Clean air is when an F1 car is free from rivals and goes alone on a track. It gives optimal aerodynamic performance due to the fact that the airflow is not hampered by any moving object around it. Racing in a condition like this is called racing in clean air.
What is Dirty air in F1?
Dirty air refers to a situation when an F1 vehicle is behind a leading car. The car behind will face turbulent air that reduces the aerodynamic performance and downforce of the car. Racing like this is called racing in dirty air. Also, when there is dirty air the engine cooling system will be affected.
Racing in dirty air has some advantages like reduced air resistance because of the leading car. Racing directly behind a leading car like this is called slipstreaming. However with slipstreaming it’s harder to steer and there will be a loss of downforce.