Seasonal dynamics of polycyclic aromatic hydrocarbons in different-sized urban areas assessed by moss transplants

Moss bag biomonitoring has been applied to investigate airborne organic pollutants. Two moss species, Hypnum cupressiforme and Sphagnum girgensohnii, were exposed for two months within different-sized urban areas - metropolis, city, and town, and a rural site during winter and summer seasons. The bags were exposed at nine regulatory Air Quality monitoring stations, which represent different land use classes within the urban areas. After exposure, 16 polycyclic aromatic hydrocarbons (PAHs) were determined in the moss samples by gas chromatography‒mass spectrometry (GC-MS). At the urban sites, the mosses primarily accumulated three to six-ring PAHs: Phen, Fl, and Pyr, followed by B[k]F, B[a]P, I[cd]P, B[ghi]P, etc., while Nap was recorded in the summer samples. Both moss species identified the sites with the highest and lowest PAH levels in the air - typical urban sites with heavy traffic and those with thermal power plants (TPP) and seasonal residential heating as additional pollution sources, while the rural site was recognized as a proper control one. Mosses showed a strong seasonal fluctuation in PAHs with markedly higher prevalence in the cold winter season. Combustion-derived PAHs (COMPAHs) accounted for about 70% in the winter season, while in the summer, they fell to 40%. These results suggest activation of residential heating systems/units. Correlation analysis, principal component analysis, and diagnostic ratios confirmed that PAH emissions vary between seasons. Moss bag biomonitoring showed the same temporal distribution patterns as the instrumental measurements, but with similar spatial distribution patterns, for available comparative B[a]P and ∑PAH measurements.