Geoffrey Caruso

Understanding how nitrogen dioxide (NO ₂ ) varies both within and across cities is essential for assessing urban health inequalities, yet the joint influence of city size and internal structure remains poorly quantified. While it is expected that agglomeration size increases NO ₂ concentrations and that distance from major urban activities reduces them, the magnitude and form of their combined effect have not been established. Our objective is to move beyond city-specific local context effects and to characterize the general structural form of NO ₂ distributions, understood as their systematic variation with distance from the center across cities of different sizes. Using both ground monitoring stations and satellite data for 378 European Functional Urban Areas, we estimate parallel models for each measurement type and show that the same structural relationships hold in both cases. We find that NO ₂ concentrations increase with population size as a power law (with an exponent between 0.14 and 0.22) and decrease with distance from the city center (with an exponent between −0.12 and −0.18), with consistent results across measurement types and robust to local and regional controls. These effects combine into a scalable radial profile, where the total air pollution over a city is proportional to ( N / r ) ^0.16 , which generalizes the spatial distribution of NO ₂ in European cities. This formulation clarifies how total and per-capita pollution depend on the extent to which pollution is integrated and provides a simple framework for evaluating the health implications of urban growth.

The form and the size of cities influence their social, economic and environmental outcomes. The form of a city is itself influenced by the shape of its road network, but this relationship and how it is affected by city size are unclear. We analyse how road distances to the main centre vary across 300 European cities and how radial physical detours (i.e. the distance on the road network compared to the Euclidean distance) are affected by city size and extent. We use landuse and population data to sample potential residences and compute the fastest routes to the main centre. We find a linear relationship between road and Euclidean distances, and for the first time document an average radial physical detour of 1.343 across Europe. We then rescale distance bands so to make cities of different population size comparable and show the effect of different urban delineations. We find that physical detour ratios increase when core cities only are considered without suburbs. At the urban region scale, radial physical detours increase with city size, especially when other significant geographical factors (latitude, longitude, elevation change and proximity to coast) are controlled for. When the central part of cities only is considered, larger cities have smaller radial physical detours.

Air pollution bears severe health and environmental impacts and is of increasing concern to urban planners but densification strategies have ambiguous impacts. We analyse how households' aversion to generating and being exposed to traffic pollution at the residential place and during their commute influences emerging urban structures and how these structures in turn affect pollution exposure and the residential choice of households. Resulting spatial patterns are difficult to predict because of this feedback and the spatial form of urbanisation and road networks. We address this complexity with a micro-economic agent-based residential choice model dynamically coupled with a cellular automata model for pollution dispersion and its perception in neighbourhoods. Our simulation experiments on a theoretical grid suggest that the spatial scale of this perception is important. We also find that if both health and environmental concerns are to be addressed, a combination of reducing commuting distances and preserving local green spaces is necessary. In particular, locally dispersed urban development and intra-urban green spaces next to busy roads can mitigate pollution exposure.

Daily mobility has been shown to contribute to the wellbeing of older adults, as it promotes healthy and independent living. However, very little is known about how the complex relationships between locations, geographic environments and daily mobility relate to wellbeing. In the current paper, we rely on the concept of ‘motility’– defined as potential mobility– and the concept of ‘movement’– defined as actual mobility– to take a step forwards in disentangling the relationship between mobility and wellbeing. We further examine how both motility and movement relate to two complementary definitions of wellbeing: hedonic wellbeing as a measurement of happiness, and eudaimonic wellbeing as the actualisation of an individual’s human potential. To investigate this relationship, we draw up a conceptual framework stressing pathways linking mobility to wellbeing, which we empirically test using structural equation modelling on a stratified sample of 470 older adults. We first quantitatively confirm that motility is defined by access, competences, appropriation and attitudes to modes of transportation. We then observe that motility has direct effects on eudaimonic wellbeing and, to a lesser extent, on hedonic wellbeing. Part of the motility effects on wellbeing are mediated by movement. Separating mobility into motility and movement stresses the independent and complementary role that potential and realised mobility play in shaping older adults’ wellbeing.

How urban characteristics change with total population, their scaling behavior, has become an important research field since one needs to better understand the challenges of urban densification. Yet urban scaling research is largely disconnected from intra‐urban structure, and this seriously limits its operationalization. In contrast, the monocentric model of Alonso provides a residential choice‐based theory to urban density profiles. However, dedicated comparative static analyses do not completely solve how the model scales with population. This article bridges this gap by simultaneously introducing power laws for land, income and transport cost in the Alonso model. We show that the equilibrium urban structure of this augmented model matches recent empirical findings about the scaling of European population density profiles and satisfactorily represents European cities. This result is however not compatible with the observed scaling power of housing land profiles, and challenges current empirical understanding of wage and transport cost elasticities with population. Our results call for revisiting theories about land development and housing processes as well as the empirics of agglomeration benefits and transport costs.

The size and form of cities influence their social and environmental impacts. Whether cities have the same form irrespective of their size is still an open question. We analyse the profile of artificial land and population density, with respect to the distance to their main centre, for the 300 largest European cities. Our analysis combines the GMES/Copernicus Urban Atlas 2006 land use database at 5 m resolution for 300 larger urban zones with more than 100,000 inhabitants and the Geostat population grid at 1 km resolution. We find a remarkable constancy of radial profiles across city sizes. Artificial land profiles scale in the two horizontal dimensions with the square root of city population, while population density profiles scale in three dimensions with its cube root. In short, cities of different size are homothetic in terms of land use and population density, which challenges the idea that larger cities are more parsimonious in the use of land per capita. While earlier literature documented the scaling of average densities (total surface and population) with city size, we document the scaling of the whole radial distance profile with city size, thus liaising intra-urban radial analysis and systems of cities. Our findings also yield homogenous spatial definitions of cities, from which we can re-question urban scaling laws and Zipf’s law for cities.