A 2019. study has tested activated carbon filter face masks and compared them to other masks when blocking pollution from the air.
Tests were performed before Covid19 outbreak, but their goal was to test how successful cotton fabric face masks with activated carbon filters are. Before Covid19 outbreak masks were mainly worn in parts of the world that suffers mostly from air pollution. Top polluting gasses are COx that can cause fatigue and heavy breathing due to lower oxygen absorption in the body, and NOx and SOx which can cause lung damage.
When tested, activated carbon filter face masks can block most air pollution. Their performance was just slightly behind the respirator full face mask.
When compared to other masks their performance was much better at blocking out polluting gasses. They also have great ability of blocking and capturing airborne particles like pollen, dust, allergens and other small and very small microscopic particles and bacteria.
You can find a full paper here: https://www.hindawi.com/journals/jt/2019/5283971/