Broadmeadow and Freer-Smith (1996) described three methods of particular deposition: sedimentation; precipitation and impaction. Sedimentation and precipitation occur due to gravity and collision with rain droplets respectively, and are unaffected by vegetation. Impaction occurs when a laminar air stream is disrupted as it passes the aerodynamically rough plant surfaces, while the particle continues in a straight line and strikes the obstacle, either through direct interception or electrostatic attraction. Retention can be helped by rough, pubescent, moist and/or sticky surfaces, where the literature review by Beckett et al. (1998) found increased stickiness of surface particularly facilitates greater coarser particle capture, while, roughness of.
