Tree rings are increasingly used in different fields of science to reconstruct past environmental conditions. However, the potential of tree rings in reconstrcucting past enviromental conditions is not yet completely exploited. Although tree rings can provide proxy data on the chemical composition of the air in the past, their power as bioindicators is partly still undiscovered. In the past decades, air chemical composition has changed, with possible strong impacts on human health. Epidemiological studies are currently carried out comparing human health databases with data recorded by air-quality monitoring stations. However, such stations were installed during the beginnings of the 90s or, at best, at the end of the 80s. Tree-ring reconstructions of past air chemical composition may provide precious proxy data for the past century or for even longer periods of time with a much higher spatial resolution. Tree rings therefore could be useful for studying the impact of air pollution on human health. In this talk, we shall illustrate the potential and limitations of the use of tree-ring characteristics (ring width, density, stable isotopes - e.g., ¹⁸O, ¹³C, ¹⁵N -, and radiocarbon, i.e. ¹⁴C), in reconstructing past air quality. Moreover, we shall show recent examples of research carried out for studying the impact of increasing trends in nitrogen deposition, in heavy metals pollution, and in atmospheric concentrations of tropospheric ozone and carbon-dioxide on tree physiology and growth.