We investigated the use of metals accumulated on tree bark for mapping their 2 deposition across metropolitan Sheffield by sampling 642 trees of three common species. 3Mean concentrations of metals were generally an order of magnitude greater than 4 in samples from a remote uncontaminated site. We found trivially small differences 5 among tree species with respect to metal concentrations on bark, and in subsequent 6 statistical analyses did not discriminate between them. We mapped the concentrations 7 of As, Cd and Ni by lognormal universal kriging using parameters estimated by residual 8 maximum likelihood (reml). The concentrations of Ni and Cd were greatest close to 9 a large steel works, their probable source, and declined markedly within 500 metres 10 of it and from there more gradually over several kilometres. Arsenic was much more 11 evenly distributed, probably as a result of locally mined coal burned in domestic fires 12 for many years. Tree bark seems to integrate airborne pollution over time, and our 13 findings show that sampling and analysing it are cost-effective means of mapping and 14 identifying sources. 15Capsule: Multi-element analysis of tree bark can be effective for mapping the deposition 16 of metals from air and relating it to sources of emission.

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