A system includes an intake, an exhaust, and an adjustable directing member. The intake is for taking in air, the exhaust is for exhausting air, and the adjustable directing member is positioned for directing exhaust air toward the intake. Another aspect is a system that includes a source of polluted air and an air cleaning system. The air cleaning system includes an intake, an exhaust, and a directing member. The intake is for taking in polluted air and the exhaust is for exhausting air. The directing member is for directing air from the exhaust toward the intake to provide an air screen for keeping the polluted air in the vicinity of the intake.