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

Abstract. Long-term trends in atmospheric concentrations of heavy metals subject to legislative immission limits - Arsenic (6.0 ng m^-3), Cadmium (5.0 ng m^-3), Lead (500 ng m^-3), and Nickel (20 ng m^-3) - were evaluated at selected monitoring stations representing different environmental settings across the Czech Republic (in Central Europe) over twelve years. The dispersion normalisation method, which suppresses the influence of meteorological conditions on observed heavy metal concentrations, was employed to assess the effectiveness of legislative emission control measures. The results demonstrate statistically significant decreasing trends (p < 0.001) across all station types and all monitored heavy metals, except for Nickel at industrial stations, where no significant trend was detected. Furthermore, the systematic differences between original and dispersion-normalised concentration data confirm that meteorological variability can, in some cases, mask true emission levels, potentially leading to misinterpretation of air quality trends.