Chapter 6: Europe

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First-Order-Draft IGAC Report on Megacity Air Pollution and Climate

Chapter 6: Europe

In MegacityZeroDraft_091119.doc chapter 6 covers pages 183-223
Lead Authors: Mark Lawrence, Michael Gauss

Contributing authors: Erika von Schneidemesser, Paul S. Monks, Matthias Beekmann, Alexander Baklanov, Alexander Ginzburg, Michael Memmesheimer, Jochen Theloke, Balendra Thiruchittampalam, Rainer Friedrich, Melinda Uzbasich, Hermann Jakobs, Sabine Wurzler, Sandro Finardi, Paola Radice, Maria Kanakidou, Kostas Markakis, Ulas Im, Nikos Mihalopoulos, Dimitris Melas, Mihalis Vrekoussis.

Table of Contents

Chapter 6: Europe 1

Table of Contents 1

6.1 European Megacities: General and Comparative Characteristics 3

6.1.1 Population and Geography 3

6.1.2 Emissions 4

6.1.3 Pollution levels 6

6.1.4 Outflow characteristics and effects on regional ozone-related atmospheric chemistry 6

6.2 London 9

6.2.1 City Introduction 9

6.2.2 Emissions Sources, Trends, and Data 9

6.2.3 Air Quality Regulations 10

6.2.4 Monitoring Network 10

6.2.5 References 12

6.3 Paris 14

6.3.1 Population and geography 14

6.3.2 Pollutant emissions 15

6.3.3 Meteorology 16

6.3.4 General air pollution situation 17

6.3.5 Specific scientific campaigns 18

6.3.6 Conclusion and outlook 22

6.3.7 References 22

6.4 Moscow 24

6.4.1 Population, demographics, geography, and urban structure 24

6.4.2 Overview of emissions estimates 25

6.4.3 Overview of pollution levels 26

6.4.4 Major past studies or field campaigns examining the city's air pollution 29

6.4.5 Current and planned major activities focusing on the city's air pollution 31

6.4.6 References 32

6.5 Benelux/Rhine-Ruhr 33

6.5.1 Population, demographics, geography, urban structure of major population centres 33

6.5.2 Overview of emission estimates 34

6.5.3 Overview of pollution levels 37

6.5.4 Projections, modelling studies 38

6.5.5 Effects of climate change on air pollution 42

6.5.6 Major past studies or field campaigns examining the city’s air pollution 43

6.5.7 References 43

6.6 Po Valley 45

6.6.1 Introduction 45

6.6.2 Meteorology 46

6.6.3 Air pollution 46

6.6.4 References 49

6.7 Eastern Mediterranean and Istanbul megacity 50

6.7.1 Introduction – location, meteorological patterns and air pollution levels 50

6.7.2 The Greater Istanbul Area 53

6.7.3 The Greater Athens Area 57

6.7.4 Open questions for the area 59

6.7.5 References 59

6.1 European Megacities: General and Comparative Characteristics

Author: Mark Lawrence, May 2009.
Draft history: Minor edits M.Gauss, Feb 2010.

6.1.1 Population and Geography

This chapter gives an overview of the megacities and major population centers (MPCs) of Europe, namely London, Paris, Moscow, the Benelux/Rhine-Ruhr region, the Po Valley, and the Eastern Mediterranean including Istanbul.

A summary of the populations and location of the European MPCs is given in Table 1. In contrast to MPCs in several other parts of the world, e.g., Asia and Africa, the populations of the European MPCs, with the exception of Istanbul, have been relatively stable over the past several decades, and are predicted to remain so for at least the next couple decades.

Table 1: Populations and Characteristics of European Megacities and Major Population Centers.

Megacity / MPC

Population1 (Million)



Paris, France




London, England




Po Valley, Italy




Ruhrgebiet, Germany and Benelux Region (Belgium, Netherlands, Luxemburg)

28 (BeNeLux) + 5.73 (Ruhrgebiet)



Moscow, Russia




Istanbul, Turkey




1 Population Source (unless otherwise noted): Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat (2004) and World Urbanization Prospects: The 2003 Revision, Web:; compilation accessible at

2 Exact population figure not found; lower limit estimate based on the sum of the populations of Milano and Torino.


Figure 1. Map of the population density in Europe and western Asia (persons per km2), based on 0.25o gridded data for 1995 from the Center for International Earth Science Information Network (CIESIN) at Columbia University (Yetman and Balk; check for an update at

Figure 1 shows a map of the population density of Europe. For Europe, the bottom-up statistical and census-based population data plotted here are generally very consistent with top-down estimates based on analyses of stable night lights; alternate representations of the population are available on the internet, e.g., a mapping by district complied by the IIASA European Rural Development (ERD) Project ( The map shows that each of the six European MPCs listed in Table 1 is characterized by a large central region with a population density exceeding 1000 persons/km2. There are also a handful of other cities within Europe with population densities as high as this, e.g., Berlin and Madrid, but the total populations of these cities are not large enough to generally be classified as Megacities or MPCs for the sake of this overview. Beyond the commonality of a dense core region, however, there are substantial differences in the geographical locations and urban and suburban structure of the European MPCs. One interesting feature is that while a large fraction of the MPCs worldwide are either coastal or close to large bodies of water, only one of the European MPCs, Istanbul, is really coastal. London is also relatively close to the coast, while Paris, the Po Valley and the RBR are all several hundred km away from the nearest coast, and Moscow is the most land-locked of all megacities worldwide. Further differences in the demographical and geographical characteristics are elucidated in the discussions of the individual cities, below.

6.1.2 Emissions

Research on emissions from megacities worldwide has included several studies of city-specific emissions. For Europe in particular, a significant recent effort has gone into developing a collection of inventories for European cities within the City Delta project (Cuvelier et al., 2007). Four of the European MPCs were also included in the study of Butler et al. (2008), which contrasted the emissions corresponding to 32 MPCs in three widely-used global emissions datasets (EDGAR, RETRO and IIASA) with each other and with city-specific emissions, where available. The comparison shows frequently large differences (often a factor of two or more) between the emissions for individual cities within the global datasets, and normally large underestimates compared to the city-specific datasets. This applies especially to Paris, for which the CO emissions in the global datasets range over nearly a factor of two, from 263 Gg(CO)/yr (EDGAR) to 490 Gg(CO)/yr (RETRO), and are a factor of 4-7 less than the 1907 Gg(CO)/yr estimated in the City Delta project. The discrepancy determined for London is smaller, but still exceeding a factor of 2, with a range of 800-1043 Gg(CO)/yr from the global inventories versus 1993 Gg(CO)/yr from the City Delta inventory. Interestingly, a much better agreement is found for Moscow, with a range of 979-1249 Gg(CO)/yr from the global inventories versus 1324 Gg(CO)/yr from the study of Gurjar et al. (2008). A much smaller but still highly uncertain CO source is estimated for Istanbul (244-602 Gg(CO)/yr from the global inventories, with no city-specific inventory available). The discrepancies between the datasets for NOx and NMHCs tend to be even larger. This large uncertainty – even for Eurpean Megacities, which should be among the best characterized around the world – points towards the large difficulty which will be inherent in assessing the role of megacities in regional and global atmospheric pollution and climate change, and ascertaining effective mitigation strategies. On the other hand, despite the large differences in the totals, there is a notable similarity in the characteristics of the relative importance of various sectors for the different gases. In particular, similar to most OECD nations, the emissions of CO are generally dominated by road transport, and of NOx and NMHC by a combination of road transport and industrial processes, contrasted with the large role of residential biofuel use for emissions from non-OECD countries.

Figure 2: Emissions of CO, NOx, SO2 (Mark Lawrence), BC (Sarah to contact)

6.1.3 Pollution levels

The air pollution in the European MPCs which results from the emissions discussed in the previous section, as part of the broader topic of general urban air quality, has a very long history of slowly increasing recognition and research. In particular, London has a very important historical role in this respect, with the “London Smog” events dating back at least to the 17th century, culminating in the week-long tragedy in December, 1952, which caused about 12,000 deaths. Many other large cities have been renowned for their poor air quality, as well as for the substantial clean-up efforts over more recent years, e.g., the reduction of acid rain throughout Europe in the latter part of the 20th century.

6.1.4 Outflow characteristics and effects on regional ozone-related atmospheric chemistry

To our knowledge, only one published study thus far (Butler and Lawrence, 2009) has examined the impact of megacities worldwide on regional and global ozone-related atmospheric chemistry, and none have done so yet for aerosol and climate impacts. A few further studies have examined this for specific regions (e.g., for Asia in Guttikunda et al., 2005), but none to our knowledge specifically for the European MPCs. Some studies on the impacts of individual cities will be discussed in the following sections.
Butler and Lawrence (2009) used a zeroth-order approach, the so-called “annihilation scenario”, to examine the megacity effects by removing their emissions from the corresponding gridcells in a global emissions inventory (at 1o horizontal resolution) before interpolating to the global model grid, and comparing these results with a simulation including the normal total emissions. The results show that the overall impact of megacities on the major ozone precursor gases NOx and CO, as well as on O3, are of the order of 10%, corresponding to the relative contribution of megacities to the global total emissions of the precursor gases (with some exceptions, such as a disproportionately large effect on PAN). The change in July mean surface ozone is shown for four scenarios in Figure 3. The exact dependence of the regional chemistry on the emissions varies as a function of geographical location, and corresponds particularly strongly with the latitudes of the MPCs. In the individual grid cells containing megacities, the response for European megacities is like for most other extratropical megacities, with a reduction in ozone year-round, and often an increase in ozone in the downwind grid cells, particularly in summertime; in tropical megacity grid cells, on the other hand, ozone generally increases year-round. The influence is found to change for various future scenarios. Under a future scenario with a maximum feasible reduction of emissions, the influence of megacities is generally reduced, while under a high-emission future scenario, although the local influence of megacities is increased, the geographical extent of the influence becomes smaller. One note worth making about these results is that the tendency for global emissions datasets to underestimate the emissions compared to city-specific datasets, as discussed above, also means that the impacts of megacities are probably somewhat underestimated in these simulations.

Figure 3. The percentage change in the global surface July O3 mixing ratio due to megacity emissions under four scenarios (from Butler and Lawrence, 2009).

Finally, a special characteristic of the European MPCs has been pointed out and quantified by Lawrence et al. (2007), who examined results of simulations with generic, gas-phase tracers with three different representative lifetimes (1, 10 and 100 days) emitted from 36 MPCs distributed globally. Using metrics to rank different outflow characteristics (“regional pollution potentials”) of the MPCs, it was found that the MPCs in this region tend to be ranked highest amongst all global regions in terms of the tendency for pollutants to both accumulate locally in the surface layer of the region immediately surrounding each MPC, as well as to be transported extensive distances (e.g. larger than 1000 km) downwind, while still remaining in the boundary layer. Conversely, the emissions from European MPCs are least effectively transported into the upper troposphere compared to other world regions. Two major open issues for follow-up studies are currently being investigated: the same kind of simulations with aerosol tracers (including sedimentation, scavenging and deposition) are being performed for comparison to the gas-phase tracer results (D. Kunkel et al., MPIC), and comparable regional model simulations are being set up for the European region to determine the impact of using a considerably higher resolution in a non-hydrostatic model on the pollutant dispersion characteristics (I. Coll et al., LISA, pers. comm.).

6.1.5 References

Baklanov, A.: Overview of the European project FUMAPEX, Atmos. Chem. Phys., 6, 2005-2015, 2006. 

Butler, T. M., M. G. Lawrence, B. Gurjar, J. van Aardenne, M. Schultz , J. Lelieveld, The representation of emissions from megacities in global emissions inventories, Atmos. Env., 42, 703-719, DOI: 10.1016/j.atmosenv.2007.09.060, 2008.

Cuvelier, C., Thunis, P., Vautard, R., Amann, M., Bessagnet, B., Bedogni, M., Berkowicz, R., Brandt, J., Brocheton, F., Builtjes, P., Carnavale, C., Coppalle, A., Denby, B., Douros, J., Graf, A., Hellmuth, O., Hodzic, A., Honore, C., Jonson, J., Kerschbaumer, A., de Leeuw, F., Minguzzi, E., Moussiopoulos, N., Pertot, C., Peuch, V. H., Pirovano, G., Rouil, L., Sauter, F., Schaap, M., Stern, R., Tarrason, L., Vignati, E., Volta, M., White, L., Wind, P., Zuber, A., CityDelta: A model intercomparison study to explore the impact of emission reductions in European cities in 2010, Atmospheric Environment, 41(1), pp.189-207, 2007.

Gurjar, B.R., Lelieveld, J., 2005. New directions: megacities and global change. Atmospheric Environment 39, 391–393.

Gurjar, B. R., T. M. Butler, M. G. Lawrence, J. Lelieveld, Evaluation of emissions and air quality in megacities, Atmos. Env., 42, 1693-1606, DOI: 10.1016/j.atmosenv.2007.10.048, 2008.

Guttikunda, S.K., Tang, Y., Carmichael, G.R., Kurata, G., Pan, L., Streets, D.G., Woo, J.H., Thongboonchoo, N., Fried, A., 2005. Impacts of Asian megacity emissions on regional air quality during spring 2001. Journal of Geophysical Research 110, doi:10.1029/2004JD004921.

Lawrence, M. G., T. M. Butler, J. Steinkamp, B. R. Gurjar, and J. Lelieveld,

Regional pollution potentials of megacities and other major population centers, Atmos. Chem. Phys., 7, 3969-3987, 2007.

UN, 2006: World Urbanization Prospects: The2005 Revision. Work Paper No ESA/P/WP/200, United Nations, Department of Economics and Social Affairs, Population Division, wup.htm.

UNFPA, 2007: State of World Population 2007: Unleashing the Potential of Urban Growth.

UN-HABITAT, 2006: State of the World's Cities 2006/7: The Millennium Development Goals and Urban Sustainability: 30 Years of Shaping the Habitat Agenda.

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