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, the C isotope ratio (13C/12C, expressed as d13C) is susceptible to atmospheric CO2 and other pollutants (SO2, NOx, O3, and acid rain). Because current increases in atmospheric CO2 concentration are due to 13C-depleted CO2 emission from soil organic carbon decomposition and fossil fuel combustion, annual rings of trees grown without other pollutants may show a 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 low levels of pollutants, leading to less negative d13C. However, as tree ring d13C is susceptible to several other factors that affect gas exchange, supplementary data on atmospheric pollution, climate, and soil resources should be taken into consideration for more reliable interpretation of d13C in relation to atmospheric environment changes.