Air Quality Guidelines

WHO has also provided general guidelines for air quality (WHO 1999, last updated 2001). Since the problems are often different in developed and developing countries, WHO will soon offer special Air Quality Guidelines for Europe. 

The WHO emphasized that guideline values for carcinogenic substances computed using mathematical models must be considered at best as a rough estimate of the cancer risk, as these models do not usually take into account a number of biologically important considerations, such as toxicokinetics, DNA repair, or immunological protection mechanisms. However, the models used are conservative and probably err on the side of caution. 

In order to account for differences in metabolic rates between experimental animals and humans, a surface area to body weight correction (Section 5.3.2.2) is sometimes applied to quantitative estimates of cancer risk derived by low-dose extrapolation. The WHO stated that incorporation of this factor increases the risk by approximately one order of magnitude, depending on the species upon which the estimate is based, and increases the risk estimated on the basis of studies in mice relative to that in rats. The WHO considered incorporation of this factor to be overly conservative, particularly in view of the fact that linear extrapolation more likely overestimates risk at low doses. Therefore, the guideline values for carcinogens were developed on the basis of quantitative estimates of risk that were not corrected for the ratio of surface area to body weight. 

For those substances for which appropriate human smdies are available, the so-called average relative risk model has been used. Quantitative assessments using this model comprises four steps (1) selection of studies (2) standardized description of study results in terms of relative risk, exposure level, and duration of exposure (3) extrapolation towards zero dose and (4) application to a general (hypothetical) population. 

The relative risk is calculated as a measure of response and is then used to calculate the excess lifetime cancer risk expressed as unit risk (associated with a lifetime exposure to 1 p,g/m ). 

The WHO has cautioned that the risk estimates presented should not be regarded as being equivalent to the true cancer risk, and that the crude expression of risk in terms of excess incidence or numbers of cancers per unit of the population at doses or concentrations much less than those on which the estimates are based may be inappropriate. Estimated risks are believed to represent only the plausible upper bounds, and may vary widely depending on the assumptions on which they are based. 

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World Health Organization, "Air Quality Guidelines for Europe." Copenhagen, 1987. 

The main objective of air quality guidelines and standards is the protection of human health. Since fme particulates (PM,) are more likely to cause adverse health effects than coarse particulates, guidelines and standards referring to fine particulate concentrations are preferred to those referring to TSP, which includes coarse particulate concentrations. Scientific studies provide ample evidence of the relationship between exposure to short-term and long-term ambient particulate concentrations and human mortality and morbidity effects. However, the dose-response mechanism is not yet fully understood. Furthermore, according to the WHO, there is no safe threshold level below which health damage does not occur. 

Table II. WHO Air Quality Guideline Values and Health Effects...

Air Quality Guidelines for Europe. World Health Organization, European Series No. 23. 

WHO. 1987. Hydrogen sulfide. In Air quality guidelines for Europe. Copenhagen, Denmark World Health Organization Regional Publications, European series no. 23. 

WHO. 1986. Regional Office for Europe Air quality guidelines. Vol. 11. Geneva, Switzerland World Health Organization, 1-34. 

FIGURE 3.S WHO air quality guidelines for Europe and WHO guidelines for drinking-water quality. 

In relation to their air quality guidelines, the WHO has estimated the risk associated with lifetime exposure to a certain concentration of a genotoxic carcinogen by linear extrapolation and the carcinogenic potency expressed as the incremental unit risk estimate. However, the guideline sections for carcinogenic pollutants also provide the concentration in air associated with an excess cancer risk of 10 ", 10 , and 10 , calculated from the unit risk, in order to support authorities in the decision-making process. 

WHO. 2000. Criteria for carcinogenic endpoint. In Air Quality Guidelines for Europe. Second Edition. WHO Regional PuhUcations, European Series, No. 91, 20-29 Copenhagen WHO Regional Office for Europe. http /www.euro.who.int/document/e71922.pdf... 

Examples of standard settings developed by the WHO include air quality guidelines (Section 9.2.1.1) and drinking water guidelines (Section 9.2.1.2), and (in collaboration with the FAO) maximum residue limits (MRLs) for pesticides and veterinary drugs and maximum levels for food additives (Section 9.2.1.3). 

Recognizing the need of humans for clean air, the WHO Regional Office for Europe in 1987 published the first edition of the Air Quality Guidelines for Europe containing health risk assessments of 28 chemical air contaminants (WHO 1987). In 1993, air pollutants of special environmental and health significance to countries of the European Region were identified by a... 

WHO planning group, and 35 air pollutants were selected to be included in a second edition of the Air Quality Guidelines, which was published in 2000 (WHO 2000). It is noted that relevant EHC documents (Section 3.6.1.1) were of great value with respect to the selection of pollutions to be included in the second edition of the Air Quality Guidelines (WHO 2000). The publication is available via the WHO Regional Office for Europe s Web site (WHO 2007b). 

The second edition of the Air Quality Guidelines for Europe (WHO 2000) comprises four introductory chapters plus sections on health risk evaluation and guidelines of the various pollutants. 

The introductory Chapter 1 of the Air Quality Guidelines sets the scene regarding air quality issues, states the nature of the air quality guidelines, and describes the procedures used in the updating and revision process. In the following text, the most essential information in the context of this book is presented. 

The introductory Chapter 2 of the Air Quality Guidelines (WHO 2000) gives a very detailed and comprehensive description of the criteria used in establishing the guideline values including criteria for selection of NOAEL/LOAEL, adverse effect, benchmark approach, and uncertainty factors. These criteria are comparable to the principles outlined in Chapters 4 and 5 in this book. There are also criteria for selection of averaging times and for consideration of sensory effects (malodorous... 

When epidemiological studies form the basis for the risk assessment of a single chemical or even complex mixtures, such as various combustion emissions, it may be stated that in those cases the effects of combined action of chemicals have been incorporated. Examples can, for instance, be found in the updated WHO Air Quality guidelines (WHO 2000). Thus, the guideline value for, e.g., ozone was derived from epidemiological studies of persons exposed to ozone as part of the total mixture of chemicals in polluted ambient air. In addition, the risk estimate for exposure to polycyclic aromatic hydrocarbons was derived from studies on coke-oven workers heavily exposed to benzo[fl]pyrene as a component of a mixture of PAH and possibly many other chemicals at the workplace. Therefore, in some instances the derivation of a tolerable intake for a single compound can be based on studies where the compound was part of a complex chemical mixture. 

World Health Organization (WHO), Polynuclear Aromatic Hydrocarbons (PAH), in Air Quality Guidelines for Europe, WHO Regional Publications, European Series No. 23, World Health Organization, Regional Office for Europe, Copenhagen, pp. 105-117, 1987. 

This chapter provides a survey of the episodic peak ozone levels across Europe over the 1980-2009 period as recorded by the EMEP ozone monitoring network. The database of annual highest 8-h average ozone levels contains over 2,291 entries for 178 monitoring stations. All monitoring stations in almost all years show exceedance of the WHO air quality guideline of 50 ppb daily maximum 8-h average ozone level. 

World Health Organization (2006) Air quality guidelines. Global update 2005. WHO Regional Office for Europe, Copenhagen, Denmark... 

Fine particulate matter (PM) is well known to cause serious negative impacts on human health [1-4], As a consequence, ambient PM concentrations are regulated in many countries worldwide. For example, air quality standards for the mass concentration of particles with aerodynamic diameter less than 10 pm (PM10) are in the European Union set to 40 pg/m3 (annual mean) and 50 pg/m3 (daily mean). In the USA, the daily limit value forPMlOis 150 pg/m3 in addition, the mass concentration of the finer fraction of particulate matter PM2.5 is not allowed to exceed 35 pg/m3 (annual mean) and 15 pg/m3 (daily mean), respectively. The World Health Organization (WHO) has set air quality guideline values for the annual mean and daily mean concentrations of ambient PM10 (PM2.5) at 20 pg/m3 (10 pg/m3) and 40 pg/m3 (20 pg/m3), respectively [5]. 

World Health Organization (WHO) (2005) WHO air quality guidelines global update 2005. Report on a working group meeting, Bonn, 18-20 October 2005... 

WHO (2005) Air Quality Guidelines, Global update 2005, Particulate matter, World Health Organization, Geneva, Switzerland, http //www.euro.who.int/ information S ources / Publication s /Catalogue / 20070323 1 (accessed 11 May 2009). 

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