Outdoor air quality in urban areas

Setting the scene

The 7th EAP (EU, 2013) aims to significantly improve outdoor air quality and move closer to World Health Organization (WHO) guidelines (WHO, 2006) by 2020. Air pollution is the number one environmental cause of death in the EU, responsible for more than 400 000 premature deaths per year (EEA, 2017a). According to WHO studies (WHO, 2013, 2014), exposure to particulate matter (PM) can cause or aggravate cardiovascular and lung diseases, heart attacks and arrhythmias, affect the central nervous system and the reproductive system and cause cancer. Exposure to high ozone (O₃) concentrations can cause breathing problems, trigger asthma, reduce lung function and cause lung diseases. Exposure to nitrogen dioxide (NO₂) increases symptoms of bronchitis in asthmatic children and reduces lung function growth. Health-related external costs range from EUR 330 billion to EUR 940 billion per year, depending on the valuation methodology, with evidence on the impacts of chronic ozone exposure adding around 5 % to this total (EC, 2013).

Policy targets and progress

A chief cornerstone of the EU environmental acquis in the field of air quality is the Air Quality Directive (EU, 2008). This directive sets a number of air quality standards not to be exceeded by a certain year and thereafter.

The communication on the ‘Clean Air Programme for Europe’ (EC, 2013) sets the short-term objective of achieving full compliance with existing legislation by 2020 at the latest, as well as the long-term objective of seeing no exceedances of the WHO guideline levels for human health. The most troublesome pollutants in terms of harm to human health are particulate matter (PM), nitrogen dioxide (NO₂) and ground-level ozone (O₃) (EEA, 2016). The European air quality standards and the WHO air quality guidelines (WHO, 2006) for these pollutants are displayed in Table 1.

Table 1. Air quality standards, under the EU Air Quality Directive, and WHO air quality guidelines

Source: EU, 2008; WHO, 2006.

Note: 1. (*) Not considered in the indicator, where only the most stringent EU standards are used: the daily limit value for PM₁₀ and the annual limit value for NO₂. According to the WHO air quality guidelines, the annual average for PM takes precedence over the 24-hour average, since, at low levels, there is less concern about episodic excursions.
2. In line with the Air Quality Directive: ‘limit value’ shall mean a level fixed on the basis of scientific knowledge, with the aim of avoiding, preventing or reducing harmful effects on human health and/or the environment as a whole, to be attained within a given period and not to be exceeded once attained; ‘target value’ shall mean a level fixed with the aim of avoiding, preventing or reducing harmful effects on human health and/or the environment as a whole, to be attained where possible over a given period.

Figures 1 and 2 show the percentage of the urban population exposed to air pollutant concentrations above both EU standards (Figure 1) and WHO guidelines (Figure 2).

Figure 1. EU urban population exposed to air pollutant concentrations above selected air quality standards of the EU Air Quality Directive

Figure 2. EU urban population exposed to air pollutant concentrations above WHO air quality guidelines

Around one quarter of Europeans currently living in urban areas are exposed to air pollutant levels exceeding some EU air quality standards. Moreover, up to 96 % are exposed to levels of some air pollutants deemed damaging to health by the WHO’s more stringent guidelines (EEA, 2017b).

Particulate matter (PM)

Between 2006 and 2015, 8–16 % of the EU’s urban population is estimated to have been exposed to concentrations of fine particulate matter (PM_2.5) in excess of the EU limit value set for the protection of human health^[1] (Figure 1). With respect to the more stringent WHO guideline value (Figure 2), a much larger proportion of the urban population (82–97 %) was exposed to concentrations above this threshold.

Notwithstanding limitations in data coverage in the early 2000s, a significant proportion of the EU urban population (16–43 %) was exposed to concentrations of coarse dust particles (PM₁₀) in excess of the EU daily limit value set for the protection of human health during the 2000–2015 period (Figure 1). A slightly decreasing tendency can be observed throughout the whole period.

For the more stringent WHO guideline value (Figure 2), a higher proportion of the urban population (50–92 %) was exposed to concentrations above this threshold. Here, a decreasing tendency is also observed, as in the case of the EU limit value.

PM may be categorised as either primary (i.e. directly emitted to the atmosphere) or secondary (i.e. formed in the atmosphere from the so-called precursor gases). 

Primary PM originates from both natural and anthropogenic sources. The main emitter sector is ‘commercial, institutional and household fuel combustion’. For PM₁₀ ‘industry’ and ‘agriculture’ are listed in second and third place; and for PM_2.5 ‘transport’ and ‘industry’. All these sectors reduced their PM emissions in the EU in the 2000–2015 period, although higher relative reductions were observed for industry and transport and only small reductions were observed for the other two sectors.

With the exception of ammonia, in the EU, reductions in emissions of the other secondary PM precursors (nitrogen oxides, sulphur oxides, and non-methane volatile organic compounds) were much larger than those in emissions of primary PM from 2000 to 2015.

However, the reductions in both primary PM and precursors have not led to equivalent drops in the concentrations of PM. This is because chemical reactions of the precursors form secondary particles, and therefore the relationships between emissions and concentrations are not linear. It can also be explained by uncertainties in the reported emissions of primary PM from the ‘commercial, institutional and household fuel combustion’ sector, by intercontinental transport of PM and its precursor gases from outside Europe, and by the contribution of natural sources to PM concentrations (EEA, 2016).

The contributions of the different emission sources to ambient air concentrations depend not only on the amount of pollutant emitted, but also on proximity to source, emission conditions (such as height and temperature) and other factors, such as dispersion conditions and topography. Sectors with low emission heights, such as traffic and household fuel combustion, generally make a more significant contribution to surface concentrations than emissions from high stacks.

Ozone (O₃)

Although reductions in European emissions of O₃ precursors have led to lower peak concentrations of O₃, the current target value is frequently exceeded. In the 2000–2015 period, between 8 % (in 2014) and 55 % (in 2003) of the urban population was exposed to concentrations above the target value (Figure 1).

In relation to the more stringent WHO guideline (Figure 2), the proportion of the population exposed to concentrations above the guideline value is as high as 94–99 %, with no discernible change over time.

O₃ concentrations are determined by emissions of its precursors and by meteorological conditions: ozone is formed in sunny conditions with high temperatures. Apart from reductions in anthropogenic emissions of O₃ precursors, there have been increases in natural emissions and also in the intercontinental transport of O₃ and its precursors (Maas and Grennfelt, 2016). Additional factors that are also likely to mask the effects of European measures to reduce anthropogenic emissions of O₃ precursors include climate change, emissions of non-methane volatile organic compounds from vegetation (difficult to quantify) and fire plumes from forest and other biomass fires (EEA, 2010). Formation of tropospheric ozone from increased concentrations of methane may also contribute to the sustained O₃ levels in Europe.

Nitrogen dioxide (NO₂)

Between 2000 and 2015, the fraction of the urban population exposed to concentrations in excess of the EU limit value and the identical WHO guideline value gradually decreased to around 10 %, with a minimum of 7 % in 2014 (Figures 1 and 2). At 31 %, the highest exposure of the urban population to NO₂ occurred in 2003.

Enforcement of current legislation has resulted in a reduction in NO_x emissions in all sectors. Nevertheless, emissions from transport keep NO₂ concentrations high close to main roads.

Based on the current trends explained above, and because of their widespread exceedances in urban areas, it is unlikely that air quality standards for these pollutants will be met by 2020, while achieving air quality in line with the WHO guidelines is much further away (except for NO₂ for which both EU standard and WHO guideline are the same). Effective air quality policies require action and cooperation on global, European, national and local levels, which must reach across most economic sectors and engage the public. Holistic solutions must be found that involve technological development, structural changes — including the optimisation of infrastructures and urban planning — and behavioural changes. These will be necessary to deliver a level of air quality across the EU that is conducive to the protection of human health (EEA, 2016).

Country level information

Table 2 provides information on the urban population exposed to concentrations of air pollutants above the EU air quality objectives by country for the year 2015. Variations from country to country are not only related to the different pollutant concentrations but also to:

• the number of available data series (monitoring stations and/or selected cities), which will influence the total monitored population;
• the uneven distribution of traffic and background stations in the different countries.

Table 2. Urban population exposed to concentrations of air pollutants above selected air quality standards of the Air Quality Directive, 2015

Note: NA = no available data, for further information please see indicator CSI004.
Source: Air pollution country fact sheets (EEA, 2014) updated with 2015 data. The 2015 data aggregated at EU level are also available in (EEA, 2017a, 2017c).

Outlook beyond 2020

In 2013, the European Commission proposed a Clean Air Policy Package for Europe (EC, 2013), which aims to achieve full compliance with existing air quality legislation by 2020 and to further improve Europe’s air quality by 2030 and beyond. As a result of this package, the 2001 National Emission Ceilings Directive (EU, 2001) was reviewed. The new National Emission Ceilings Directive (EU, 2016) establishes national emission reduction commitments applicable from 2020 and stricter commitments from 2030 for sulphur dioxide, nitrogen oxides, non-methane volatile organic compounds, ammonia and PM_2.5. In addition, and as part of the package, a new directive, the Medium Combustion Plant Directive, was approved in November 2015 (EU, 2015). This directive regulates sulphur dioxide, nitrogen oxides and dust emissions from the combustion of fuels in medium-sized combustion plants (with a rated thermal input of 1 and up to 50 megawatts).

These new commitments, together with the on-going implementation of air quality improvement measures at national, regional and local levels, are expected to improve air quality in Europe. However, the changes in meteorological conditions due to climate change are expected to increase O₃ concentrations as a result of expected increased emissions of both specific O₃ precursors and emissions from wildfires, with the latter likely to increase under periods of extensive drought (EEA, 2015).

Finally, it is expected that the age group composition of the EU population will continue to shift towards higher numbers of the elderly because of continuing increases in life expectancy (Eurostat, 2016). The overall potential air pollution-related health impact of this change remains uncertain.

About the indicator

This indicator shows the proportion of the EU urban population that is exposed to various potentially harmful concentrations of pollutants in excess of both EU standards and WHO guidelines set for the protection of human health. For further information on the methodology, please refer to the EEA indicator CSI004 ‘Exceedance of air quality standards in urban areas (EEA, 2017b).

The indicator focuses on those pollutants that are most relevant in terms of health effects and urban concentrations: PM, both PM₁₀ and fine PM, i.e. PM_2.5; O₃; and NO₂. When there is more than one standard, only the most stringent one is used. The indicator is based on measurements of air pollutants reported under the Air Quality Directive (EU, 2008) and the Decision on the exchange of information (EU, 2011).

Most air pollution is man-made and derives from the combustion of fossil or biomass fuels used in industry, transport and heating; industrial and agricultural processes; and other sources (EEA, 2017a). As most of these sources, particularly emissions from cars, are concentrated in urban areas where most of the European population lives, air quality in urban areas is a useful proxy for tracking progress towards meeting the standards set out in the Air Quality Directive.

References

[1]    Please note that this year’s scoreboard assessed the past trend for fine particulate matter exceedances (2006-2015) as an improving trend, i.e. it was depicted by a green triangle. Last year’s scoreboard assessed the past trend (2006-2014) as unclear, i.e. it was depicted by a yellow triangle. This is because this year with an additional year of data the time series was considered by the experts sufficiently long to judge the past trend and to therefore conclude that it was improving.

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