One finding common to all places was that indoor air quality is strongly related to the outdoor air, and open windows and doors, as well as leaks around them, can quickly cause indoor air quality to rise and fall with outdoor air levels.
I also noticed that on the worst outdoor days when levels were over 600, the indoor air in all places, while lower than outside, was still at unhealthy levels over 300. That’s because those pollution particulates are so small, they simply diffuse rapidly and easily into buildings.
In general, most buildings’ indoor air was 40%-80% better than outdoors. For example, on December 7th the outdoor air was 1140, and indoor air in my office was 750; a mall was 920; and home was 380. (Don’t forget that readings 300 and above are unhealthy).
Malls, Offices, Restaurants:
One enclosed mall had a level of 920 with outdoor air at 1500. Another open-air mall had readings 1150-1490, with outside air 1560.
One very popular expat bookstore/cafe had indoor levels even higher than the already hazardous outdoor levels, which was quite rare. Their indoor air smoking section was 1720, and non-smoking room was 1600, and outside was 1320. This seemed due to a lack of proper ventilation as well as their smoking section, which easily permeated into their non-smoking rooms.
Most indoor malls and offices had levels 50-90% of the outside air, depending on how well sealed and ventilated they were. Again, many times the indoor air was far above healthy levels, and was always related to the outdoor air levels.
The gyms I sampled did well, usually about half the levels of outdoor air. One gym had a level of 65, with outdoor air 120. That healthy level probably was due to their good HVAC systems and filters. But each gym is different, so it’s good to ask your gym what they do to keep their air quality healthy.
My home, after weatherproofing some drafty windows, had levels 70% of outdoor air with no air purifiers. After cranking up both of my imported air purifiers to the max for two hours, I dramatically improved the ratio to 9-21% (indoor levels 140-320, outside 1500). On a usual day when my air purifiers are at a quieter middle setting, the indoor air was 20-40% better than outside.
For example, on a good day with outdoor air 200, my indoor air was 60. Usually, outdoor air — and therefore, indoor air — is worst overnight due to diesel trucks and construction sites. So, I feel more comfortable keeping my windows closed with my bedroom air purifier set at a higher level, yet still quiet enough for sleep.
One benefit of these new air quality websites (iphone.bjair.info) is that I will check the current Air Quality Index (AQI), and if it is high I will turn up my purifiers a level or two.
What about smoking?
I did a few samples from smoky restaurants and bars and found all samples in smoking areas far above the safety threshold of 300. My highest recording anywhere, at 1720, was in a bookstore cafe smoking section. A five-star hotel’s lobby lounge had a level of 1126, much higher than the outdoor air at 720.
All readings were at levels hazardous to health, and it’s crucial for these places to have proper ventilation and air filters. The long-term effects of indoor smoking are a well-documented health risk to their full time staff, not to mention the short-term risks to their customers.
The ideal option, of course, is to ban indoor smoking entirely, as I found all non-smoking sections entirely ineffective in improving the air quality in any meaningful way.