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From what I recall it is a screen used to trap debris and create some mild turbulence as to allow good air mix at the entrance of the Mass AirFlow sensor. The MAF is located in the area between the air-box and intake throttle body. The wire harness going to the cylindrical thingy in the middle of it all is the MAF sensor housing. The sensor itself is inside, behind the screen. I think it works by heating up a platinum wire strung across the area in which air flows. The wire is delivered a specific amount of current at one end and the current is measured at the other end. The difference between the two measurements is then calculated into airflow. I guess that with the current air temperature known, the resistance of the platinum wire at its given temperature, and a high sample rate measurement of the remaining current at the other end of the wire, the rate of air flowing across the wire is pretty accurate. But that info is from many years ago. What the Volvo has could be different. I am sure that I will be corrected if wrong. Hope this helped and did not further confuse you.

Prospero