Tree rings are datable archives of environmental changes such as atmospheric pollution as tree annual growth rings store information on the growth conditions in the year of specific ring formation. Particularly, C isotope ratio (¹³C/¹²C, expressed as d¹³C) is susceptible to atmospheric CO₂ and other pollutants (SO₂, NO_x, O₃, and acid rain). Because current increase in atmospheric CO₂ concentration is due to ¹³C-depleted CO_{2 emission from soil organic carbon decomposition and fossil fuel combustion, annual rings of trees grown without other pollutants may show decreasing d¹³C pattern since the industrial revolution. Meanwhile, trees exposed to atmospheric pollution (e.g. in metropolitan or industrial areas) may show increases in d¹³C during the exposure period as atmospheric pollutants tend to decrease C isotope discrimination via reduced stomatal conductance or enhanced carboxylation particularly at a low level of pollutants, leading to less negative d¹³C. However, as tree ring d¹³C is susceptible to several other factors that affect gas exchanges, supplementary data on atmospheric pollution, climate, and soil resources should be taken into consideration for more reliable interpretation of d¹³C in relation with atmospheric environment changes.}