The Turkey oak is a frequent tree species in the Mediterranean climate zones of southern Europe and Asia Minor. It has been used in the human diet, for medicinal purposes, firewood and charcoal production. Like all oaks, Turkey oak is suffering from dieback and decline owing to the combination of several detrimental factors, such as insects, diseases and unfavorable environment, leading to their deterioration and sometimes resulting in their early death.

Air pollution arising from different sources represents a serious environmental threat to all living organisms, including vegetation. Monitoring air contamination levels is necessary to detect pollution levels, regulate atmospheric pollution, and ultimately improve ambient air quality. The current study evaluated the effects of air pollutants with a focus on dust and some biochemical and physiological properties of Quercus cerris L., which is growing in Lebanon's Ezer forest, threatened by the presence of a public road on its northern side. The studied parameters include leaf extract pH, stomatal conductance, relative water content, hydrogen peroxide, proline, carotenoids, and air pollution tolerance index. These parameters can provide reliable information about the tolerance status of plants towards pollutants. Three sites with different exposure to vehicular activities were used to conduct this study, including a control site (unpolluted) and two polluted sites (S1 and S2). The results showed a significant reduction in stomatal conductance and relative water content at polluted sites compared with the control site. Hydrogen peroxide, proline, and carotenoids showed the highest levels at the S2 site, which is indicative of the fact that Quercus cerris undergoes established physiological and biochemical changes in response to environmental stress. Based on the air pollution tolerance index (4.97-9.85) Quercus cerris is categorized as a sensitive species that can be used as a biological monitor of environmental pollution. Thus, the development and implementation of efficient environmental action plans based on biomonitoring should be considered for protecting the forests.