A leaf blower is garening tool that propels air out of a nozzle to move yard debris such as leaves. Leaf blowers are usually powered by two-stroke engine or an electric motor, but four-stroke engines were recently introduced to partially address air pollution concerns. Leaf blowers are typically self contained handheld units, or backpack mounted units with a handheld wand. The latter is more ergonomic for prolonged use. Some units can also suck in leaves and small twigs via a vacuum, and shred them into a bag.