Urban air pollution has become a serious environmental problem to trees and crops. This study was conducted in order to assess the impact of air pollutants on some physiological, morphological and physiological parameters of the Populus x canadensis Moench cultivated for ornamental purposes across the five air quality monitoring stations in Iaşi city area. This stations are equipped with analyzers for determination of gaseous pollutants (SO₂, NO₂, ozone), and solid pollutants (PM10). Measurements were made in vivo, as well on fresh material measured in different phenological stages, in the months May, July and September, 2012. The most significant response reactions to pollutants was showed by the individuals of Populus x canadensis grown at the site of the traffic station Podul de Piatră where SO₂ and particulate solids in suspension are the predominating pollutants with higher values. The SO2 level was 4.09 μg/m³ in May, 3.48 μg/m³ in July, 4.95 μg/m³ in September. The PM10 gravimetric level was 48.91 μg/m³ in May, 39.98 μg/m³ in July, 44.57μg/m³ in September. The air pollution around Podul de Piatră traffic station lead to a significant leaf area reduction of 72.04% in May, 48.46% in July and 48.46% in September. A photosynthetic rate reduction was observed by 43.95% in May, 43.91% in July and 43.92% in September, a transpiration reduction by 84.23% in May, 77.51% in July and 55.15% in September and stomatal conductance reduction by 29.82% in in May, 26.47% in July and 16.66% in September. Also the amount of chlorophyll a was reduced by 37.04% in in May, 37.34% in July and 62.18% in September and the chlorophyll b was reduced by 40.81% in in May, 36.79% in July and 18.55% in September. The study highlights that the emitted pollutants by the traffic affect the individuals of Populus x canadensis Moench.