AbstractBio-monitoring of air quality in TehranCity was investigated by analyzing 36 pine tree (Pinus eldarica Medw.) barks. The samples were taken from different locations with different degrees of metal pollution (urban, industrial, highway, and control sites). Then, the concentrations of lead (Pb), zinc (Zn), copper (Cu), nickel (Ni), and chromium (Cr) were measured using a flame atomic absorption spectrophotometer. The results of this study showed that the highest and lowest metal concentrations were found in the heavy traffic sites and the control site, respectively. Lead content was found to be the highest in high traffic density areas. The industrial part of the city was characterized by high Zn, Cr, and Ni contents. Variation in heavy metal concentrations between sites was observed and attributed to differences in traffic density and anthropogenic activities. The research also confirms the suitability of Pinus eldarica Medw barks as a suitable bio-indicator of aerial fallout of heavy metals.