Simulated rainfall fails to reflect trace element wash-off under natural conditions

Vegetation mitigates air pollution with trace elements (TEs), by capturing them on plant surfaces. However, retention on foliage is typically temporal and TE can be washed off by precipitation. Due to the inherent variability and unpredictability of natural rainfall, as well as complex environmental factors, pollutant removal <i>via</i> precipitation is often studied using simulated rain. This study aimed to determine whether simulated rainfall can reliably replace natural rainfall in experiments assessing the wash-off of TEs from leaf surfaces. Plant material was foliage of 17 plant species (herbaceous plants, deciduous and evergreen trees, and shrubs), growing in an urban park in Wuhan, China. Across all examined TEs (Mn, Fe, Cu, Zn, As, Ba, Pt), simulated rainfall generally removed a higher fraction of pollutants than natural rainfall. Interestingly, natural rainfall was associated with increased amounts of Cu and Zn on foliage after precipitation. Pollutant removal efficiency varied depending on the type of rainfall and plant groups, with natural rainfall being more effective in TEs removal from evergreen trees, while simulated rainfall performed better with deciduous shrubs and herbaceous species. These inter- and intra-group variations suggest that simulated rainfall does not fully replicate the mechanisms of pollution removal occurring in real-life conditions.