Effect of simulated rain and rain frequency on particulate matter re-accumulation in roadside climbers Parthenocissus quinquefolia

Simulated rainfall effectively removes particulate matter (PM) from plant surfaces and facilitates subsequent PM re-accumulation, offering potential for enhancing atmospheric PM mitigation. However, comprehensive studies on its efficacy remain limited. This study examined the impact of varying simulated rainfall frequencies on washable PM (_RPM) removal efficiency and PM re-accumulation dynamics in Parthenocissus quinquefolia cultivated on a green screen. PM was categorized into three fractions-_RPM, surface PM (_SPM), and wax PM (_WPM)-and quantified using filter-based assessments. Results indicated that daily simulated rainfall (ED) consistently removed _RPM across all PM fractions (total _RPM, _RPM_10-100, PM_2.5-10, and PM_0.2-2.5) throughout the study. While twelve-day (12D) numerically led to the most _RPM removal, its efficiency was comparable to single ED and six-day (6D) frequencies, with no significant statistical difference. Cumulative _RPM washed off in the ED treatment was significantly higher than in the 12D treatment for all PM fractions (3.0-3.3 times greater), with no adverse effects on plant physiology. Notably, no consistent patterns of _RPM re-accumulation were observed, and simulated rainfall had minimal influence on daily _SPM and _WPM re-accumulation. Extended experimental durations are recommended to validate these findings. This study highlights the simplicity and scalability of frequent simulated rainfall as an effective strategy for accelerating PM phytoremediation in urban environments with persistent air pollution, contributing to sustainable air quality management.