Great ask, I am very curious about this too. I spent a year in Cairo, but luckily on the island in the middle of the Nile (better airflow). Living downtown was

Great ask, I am very curious about this too. I spent a year in Cairo, but luckily on the island in the middle of the Nile (better airflow). Living downtown was supposed to be the equivalent of smoking a pack of cigarettes a day. I am most concerned about pm 2.5 particles, and my understanding is the masks are better at blocking those because they are bigger? I see a lot of people in London wearing those masks when they are biking...