For one thing, the concentration has to be a thousand times less. For another, you're just not around it that much. For a third, how can one reliably measure the exposure? Far too many variables.
PM2.5 concentrations tend to be very high around smokers. I live next to one, and even though we're separated by a door and he smokes in his own apartment, the smoking frequently pushes air in my apartment above 200 µg/m³. (I have 3 years of data to prove it.)
Since the outside air is typically even more dangerous here, I can't simply open a window and have to use air filters to combat this.
