Dispersion normalisation method for improved long-term trend evaluation: heavy metals in ambient air in the Czech Republic, Central Europe (2010–2021)

Long-term trends in atmospheric concentrations of heavy metals subject to legislative immission limits (As, Cd, Pb, Ni) were evaluated at selected monitoring stations representing different environmental settings across the Czech Republic (in Central Europe) over 12 years. Dispersion normalisation was applied to reduce the influence of meteorological variability on measured concentrations and to assess the effectiveness of legislative emission control measures. The results demonstrated statistically significant decreasing trends ( p < 0.001) across all station types and for all monitored heavy metals, aside from Ni at the industrial station, where no significant trend was detected. Furthermore, systematic differences between original and dispersion-normalised concentration data indicate that meteorological variability can, in some cases, mask actual emission levels, potentially leading to misinterpretation of air quality trends. Dispersion normalisation proved to be a suitable method for long-term trend assessment and for quantifying the impact of regulatory measures on air quality. The method's key advantages include simplicity and the availability of input data required to calculate the ventilation coefficient (e.g. from ERA5).