European cities pollute half as much as those in the U.S. when growing, according to the Bank of Spain

A report from the Bank of Spain reveals that, with the same increase in population density, European cities raise their exposure to PM2.5 particles by 6%, compared to 14% in the U.S. Low-emission zones and public transport are key.

A study by the Bank of Spain has quantified a structural difference between the urban models of Europe and the United States. When population density increases by 1%, exposure to PM2.5 pollutant particles grows by 6% in European cities, compared to 14% in American ones. The elasticity, that is, the response of pollution to urban growth, is less than half in the Old Continent.

The report, prepared by the agency's research team, analyses how the increase in inhabitants per square kilometre affects air quality. PM2.5 are fine particles considered one of the main environmental risks to public health, as they penetrate the respiratory system and can cause cardiovascular and pulmonary diseases.

The data indicates that the European urban model manages to combine greater compactness and proximity among residents with a lower environmental cost. Among the factors explaining this, the study mentions urban configuration, the weight of public transport, commuting distances, and the characteristics of the vehicle fleet.

For the Bank of Spain, the evidence supports the possibility of promoting higher densities in European cities without assuming a proportional increase in pollution, something that does not occur to the same extent in the American case. The design of urban policies must consider these structural differences.

The role of low-emission zones

The report also explores the reasons behind this lower elasticity. One of the key factors identified is the existence of more restrictive mobility policies, such as low-emission zones (LEZ), which limit access for highly polluting vehicles. These measures, widely implemented in European cities, help reduce the amount of suspended particles even when urban density is high.

According to the document, the implementation of these zones has allowed for a 4% reduction in exposure to PM2.5 within regulated areas, and the benefits extend up to 3 kilometres outside their boundaries. This demonstrates that measures adopted in one area can also improve air quality in neighbouring districts.

However, the report warns about the heterogeneity of the results.

“Reductions are concentrated in larger and denser cities, as well as in those with medium-sized zones relative to the total urban area. In contrast, no significant effect is observed in smaller cities and areas,” the study notes.

This difference between cities makes it necessary to adjust policies according to the characteristics of each place.

Renewal of the vehicle fleet, not just displacement

The Bank of Spain points out that the positive effects of low-emission zones cannot be explained by a simple displacement of economic activity to unregulated areas, but rather by a renewal of the vehicle fleet. By restricting the circulation of the most polluting vehicles, these measures encourage the adoption of cleaner technologies and impact the air quality of the entire city.

The study reinforces the idea that urban densification can be compatible with environmental improvement if accompanied by ambitious and well-designed policies. The European experience shows that it is possible to build compact, efficient, and less polluted cities, provided there is an adequate regulatory framework and sustained investment in sustainable mobility.

Among the recommendations, the report underscores the importance of combining population growth with innovation in transport and technological renewal. The challenge, according to the Bank of Spain, is to ensure that urban development does not lead to a deterioration in air quality, but rather an opportunity to move towards healthier and more resilient models.