The magnetic signal from trunk bark of urban trees catches the variation in particulate matter exposure within and across six European cities - Anskje Van Mensel; Karen Wuyts; Pedro Pinho; Babette Muyshondt; Cristiana Aleixo; Marta Alos Orti; Joan Casanelles-Abella; François Chiron; Tiit Hallikma; Lauri Laanisto; Marco Moretti; Ülo Niinemets; et al. (Environmental Science and Pollution Research, 2023)