many health economists. This approach has been seen as preferable to one based only onsuch indices as loss of production, earnings or hospital expenses.
Factors other than monetary factors also need to be considered when considering the setting of national airquality standards. These include the technical capacity of a country to achieve and maintain an air qualitywithin the desired standards, the social implications of adopting certain standards to ensure equity of costsand benefits among the population, and environmental costs and benefits.
Health-based Guidelines
For the purpose of presenting the health-based air quality guidelines, the key air pollutants, also termed“classical” air pollutants - SO2, NO2, CO, O3, SPM, and lead are briefly described with respect to healthrisk evaluations and recommended guideline values. Particular emphasis is given to suspended particulate Guidelines for Air Quality, WHO, Geneva, 1999 matter <10 µm diameter (PM10) and < 2.5 µm diameter (PM2.5). The guidelines are presented in Chapter3 in tables 3.1 to 3.5 and in figures 3.1 to 3.9. The information available for a number of other airpollutants (including carcinogens and non-carcinogens) is also summarized and presented in synoptictables.
Classical air pollutants: applicability of WHO Air Quality Guidelines for Europe
on a world wide scale

In the derivation of the WHO Air Quality Guidelines for Europe, assumptions were made forsome compounds, which may not be applicable in some parts of the world. For example, theimportance of different routes of exposure for some pollutants may vary from country to country.
It should be understood that if such factors were to be taken into account then differentguidelines could be derived. For a number of pollutants a Unit Risk (UR) assessment has beenprovided. These assessments are also dependent upon considerations of the comparativeimportance of different routes of exposure.
It is important that regulatory authorities should evaluate whether local circumstances give cause to doubtthe validity of the guideline set out in the WHO Guidelines for Air Quality as a basis for setting localguidelines or standards.
12. Indoor Air Quality
Indoor spaces are important microenvironments when assessing risks from air pollution. Formany air pollutants most of the daily exposure by inhalation occurs indoors because of theamount of time spent indoors or because of the pollutant concentration levels encountered. Theair quality inside buildings is affected by many factors. In an effort to conserve energy, modernbuilding design has favoured tighter structures with lower rates of ventilation. By contrast, insome areas of the world, natural ventilation only is used; in others, mechanical ventilation iscommon. In modern buildings most of the pollution problems arise from low ventilation ratesand the presence of products and materials that emit a large variety of compounds, whereas theinhabitants of many less developed countries face problems related to pollutants generated byhuman activities, in particular by combustion processes. If only the health effects of air pollution are being considered, it does not matter if a pollutant is inhaledby breathing outdoor or indoor air. However, there are important differences in the composition ofpollutant mixtures in outdoor and indoor air. For example, in outdoor air there are traffic-generatedemissions, whereas indoor air pollution is generated from tobacco smoke or from cooking with biomass-fuelled stoves. Not all of these compositions have been taken into account in developing the Guidelinesfor Air Quality, and they may not be applicable under all circumstances, so care should be taken to avoidmisinterpretation.
Ambient Air Quality Monitoring and Assessment
The three main air quality assessment tools are: i) ambient monitoring; ii) models and iii) emissioninventories/measurement.
The ultimate purpose of monitoring is not merely to collect data, but to provide the necessary informationrequired by scientists, policy makers and planners to enable them to make informed decisions onmanaging and improving the environment. Monitoring fulfils a central role in this process, providing thenecessary scientific basis for policy and strategy development, objective setting, compliance measurementagainst targets and enforcement action. However, the limitations of monitoring should be recognised.
No monitoring programme, however well funded and designed, can hope to comprehensively quantify Guidelines for Air Quality, WHO, Geneva, 1999 patterns of air pollution in both space and time. In many circumstances, measurements alone may beinsufficient or impractical for the purpose of fully defining population exposure in a city or country. Monitoring therefore often needs to be used in conjunction with other objective assessment techniques,including modelling, emission measurement and inventories, interpolation and mapping. At best,monitoring provides an incomplete, but useful, picture of current environmental quality.
Reliance on modelling alone also is not recommended. Although models can provide a powerful tool forinterpolation, prediction, and optimisation of control strategies, they are effectively useless unlessproperly validated by real-world monitoring data. It is important, also, that the models utilised areappropriate to local conditions, sources and topography, as well as being selected for compatibility withavailable emission and meteorological datasets. Many models depend on the availability of reliableemission data. A complete emissions inventory for a city or country may need to include emissions from point, area andmobile sources. In some circumstances, assessment of pollutants transported into the area under studymay also need to be considered. Inventories will, for the most part, be estimated using emission factorsappropriate to the various source sectors (verified by measurement), and used in conjunction withsurrogate statistics such as population density, fuel use, vehicle kilometres or industrial throughput. Emission measurements will usually only be available for large industrial point sources or fromrepresentative vehicle types under standardised driving conditions.
All three assessment tools are interdependent in scope and application. Accordingly, monitoring,modelling and emission assessments should be regarded as complementary components in any integratedapproach to exposure assessment or in determining compliance with air quality criteria.
Ambient Air Quality Management
Some basic principles guide international and national policies for the management of all forms of airpollution. An important global initiative occurred in 1983 when the UN General Assembly establishedthe World Commission on Environment and Development, headed by Gro Harlem Brundtland. Thereport produced by the Commission was entitled Our Common Future and it was presented by the UNGeneral Assembly in 1987 and endorsed by it. It has been influential in bringing environmental issuesinto the global arena, and in expressing some concepts that have been influential in air qualitymanagement.
The Brundtland Commission suggested that to meet the legitimate aspirations of the world's population
without destroying the environment, sustainable development would be required. It defined sustainable
as: development that meets the needs of the present without compromising the ability of
future generations to meet their own needs
. This concept has been embraced as an apparent means of
integrating environmental policy and economic development.
Following from the Brundtland Commission, the UN Conference on the Environment and Developmentwas held in Rio in 1992. The aim was to ensure that practical foundations for sustainable developmentwere put into place. The Agenda 21 document and the Rio declaration were the most obvious results ofthis conference. Agenda 21 is a document covering sustainable development which is not binding oncountries, but national implementation is reviewed by the Sustainable Development Commission and theUN General Assembly. Agenda 21 supports a number of environmental management principles on whichsome government policies including air quality management are based. These include: • precautionary principle - where there is a clear possibility of damaging environmental
consequences, action should be taken to protect the environment without awaiting the full scientificproof that the environment will be damaged by the proposal.
Guidelines for Air Quality, WHO, Geneva, 1999 • polluter pays - the full costs associated with pollution (including monitoring, management, clean-up
and supervision) should be met by the organisation responsible for the source of the pollution.
In addition, many countries have adopted the principle of pollution prevention, which aims to reduce
pollution at sources.
The responsibility of national governments for international reporting on the environment of their countryhas enabled greater exchange of air quality information around the world.
The foundation for air quality management is the government policy framework. Without a suitablepolicy framework and adequate legislation it is difficult to maintain an active or successful air qualitymanagement programme. A policy framework refers to transport, energy, planning, development, andpolicy in other areas, as well as environmental policy. Air quality objectives are more readily achievedif these interconnected government policies are compatible, and if mechanisms exist for co-ordinatingresponses to issues, which cross different areas of government policy. Measures to achieve someintegration of air quality policy with health, energy, transport and other policy areas have been adoptedin many developed countries.
The goal of air quality management is commonly stated to be to maintain a quality of air that protectshuman health and welfare. This goal recognises that air quality must be maintained at levels, whichprotect human health, but it also must provide protection of animals, plants (crops, forests and naturalvegetation), ecosystems, materials and aesthetics, such as natural levels of visibility. To achieve an airquality goal requires the development of policies and strategies.
Management of indoor air quality
Most human beings spend most of their time in indoor environments, where they can be exposedto poor air quality. Pollution and degradation of indoor air cause illness, increased mortality, lossof productivity and have major economic and social implications. Health effects can includeincreased rates of cancer, lung disease, allergy and asthma as well as fatal conditions such ascarbon monoxide poisoning and legionnaires' disease, as discussed in Section 4.1. The medicaland social cost associated with these illnesses, and the related reduction in human productivity,result in staggering economic losses.
Indoor air quality problems affect all types of buildings including homes, schools, offices, healthcare facilities and other public and commercial buildings. Indoor air problems can be reducedby better urban planning, design and operation, as well as maintenance of buildings, materialsand equipment in buildings.
This document considers the management of indoor air quality in developed countries, and insome situations in developing countries, and then focuses on the important and widespreadproblem of how to manage indoor air quality associated with biomass fuel combustion indeveloping countries.
Priority Setting in Air Quality Management
It is important to give guidance to countries on how to set priorities in rational air quality management.
Actual priorities will differ for each country; therefore, each country sets priorities in air qualitymanagement according to its policy objectives, needs and capabilities. Priority setting in air qualitymanagement refers to prioritising health risks to be avoided, with corresponding prioritisation of airpollutant compounds, and concentrating on the most important sources of the pollutants. Conceptually,prioritising health risks is straightforward. High priority of health risks will be given to those compounds Guidelines for Air Quality, WHO, Geneva, 1999 for which “high” toxicity and “high” exposure of the population are entailed. Conversely, low priorityhealth risks involve agents of “low” toxicity and “low” exposure. “Medium” priority risks includecompounds in which either toxicity or exposure is “low" while the other is “high”.
A framework for a political, regulatory and administrative approach is required to guarantee a consistentand transparent derivation of air quality standards and to ensure a basis for making decisions on risk-reducing measures and abatement strategies. In such a framework the following considerations need tobe included: - The legal aspects.
- The potential of air pollution to cause adverse effects on health, taking into account the - The exposure-response relationships of pollutants and pollutant mixtures and the actual exposure responsible for related health and/or environmental risks.
- The acceptability of risk.
- The cost-benefit analysis.
- The stakeholder contribution in standard setting.
Enforcement of air quality standards: Clean air implementation plans
The enforcement of air quality standards aims to evaluate the need for control action on emission sourcesto attain compliance with the standards. The instruments used to achieve this goal are the Clean AirImplementation Plans (CAIPs). The outline of such a plan should be defined in regulatory policies andstrategies. Clean air implementation plans were developed in several developed countries during the1970s and 1980s. Air pollution was characterized by a multitude of sources of many different types ofair pollutants. Consequently it was extremely difficult to assess the public health risks associated witha single source, or even a group of sources. As a consequence, on the basis of the polluters pay principle(Chapter 6), sophisticated tools were developed which assessed the sources, air pollutant concentrations,health and environmental effects and control measures, and which made a causal link between emission,air pollution and the necessary control measures. A typical clean air implementation plan (CAIP)includes: A description of the area.
An emissions inventory.
An air pollutant concentrations inventory - monitored and simulated.
A comparison with emissions and air quality standards or guidelines.
An inventory of the effects on public health and the environment.
A causal analysis of the effects and their attribution to individual sources.
Control measures and their costs.
Transportation and land-use planning.
Enforcement procedures.
Resource commitment.
Projections for the future.
In developing countries, the air pollution situation is often characterized by a multitude of sources of fewtypes, or sometimes few sources. Using the experience obtained in developed countries, the controlaction to be taken is very often obvious. As a consequence, in cases where little useful monitoring dataare available, less monitoring could be sufficient, and dispersion models could help to simulate spatialdistributions of pollutant concentrations. Much simplified CAIPs would have to be developed for citiesof developing countries or countries in transition. At present, the main sources of emissions in manycities of the developing world are old vehicles and some industrial sources such as power plants, brickkilns, cement factories and a few others. Their relative contribution to air pollution could be determinedby use of rapid emission inventories. The emission factors used in such inventories are published and aPC programme is available, which enables an estimation of emissions and ambient air concentrations, and Guidelines for Air Quality, WHO, Geneva, 1999 evaluates the impact of possible control measures. Projections for the future can also be evaluated by theprogramme.


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