The BR500's four-stroke engine is five times cleaner than the standard two-stroke models.

NPR: L.A. Looks to Cut Smog with Leaf Blower Trade-In

EcoMotors and Achates are developing two-stroke, opposed piston diesel engines while Pinnacle is working on a four-stroke opposed piston gasoline engine.

FORBES: Engine Startup EcoMotors Signs Deal with Chinese Manufacturer