The air quality decrease, especially in urban areas, is related to local-scale conditions
and to dispersion of air pollutants (regional and long-range) as well. The main objective
of this study was to decipher the seasonal variation of PM10, NO, NO2, NOx, SO2, O-3,
and CO over a 1-year period (2017) and the possible relationships between air pollution
and meteorological variables. Furthermore, trajectory cluster analysis and concentration-weighted
trajectory (CWT) methods were used to assess the trajectories and the source-receptor
relationship of PM10 in the Ciuc basin Transylvania, known as the "Cold Pole" of Romania.
The pollutants show lower concentrations during warmer periods, especially during
summer, and significantly higher concentrations were observed on heating season in
winter due to seasonal variations in energy use (biomass burning) and atmospheric
stability. Subsequently, in February, the highest concentration of PM10 was 132 mu
g/m(3), which is 4 times higher than the highest recorded monthly mean. Our results
indicate a negative correlation between CO/temperature (- 0.89), NOx/temperature (-
0.84) and positive between NOx/PM10 (0.95), CO/PM10, (0.9), and NOx/CO (0.98), respectively.
Dominant transport pathways were identified and the results revealed that slow-moving
southerly (similar to 45%,) and northwesterly (similar to 32%) air masses represent
almost 80% and mainly regional flows were discerned. During 2017, increased PM 10
levels were measured at the study site when air masses arrived mostly from northwest
and southeast. The CWT and polarplot models show a strong seasonal variation and significant
differences were observed between weekdays and weekends, namely highest PM10 concentrations
during weekends at low wind speed (2-4 m/s).