Boron is one of the most important elements on the agenda in recent years, both because it is a micronutrient for plants and because it is used in more than 250 fields in industry. Due to its intensive use and the continuous expansion of these areas of use, the concentrations of boron, which is produced more and more, are constantly increasing in receiving environments. However, boron, one of the important heavy metals, can cause significant health problems when inhaled from the air and taken into the human body. Therefore, monitoring the changes in boron concentration in the air is of great importance. In this study, the change of boron concentration in Pinus pinaster, Cupressus arizonica, Picea orientalis, Cedrus atlantica and Pseudotsuga menziesii species growing in Düzce, which is among the 5 most polluted cities in Europe, was examined on the basis of species, organ, direction and period in the last 40 years. The results of the study generally showed that boron concentrations did not change significantly on the basis of direction and year interval. Similarly, boron concentration in wood did not change significantly by species, whereas the change in boron concentration in bark was found to be statistically significant. According to the mean values, the lowest values were obtained in P. menziesii and the highest values were obtained in C. arizonica.