Influence of rainfall duration and intensity on particulate matter removal from plant leaves.

Rainfall influences removal of airborne particulate matter (PM) from leaf surfaces through a process called wash off resulting in throughfall that carries PM to the ground. The present study examined the effects of rainfall characteristics on PM wash-off mass and rate from the foliage of four broadleaf species, to investigate retention of PM pollution. In a controlled rainfall simulation experiment, rainfall intensity was set to 15, 30, and 50 mm h − 1 , and sampling intervals for the three rainfall intensities were divided into 10, 5, and 3 min, respectively. Of the plants examined, the evergreen shrub Euonymus japonicus had the greatest surface PM accumulation before rainfall (165 μg cm − 2 ), maximum wash-off during the first 2.5 mm of rain (30 μg cm − 2 ), and maximum surface PM retention after rainfall (24 μg cm − 2 ). Fitting observations with the Box Lucas regression model, cumulative PM wash-off rates increased with cumulative rainfall amount, until the curves tended to become steady after rain exceeded 12.5 mm. Wash off removed 51 to 70% of surface PM accumulation. As rainfall intensity increased, the duration of PM wash-off decreased, and wash-off rates were highest during the first rainfall interval. However, there was no significant difference between PM wash-off rates for rainfall intensities of 30 and 50 mm h − 1 in each rainfall interval. In addition, rain did not remove all PM completely, and PM retention following rainfall differed with rainfall intensity, except for Populus tomentosa . [ABSTRACT FROM AUTHOR]