4. Conclusion
Saturation isothermal remanent magnetization (SIRM) of S. girgensohnii moss bags, exposed in three different urban microenvironments in Belgrade – street canyons, city tunnel and parking garages – showed statistically significant differences (p < 0.05) between sites. The highest moss SIRM values were obtained in the city tunnel as a result of the high traffic intensity passing through it and the specific tunnel geometry with dragged air flow caused by the so-called “piston-type effect”. The lowest moss SIRM was measured in the parking garages due to limited turbulence at these sites leading to a reduction in PM captured by the moss bags.
The specific vertical variation of the moss SIRM distribution in the street canyons depends on their geometry disrupting natural ventilation. The best correlation between SIRM and element content in the moss was observed for the first moss bag exposure height (4 m), making this more representative for biomonitoring surveys of traffic-induced air pollution in comparison with other studied heights (8 m and 16 m).
Under conditions of increased ambient pollution as in city tunnels, moss exposure time could be less than 10 weeks. The results showed that exposure time enough for sufficient moss enrichment with PM in the tunnel is 5 weeks.
Very high correlation coefficients (R ≥ 0.95, p < 0.05) were found between moss SIRM values and the concentration of certain trace elements (Cr, Cu, Fe and Ni) in the moss. As a significant correlation was observed between moss SIRM and traffic intensity, it could be assumed that moss particle enrichment is mainly due to traffic related pollution.
The results imply the possibility of using moss bags for small-scale spatial biomagnetic monitoring of particle-bound airborne pollutants in urban areas.
Acknowledgements
This paper was realized as a part of the project no. III43007 financed by the Ministry of Education and Science of the Republic of Serbia. We are grateful to Leen Van Ham for SIRM analysis of the moss samples.