Assessment of the air pollution in the town of Smolyan (Bulgaria) through instrumental and biomonitoring techniques

Air pollution is a significant health risk factor in Europe and the worldwide. The World Health Organization identifies it as a major health risk factor, responsible for almost 20% of all deaths in the European Union. Each city struggles with different types of pollution, as pollutants are influenced by a wide range of factors – both natural and anthropogenic. Air quality in Bulgaria is a matter of serious concern: measurements show that citizens across the country are breathing air that is considered harmful to health. The present study integrates the potential of instrumental monitoring and passive biomonitoring in the town of Smolyan, in order to make a complex assessment of the air pollution level and its impact on biota. Parallel measurements of selected air pollutants level into the ambient air and their bioaccumulation into tree leaves provide a more detailed knowledge of the process. Statistical evaluation confirmed the correlation between the elevated concentrations of particulate matter (detected through sensors) and the elevated content in tree leaves, as well as the visible symptoms such as chlorosis and necrosis. The involvement of antioxidant defense system was also registered through the synthesis of some key metabolites. The results obtained were used to develop an interactive map of "urban hotspots" and recommendations for application of nature-based solutions according to the type of zones and the level of air pollution.