There's nothing inside, so the cover is glued on, presumably to avoid leaks, or anyone fitting a filter, although no reason why a non-aircon shouldn't have one.
So sit back, and enjoy the fresh air including the pollen and the soot from diesels.
(The most harmful soot from diesels is larger than pollen, so gets caught in the filters. Although, the use of particulate filters that incinerate the soot may be creating smaller particles. Hopefully they are less harmful.)
So sit back, and enjoy the fresh air including the pollen and the soot from diesels.
(The most harmful soot from diesels is larger than pollen, so gets caught in the filters. Although, the use of particulate filters that incinerate the soot may be creating smaller particles. Hopefully they are less harmful.)