Fifty samples of Eucalyptus tree leaves were collected in such a way that 25 samples were collected from the vicinity of roads where traffic density is high and 25 samples were collected away from roads where traffic density is low or almost negligible. The purpose was to assess whether inhabitants away from main roads on the outskirts of metropolitan cities are exposed to the same amount of SO_x as those who live close to main roads using the Eucalyptus tree as a bioindicator. The mean concentration values showed alarming differences of accumulation for both types of areas, which concluded that the inhabitants close to the main roads on average are exposed to more than double (2.23 times) SO_x as those away from the roads.