Here's how I am prepared:
And I am better informed by having watched the movie "Chai Jing's review. Under the Dome":
I wear the mask now when I go jogging on days with higher than 60 or 70 microgram/cubic meter of PM2.5 (particulate matter smaller than 2.5 microns) The above movie explains the dangers of PM2.5 and the above mask is tested to remove 95% of particles of 0.3 micron.
I have also found a better phone app and website that tells us the PM2.5 levels of the town closest to us: http://aqicn.org/city/beijing/yanqingzhen/
By the way, this town, Yanqing, 15 KM to the east of us is in the movie. It is the town where they went at night to test the emissions from illegal diesel trucks. And in the past week, the PM2.5 levels in Yanqing have only dropped below 100 for one 4 hour period (and they peaked at just over 200 once this week. It is usually better than that here. So this week, we even wear the mask to go out for a walk. We aren't the only people wearing masks but almost - and we have better masks than what most others wear.
This past week the view has been :
This picture is taken from a different hilltop but is viewing the same valley as below - except that this week we can't see the valley.
Usually it looks like this (copied from last post):