Air quality indicators: long term health effects

Sector Air quality, health
Description Estimated 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.
End User Health authorities, environmental authorities, general public
Calculation method

Population data have been obtained for each city, region or country. For Stockholm national data for 2012, with a spatial resolution of 100×100 m2, have been obtained from Swedish statistics. For Bologna and Amsterdam/Rotterdam,  a 1 * 1 km2 population grid disaggregated data has been applied (Gallego 2010).  

Baseline mortality in age group 30+ for the city or region is used in combination with population exposure data for the city according to the HIA tool AirQ developed by WHO (2004), where the attributed mortality is calculated as
∆Y = (Y0 * P) * (eβ*X – 1),
where Y0 is the baseline rate; P the number of exposed persons; β the exposure-response relationship (relative risk) and X the estimated mean exposure (with impact/above any assumed threshold).

The data on baseline mortality are from national official sources, for Stockholm from Swedish statistics, for Bologna from the Bologna province statistics and for Amsterdam from Centraal Bureau voor de Statistiek. The estimated mortality is presented both for a normalized population of 100 000 inhabitans on each grid (without using local population data from the city, the impact reflecting the concentrations only) and as mortality based on local population data.

Final relative risks (RRs) – see motivation below – are for PM2.5  1.062 per 10 µg m-3 and for NO2  1.025 per 10 µg m-3 without the use of any threshold (cut-off). The indicator also follows the COMEAP recommendation to compensate an effect overlap by reducing the RR for NOby up to 33% when impacts associated with PM2.5 are summed together with the estimates for NO2.

ID Title Period Statistical processing Unit Threshold Comment
mortNO2y Annual deaths due to NO2 long-term exposure  yearly  See above deaths per year    
mortNO2ynorm Annual deaths per 100 000 inh due to NO2 long-term exposure  yearly  See above deaths per year/100 000    
mortPM25y Annual deaths due to PM2.5 long-term exposure   yearly  See above deaths per year    
mortPM25ynorm  Annual deaths per 100 000 inh due to PM2.5 long-term exposure  yearly  See above deaths per year/100 000    
mortNO2PM25yearly Annual deathts due to NO2 and PM2.5 long-term exposure yearly See above deaths per year    
mortNO2PM25ynorm  Annual deaths per 100 000 inh due to NO2 and PM2.5 long-term exposure  yearly  See above deaths per year/100 000    
Provenance This indicator is based on output from the MATCH model
Validation The downscaling made by MATCH in Urban SIS has been validated against observations in Urban SIS deliverable 5.2, where an overview is given in Table 4.
Calculation caveats Spatial representation: S2, S3
Other caveats:
Could be compared to:
Could be used with:

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.

However, the REVIHAAP report concludes that  more studies have now been published showing associations between long-term exposure to NO2 and mortality (WHO 2013a). This observation makes it more complicated for impact assessments from vehicle exhaust particles as the close correlation between long-term concentrations of NO2 and exhaust particles make it difficult to separate the effects without measuring EC instead of PM2.5.

The potential confounding problem of effects from NO2 and PM2.5 on mortality was the focus of 19 epidemiological long-term studies of mortality using both pollutants as exposure variable reviewed by Faustini et al. (2014). Studies with bi-pollutant analyses (PM2.5 and NO2) in the same models showed decrease in the effect estimates of NO2, but still suggest partly independent effects. The greatest effect on natural or total mortality was observed in Europe for both NO2 and PM2.5. In Europe, there was a 7% increase in total mortality for both NO2 and fine particles, the RR for NO2 was 1.066 (95% CI 1.029-1.104) per 10 μg m-3 and RR for PM2.5 was 1.071 (95% CI 1.021-1.124) per 10 μg m-3.

After judging evidence (and introduction of a group B with more uncertainty), the HRAPIE project recommend to calculate a long-term effect on mortality of NO2 in the age category 30+, added to the impacts estimated using the common RR associated with all PM2.5 (WHO 2013b). HRAPIE recommend to calculate this impact over the annual mean 20 μg m-3, applying a RR of 1.055 (95% CI 1.031-1.08) per 10 μg m-3 based on a meta-analysis of 11 studies (Hoek et al. 2013).

COMEAP (2015, UK Committee on the Medical Effects of Air Pollutants) provide interim recommendations on how to estimate the mortality effects associated with long-term average concentrations of NO2 in UK using a RR of 1.025 (1.01-1.04) per 10 μg m-3 without any threshold (cut-off level). In addition, COMEAP discuss that it is possible that this RR should be reduced by up to 33% when impacts associated with PM2.5 are added to the estimates for NO2.

Experience user  

COMEAP 2015: Interim Statement on quantifying the association of long-term average concentrations of nitrogen dioxide and mortality. Public Health England, COMEAP: reports and statements. m_Statement.pdf

EMRC/IIASA 2014: Implementation of the HRAPIE Recommendations for European Air Pollution CBA work. Mike Holland, EMRC.

ExternE 1999: ExternE – Methodology 1998 update. European Comission. ISBN 92-828-7782-5

ExternE 2005: Externalties of Energy – Methodology 2005 Update. Ed. P Bickel and R Friedrich, European Commission EUR 21951.

Faustini A, Rapp R, Forastiere F 2014: Nitrogen dioxide and mortality: review and meta-analysis of long-term studies. Eur Respir J. Eur Respir J. 44:3,744-53.

Gallego FJ 2010: A population density grid of the European Union. Population and Environment. 31:6, 460-473.

Héroux ME, Anderson HR, Atkinson R, Brunekreef B, Cohen A, Forastiere F, Hurley F, Katsouyanni K, Krewski D, Krzyzanowski M, Künzli N, Mills I, Querol X, Ostro B, Walton H 2015: Quantifying the health impacts of ambient air pollutants: recommendations of a WHO/Europe project. Int J Public Health.60:5, 619-27.

Hoek G, Krishnan RM, Beelen R, Peters A, Ostro B, Brunekreef B, Kaufman JD 2013: Long-term air pollution exposure and cardio-respiratory mortality: a review. Environmental Health 12:43.

Janssen NA, Hoek G, Simic-Lawson M, Fischer P, van Bree L, ten Brink H, Keuken M, Atkinson RW, Anderson HR, Brunekreef B, Cassee FR 2011: Black carbon as an additional indicator of the adverse health effects of airborne particles compared with PM10 and PM2.5.  Environ Health Perspect. 119:12,1691-9. doi: 10.1289/ehp.1003369.

Jerrett M, Burnett RT, Ma R, Pope CA 3rd, Krewski D, Newbold KB, Thurston G, Shi Y, Finkelstein N, Calle EE, Thun MJ 2005: Spatial analysis of air pollution and mortality in Los Angeles. Epidemiology. 16:6, 727-36.

Pope CA, III, Thun MJ, Namboodiri MM, Dockery DW, Evans JS, Speizer FE, Heath CW Jr 1995: Particulate air pollution as a predictor of mortality in a prospective study of U.S. adults. Am. J. Respir. Crit. Care Med. 151: 669-674.

WHO 2003: Health Aspects of Air Pollution with Particulate Matter, Ozone and Nitrogen Dioxide, World Health Organisation, Copenhagen. WHO 2004: Tools for health impact assessment of air quality: the AirQ 2.2 software. software

WHO 2006a: Air Quality Guidelines Global Update 2005, Copenhagen.

WHO 2006b: Health risks of particulate matter from long-range transboundary air pollution. Copenhagen.

WHO 2007: Health relevance of particulate matter from various sources. Report on a WHO Workshop Bonn, Germany, 26- 27 March 2007.

WHO 2013a: Review of evidence on health aspects of air pollution – REVIHAAP Project Technical Report. Copenhagen

WHO 2013b: Health risks of air pollution in Europe – HRAPIE. Recommendations for concentration-response functions for cost-benefit analysis of particulate matter, ozone and nitrogen dioxide. Copenhagen WHO 2016. European Health For All.