Actually, if the PM2.5 and PM10 are high, you can see it very easily. If you can't see it, that means the air isn't polluted. Obviously some people confuse fog

Actually, if the PM2.5 and PM10 are high, you can see it very easily. If you can't see it, that means the air isn't polluted. Obviously some people confuse fog with smog, or can't see haze in some situations (failure to see). But it's always there and always visible. You can't have pollutions at that scale and not see them.