Can rain from a laboratory replace real rain?
This question has accompanied research into the role of plants in air purification for years. It is known that leaves capture suspended dust, but their retention capacity is temporary—after rain, some of the pollutants are washed off the leaf surface. Since natural rain is variable and difficult to control, simulated rain generated in laboratory conditions is often used in experiments. On this basis, conclusions are drawn about how rain affects the retention of pollutants on plants in the environment.
However, the latest research by a team from the Centre for Climate Research and the Department of Biometrics at the Warsaw University of Life Sciences, conducted in collaboration with scientists from the College of Horticulture and Forestry, Huazhong Agricultural University in Wuhan (China), shows that in the case of trace elements, such a model can lead to misleading interpretations.
The study covered the leaves of 17 plant species—from perennials and shrubs to conifers and deciduous trees—growing in a city park in Wuhan. The washing away of seven elements (Mn, Fe, Cu, Zn, As, Ba, Pt) by natural and simulated rain was analyzed.
The most important finding? 🔎
Simulated rain typically removed significantly more elements from the leaves than natural rainfall. What’s more, in the case of zinc, copper, manganese, arsenic, and barium, their amount on the leaves… increased after natural rain. This surprising phenomenon may be due to the specific nature of urban aerosols and the processes that occur during real rainfall, which cannot be accurately reproduced in a laboratory.
It also turned out that the effectiveness of washing away pollutants varies between plant groups:
- natural rain was more effective in the case of evergreen trees 🌲
- simulated rain was better at “cleaning” deciduous shrubs and herbaceous plants 🌿
These results clearly show that simulated rain does not fully reflect the mechanisms of pollutant removal that occur under natural conditions. This applies to both the amount of elements washed away and the differences between plant groups. Therefore, caution should be exercised when extrapolating laboratory results to urban ecosystems in the context of the impact of rainfall.