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Particulate matter (PM) accounts for a complex group of air pollutants with properties and impacts that vary according to its composition and size. The emission rates, size and composition of primary PM emissions are challenging to determine since they depend not only on the sector considered, but also on the fuel properties, technology and other characteristics of the emission process. At the European level, fine carbonaceous particles are generally the dominant components of primary PM emissions, the most important sources of organic and black carbon being residential biomass combustion and diesel vehicle engines, respectively. On the other hand, soil particles generated by wind erosion processes, traffic resuspension, mining and construction operations, and agricultural land management activities are large contributors to the coarse fraction of primary PM emissions. European PM emissions are decreasing as a result of implemented EU legislation mainly focused on road transport and large point sources. Nevertheless, emissions released by residential solid fuel appliances have been increasing due to a lack of regulations, a tendency that is expected to change with the eco-design directive. The decrease of traffic PM exhaust emissions has also increased the importance of traffic non-exhaust emissions, a major source of metals in urban areas.

Particulate matter (PM) is a generic term used to describe a mixture of solid particles and liquid droplets (aerosols) that vary in size and composition, depending on the location and time1  (Table 1).

Table 1

Sources of origin and main components of coarse PM10–2.5, fine PM2.5 and ultrafine PM0.1 primary particles.a

PM fractionSources of originMain componentsContribution
Coarse particles (PM10–2.5Agricultural activities Agricultural soil, OC +++ 
 Traffic resuspension Road dust +++ 
 Windblown dust/construction and mining activities/industrial resuspension Si, Al, Ti, Fe +++ 
 Tyre and brake wear Cu, Zn ++ 
 Combustion in energy and manufacturing industries (coal, coke, heavy oil) EC ++ 
 Wind-land fires and volcanoes Volcanoes’ ashes, burned OC 
 Biological sources Plant debris and fungal spores 
 Ocean spray Na, Cl, Mg 
  
Fine (PM2.5) and Diesel-fuelled vehicle engines BC +++ 
Ultrafine particles (PM0.1Biomass combustion OC, PAHs +++ 
 Maritime traffic BC, OC, SO4−2 ++ 
 Combustion in energy and manufacturing industries Pb, Cd, As, Cr, V, Ni, Se, SO4−2 ++ 
 Processes in non-metallic industries Si, Al, Fe 
 Metal processing activities Pb, Cd, Cr, Zn 
PM fractionSources of originMain componentsContribution
Coarse particles (PM10–2.5Agricultural activities Agricultural soil, OC +++ 
 Traffic resuspension Road dust +++ 
 Windblown dust/construction and mining activities/industrial resuspension Si, Al, Ti, Fe +++ 
 Tyre and brake wear Cu, Zn ++ 
 Combustion in energy and manufacturing industries (coal, coke, heavy oil) EC ++ 
 Wind-land fires and volcanoes Volcanoes’ ashes, burned OC 
 Biological sources Plant debris and fungal spores 
 Ocean spray Na, Cl, Mg 
  
Fine (PM2.5) and Diesel-fuelled vehicle engines BC +++ 
Ultrafine particles (PM0.1Biomass combustion OC, PAHs +++ 
 Maritime traffic BC, OC, SO4−2 ++ 
 Combustion in energy and manufacturing industries Pb, Cd, As, Cr, V, Ni, Se, SO4−2 ++ 
 Processes in non-metallic industries Si, Al, Fe 
 Metal processing activities Pb, Cd, Cr, Zn 
a

+++ High contribution; ++ Medium contribution; + Low contribution.

PM is made up of a large number of components, including elemental or black carbon (BC) and organic carbon (OC) compounds, sulfate (SO4−2), nitrate (NO3), trace metals, crustal material (i.e. soil particles) and sea salt.2  PM also comes in a wide range of sizes and includes PM with diameter less than or equal to 10 μm (PM10), PM with diameter less than or equal to 2.5 μm (PM2.5), also denoted as fine particles, PM with diameter less than or equal to 0.1 μm (PM0.1), also denoted as ultrafine particles (UFP), and PM with diameter less than or equal to 0.05 μm (PM0.05), also denoted as nanoparticles.3 

In terms of source of origin, PM can be directly emitted from anthropogenic (man-made) or natural sources (i.e. primary PM), or formed in the atmosphere from a series of gaseous combustion by-products such as volatile organic compounds (VOCs), ammonia (NH3), oxides of sulfur (SOx) and oxides of nitrogen (NOx) (i.e. secondary PM). Primary PM originates predominantly from combustion (e.g. vehicle engines) and high-temperature processes (e.g. smelting and welding industrial operations),4,5  as well as from mechanical disruption processes and man- or wind-induced events causing suspension of particles (e.g. traffic resuspension of street dust).6,7  On the other hand, secondary PM is formed by gas-to-particle conversion in the atmosphere and/or condensation of gaseous compounds on pre-existing aerosol particles, mainly involving NOx, SOx, NH3 and VOCs, which may react with O3, ˙OH and other reactive molecules forming secondary inorganic aerosols (SIA) and secondary organic aerosols (SOA).3 

Unlike other pollutants, such as SO2 or NH3, PM describes a complex group of air pollutants with properties and impacts that vary according to their composition and size. For instance, BC is linked to a range of climate impacts (e.g. increased temperatures) owing to its capability of directly absorbing light, reducing the albedo of snow and ice and interacting with clouds.8  On the other hand, several European cohort studies have reported that short- and long-term exposure to PM2.5 is associated with a number of health risks, such as lung cancer.9  The results of these studies have formed the basis for the International Research Agency on Cancer (IARC) to classify PM as carcinogenic to human beings (Group 1).10 

The main objective of the present chapter is to describe and analyse the main factors that characterize European primary PM emissions, including: main sources of origin, size distribution and chemical composition (speciation), current emission inventories, trends and regulations, and mitigation measures. Despite having a significant contribution to ambient particle concentrations,11  secondary PM is not considered in the present chapter. The complexity of the atmospheric aerosol processes and other factors (e.g. precursor gases) influencing its formation suggest the need for treating it separately in a more extensive study.

Section 2 of this chapter lists and describes the main anthropogenic and natural emission sources that contribute to total PM emissions in Europe. In Sections 3 and 4 a thorough analysis of the size distribution and speciation of PM emissions is conducted, respectively. Section 5 describes the main European PM emission inventories currently used, while Section 6 performs an analysis of PM trends in Europe. Finally, Section 7 focuses on current regulations and mitigation measures that affect PM emissions.

Primary PM is derived from a wide range of sources (both natural and anthropogenic), the contribution of each one varying with the location, season and time of day12  (Figure 1).

Figure 1

PM10 and PM2.5 annual emissions (Mg year−1) per pollutant sector in the EU-28 region (a) and contribution (%) of each pollutant sector to total PM10 and PM2.5 emissions in France, Poland and The Netherlands in the year 2013 (b).14 

Figure 1

PM10 and PM2.5 annual emissions (Mg year−1) per pollutant sector in the EU-28 region (a) and contribution (%) of each pollutant sector to total PM10 and PM2.5 emissions in France, Poland and The Netherlands in the year 2013 (b).14 

Close modal

This section introduces and describes the sources that currently present the most significant contributions to European PM emissions.

Recently, interest has grown in biomass combustion as an environmentally friendly way of heating homes whilst at the same time reducing climate change impact and contributing to energy security. In this sense, the use of wood and other biomass in residential small combustion installations has been enhanced by several greenhouse gas strategies and targets for renewable energy. For instance, in 2014 the United Kingdom introduced the Domestic Renewable Heat Incentive (RHI), a financial support programme for renewable heat that offers payments to households for the installation of biomass heating systems to provide central heating and hot water. Moreover, the increase during the economic crisis of other fuel prices typically used in the residential sector (e.g. fuel oil) also triggered the use of biomass, which is less expensive, especially in those countries more affected by the recession, such as Greece.13 

Despite being labelled as a renewable fuel that can contribute to mitigating climate change, the combustion of biomass in small heating combustion installations is currently a major source of primary PM emissions, especially in wintertime. In 2013, emissions released from small residential combustion appliances were reported as the largest source of PM10 (38%) and PM2.5 (52%) in the EU-28 region.14  The high contribution of residential wood combustion (RWC) is mainly owing to the fact that: (i) burning conditions are often inefficient (i.e. low combustion temperatures, which leads to incomplete combustion) and (ii) household appliances used for the combustion of biomass usually lack emission controls or regulations.

In each European country, the contribution of RWC towards the total PM10 and PM2.5 emissions varies depending on its energy balance (i.e. relative amount of biomass consumed at the residential level with respect to other fuels) and the type of appliances used and fuels burned. The amount of appliances (e.g. fireplace, woodstove, pellet stove, pellet boilers) and biofuels (e.g. cork oak, pine, olive pit) used for RWC is very large and their use varies from one country to another. A survey conducted in Portugal reported that the main appliances used for RWC in the country are fireplaces (43%) and woodstoves or traditional ovens (24%).15  On the other hand, in Finland the biggest portion of wood is burnt in masonry heaters and ovens (38%), log boilers (24%) and sauna stoves (15%), with fireplaces representing only 5% of the total combustion installations used.16  Masonry heaters and ovens have qualities that allow better burning conditions, higher efficiency and subsequently lower PM emissions than conventional fireplaces. While in 2013 the amount of biomass used in the residential sector was 62% higher in Finland than in Portugal,17  the amount of Finish PM2.5 emissions reported for the same year and sector was just 28% larger than in Portugal.14 

Several studies have shown that the amount of PM emitted varies widely with category of burning appliance and biomass type.18–20  One of the most recent studies focusing on this topic was developed under the framework of the AIRUSE LIFE project. Emissions from different biofuels and appliances (those most prevalent in southern Europe) were analysed to obtain a detailed characterisation of emission profiles resulting from RWC. Results from this and previous studies shown that open fireplaces are the appliances that present the highest particulate emission factors (EFs; amount of pollutant emitted per activity unit) owing to low temperatures, which contribute to inefficient combustion. Compared to modern eco-labelled woodstove, PM2.5 EF from traditional fireplaces can be up to 10–50 times higher.18,19  Variations in the PM emissions can also be found within the same type of appliance owing to the operation conditions (e.g. air-staging settings and the thermal load).21  On the other hand, the highest EF are observed for biomass fuels other than pellets (e.g. olive pit, shell of pine, nuts, almond shell), the variations being related to the different ash contents of the fuels.22 

Apart from fuel parameters and operation conditions, the measurement protocol applied is another important factor that influences the variation of EF for the same appliance type. A detailed survey and review of the various RWC EF in use in Europe concluded that the most important type of measurement techniques are filter measurements, which measure only solid particles, and dilution tunnel measurements, which measure solid particles and condensates of semi-volatile organics.23  The EF compiled by the study presented a high variation as a function of the technique used. For instance, EF for conventional wood stoves obtained with filter measurement ranged from 64 to 87 mg MJ−1, while measurements in dilution tunnels showed results in the range from 340 to 544 mg MJ−1. The choice to use a filter measurement- or dilution tunnel measurement-based EF can have a great impact when estimating PM RWC emissions and analysing the contribution of this source to primary organic aerosols (POA).24 

Road transport is one of the main sources of PM in urban areas. In 2013, road transport alone was responsible for 12% and 13% of total primary PM10 and PM2.5 emissions in the EU-28 region, respectively.14  Nevertheless, at the city level these contributions can go up to 40–50%, thus constituting the main urban emission source.25–27 

PM emissions from traffic are categorised according to the mode of formation.28  The combustion of fuels, mainly gasoline and diesel, in internal combustion engines (exhaust emissions) is generally assumed as the principal mechanism by which PM is formed. On the other hand, road transport also involves the interactions between vehicles and the road surface and the use of brakes, which can result in the release of PM emissions. This category of emissions is known as non-exhaust emissions and includes: (i) tyre wear, (ii) brake wear, (iii) road surface wear and (iv) resuspension. The first three sources involve mechanical abrasion, grinding, crushing and corrosion processes, while the last one refers to the resuspension of the dust collected on the road surface owing to vehicle-generated turbulence.

The quantification of exhaust traffic emissions mainly depends on the engine type, engine age (i.e. Euro categories set up by European legislation), after-treatment technology, fuel properties (e.g. fuel sulfur content), level of maintenance of the vehicle, environmental conditions and driving conditions.5  Exhaust emission rates from vehicles can be estimated from controlled conditions in laboratories (i.e. engine and chassis dynamometer studies) or real-world conditions (i.e. tunnel, remote sensing, on-road and on-board measurements).29  The use of both approaches indicates that in general PM emission rates from diesel vehicles are significantly higher compared to those from gasoline ones, and that Heavy Duty Diesel Vehicles (HDDVs) are the highest emitters among the different diesel vehicle categories.30–32  However, increasingly restrictive European diesel emission standards (Section 7) have resulted in a clear reduction of diesel PM emission levels by about 80–90%. In some cases vehicles equipped with diesel particle filters (DPF) (part of Euro 4 and all from Euro 5 and on) even show lower PM levels than gasoline vehicles.33  The effect of speed on PM exhaust emissions is also increasingly reduced with the introduction of new Euro standards. Generally speaking, low-speed operations lead to higher emission rates. Nevertheless, and as shown by the two reference vehicle emission models in Europe (COPERT; COmputer Programme to calculate Emissions from Road Transport and HBEFA; Handbook of Emission Factors), the shape of emission rates vs. speed curves is flatter for the new emission standards than the old ones.30–32  On the other hand, PM emission rates significantly increase during acceleration as well as with aggressive driving or heavy load conditions.33 

Non-exhaust emissions are more difficult to quantify than exhaust emissions owing to the strong influence of not only the type of vehicle and traffic conditions, but also the material properties (e.g. tyre type, road pavement, grain size) and meteorological factors (e.g. temperature, road wetness).6,34  Non-exhaust particles derived from resuspension processes seem dominant in terms of mass, although this can vary from one country to another owing to the effect of humidity, the use of studded tyres and the contribution from road sanding.35  Resuspension PM10 emission rates estimated by roadside measurements on inner-city urban roads across Europe present a wide variation: UK (14–23 mg VKT−1), Germany (57–109 mg VKT−1), Denmark (46–108 mg VKT−1), Finland (121 mg VKT−1), Sweden (198 mg VKT−1).36–38  Several campaigns have pointed out a strong correlation between HDDVs and resuspension, the emission rate for this class of vehicle being up to 20 times higher than that for passenger cars.39  Resuspension emissions in motorways tend to be lower than those in other types of roads (especially urban streets) since higher average vehicle speeds and traffic intensity lead to a lower on-road dust reservoir.36  The large variation in the resuspension emission rates make them applicable only to the site of study or areas with similar characteristics. During recent years, different numerical approaches have been developed with the intention of reducing the dependency of non-exhaust emission quantification on local measurements.40  One of the most recent models, the NORTRIP model, is capable of estimating non-exhaust traffic PM emissions based on the impact of surface wetness, the buildup of dust on the road surface, the surface moisture and the effects of applying traction maintenance measures (e.g. salting and sanding).41 

Several studies across Europe have pointed out that the contribution of non-exhaust emissions to PM10 can be comparable or even higher than that of exhaust emissions, especially in Scandinavian and Mediterranean countries, owing to studded tyres and road sanding in the former and drier climates in the latter.42  The contribution of non-exhaust emissions to total PM10 in urban areas is expected to grow during the coming years up to approximately 80–90% by 2020.43  This increase is the result of a combination of several actions that are currently in place to reduce PM emissions from motor exhausts (both at legislative and technological levels) and a lack of abatement measures for non-exhaust emissions.

Emissions from energy (power plants and refineries) and manufacturing industries represent the second-largest source of primary PM10 (28%) and PM2.5 (21%) in the EU-28 region.14  However, and with the exception of certain cities close to industrial environments,44  the contributions of these activities to primary PM in urban areas is less pronounced than that of road transport (around 10%).25,45 

There are three main mechanisms by which industrial PM is formed. The first involves fuel combustion processes (e.g. coal, oil, coke) in conventional boilers, furnaces, gas turbines, reciprocating engines or other combustion devices. PM emissions can also arise from non-combustion processes, such as mechanical treatments of raw materials (non-metallic industries) or casting operations (iron and steel industries). Emissions derived from both combustion and non-combustion processes are usually channelled through ducts (i.e. stacks), which makes them more controllable. Finally, industrial PM emissions can also occur during the handling, transport and storage of dusty raw materials (e.g. clinker, cement). These emissions, referred to as “diffuse”, are more complicated to quantify and control than the channeled ones, owing to the difficulties in determining their flux and location of occurrence inside the industrial areas.

PM emissions from combustion processes are mainly characterized by the type of fuel and technology used. Once released into the atmosphere, meteorological parameters (e.g. temperature, pressure) also play a key role in their vertical distribution and subsequent transportation.46  Fuels with significant ash content (i.e. coal, oil and coke) have the highest potential to emit primary channeled PM. In the past, the Best Available Techniques (BAT) in large coal-fired power plants have been translated into abatement technologies, such as electrostatic precipitators (EP) or fabric filters (FF), which have allowed a great reduction of PM emissions. As a result, the current emission rate from a fluidised bed boiler (≥300 MW) working with brown coal can be up to 4 times lower than the emissions derived from a gas oil reciprocating engine.47  Combustion processes related to public electricity and heat production facilities alone presented a contribution of 4% to total PM10 and PM2.5 primary emissions (in the EU-28 region in 2013.14  These contributions largely vary from one country to another owing to the different energy generation systems. In Poland, where the production of electricity and heat mainly comes from coal-fired power plants, contribution from the public power sector goes up to 11% (PM10 and PM2.5), while in France, where the main source of energy is nuclear, public power only accounts for 1% of total PM10 and PM2.5 (Figure 1).17 

Non-combustion channeled emissions are mainly associated with non-metallic mineral and iron and steel industries.47  In the first case, PM emissions largely originate from pre- and after-treatments (e.g. milling processes in the cement industry), while in the iron and steel sector emissions are generated in sintering and pelletizing plants as well as in blast furnaces, used for the production of pig iron, and basic oxygen, open hearth and electric arc furnaces, used for the production of steel. Most of the time these emissions are conducted through stacks and subsequently controlled by efficient filters. Nevertheless, specific industrial processes, such as laser sintering of ceramic tiles, can entail non-controlled particle emissions, which can impact worker exposure.4 

Cement, steel, ceramic and mining industries, in which bulk materials are usually stored, transported and handled in open air, are the facilities that present more potential for diffuse PM emissions.48  These types of emissions are not only influenced by the characteristics of the industrial processes but also by meteorological factors (e.g. wind speed, precipitation) and material characteristics (e.g. raw material moisture content and particle size). The estimation of EF for this source has shown a large variation (from 7 to 400 g PM10 t−1 product) depending on the type of operation (e.g. transport of material on unpaved road) and control measure applied (e.g. enclosure and use of bag filters during handling operations).49 

Maritime traffic is a key component of the European economy. Compared to other modes of transport (e.g. trucks, trains) ship traffic is more fuel-efficient (i.e. fuel used per tonne-kilometre). The use of ships increased by more than 20% during the 1995–2012 period (with an average growth rate of 1% per year), and in 2012 the shipping sector was the second most used mode of freight transport in the EU-28 with 1401 billion tonne-kilometres (tkm), right after road transport (1692 billon tkm).50  According to a recent report by the International Maritime Organization (IMO), it is expected that this form of transport will continue increasing in the future owing to globalization and the increase of global-scale trade.51 

At the same time, maritime transport is considered an important contributor to primary PM in coastal areas52  and subsequently to European coastal air quality degradation,53  especially in the North Sea and the Mediterranean basin. Ship manoeuvring and hoteling operations (ships at berth), which occur in port areas usually located near cities, have been reported to contribute largely to primary PM emissions. In the Greek ports of Piraeus, Santorini, Mykonos, Corfu and Katakolo a total of 94.3 t year−1 PM emissions from cruise ships was estimated for the year 2013,54  85% of which was related to hoteling operations and 11.5% to the manoeuvring phase. On the other hand, ship hoteling in the port of Rotterdam (the Netherlands) was estimated to generate 248 t year−1 of PM10 in 2010.55  At the European level, primary shipping emissions have been reported to influence atmospheric aerosol concentrations in coastal areas within about 1–7% of PM10 and 1–20% of PM2.5.53 

PM emissions from maritime traffic are mainly owing to combustion processes that take place in the ship engines. There are three main factors that control the total amount of emissions released by ships: engine load factor, engine type and fuel type.52,56,57 

The powering of ships is delivered by their main engines (ME) and auxiliary engines (AE), which present different load factors (from 0 to 100%) depending on the operative profile of the ship. During the cruising and manoeuvring operations, the ME usually presents the highest load factor (50–75% during cruising and 10–30% during manoeuvring), while during the hoteling phase the AE is the main source of emissions (i.e. to cover the electricity requirements of the ship) and the MEs are switched off or running at low load (e.g. to provide power for pumps to load and unload liquid cargo). The dependence of PM emission factors on engine load may vary from ship to ship. Nevertheless, a recent review reported that at loads lower than 25%, emission rates can be significantly increased (up to 6.5 times).58 

In terms of type of engine, ships can be equipped with marine diesel engines (slow-speed diesel engines, SSD; medium-speed diesel engines, MSD and high-speed diesel engines, HSD), steam turbines or gas turbines. SSD generate a greater fraction of hydrocarbons (HCs) than MSD and HSD, which may result in an increase in total PM emissions because of the formation of HC aerosols.59 

The fuels used in maritime transport include marine heavy fuel oil (HFO), marine diesel oil (MDO), marine gasoline oil (MGO) and, more recently, liquefied natural gas (LNG). HFO is a residual product of the oil refinery process and its fuel sulfur content (FSC) can be up to 3.5%, while in the case of MDO/MGO the FSC is around 0.03%. The FSC has a crucial influence on PM emissions as primary sulfate is linearly dependent on it.51  A review of published data from on-board studies on PM emissions from ships indicated ranges of emission rates between 0.18 and 0.48 g kWh−1 for MDO and 0.56 to 2.12 g kWh−1 for HFO.57  Nevertheless, the same review study also indicated that the levels of fine and UF particle emissions are not necessarily reduced by this fuel shift.

PM emissions within port areas are not only produced owing to maritime traffic but also during loading/unloading operations of solid cargoes from ships (e.g. clinker, tapioca, phosphate). These operations generate dust that is firstly deposited in the dockside and later resuspended by the effects of port-related traffic or wind. The problematic issue relating to this emission source is similar to that found for diffuse industrial emissions (Section 2.3). In the framework of the LIFE project HADA (Automatic Tool for Environmental Diagnostic), average PM10 EF up to 140±30 g min−1 were estimated for several operations and types of cargoes in Spanish harbours, which states the relevance of this source to port dust emissions.60 

During the last few years, agricultural activities, including fertilizer application, manure management and animal housing, have attracted scientific attention since they are the main European sources of NH3 (their contribution is around 90%) and subsequently important contributors to secondary PM.61  Nevertheless, agriculture also presents a notable contribution to primary PM10, with a contribution of up to 14% in the EU-28 emission inventory in 2013.14  The main activities that contribute to the formation of this pollutant include storage, handling and transport of agricultural products, manure management, agricultural waste burning, land preparation and harvesting.

Just as in the case of traffic resuspension (Section 2.2), emissions from land preparation and harvesting are not regulated by the Convention on Long-range Transboundary Air Pollution (CLRTAP) and are not included in the official emission inventories reported by the Member States (MS). Consequently, studies about the contribution of land management activities are currently scarce and a significant knowledge gap exists. Despite the small amount of available dedicated research, some studies have acknowledged that agricultural land operations (e.g. ploughing and harrowing) together with harvesting may create dust plumes, and although much of this dust is rather coarse-sized, significant amounts are carried in suspension over long distances, contributing to the background atmospheric dust load.62  The contribution of these activities have been estimated to be around 5% of total primary PM10 in the EU-27 emission inventory,63  but it can be more significant in countries and regions characterised by large agricultural regions ,such as The Netherlands.64  Nevertheless, studies in which emission potentials were estimated for different land management activities present a wide range of values, showing EF variations of a factor of up to 50.65 

Natural sources, which involve no direct or indirect human activity, can present high contributions to total PM emissions. The sources included under this category are: (i) windblown (desert and local) dust, (ii) sea salt aerosols, (iii) volcanoes, (iv) primary biological aerosol particles and (v) wild-land fires.74,77,84 

Windblown dust defines the fugitive dust generated and transported by wind action. This occurs mainly in arid and semi-arid regions, although the process can also occur in surfaces covered by vegetation or man-made covers (e.g. roads, buildings). The major sources of dust are located in North Africa, the Saharan sources being considered as the most active ones in the world.66  Recent estimates of the amount of dust exported annually from North Africa (usually referred to as desert dust or African dust) suggest that 400–2200 Tg year−1 is a plausible emission range.67  A large fraction of the African dust is regularly transported from its source northwards across the Mediterranean to southern Europe,68  and sometimes as far north as the United Kingdom.69  Desert dust emissions have a significant impact on the background particle levels in the Mediterranean basin as they are responsible for a significant percentage (up to 70%) of PM10 daily level exceedances of the EC standard at background monitoring stations, especially in Spain and during the summertime.70  On the other hand, in Europe there are also potentially erodible surfaces (local dust reservoirs) that can generate fugitive dust emissions. According to a study developed under the NatAir European project, the yearly amount of PM10 emitted by wind from the European territory is approximately in the range of 0.66–0.88 Tg year−1,7  of which emissions from agricultural areas constitute an estimated 52%. Spain, together with France and Italy, are the European countries where the most important local dust reservoirs are located.71  In the case of Spain, loamy soils in central Aragon (NE Spain) are often eroded by strong Cierzo winds, reporting observed dust events with vertical flux ranging from 0.4 to 70 μg m−2 s−1.72 

Sea salt aerosols under 10 µm in diameter are the dominant aerosols in marine surface air and can make a significant contribution to land-based PM levels, especially when surface wind speeds are high.73  At the European level, the annual contribution that sea-salt emission makes to PM10 was estimated as 20 Tg year−1 for the year 2009,74  the highest production of sea-salt found on the Atlantic Ocean during winter time, while in the Mediterranean Sea the highest emissions were estimated over the Aegean Sea during summer. A significant part of the variability in the emission estimation comes from the uncertainty associated with the parameterization of the sea-salt emission process, which mainly depends on surface wind speed as well as sea surface temperature, wave height and water salinity, among other parameters.75 

Primary particles emitted by volcanic eruptions are formed through magma fragmentation and erosion of the vent walls. Volcanic aerosol emissions generally exhibit coarse size distribution and are mainly characterised by their plume height, mass eruption rate and their vertical distribution of mass (with the fine ashes concentred at the top).76,77  Volcanic ash emission rates vary according to the eruptive style and the intensity and duration of the eruption. During the Eyjafjallajökull eruption, which took place in Iceland between April and May of 2010 and caused significant economic and social disruption in Europe, a total fine ash (diameter 2.8–28 µm) emission of 8±4 Tg was found.77  European volcanic activity is mainly limited to Iceland and the Mediterranean areas of Greece and Italy.76,78  Nevertheless, volcanic particles can undergo long-range transport in the atmosphere since they have the potential to produce transient peaks in PM levels not only near the volcano area but also within distances of thousands of km.79  Besides direct emissions, resuspension and dispersal of freshly deposited volcanic fine ash by wind also have a large impact on PM10 levels. Looking again at the example of the 2010 Eyjafjallajökull eruption, PM10 concentrations of up to 2000 µg m−3 were registered in areas that were never hit directly by the eruptive plume owing to resuspended ash.80 

Primary biological aerosol particles consist of material that derives from biological processes.74,81  These types of aerosols are transferred into the atmosphere without any change in their chemical composition and they mainly include pollen, plant debris, fungal spores, bacteria and viruses. At the European level, the contribution of plant debris and fungal spores to PM10 emissions has been estimated at 0.12 Tg year−1.74  However, there is currently a rather unsophisticated approach applied for the estimation of these emissions. The EF are not directly obtained but derived from a few sets of measured plant debris atmospheric concentrations that are compared to atmospheric concentrations of other compounds, for which the emission fluxes are known.81  Moreover, emission rates are considered independent of the surface type or vegetation (excluding barren land and water area) and are temporally scaled (3 month periods) using observed seasonal cycles of plant debris and spore mass.74  Hence, there is a need to better understand the release mechanisms associated with these primary biological aerosols (e.g. meteorological patterns that may influence the emission fluxes) and subsequently refine their emission estimates.

Wind-land fires, also referred as wildfires, are caused by burning forests, shrublands, grasslands and other vegetation (excluding agricultural waste burning). For the region of Europe, the global Fire INventory model (FINN) reported a total of 0.39 Tg year−1 and 0.22 Tg year−1 PM10 and PM2.5 annual average emissions (2005–2009),82  while the Global Fire Assimilation System (GFAS) estimated an average of 0.74 Tg year−1 and 0.46 Tg year−1 for annual PM10 and PM2.5 emissions (2003–2011).83  Wildfire emissions are especially relevant in forested Mediterranean countries, such as Spain, Portugal, France, Greece and Italy, where summers are drier and hotter than other European countries. These five southern MS present a combined average of 400 000 hectares of forestland burn every year and are estimated to be responsible for 0.17 Tg year−1 PM2.5 average annual emissions (2003–2011).84  Emissions from open vegetation fires basically depend on the land area burnt, the type of vegetation (i.e. fuel material), the amount of organic matter available, the properties and condition of the fuel material (e.g. dry, wet, decayed), and the combustion stage (i.e. flaming, smouldering).82–84  Several laboratory studies and field campaigns indicate a wide variation in the emission factors associated with specific fuel types, most of them confirming that PM10 mass is dominated by PM2.5 mass concentration.85  As in the case of volcano emissions, the injection height of wildfire emissions is a critical parameter in the transport of the particles released to the atmosphere. Several factors, such as the energy released from the fire, fuel type and local meteorological conditions, determine the plume height, which can reach altitudes of up to 6.1–8.7 km above the surface.86 

As previously stated, PM comes in a wide range of sizes according to its aerodynamic diameter, including: coarse particles (PM2.5–10; diameter between 10 μm and 2.5 μm), fine particles (PM2.5; diameter less than or equal to 2.5 μm), ultrafine particles (UFP) (PM0.1; diameter less than or equal to 0.1 µm) and nanoparticles (PM0.05; diameter less than or equal to 0.05 μm). The size of PM is directly linked to its potential for causing health problems since smaller particles penetrate further down the respiratory tract and even transfer to extrapulmonary organs, including the central nervous system.87  While most severe adverse health effects have been typically associated with PM2.5, other epidemiological studies suggest that PM1 may have a greater potential for adverse health impacts.88  The relative amounts of particles present in each size are expressed by mass concentration in the case of PM2.5–10 and PM2.5 and by number concentration (PNC) in the case of aerosols with diameters between 0.1 and 0.05 μm owing to their negligible mass.

Coarse particles are usually associated with mechanical disruption processes (e.g. crushing, grinding, and abrasion of surfaces) and the suspension of dust. Traffic non-exhaust emissions (wear processes and resuspension) are assumed to be dominated by the PM2.5–10 fraction,38  although in some cases particles in the fine particle range have also been found (approximately 15%).89  Similarly, emissions derived from agricultural activities are mainly associated with the coarse size62  as well as the diffuse emissions related to handling, transport and storage of dusty raw materials.60  Regarding sea salt aerosols, approximately 95% of their total mass is in the coarse mode,90  although in Atlantic zones its contribution to PM2.5 can be up to 11%.11  PM2.5–10 tends to have a local impact (1 to 10s of km) and to settle on the ground through dry deposition processes (e.g. gravitational sedimentation) in a matter of hours. This is not the case for coarse particles related to wind-blown desert dust, which can be transported over thousands of km (Section 2.6).

Primary PM2.5, UFP and nanoparticles are mainly formed from combustion and high-temperature processes, and industrial operations. Road transport, in particular diesel engines, is the major source of primary PM0.1 and PM0.05 emissions in urban environments,91,92  with reported contributions of up to 97% of the total PNC.93  Many of the PM produced by RWC as well as maritime traffic is also below 1 μm.22,56  On the other hand, primary UFP and nanoparticle emissions from industrial processes such as tile sintering and laser ablation operations are also receiving increasing attention.4  As opposed to coarse particles, PM in the accumulation mode (diameter between 0.1 and 2.5 μm) tend to have longer lifetimes (days to weeks) as they settle slowly and have low diffusivities, their travel distance being up to thousands of km.3  On the other hand, UFP usually present lifetimes that go from minutes to hours owing to their tendency towards growth into the accumulation mode.

According to European official reported emissions in the year 2013, 32% of total primary PM10 emissions are considered to be in the PM2.5–10 fraction and 68% in the PM2.5 fraction.14  In the coarse fraction, agricultural activities are the ones that present the largest contribution (36%), together with mining and construction activities (10%) and non-exhaust traffic emissions (9%). On the other hand, the fine fraction is mainly dominated by residential combustion (58%), energy and manufacturing industries (21%), and road transport (13%). Regarding UFP emissions, they can be indirectly obtained from primary particle number (PN) emission inventories (expressed as numbers of particles instead of mass) since PN emissions are dominated by UFP emissions and the difference between them is relatively small.92  Recent primary PN emission inventories for Europe indicate a significant contribution from traffic as well as shipping emissions, especially in coastal urban areas such as Oslo, with total shares of 75% and 15%, respectively.91  France, Spain, Germany, Italy, UK and Poland are reported as the major PN emitters in the EU-28 region, the sum of their traffic emissions representing approximately 72% of the total PN road transport emissions in EU-28.93 

Primary PM includes as principal components organic carbon (OC), black carbon (BC), trace metals, crustal material (i.e. soil particles), sea-salt and, to a lesser extent, sulfates (SO4−2). The chemical makeup of PM varies across Europe, depending on the emission source categories that characterize the region of study.

Carbonaceous particles (BC and OC) are generally the dominant components of primary PM emissions. The carbon fraction of PM is identified as having significant impacts on health, climate change, atmospheric photochemistry and aerosol–cloud interactions.94  Primary BC and OC are mainly formed by incomplete combustion processes and are predominantly present in the fine and UF particle fractions.67,92,95,96  BC is sometimes also defined using other terms, such as elemental carbon (EC), soot or graphitic carbon. While all the terms are used to denote light-absorbing carbon in atmospheric aerosol particles, each one of them identifies the specific instrument or measurement technique used to measure the quantity of the component. For instance, BC and EC are often used to indicate optical and thermal measurement methods, respectively. In this chapter, the term BC is generically used.

According to the EDGAR-HTAP_v2 global emissions inventory, the total amounts of primary anthropogenic (land-based, excluding ship emissions) BC and OC emissions released in Europe during 2010 were 0.38 Tg year−1 and 0.64 Tg year−1, respectively, since the transport and residential sector is responsible for around 90% of the total emissions.97  On the other hand, European official BC anthropogenic emissions report a total of 0.14 Tg year−1 released in the EU-28 region during 2013, the largest contributions being those of the residential (34%), traffic (32%), and national and international shipping (6%) sectors.14  The contribution of emission sources to particulate carbonaceous emissions may vary according to PM size. The size-resolved emission inventory of carbonaceous particles addressed in the EUCAARI project indicates that the emission of OC in the fine fraction is dominated by the residential combustion of wood and coal, while the largest sources of EC in the UFP fraction are diesel transport and residential combustion.95  On the other hand, and according to the TNO_MACC_II emission inventory, the most important sources of coarse OC and coarse BC in terms of total mass are not the transport and residential sectors but rather the agriculture (agricultural waste burning) and the power plants and industry sectors, respectively.96 

Emission ratios of BC and OC to PM are critical to determine since they vary according to a large number of parameters, including fuel type, technology, combustion process efficiency, emission control and size of particles. Diesel engines are estimated as the largest contributors to primary BC emissions,26,95  while gasoline engines are known to release a higher fraction of OC.98  Nevertheless, some studies have pointed out that gasoline vehicle UFP emissions are dominated by the BC fraction.99  In cases where advanced after-treatments are used (e.g. DPFs), a significant reduction of the BC fraction is also observed.100  In the case of biomass combustion, OC generally dominates the PM emissions in small traditional appliances (e.g. fireplaces), while more efficient combustion installations show larger EC relative fractions owing to higher combustion temperatures and flaming combustion.18  Fuel properties also influence the OC and BC contents in the particles emitted, with higher hydrocarbon (HC) emission rates contributing to higher OC contents.20  The OC fraction released from biomass burning provides an important contribution to benzo[a]pyrene (BaP),101  a polycyclic aromatic hydrocarbon (PAH) reported by the IARC as a probable carcinogen in humans.102  In the case of maritime traffic, the OC fraction is typically larger than the BC one.56  PM ship emissions of OC increase with the fuel sulfur content, whereas BC appears to have a significant dependence on the engine load and engine settings but not on the FSC.56–58  SSD engines are found to generate a greater amount of OC fraction since they typically have a larger fraction of HCs coming through the engine.58 

Crustal material includes soil particles generated by wind erosion processes (including desert dust contributions), traffic resuspension, handling, transport and storage of materials, and agricultural land management activities, among others. The main components that can be associated with crustal material include aluminium (Al), silicium (Si), calcium (Ca) and iron (Fe), which are usually associated with the coarse fraction (PM2.5–10).103  In Europe, soil particle emissions typically represent 5 to 20% of the ambient PM10 mass;104  the contribution is higher in south-western and south-eastern Europe owing to the warmer and drier climate and the higher influence of African dust intrusions.

Tyre and brake wear emissions (as well as resuspension) are a major source of metals in urban areas.28,103  In terms of heavy metals, brake wear is the most important source of emissions for copper (Cu), while for tyre wear the most important emission is zinc (Zn).35  Tyre and brake wear sources represented 77% and 33% of total Cu and Zn emissions in the EU-28 region in 2013, respectively.14  These two emission sources together also significantly contribute to total lead (Pb) emissions (10%), which in the past was dominated by gasoline exhaust emissions until the phasing out of leaded fuels in Europe.105  Tyre and brake emissions also include other trace metals, such as arsenic (As), nickel (Ni), antimony (Sb), iron (Fe) and barium (Ba), the composition presenting a large variability across Europe owing to the dependence on the manufacturer and brand.28,42  Outside urban areas, the metal concentrations of PM may partly originate from different sources such as energy and manufacturing combustion or industrial processes. Heavy metals are most abundant in high-temperature metal processing activities,2,103  and hence the production of iron and steel is a key contributor to total European emissions of Pb, cadmium (Cd), mercury (Hg), chromium (Cr) and Zn.14 

Primary sulfate aerosols usually present a residual fraction of total PM emissions (between 2 and 4%).27,96  Nevertheless, sulfur emitted in the form of particles is important in combustion processes of high-sulfur fuels, which mainly occur in energy and manufacturing industries and in shipping. The fraction of primary sulfate to total PM is mainly influenced by the FSC of the fuel consumed; during coal combustion it has been reported to range from 10 to 45%,106  while in the case of marine residual oil combustion (i.e. HFO) it can account for up to 80% of the weight of the emitted particles.51,56  Sulfate is becoming less and less significant as a primary PM component owing to the general tendency to substitute coal for natural gas in the public power sector and HFO for MDO and LNG in the maritime sector (Section 7.4).

PM speciation source profiles indicate the chemical species that comprise the PM emissions released from a specific source. These speciation profiles, commonly expressed as the mass ratio of each species to the total PM, are used to characterize the different components that are associated with individual pollutant sources. Currently there are different repositories of PM speciation source profiles freely accessible, with the objective of being used for different purposes, such as creating speciated PM emission inventories for photochemical air quality modelling27  or providing input to the Chemical Mass Balance (CMB) receptor models (RM).101  One of the best-known repositories is the United States EPA SPECIATE database, which has been publicly available since 1988, and it currently contains around 3000 entries.107  Source profiles from this American repository are usually used in European emission and air quality modelling exercises owing to the scarcity of official and well-established European databases. With the objective of filling this gap, a new database of PM speciation source profiles in Europe has been recently developed (SPECIEUROPE).2 

The SPECIEUROPE is a repository developed in the framework of the Forum for Air quality Modelling in Europe (FAIRMODE) that contains the chemical composition of PM emission sources reported in European scientific papers and official reports. Currently, SPECIEUROPE consists of 209 PM speciation profiles, combining measured, composite, calculated (from stoichiometric composition) and derived (results of source apportionment studies) profiles.

Emission inventories are datasets used to estimate the amount of air pollutants being emitted to the atmosphere, caused by an anthropogenic or natural activity, at a certain geographical location for a given period of time. Emission inventories are generally recognized as key inputs to atmospheric modelling, especially when they are used to design effective control measures to mitigate the adverse impact of air pollution.45  Statistical methods of source apportionment to indirectly assess pollutant sources from measurements have also proved the requirement of emission inventories as input data.103  Therefore, during recent years a significant amount of emission datasets have been developed either for scientific or regulatory purposes.108 

At the European level, the most used inventories to determine PM emissions and its impacts on air quality are: the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP),109  the Emission Database for Global Atmospheric Research (EDGARv4.2),110  the EDGAR-HTAP_v2,97  the EMEP emission inventory,111  the TNO-MACC-II emission inventory96  and the Greenhouse gas and Air pollution INteractions and Synergies (GAINS) model.112  Each of them presents different emission estimation methodologies, spatial resolutions, temporal coverages and applications (Table 2).

Table 2

Summary of European emission inventories currently used in the scientific community for scientific and regulatory purposes.

NameSourceEmission sourcesPollutantsTemporal resolution/coverageSpatial resolution/coverageUseApproach used
ACCMIP 109  Anthropogenic biomass burning SO2, NOx, CO, NMVOC, CH4, NH3, BC and OC Decadal, 1850–2000 0.5°×0.5°, Global Scientific Combination of other inventories (RETRO, GAINS, EMEP) 
EDGARv4.2 110  Anthropogenic biomass burning SO2, NOx, CO, NMVOC, CH4, NH3, PM10 Annual, 1970–2008 0.1°×0.1°, Global Regulatory scientific Combination of national AF with specific EF, disaggregated using different spatial proxies 
EDGAR-HTAP_v2 97  Anthropogenic biomass burning SO2, NOx, CO, NMVOC, CH4, NH3, PM10, PM2.5, BC and OC Annual, 2008–2010 0.1°×0.1°, Global Regulatory scientific Compilation of different regional gridded inventories with EDGAR v4.2 spatial proxies 
EMEP 111  Anthropogenic SO2, NOx, CO, NMVOC, CH4, NH3, PM2.5–10, PM2.5 Annual, 1980–2013 0.1°×0.1°, European Regulatory scientific National emission inventories reported by parties and assigned to the EMEP grid 
TNO-MACC-II 96  Anthropogenic SO2, NOx, CO, NMVOC, CH4, NH3, PM10 and PM2.5 (broken down into EC, OC, SO4−2, Na and other minerals) Annual, 2003–2009 1/8°×1/16°, European Scientific Downscaling of National emission inventories through the use of specific spatial proxies 
GAINS 112  Anthropogenic SO2, NOx, CO, NMVOC, CH4, NH3, PM10, PM2.5, PM0.1 Annual, 1990–2030 50 km×50 km, European Regulatory Combination of national AF with specific EF and grid maps 
NameSourceEmission sourcesPollutantsTemporal resolution/coverageSpatial resolution/coverageUseApproach used
ACCMIP 109  Anthropogenic biomass burning SO2, NOx, CO, NMVOC, CH4, NH3, BC and OC Decadal, 1850–2000 0.5°×0.5°, Global Scientific Combination of other inventories (RETRO, GAINS, EMEP) 
EDGARv4.2 110  Anthropogenic biomass burning SO2, NOx, CO, NMVOC, CH4, NH3, PM10 Annual, 1970–2008 0.1°×0.1°, Global Regulatory scientific Combination of national AF with specific EF, disaggregated using different spatial proxies 
EDGAR-HTAP_v2 97  Anthropogenic biomass burning SO2, NOx, CO, NMVOC, CH4, NH3, PM10, PM2.5, BC and OC Annual, 2008–2010 0.1°×0.1°, Global Regulatory scientific Compilation of different regional gridded inventories with EDGAR v4.2 spatial proxies 
EMEP 111  Anthropogenic SO2, NOx, CO, NMVOC, CH4, NH3, PM2.5–10, PM2.5 Annual, 1980–2013 0.1°×0.1°, European Regulatory scientific National emission inventories reported by parties and assigned to the EMEP grid 
TNO-MACC-II 96  Anthropogenic SO2, NOx, CO, NMVOC, CH4, NH3, PM10 and PM2.5 (broken down into EC, OC, SO4−2, Na and other minerals) Annual, 2003–2009 1/8°×1/16°, European Scientific Downscaling of National emission inventories through the use of specific spatial proxies 
GAINS 112  Anthropogenic SO2, NOx, CO, NMVOC, CH4, NH3, PM10, PM2.5, PM0.1 Annual, 1990–2030 50 km×50 km, European Regulatory Combination of national AF with specific EF and grid maps 

All of these European inventories focus their attention on the PM10 and PM2.5 fractions (carbonaceous components included in some cases) giving no particular attention to UFP. This is a consequence of the fact that current European legislation on primary PM emissions is based on particle mass and not on particle number. However, the increasing evidence of the adverse health impacts related to UFP has also increased the attention on PN emission inventories. Numerous research studies and European projects, such as PARTICULATES or TRANSPHORM, have consolidated emission factor databases for constructing PN emission inventories in Europe. As a consequence, during recent years some of the aforementioned emission inventories have been revised in order to include PN emission estimations.91,93,95  Nevertheless, the estimation of PN emissions is associated with a higher uncertainty than that linked with PM10 and PM2.5 emission estimations. For instance, while the uncertainty of PM emissions from traffic sources has been reported to be between 10 and 20%,113  the overall uncertainty of vehicular PN emissions can be up to 144–169% when after-treatment device effects are included.91  This increase of the uncertainty is mainly related to the set-ups of the measurements that define PN vehicle emission factors, including: (i) the consideration or not of volatile PN and (ii) the definition of the lower size cut-off used in the measurement. Considering that traffic is the most intensively studied source category for PN emissions, similar or higher uncertainty values can be assumed for other pollutant sectors.

Despite being well established and showing important improvements, European inventories are still not able to characterize primary PM emissions to a satisfying level of detail. Reported emissions often present data gaps, missing sources and high uncertainties for the applied emission factors,114  which entail high discrepancies between the different emission datasets.115  This fact is especially relevant for fugitive emissions related to industrial and agricultural activities, where a problem of data gaps exists. On the other hand, the non-inclusion of key sources, such as traffic resuspension, in the national emission inventories reported under the CLRTAP, which are later used in well-established emission inventories such as EMEP or TNO_MACC-II, also entails large uncertainties.

Comparisons between European emission inventories with local emission inventories developed at the regional or urban scale have also pointed out significant discrepancies, especially in terms of allocation and total amount of PM residential biomass emissions.116,117  These differences mainly come from the fact that emission inventories at European or national levels usually tend to rely to a larger degree on top-down approaches, while emission inventories developed for local and urban applications rely to a larger degree on bottom-up approaches. Both methods require information concerning activity factors (e.g. total amount of fuel consumed) and emission factors per activity (e.g. amount of pollutant emitted per activity unit). Nevertheless, emissions compiled through a bottom-up approach are based on specific information for each sector, such as housing units or number of vehicles per road link for domestic heating and traffic emissions, respectively. Alternately, top-down approaches are based on the disaggregation of variables defined at the regional or national level (e.g. fuel sold or consumed) in smaller areas based on auxiliary spatial surrogates that represent the activity (e.g. population density for wood burning emissions), thus achieving a higher spatial detail. Bottom-up approaches allow high spatial and temporal detail, although they also require a greater amount of data and thus more resources.

According to the European Union emission inventory report under the UNECE Convention on Long-range Transboundary Air Pollution (CLRTAP),14  total emissions of primary PM10 have reduced by 19% across the EU-28 region between 2000 and 2013, driven by an 18% reduction in emissions of PM2.5. On the other hand, BC emissions have seen a reduction of 35% over the same period.

The difference between the BC trend and that of PM10 and PM2.5 is owing to significantly decreasing emissions in BC from road and off-road transport since 2000 (a decrease of 50% and 60%, respectively). The majority of the reduction in PM10 and PM2.5 emissions has taken place in the anthropogenic sectors of public power (20% and 13%), industry (35% and 27%) and road transport (25% and 34%) owing to: (i) a fuel-switching from coal to natural gas for electricity generation, (ii) an introduction of after-treatment technologies in new vehicles, such as DPF (driven by the legislative Euro standards) and (iii) an implementation of BATs in the industrial sector, including improvements in the performance of pollution abatement equipment. Moreover, a marked decrease has been recorded since 2008 in the hardest-hit countries by the economic crisis (i.e. Italy, Portugal and Spain). The influence of the economic recession on PM has also been reported by different European interpretation trend studies.118 

During 2013 the contribution of residential combustion to total PM emissions significantly increased in comparison to 2000 (by 13% in PM10 and 17% in both PM2.5 and BC) and it is the only sector in which emissions have risen between 2000 and 2013 (by 11% for PM10, 13% for PM2.5 and 12% for BC) (Figure 2). This evolution can partly be explained by the increase of biomass burning at the residential level, especially in Eastern European countries (see section below). Moreover, during this period, European efforts have been especially focused on exhaust diesel PM emissions control strategies, which has caused an important decrease in the exhaust road transport's contribution to total BC (from 43% to 33%). The decrease of traffic PM exhaust emissions has increased the importance of non-exhaust emissions in the coarse fraction; the relative contribution from non-exhaust emissions in road transport has increased from 27% to 49% for PM10 from 2000 to 2013 (Figure 2). For these results it is important to note that traffic resuspension emissions are not included in the official MS inventories and subsequently road transport non-exhaust contributions may be underestimated.

Figure 2

Trend of PM10 and PM2.5 emissions (%) from total pollutant sources and residential combustion sources (a) and trend of the contribution (%) of exhaust and non-exhaust emissions in total road transport PM10 emission in the EU-28 region (b).14 

Figure 2

Trend of PM10 and PM2.5 emissions (%) from total pollutant sources and residential combustion sources (a) and trend of the contribution (%) of exhaust and non-exhaust emissions in total road transport PM10 emission in the EU-28 region (b).14 

Close modal

Looking at the variations between countries, the largest reductions of PM10 for 2000–2013 have been reported by Cyprus (66%), France (35%) and Hungary (35%). In the case of PM2.5, Cyprus and France are also among those countries that have shown the greatest reduction (73% and 42%, respectively) together with The Netherlands (50%). BC emission reductions are led by The Netherlands (61%), the United Kingdom (53%) and France (44%). The large reduction of BC observed in the case of The Netherlands is partly explained by the increase of the market share of hybrid-electric vehicles during this period (9.7%), the largest of the whole EU-28 region.119  However, despite all the reductions observed, France was the MS with the largest contribution to total PM10, PM2.5 and BC emissions in 2013 (14.4, 14.2 and 26.7%, respectively), which was also the case back in 2000. These results can be explained by the patterns observed in the road transport and residential combustion sectors: (i) diesel dominated the French passenger car market with a 66% of the total share119 —the EU-28 share was 53% in 2013—and (ii) biomass was, after natural gas, the fuel most used in French households (28%) and represented 19% of the total biomass consumed in the EU-28 region.17 

In contrast to the aforementioned countries, PM emissions have increased in some countries since 2000; the greatest increases have been reported by far in Romania for all PM emissions (PM10, 21%; PM2.5, 31% and BC, 43%). The explanation for this lies in the fact that the use of biofuels and waste in the residential combustion sector increased by 27% during this period.17  With this increase, Romania rose from the 7th to 4th position in the list of top contributors to PM2.5 and BC emissions in EU-28 (just after Italy). Similarly, Bulgaria has also increased its levels of PM emissions during the same period owing to a rise in residential biomass consumption (53%). Although the emissions have dropped by 11%, Poland is another Eastern European country in which residential emissions have a significant impact (50% of total PM2.5). In this case, the main fuel consumed is coal, which represented 68% of the total coal consumed at the residential level in the EU-28 region in 2013.17 

Emissions of primary PM10, PM2.5 and BC are expected to decrease across the EU-28 region in the coming years as vehicle technologies are further improved and stationary fuel combustion emissions are controlled through abatement techniques or the use of low-sulfur fuels (natural gas). However, it is possible that Eastern European countries experience a different evolution if the tendency towards biomass and coal combustion in the residential sector continues to increase. In this sense, regulations and mitigation measures targeting solid fuel appliance and their energy efficiency are necessary (Section 7). Moreover, the impact of international energy markets and human-induced global warming can entail changes in PM trends. For instance, and according to the Spanish Electric System statistics, the use of coal in the Spanish energy production system has increased from 14.6% to 21.3% between 2013 and 2015. This increase has been mainly triggered by two elements: (i) the extreme dry and warm conditions that affected the country during this year, which entailed a reduction of hydroelectric power (from 14.2% to 11.2%) and (ii) the reduction of the use of coal in the United States (owing to an increase of fracking technology to extract natural gas) and the subsequent reduction of coal prices.

There are currently three air pollutant emission reporting obligations in the EU: the 1979 CLRTAP, the National Emission Ceilings Directive 2001/81/EC (NECD) and the EU Greenhouse Gas Monitoring Mechanism. All of them require MS and other Parties to annually report their national atmospheric emission inventories. Additionally, the NECD sets pollutant-specific emission ceilings for each country, which were to be met by 2010 as well as in future years. Nevertheless, NECD emission targets are currently focused on emissions of the secondary PM precursors (i.e. NOx, SO2, NMVOCs and NH3) and do not include primary PM. The proposal to amend the NECD is currently still under preparation and should set emission ceilings to be respected by 2020 and 2030 for the four already regulated substances and for PM2.5 and CH4 as well.120 

Although EU emission targets for primary PM are currently non-existent, there are several directives and regulations that affect the emissions of this pollutant. The following sections describe some of the most important European regulations and mitigation measures that are currently being applied with the objective of reducing PM emissions.

Whereas emissions from large point sources have decreased during the last decade as a result of several EU legislations (Large Combustion Plant Directive 2001/80/EC and Industrial Emissions Directive 2010/75/EU), emissions released by small residential solid fuel appliances have been increasing, especially in Eastern European countries, owing to a lack of regulation at EU level (Section 6). In order to tackle this problem, the European Commission launched the Directive 2009/125/EC (Eco-design Directive) to establish a framework for the setting of eco-design requirements for energy-related products. The Eco-design directive provides a framework and tools for improving the environmental performance of residential combustion appliances.

According to studies conducted to estimate the impact of implementing the European Eco-design Directive, the introduction of the Eco-design standards without requirements for improved energy efficiencies would imply a decrease of total European PM2.5 emissions from residential small combustion sources of 38% in 2020, 70% in 2030 and 83% in 2050.121  Similarly, BC emissions would be reduced by 25% in 2020 and by 75% in 2050. If Eco-design standards include all the requirements for improved energy efficiencies, reduction of emissions would be larger. However, the study concludes that this scenario of application is very unfeasible since it assumes a very fast replacement of the existing inefficient devices by new equipment and an unlimited availability of pellets.

In parallel to the development of the Eco-design Directive, some European countries have also issued national emission standards for small residential heating installations, which are already in effect. This is the case in countries such as Germany and Sweden, for example, which have introduced voluntary eco-labelling of stoves with standards for efficiency and emissions.94 

The process of dieselization that European vehicle fleets have suffered during the last decades,119  combined with the significant contribution of diesel-fuelled vehicles to BC emissions95  and the classification of diesel engine exhaust as carcinogenic to humans (Group 1),102  has resulted in more stringent emission regulations and new abatement technologies.

In particular, the adoption of DPF has contributed greatly to reducing emissions, with mass basis PM reductions typically cited as between 85 and 95% when compared to direct engine emissions.5  The application of DPF has been indirectly incentivized by the increasing restrictions of the European emission standard PM limits for diesel Euro 5/V (applied from 2009) and 6/VI (applied from 2014) vehicle categories. In the case of passenger diesel cars, the standard has been reduced from 140 mg km−1 (Euro 1) to 5 mg km−1 (Euro 5 and 6), while in the case of HDDV the limits have changed from 0.612 g kWh−1 (Euro I) to 0.02 g kWh−1 (Euro V) and 0.01 g kWh−1 (Euro VI). These emission standards, however, have proved to be largely ineffective in reducing diesel NOx emissions; several real-world measurement campaigns showed that real-world diesel NOx emissions exceed certification limits.33 

Regarding HDDV, the utilisation of natural gas in diesel engines has also become a promising and highly attractive alternative in the transportation sector. Emissions in natural gas and diesel dual-fuelled engines have been largely investigated, the results indicating that there is a significant decrease in PM emission under dual fuel mode.122 

Besides the application of emission standards and abatement technologies, another way to reduce traffic PM emissions in urban areas is through the reduction of traffic congestion and traffic jams. With this objective in mind, in recent years several European cities have set up regulations for vehicles entering their area, including: (i) urban road tolls (entrance to an area is subject to payment), (ii) low emission zones (LEZs; entrance to an area is regulated by vehicle emission standards) and (iii) Key Access Regulation Schemes (Key-ARS; entrance to an area is regulated by other elements, such as special permits or time of the day). While urban road tolls and Key-ARS have a clear impact on the amount of vehicles that circulates throughout the area of application, LEZs also contribute to renewing and modernizing the vehicle fleet of the city (i.e. citizens buy newer vehicle or retrofit the ones they have in order to reduce their emissions and comply with the restrictions of the LEZs). Several studies have shown how the application of urban access regulations has had a positive impact on urban traffic emissions, with PM10 primary emission reductions increasing to almost 20%.123  Nevertheless, there is currently a debate about the effects of these measures on PM urban concentration levels. A review on the efficacy of LEZs to improve urban air quality in five EU countries (Denmark, Germany, Netherlands, Italy and UK) concludes that there have been mixed results. While German cities have reported reductions in annual mean PM10 concentrations up to 7%, no clear effects have been observed in other urban areas.124  These results may be related to different causes, including the types of vehicles restricted in the LEZs (German LEZs restrict HDDVs and passengers cars, while in the rest of the cities the restriction is limited to HDDVs). The reduction of PM10 concentration by only a few percent may be also related to the fact that LEZs do not impact on non-exhaust traffic PM10 emissions, which present a significant contribution to total urban road transport primary emissions (Figure 2).

IMO is an international agency of the United Nations (UN) that addresses maritime traffic air pollution through the International Convention for the Prevention of Pollution from Ships (MARPOL) and its Annexes, which limits ship emissions for SOx, NOx, O3-depleting substances and VOCs.

Although the regulation does not include explicit PM emission limits, there are caps on FSC that directly control SOx and indirectly primary sulfate compounds. MARPOL designates emission control areas (ECAs; the Baltic Sea area and the North Sea area in Europe) where ships have to use on-board fuel oil with an FSC of no more than 0.10% (m/m) from 1 January 2015, while outside these ECAs (in which the Mediterranean Sea area is included) the current limit is 3.50%, falling to 0.50% after 1 January 2020. In line with this regulation, the EC published the Marine Fuel Oils Directive 2005/33/EC with the obligation on ships to use 0.1% FSC while at berth (i.e. securely moored or anchored in the port while loading, unloading or hoteling) from 1 January 2010.

Both the ECA regulation and the EC Directive do not prohibit the use of HFO; its use is allowed as long as the fuel meets the applicable FSC limit or if approved emission abatement technologies are used in the ship to limit SOx emissions. Nevertheless, one of the main goals of these regulations is to force maritime transport to the use of cleaner maritime fuels. Traditionally, LNG has been basically used in LNG carriers. However, the use of this fuel is currently becoming more interesting for liner service ships (i.e. ferries) and other merchant ships. In this sense, LNG is increasingly being adopted as a marine fuel with solutions that include a dual-fuel engine that can run on either LNG or HFO, with LNG being expected to take 11% of the market share in 2030.51 

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