Your Alfresco area needs to breath just like you!

Without air it will not operate properly! the smoke grease,oil & fatty residue will linger in the air ! The smoke can be very off putting & the grease,oil & fatty residues will deposit themselves all round the Alfresco Are

Why is the happening when I have a BBQ Rangehood that can suck up /exhaust all these cooking residues?

Presuming, you have installed a BBQ Rangehood( that is one designed specifically to exhaust BBQ Cooking residues! Your BBQ Rangehood cannot work properly without having AIR coming into the Alfresco area. you might think that the BBQ Rangehood once turned on will just exhaust the BBQ Residues& if you have a lot of smoke etc just increase the BBQ Rangehood exhaust speed!

The BBQ Rangehood needs the Air into the Alfesco so that it can function as a Rangehood & exhaust most of the Fatty Residues & smoke!

It need access to outside air so that it can create a circumstance where the Exhaust/suction will move the Air Arround the Alfresco
Creating a simple cyclonic atmosphere which will enable the BBQ Rangehood to Exhust the smoke & the Fatty Residue!