Urban Air Quality in Europe

The Directive on ambient air quality and cleaner air for Europe (2008/50/EC) requires compliance with limit values inter alia for PM₁₀ and nitrogen dioxide (NO₂), to be achieved by Member States by 2005 and 2010, respectively. Member States have been allowed to postpone compliance with these limit values until 2011 and 2015, respectively, under certain conditions.

Within Europe there are several regions where compliance with these limit values is expected to be very difficult even after the postponement period.

In this study criteria for the identification of such critical areas have been developed, and the respective areas are described.

A subset of these areas has been selected and analysed in more detail. Critical factors that hamper compliance in these selected areas have been identified. These include adverse dispersion conditions, sheer size of agglomerations, emission densities from traffic, industry, domestic heating, and deficiencies in air quality assessment and management.

For the selected areas air quality management approaches have been analysed and suggestions for suitable courses of action are made, based on these findings.

Road transport is the largest contributor to NO_x emissions in the EU. This chapter discusses NO_x formation mechanisms, control strategies, trends in emissions and possible future developments. Control strategies include vehicle emission legislation, engine design, exhaust after-treatment, modification of fuel properties, alternative fuels and new powertrain technologies. Calculations show that NO_x emissions from the sector decreased substantially between 1990 and 2010. Such calculations are based on the assumption that the systematic tightening of emission limits has been effective. However, there is evidence that modern diesel vehicles are not delivering the expected reductions in emissions during real-world driving. Moreover, diesel vehicles emit more NO_x than petrol vehicles (with a larger proportion of “primary” NO₂), and their market share has increased in many countries. These factors partly explain the observation that ambient NO₂ concentrations continue to exceed health-based limits in urban areas. Up to 2020 there is a need for a more effective regulation of emissions, and the chapter proposes several measures that can be taken. Beyond 2020 emissions of NO_x from the sector will depend on the market penetration of low-carbon technologies.

Episodic peak ozone levels in rural areas have been declining during the last three decades due to regional pollution emission controls applied to the VOC and NO_x emissions from petrol-engined motor vehicles. Long-term downwards trends have been observed at many long-running rural monitoring stations in the EMEP ozone monitoring network. Downwards trends appear to be more pronounced at those stations where initial episodic peak levels were highest and insignificant at those stations where initial levels were lowest. This behaviour has been interpreted as resulting from the combined effect of regional pollution controls and increasing hemispheric ozone levels. Hemispheric ozone levels have been steadily rising in the northern hemisphere because of growing man-made emissions of tropospheric ozone precursors. Episodic ozone levels in major European towns and cities are rising towards the levels found in the rural areas surrounding them, as exhaust gas catalysts fitted to petrol-engined motor vehicles reduce the scavenging of ozone by chemical reaction with emitted nitric oxide.

Since the beginning of the last century, European air has received increasing amounts of organic compounds. Some of them were released as consequence of combustion processes and others were synthesised for specific applications in industry or agriculture. A group of these organic compounds are semi-volatile, resistant to degradation processes, bioaccumulative and toxic. Because of these properties, they are grouped under the general name of persistent organic pollutants (POPs). These physical–chemical properties are found in polycyclic aromatic hydrocarbons or in organic molecules with 5–12 carbon atoms and a high degree of halogen substituents. The present chapter is devoted to describe these two groups of compounds. However, in other review papers, only the organohalogen compounds are considered under the POP concept.

The properties of semi-volatility, bioaccumulation and persistent to degradation processes provide a potential for long-range atmospheric transport of these compounds. They may therefore be deleterious for the ecosystems and human health even in sites located far away from the areas of production and application. Furthermore, nearly all organohalogen POPs are man-made. In nature, there are no compounds with similar chemical structure (or these are in very low concentrations). Thus, human and animal evolution has not had the opportunities to generate specific metabolic ways for their elimination. Thus, they accumulate and remain in the body throughout all life and during all life stages (including in utero development). By the end of the twentieth century, international protocols have been established to reduce the emissions and impact of POPs into the environment and humans.

The following chapter describes the changes in concentration of POPs in ambient air in Europe through time, with a focus on current concentrations. It also describes the differences in physical–chemical properties of these pollutants and relates them with the mechanisms of atmospheric transport. Strategies to reduce the ambient air concentrations are discussed. Information is also given on future perspectives in view of “emerging” pollutants and emission sources.

Each year large areas of forested land in Europe are burned by more than 50,000 fires. Over the past few years, climatic anomalies in temperature and precipitation have resulted in an increase in fire events. The exceptional fire occurrences in the 2000s and their regional consequences on atmospheric air quality have been observed in the northern European regions. In the last 10 years almost annually the episodes of long-range transported (LRT) biomass smokes from Eastern European fires have been reported, exceptionally intense smoke plumes having been detected in 2002 and 2006. Typically, the smoke episodes occur in spring or/and late summer and they last for few days. As the particulate matter (PM) concentrations are generally quite low in Northern Europe, the LRT smoke plumes increase the PM concentrations in several folds even at the background sites with no local emissions. As a result, there are exceedances in the European Union PM daily limit values, which result in serious health problems. This chapter describes the episodes of wildfire particles observed in Northern Europe in the last 10 years. It discusses the chemical and physical properties of particles, the transformation during the transport as well as the methods to investigate the composition and source areas of smoke plumes.

Residential wood burning is one of the important sources of ambient particulate matter (PM) in many European regions. Besides total PM, residential wood burning is at many locations an important source of other air pollutants such as polycyclic aromatic hydrocarbons (PAHs), benzene, particulate organic carbon (OC), and black carbon (BC), especially in regions such as the Alpine region, where wood fuel is, on one hand, traditionally used for domestic heating during the cold season in small stoves and, on the other hand, meteorological conditions during winter are often favourable for accumulation of wood smoke in a shallow boundary layer. As a consequence, wood burning in the Alpine region can be the dominating source of PM, OC, and BC during the cold season. This is true for both larger cities and small villages in rural areas. The absolute contribution of wood burning emissions to particulate air pollutants tends in rural environments to be even larger than in urban areas. This chapter gives an overview about the results of studies on ambient particulate pollutants from residential wood burning in the Alpine region.

Ammonia emissions are mainly related to agricultural activities, and depositions related to these emissions constitute a treat to local ecosystems but possibly also to human health through the contribution for formation of secondary fine fraction particles in ambient air. European ammonia emissions are highly heterogeneously distributed, and the temporal variations in these emissions follow very different pattern as a result of differences in climate but also as a results of significant differences in agricultural practice over Europe. A minor fraction of ammonia emission is related to nonagricultural sources, especially traffic. These sources are mainly found in areas with intense traffic and the use of catalyst converters. Simple and comprehensive models for the spatial and temporal variation in ammonia emissions have been shown useful in modelling of atmospheric nitrogen input to sensitive ecosystems for assessments of critical loads. For the spatial distribution various emission inventories are available at different resolutions. These inventories are derived using different approaches, and as a result they can differ up to a factor of two for certain areas. The overall European ammonia emissions are decreasing as a result of regulation related to the National Emission Ceiling Directive (NEC) and the Integrated Pollution Prevention and Control (IPPC) directive, regulation that has been implemented in national legislation in the single European countries. Some countries have adopted screening methods to be used by local authorities when assessing impact on local ecosystems in relation to applications from farmers to obtain permissions to increase agricultural production. In general Northern European countries have more strict regulation of ammonia emissions compared with Central and Southern European countries.

Gaseous and particulate emissions from vehicles represent a major source of atmospheric pollution in cities. Recent research shows evidence of, along with the primary emissions from motor exhaust, important contributions from secondary (due to traffic-related organic/inorganic gaseous precursors) and primary particles due to wear and resuspension processes. Besides new and more effective (for NO_x emissions) technologies, non-technological measures from local authorities are needed to improve urban air quality in Europe.

Methodologies and results of approaches used for the source apportionment of particulate matter in Germany are reviewed. Due to the relatively large number of interested parties and stakeholders, in particular the 16 German Federal States and the Federal Environment Agency, the information was found to be quite dispersed.

Based on the PM levels measured in the state monitoring networks the incremental increase of PM from rural to hot-spot conditions is one of the most widely investigated aspects. As a general conclusion a large-scale PM10 background contribution of ca. 50% appears to be typical, with the other 50% originating from urban and local (traffic, industrial) influences. Combination of this spatial information with emission registers reveal detailed information on the shares of the various sources; however, PM formation processes not included in the emission inventories as well as trans-boundary impacts are neglected in such analyses. Complementary information thus is provided by receptor models and chemical dispersion models, both showing significant importance of secondary aerosol formation and, especially in the eastern part of the country, transboundary intrusion.

Many source categories have been investigated in more detail and are presented in separate sections, as e.g. exhaust and non-exhaust traffic emissions and domestic wood combustion.

The Eastern Mediterranean Basin, EMB, is characterised as an air pollution hotspot, located at a crossroad of air masses coming from Europe, Asia and Africa. The Eastern Mediterranean region is subject to several inputs of natural and anthropogenic pollutants that are generated from numerous regional and local sources. Pollution in the area results from industrial and traffic sources and domestic heating mostly from Europe, Balkans and the Black Sea. In addition dust storms coming mainly from the Sahara desert and to a lesser extent from the Middle East transport high quantities of mineral aerosols which increase significantly the levels of particulate matter. Forest fires and agricultural burning emissions are also affecting the area during the dry season. Moreover, marine aerosols and ship emissions originated from the highly busy shipping routes of the Mediterranean Sea are considered to be an important contributor to the EMB aerosol burden. Finally, other specific features of the Mediterranean Basin such as the high radiation intensity all year long and the high temperature significantly enhance the formation of secondary aerosols.

This study focuses on north-western region of Europe discussing questions like the following: Which anthropogenic and natural constituents build up the particulate matter? To what extent do they contribute to the total mass? And where do these constituents originate? To answer, we elaborated data sets containing chemical information of PM recently becoming available in the Netherlands, Germany and Belgium.

The chemical composition of PM10 shows a considerable conformity in these countries. Always, secondary inorganic aerosols (SIA) are the major constituent (±40%) followed by the carbonaceous compounds (±25%). Contributions of sea salt and mineral dust vary between 10% and 15% depending on presence and distance of respective sources. The unidentified mass is some 15% indicating that the composition of PM10 in this region is fairly well known.

PM10 concentrations and constituents appear systematically higher at urban sites. Urban increments have been measured for most chemical constituents. Nearby (anthropogenic) sources and reduced dispersion in the urbanised areas are the main determining factors here. The observed increment for SIA is caused by more nitrate and sulphate. It is explained by depletion of chloride stabilising part of the nitrate and sulphate in the coarse mode. The question then arises how to assign the coarse mode nitrate (and sulphate) in the mass closure exercise as they replace the chloride.

Important for the national and European air pollution policy is how much of the measured particulate matter is of anthropogenic origin. A simple assessment indicates that 20–25% of PM10 is of natural origin; hence, the majority of PM10 in the north-western-European region is of anthropogenic origin. The uncertainty in this analysis is considerable, and the result is indicative.

A chemical transport model (LOTOS-EUROS) was used to obtain a detailed source apportionment. In total, 75% of the modelled PM10 mass could be explained. The important contributions to PM10 come from agriculture, on- and off-road transport and natural sources (sea salt). Secondary contributions are derived from power generation, industrial processes and combustion as well as households. Of the modelled part, 70–80% of PM10 over the Netherlands is anthropogenic. The increase in source contribution going from low to high PM levels is proportional for most sectors, except for agriculture and transport, which become more important mainly due to the more than proportional rise in ammonium nitrate concentrations. Sea-salt concentrations decline with rising PM10. The same was found for Spain, but here, the impact of Saharan dust on PM episodes is clearly recognisable and much larger than in north-western Europe. Natural sources in Spain contribute about half of the modelled PM10 concentrations. Significant anthropogenic sources are similar to those in north-western Europe.

Recent estimates delivered by the European Environment Agency indicate that exposure to atmospheric particulate matter (PM) causes approximately three million deaths per year in the world. Exceedances of PM thresholds have been reported by the majority of the European Union member countries, mainly in urban agglomerations where human exposure is also higher.

Health effects of air pollution, namely of PM levels, are the result of a chain of events, going from the release of pollutants that lead to an atmospheric concentration, over the personal exposure, uptake, and resulting internal dose to the subsequent health effect.

The focus of this chapter will be on PM ambient concentrations as input for population exposure estimation, which are key variables for exposure models, and are generally measured at air quality monitoring stations or estimated by an adequate air quality modelling system. This chapter critically overviews PM modelling activities going on in Europe in the scope of exposure assessment, identifying advantages and gaps and recommending future uses and developments.

Current ambient air quality monitoring is solely based on fixed monitoring sites, not always reflecting the exposure and effects on humans. This article reviews the current situation in Europe, the USA and Asia and discusses the main differences and similarities. Based on the analysis of the relation between monitoring techniques and strategies as well as the analysis of current trends and developments in monitoring strategies, new concepts and directions of future urban monitoring networks and strategies are presented and discussed.

The aerosol particle number size distribution is a key component in aerosol indirect climate effects, and is also a key factor on potential nanoparticle health effects. This chapter will give background on particle number size distributions, their monitoring and on potential climate and health effects of submicron aerosol particles. The main interest is on the current variability and concentration levels in European background air.

The submicron particle number size distribution controls many of the main climate effects of submicron aerosol populations. The data from harmonized particle number size distribution measurements from European field monitoring stations are presented and discussed. The results give a comprehensive overview of the European near surface aerosol particle number concentrations and number size distributions between 30 and 500 nm of dry particle diameter. Spatial and temporal distributions of aerosols in the particle sizes most important for climate applications are presented. Annual, weekly, and diurnal cycles of the aerosol number concentrations are shown and discussed. Emphasis is placed on the usability of results within the aerosol modeling community and several key points of model-measurement comparison of submicron aerosol particles are discussed along with typical concentration levels around European background.

Human exposure to air pollutants is often characterized by measured or modeled outdoor concentrations. In Western societies, subjects spend about 90% of their time indoors, of which a large fraction in their own home. Hence indoor air quality is an important determinant of the true personal exposure for many components. Indoor air quality is affected both by infiltration of outdoor air in buildings and indoor sources such as smoking, gas cooking, and use of consumer products. In this chapter we separately describe the impact of indoor sources and outdoor air on indoor pollution. We first illustrate differences in outdoor and personal exposure using data on real-time particle number concentrations from a recent study in Augsburg, Germany. We then present a model of indoor PM concentrations, illustrating the factors that affect indoor air quality. We summarize empirical studies that have assessed indoor–outdoor relationships for particle mass, particle number, and specific components of particulate matter.

Outdoor air pollution significantly infiltrates in buildings. Combined with the large fraction of time that people typically spend indoors, a major fraction of human exposure to outdoor pollutants occurs indoors. Understanding the factors affecting infiltration is therefore important. Infiltration factors have been shown to vary substantially across seasons, individual homes and particle size and components. Important factors contributing to these variations include air exchange rate, characteristics of the building envelop (e.g., geometry of cracks), type of ventilation, and use of filtration. Penetration and decay losses are particle size dependent with the lowest losses for submicrometer particles and higher losses for ultrafine and especially coarse particles. The largest infiltration factors are consistently found for sulfate and black carbon. Volatilization and chemical decay may also result in losses of specific components, including nitrates and organic components. The large variability of PM_2.5 infiltration factors reported may further be due to different composition of PM across locations. In locations with relatively high sulfate and EC contributions, higher infiltration factors can be anticipated than in locations with high nitrate and OC concentrations.

Atmospheric nanoparticles are a pollutant currently unregulated through ambient air quality standards. The aim of this chapter is to assess the environmental and health impacts of atmospheric nanoparticles in European environments. This chapter begins with the conventional information on the origin of atmospheric nanoparticles, followed by their physical and chemical characteristics. A brief overview of recently published review articles on this topic is then presented to guide those readers interested in exploring any specific aspect of nanoparticles in greater detail. A further section reports a summary of recently published studies on atmospheric nanoparticles in European cities. This covers a total of about 45 sampling locations in 30 different cities within 15 European countries for quantifying levels of roadside and urban background particle number concentrations (PNCs). Average PNCs at the reviewed roadside and urban background sites were found to be 3.82 ± 3.25 × 10⁴ and 1.63 ± 0.82 × 10⁴ cm⁻³, respectively, giving a roadside to background PNC ratio of ~2.4. Engineered nanoparticles are one of the key emerging categories of airborne nanoparticles, especially for the indoor environments. Their ambient concentrations may increase in future due to widespread use of nanotechnology integrated products. Evaluation of their sources and probable impacts on air quality and human health are briefly discussed in the following section. Respiratory deposition doses received by the public exposed to roadside PNCs in numerous European locations are then estimated. These were found to be in the 1.17–7.56 × 10¹⁰ h⁻¹ range over the studied roadside European locations. The following section discusses the potential framework for airborne nanoparticle regulations in Europe and, in addition, the existing control measures to limit nanoparticle emissions at source. The chapter finally concludes with a synthesis of the topic areas covered and highlights important areas for further work.