Nitrogen stable isotope (δ15N), PCBs, PAHs and their nitro derivates (NPAHs) in tree rings as a reliable tool for air pollution reconstruction in urban areas: A study of CO, NO2, PM10, PM2.5, and SO2 concentrations in the air.

London plane (Platanus × acerifolia (Aiton) Willd.) tree ring chronologies from urban contaminated street and non-contaminated park were compared regarding accumulation of 15 polycyclic aromatic hydrocarbons (PAHs), 10 polychlorinated biphenyls (PCBs) and 6 nitro (-NO2) PAH derivates (NPAHs), and nitrogen stable isotope ratio (δ15N). Temporal annual accumulations were tracked from 1970 to 2021 with the goal to reconstruct concentrations of air pollutants (nitrogen dioxide (NO2), carbon monoxide (CO), sulfur dioxide (SO2), particulate matter (PM)2.5 and PM10), using complex generalized additive mixed model (GAMM). Results indicate that tree rings accumulated all 31 targeted pollutants, while trees from contaminated site accumulated two-to three-fold higher amounts of pollutants in their tree rings. Likewise, δ15N clearly indicate that trees from the contaminated site accumulated more heavier N stable isotope. Trees from park had greater radial increment, while their chronologies did not correlate with air pollutants, unlike the targeted organic pollutants and δ15N. The GAMM results showed that only air PM10 is weakly correlated with tree rings (Adj. R2 < 0.35), while air NO2 and SO2 had the best fit with tree rings (Adj. R2 = 0.4-0.8). Finally, this study showed that air pollution could be reconstructed by using organic pollutants accumulated in tree rings, while δ15N can be a key indicator for air pollutant reconstruction by using complex environmental models.