Ambient air pollution is one of the leading contributors to the global health burden according to the Global Burden of Disease study of 2021. Nevertheless, most air pollution exposure assessments present one major inaccuracy: they assume populations are static and that people are only exposed to air pollution in their residence areas, ignoring their mobility patterns. In the study “The effect of recurrent mobility on air pollution exposure and mortality burden in Catalonia”, carried out within the framework of the MePreCiSa project, assessed how air pollution exposure changes when considering recurrent mobility for Catalonia in 2022.

Previous works on the effect of mobility on air pollution exposure had to limit themselves either to fine-grained studies for small areas and short time periods, or coarser studies for a greater spatiotemporal extent. Here, the data sources used for the study make it possible to work with all of 2022 and the entire region of Catalonia, with a population of 7.76 million people, without having to greatly compromise the resolution of the study. This has been accomplished thanks to the origin-destination data derived from mobile phones and released by the Spanish Ministry of Transport and Sustainable Mobility, which allows to approximate the presence of people in each of the 584 districts of the study for each hour of the day. Furthermore, the outputs of the CALIOPE model, developed by the Barcelona Supercomputing Center, have been used with bias correction at a 1 x 1 km resolution for the air pollutants NO₂, O₃, PM_2.5 and PM₁₀, enabling us to make comparisons between them.

In the study mentioned, published by the International Journal of Health Geographics, both data sources were used to obtain air pollution exposure estimates weighted by the presence of residents in each district. It can be observed that the residents of most districts present different exposures when mobility is considered (between 76% and 86% of districts). A pattern is observed where the residents of rural areas which regularly travel to cities are more exposed to NO₂, PM_2.5 and PM₁₀, which are pollutants that present higher levels in cities. On the other hand, they are less exposed to O₃, which presents lower levels in cities. The most extreme differences are found in travelers heading to the Barcelona Metropolitan Area, which is notorious for its pollution spikes. The change in the annual average exposure of the commuting population can be quite high, reaching differences of up to 8.8 μg/m³ of additional exposure to NO₂, 2.0 μg/m³ of additional exposure to PM_2.5 and PM₁₀, and -5.9 μg/m³ of less exposure to O₃. The effect over the total population is more diluted and it depends on the proportion of regular travelers.

Overall, the study carried out by the MePreCiSa project team shows the importance of considering mobility for air pollution exposure assessments, especially for the population of rural areas. Incorporating mobility-corrected air pollution exposure profiles in future public health studies will result in less biased estimates of the effect of air pollution on health and the resulting burden. Moreover, taking mobility into account might be critical for certain population segments with different mobility habits, like children or the elderly.