Antwerp is the second largest city in Belgium (pop. 529,417) with a maritime climate. The port of Antwerp is the 2nd largest seaport in Europe, handling 290 Mtonnes of cargo annually, and home to the largest integrated chemical cluster in Europe. Brussels International Airport (19 million passengers and 776 kton cargo in 2022), located only 30 km from Antwerp, is the main airport serving Flanders, incl. the Antwerp region.

The combination of dense population, high traffic volume (large share of diesel cars and freight traffic), port, and industrial activities has raised air quality concerns. Transport emissions contribute strongly to AQ in the city, and a Low Emission Zone was introduced in 2017.

Barcelona is the second-largest city in Spain, located on the country’s north-eastern coast (pop. 1.6 million; 3.2 million metro area). The Port of Barcelona is the third largest container in the country and the ninth largest in Europe.

The volume of traffic and the growth of the diesel vehicle fleet is the main source of air and noise pollution in the city. Measures have been implemented to mitigate air pollution, such as the introduction of Low Emission Zones.

Berlin (pop. 3.7 million; 6.1 million metro area) is an economic hub in Germany and Europe with an oceanic climate and continental influence. Berlin Brandenburg Airport is the third busiest airport in Germany and is one of the fifteen busiest in Europe.

Given its unique history, Berlin’s transportation infrastructure has developed heterogeneously across the city, leading to imbalances in transportation capabilities. Combined with its spatial extent, it has a large fleet of diesel trucks and cars that contribute to high levels of urban air and noise pollution alongside a large public transportation network.

Düsseldorf (pop. 632,000; 10.2 million Rhine-Ruhr metro region) has an oceanic climate due to the relief-related opening towards the North Sea. Düsseldorf is a trade fair city and home to many stock exchange-listed companies and has several harbours on the Rhine. The airport is an intercontinental hub and the fourth largest in Germany.

Energy production, industry and transport are the main causes of air pollution in the city. As traffic is a major source of pollution, Düsseldorf wants to establish an „environmentally sensitive traffic management system“ that collects environmental and traffic information and controls traffic in the city. In 2019 the goal of becoming climate neutral by 2035 was adopted.

Heraklion (pop. 174,000) is the largest city in Crete and has a Mediterranean climate. It has a port and an airport in the vicinity. The port has frequent domestic and international traffic serving international ports, with traffic increasing exponentially during the tourist season (ca. 8 months). During that period, Heraklion airport is the 2nd most frequently used in Greece, after Athens.

Heraklion experiences significant air pollution episodes during spring and fall due to dust episodes, during winter due to domestic heating, and year-round due to traffic during peak morning and afternoon hours. Pollution is most pronounced during summer when population and traffic peak in Heraklion. Particulate matter pollution levels represent a concern, especially from non-exhaust emissions.

Limassol (pop. 154,000) is a port city located on the south coast of Cyprus, the second biggest urban area of the island and hosts the island’s principal port. It is situated 40 km west of the largest industrial area and fossil fuel power plants.

Limassol is the most polluted city in Cyprus, frequently exceeding the legislated standards for particulate matter. This is exacerbated during winter months due to the combustion of biomass for residential heating and the occurrence of low thermal inversions.

Oslo metropolitan area (pop. 1,600,000) has a Nordic humid continental climate. The city of Oslo has a port with frequent domestic and international traffic serving international ports and a dense of rail-network that includes trains and trams.

Oslo experiences significant air pollution episodes in winter associated with thermal inversions. Even though around 50% of the fleet composition in Oslo is electric, particulate matter pollution levels still represent a concern, especially associated with non-exhaust emissions.

Rotterdam (pop. 660,000) has a maritime climate and hosts Europe’s largest port and a big industrial area. Rotterdam is a logistical hub with seagoing and inland shipping, rail links, substantial road transport and a small airport.

Dense population, high traffic volume, and shipping emissions contribute to poor air quality. The city will implement a Zero Emission Zone for medium and heavy-duty vehicles to achieve emission-free city logistics in 2025. However, the impact of non-exhaust emissions remains a concern. The recent introduction of new shipping fuels may increase heavy metal ship emissions.

Southampton is a port city (pop. 269,781) in the southern coast of the United Kingdom with an oceanic climate. The city is bounded by motorways to the north and west and the river Test estuary to the south. The port is the second largest by annual volume in the United Kingdom.

Southampton experiences high particulate matter pollution levels during winter periods due to adverse meteorological conditions and increases in residential wood combustion. Combustion emissions from shipping, ports, and traffic contribute to the pollution burden in selected areas. Southampton Airport is adjacent to the city boundary, with its flight path directly overhead.

Tbilisi is the capital of Georgia (pop. 1.5 million) and its largest city, located in the South Caucasus on the Kura River and has a humid subtropical climate with substantial continental and semi-arid influences.

Historically, the main source of air pollution was from industry, but today the increasing number of light vehicles, especially older models, is the main source of pollution. Current policies seek to strengthen public transport by expanding the network of compressed natural gas buses.

Zürich (pop. 427,000) is a business hub in northern Switzerland with a temperate climate. Zurich has a busy international airport (~31.5 million passengers in 2019).

To improve local air quality, the Zurich Airport administration is making modifications in flight routes, fuels used, and ground support equipment and practices. For road traffic, efforts are being made to shift towards low or zero local emission options and to reduce noise pollution through shifts to electric or alternative fuels or Euro 6(d) vehicles, improving and subsidizing the public transport options, reducing speed limits to 30km/h to improve traffic flow, and increased application of automated traffic steering and control systems.