4.3.4 AQElong – Air quality indicators: long term health effects
Version 4.2 by Emily West on 2022/01/10 14:39
AQElong – Air quality indicators: long term health effects
| Topic | Urban challenges | Sub-challenges |
|---|---|---|
| Social | 4 - Public Health and Well-Being | 4.3 - Health |
Description | The ALE estimates the number of deaths in age group 30+ associated with long-term exposure to urban background levels of PM2.5 and NO2. Relative risks based on recommendations from WHO HRAPIE Project (WHO, 2013b) regarding PM2.5 and UK COMEAP (2015) regarding NO2. Estimates are presented both separately and combined for exposure to both pollutants.It has long been recognized that particle concentrations correlate with mortality, both temporally (short-term fluctuations) and spatially based on mortality and survival (WHO 2003, WHO 2006a). Short term effects are usually assumed to be included in the long-term impacts on mortality. Particles in ambient air (indicated by PM2.5) are one of the major causes of preterm death in Europe, but also exposure to NO2 and ozone has been associated with mortality. The WHO Review of evidence on health aspects of air pollution (REVIHAAP, WHO 2013a), concludes that recent long-term studies are showing associations between PM and mortality at levels well below the current annual WHO air quality guideline level for PM2.5 (10 µg m-3). The WHO expert panel thus concluded that for Europe it is reasonable to use linear exposure response functions, at least for particles and all-cause mortality, and to assume that any reduction in exposure will have benefits. The findings from REVIHAAP are used as a basis for the WHO Project Health risks of air pollution in Europe – HRAPIE (WHO 2013b). The conclusions from the HRAPIE project (Heroux et al. 2015) are implemented in costbenefit calculations done by EMRC/IAASA for the European Union. For the WHO HRAPIE impact assessment (WHO 2013b) for long-term exposure to PM2.5 and all cause (natural) mortality in ages 30+ recommended use of exposure-response function from a meta-analysis of 13 cohort studies (Hoek et al. 2013). The RR for PM2.5from this meta-analysis was 1.062 (95% CI 1.040-1.083) per 10 µg m-3 is similar to the 1.06 per 10 µg m-3 increment of the annual average PM2.5 of the American Cancer Society Cohort Study (Pope et al. 1995). This assumption (6% per 10 µg m-3) has been used in many health impact assessments. Although, different types of particles and reasoning explain the impacts on mortality (WHO 2007, WHO 2013a), the WHO REVIHAAP panel of experts consider current knowledge does not allow precise quantification of the health effects of PM emissions from different sources. Current risk assessment should consider particles of different: sizes, sources and composition, as equally hazardous to health (WHO 2007). Practice has treated both PM10 and fine fraction PM2.5 (quite often considered to be more detrimental to health than the coarse fraction of PM10) as being equally toxic by mass, irrespective of the origin. Thus, commonly exposure-response functions obtained using urban background PM2.5 as the exposure indicator are converted to be used for PM10 through a factor based on their mass relation. In the new impact assessment HRAPIE no such conversion is recommended for PM10 and mortality. Different types of PM have been assumed to influence mortality differently; e.g., ExternE3 (2005) includes assumptions about the toxicity of other different types of PM. This reflects results that indicate a higher toxicity of combustion particles, especially from internal combustion engines. They treat nitrates as equivalent to half the toxicity of PM10, sulphates as equivalent to PM10, primary particles from power stations as equivalent to PM10, and primary particles from vehicles as equivalent to 1.5 the toxicity of PM2.5. Effects of combustion-related particles have been studied using black smoke, black carbon (BC) or elemental carbon (EC) as the exposure variable. REVIHAAP (WHO 2013a) recommended that BC should be used as exposure variable in more studies, but did not recommend it to be used for the HRAPIE impact calculations (WHO 2013b). A review of mortality and long term exposure to the combustion-related particle indicators (Hoek et al. 2013) used different methods. Their relation and conversion factors have been described before (Janssen et al. 2011). All cause mortality was significantly associated with EC, the meta analysis resulted in a (relative risk) RR of 1.061 per 1 µg m-3 EC (95% CI 1.049-1.073), with highly non-significant heterogeneity of effect estimates. Most of studies assessed EC exposure without accounting for small-scale variation related to proximity to major roads. These results suggest that using the common RR for long-term exposure to PM2.5 and mortality, may lead to an underestimation of impacts of particle mass from motor vehicle exhaust. |
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