This is a campus building in Aalto University where you have a tree about 10 cm away from the window. The Espoo city does not allow the student organisation AYY to cut down the tree. There is a poor air-conditioning in the room so the fan is essential to speed up the airflow. Without the fan, the window becomes smoky and the room very hot.
I need to find filter to the window so I can keep the fan on also during times of heavy pollen times (15x100cm for the above window). The filter must be sturdy because birds get into the room.
I tested a novel idea of using computer fans with polycarbonate plastic thing for a smaller window but the computer fans provide very small airflow in comparison to the large fan.
Which kind of filters should I use in windows like above? Is it enough to have a cloth pinned to the sides of the window? Or do I need carbon filter? Can I use filters meant for computer fans like the above?