Resuspension of Particulate Chemical Species at Forested Sites

The resuspension rates of particulate chemical species have been estimated using aerodynamic surrogate surfaces (symmetrical airfoils) at a mixed deciduous forest site, and also using throughfall sampling at a loblolly pine forest site. The airfoils were placed above, within, and below the crown of the deciduous canopy to determine the vertical variation of deposition and resuspension. The resuspension rates of SO₄^2-, C₂O₄^2-, and Ca from the airfoils are estimated to be on the order of 10^-6-10^-5 s^-1. The resuspension rates within the crown are only slightly less than those above the canopy. This is in contrast to the mean wind speed, which is much smaller within the crown than above the canopy. The smaller differences in the resuspension rate compared with differences in mean wind speed may be due to the effects of wind gusts which penetrate deep within the canopy. Based on the throughfall data, the resuspension rates for Ca, Mg, and Na are also in the range 10^-6-10^-5 s^-1. Overall, these results suggest that resuspension may need to be taken into account when particle deposition to vegetation is estimated.