Estimation of Urban Forest Pollution in Irkutsk According to the Level of Adsorption of PM_x Particles by Scots Pine Needles

Abstract

Studies have been carried out in natural forests on the territory of a large industrial center of Eastern Siberia (the city of Irkutsk). On the selected eight test sites, the concentration of suspended particles in the atmospheric air was measured in the following size range: PM_0.3, PM_0.5, PM_1.0, PM_2.5, PM_5.0, and PM_10.0 and the AQI air quality index is calculated. Forest pollution is assessed by the degree of accumulation of particulate matter (PM_x) in pine needles (Pinus sylvestris L.)—the main forest-forming species. Using scanning electron microscopy on the surface of the needles, the concentration, size, and chemical composition of PM_x were determined. These particles were found to contain a high proportion of heavy metals. A direct correlation was found between the sum of 20 heavy metals (∑₂₀ HM) adsorbed by needles, the content of PM_x in the atmospheric air, and the AQI index (r = 0.52–0.85). It has been found that the adsorption of a solid aerosol results in the formation of metallized accumulations of PM_x of different sizes, which actively penetrate into the tissues of the needles through the stomata and cuticle, exerting a toxic effect on the plant organism. It is shown that urban forests are a powerful factor in cleansing the air environment of the city; however, the currently observed significant pollution of the forests themselves requires the optimization of their condition.