We might remember that a few years ago the advice from FEMA was plastic sheeting and duct tape. They apparently cribbed this strategy from the American Red Cross First Aid and Safety Handbook, 1992 edition, p. 255.

"If you are told by local officials to "shelter in place" rather than evacuate, immediately to inside and seal off your home. Close all windows and doors, turn off the heat or air conditioning, turn off any fans, close any ducts or outside vents (including those to the dryer and stove), and close the fireplace damper. If there is danger of explosion, close the window shades and curtains, then stay away from the windows.

Next, grab your emergency supplies (see page 254) and go at once to the room with the fewest windows and doors (but avoid the basement, where toxic fumes may settle). Once you are inside this room, seal all gaps....with thick tape or wet towels. A wet cloth over your nose and mouth will help filter out dangerous chemicals. Listen to the radio for updates, and stay inside until you are notified that it is safe to leave."

Err, right......

N95 masks might be useful if particulates are the problem. Respirators may be useful, if you have the correct canisters for the particular hazard. Obviously, avoiding physical exertion and exercise is a good idea.

Actually, I practice a mild form of these procedures whenever air quality degrades in my area - usually the degraded air quality is due to particulates (often from our forest fires). I curtail my bike ride, perhaps substituting an abbreviated ride indoors on my stationary bike early in the day, restrict outdoor activity, and (sometimes)wear an N95 mask. The N95 looks really, really dorky, but I have only one set of lungs, and they have been abused enough.

If I have any option, the prospect of bad air quality is a good inducement to flee in the first place. Depending upon circumstances, it might be time to bug out if you had first decided to shelter.