As mentioned upthread, easy enough to look up, but will it in any material way change your plans?

Regardless of how bad the pollution, if this was my only trip to BJ, I would still go to the GW etc. (although the view will be terrible).

You could invest in an N95 respirator mask I suppose, but wouldn't recommend it: the vast majority of people don't know how to fit it properly on their face, so it is just a (bad) cosmetic effort.

tb