Category Archives: Air Pollution Essentials

Air Pollution Essentials

Here is my collection of evidence-based articles regarding air pollution’s effects, as well as what you can do to decrease your risks.

Leave a Reply

Good News: Biking In Beijing Helps More Than Hurts

Here’s a very common expat question: is riding a bike in a city helping or harming your health? Fortunately, someone researched this exact question and now we can breathe with some relief, as the verdict is in: biking is beneficial.

The article was just published in Environmental Health Perspectives journal and is an essential read for those bikers out there, or the many fence-sitters a bit scared of Beijing’s streets and air. The paper, from a Netherlands group, reviewed all the current literature and data from multiple cities around the world and came up with some very encouraging figures:

For the individuals who shift from car to bicycle, we estimated that beneficial effects of increased physical activity are substantially larger (3 – 14 months gained) than the potential mortality effect of increased inhaled air pollution doses (0.8 – 40 days lost) and the increase in traffic accidents (5 – 9 days lost). Societal benefits are even larger due to a modest reduction in air pollution and greenhouse gas emissions and traffic accidents.

Conclusions: On average, the estimated health benefits of cycling were substantially larger than the risks relative to car driving for individuals shifting mode of transport.

The article has many good points, for example by noting that car drivers actually breathe in dirtier air than bikers, but bikers inhale more deeply. From the article:

Overall, air pollution exposures experienced by car drivers were modestly higher than those experienced by cyclists, with mean ratios of 1.16 for PM2.5, 1.01 for ultrafine particles and 1.65 for elemental carbon or soot. However, increased physical activity results in higher minute ventilation in cyclists than car drivers, with estimates from two Dutch studies reporting that the minute ventilation of cyclists was 2.3 times (van Wijnen et al. 1995) and 2.1 times (Zuurbier et al. 2009) higher than that of car drivers. Therefore, inhaled doses of fine particles and to a lesser extent elemental carbon may be higher in cyclists.

You can also read a news report about this article from Bloomberg: City Cycling Seems to Have More Upsides Than Down.

Biking To Work: Get All The Exercise You Need!

I think this is a very encouraging article, as it may sway some of you to bike more in Beijing as a form of exercise. Those few minutes each way on your commute can add up enough to give you the recommended heart-healthy exercise levels. Here are more details why:

In several physical activity studies, metabolic equivalent (MET) is used as an indicator of physical activity and the minimum goal should be in the range of 500 to 1000 MET·min·week. Leisure cycling or cycling to work (speed 15 km·hr) has a MET value of 4 and is characterized as a moderate activity. Hence, a person shifting from car to bike for a daily short distance of 7.5 km would meet the minimum recommendation (7.5 km / 15 km·hr = 30 minutes) for physical activity in 5 days (4 MET x 30 minutes x 5 days = 600 MET·min·week).

太可怕!My Air Quality Journal, Part Two

Last autumn I wrote a very popular piece covering my escapades around town with an air particle monitor. I had so much fun that I borrowed the monitor again last winter and published my findings in CityWeekend Beijing Parents & Kids magazine, now published every two months. Here is my reprint:

Winter this year started early, and so did the seasonal decrease in air quality, traditionally due to home coal burning and weather patterns. As we are now snuggled away indoors, this is the perfect time to review how indoor air quality can also affect the health of you and your family. Some indoor chemicals such as formaldehyde and benzene are well known hazards, but probably the biggest indoor worry in Beijing is the same outdoor air pollution that easily seeps indoors. Many schools monitor outdoor air quality data for their pollution alert systems, but is their indoor air safe enough? And what about other buildings, such as your home or office, or malls, restaurants and hotels? How is their air quality, and what can we do to minimize indoor pollution’s effects?

To assess these issues, I borrowed a ParticleScan Pro portable monitor from the IQAir air purifier company for one week, and I took dozens of readings from multiple indoor and outdoor spots. I measured tiny particles 0.3 microns in size, which the World Health Organization considers the most dangerous to your health — especially for young children, the elderly, and those with heart and lung diseases. These particulates are created mostly by coal burning, factories and vehicle exhaust, especially diesel.

The scanner uses a laser to tally the number of particles per liter of air. The IQAir guidelines recommend indoor air readings under 100,000 as safest, and anything over 300,000 as hazardous. For simplicity in this article, we will lop off 3 zeroes (i.e. anything over 300 is hazardous). Please note that this number cannot be directly compared to other official pollution indexes as the technique and particle sizes are different.

Major findings:

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 ( 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. Let’s say that again:

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.

What can you do?

  • All owners of indoor spaces should periodically reevaluate and update their weatherproofing and air filters and purifiers. I bought weatherproofing strips (menchuang mifeng jiaotiao 门窗密封胶条) at B&Q for 35RMB a box, and instantly noticed a 10% improvement in indoor air particle numbers, not to mention the gains in heating and AC efficiency.
  • Air filters and purifiers also play a key role, especially on the worst outside days.
  • Large buildings, homes and schools should ensure that their HVAC ventilation systems use filters with a minimum efficiency rating value (MERV) of 13 or above, and replace them at the proper intervals. Stand-alone air purifiers can be placed in poorly ventilated areas or places with the most vulnerable people (preschool rooms, bedrooms).
  • Children are most at risk of pollution’s ill effects, so schools should be especially vigilant in monitoring real-time pollution data via websites and implementing action plans as needed. For example, a reported AQI higher than 200 may call for postponing all outdoor PE and sports.
  • Also, we should all encourage non-smoking in all indoor areas, especially your own home.


The Bottom Line:

We all spend 80-90% of our time indoors, especially in winter, so it’s important to be proactive and take control over our indoor air quality. Even while indoors, fine particulate pollution levels can be high enough to cause both short-term and long-term health effects, especially for small children. Fortunately, with a bit of indoor maintenance and monitoring websites such as, you can dramatically reduce those risks.

Plants Can Improve Indoor Air

I’ve talked a lot about indoor air quality, and I’m happy to report that Beijing Kids has an excellent post this week about indoor plants. They discuss a short video from the TED Conference series; this presentation discusses three common house plants and details how efficiently they can remove CO2, create oxygen, and also absorb toxins. Continue reading Plants Can Improve Indoor Air

My Air Quality Journal: 太可怕!

I’ve been writing quite a few posts on air pollution lately, and I decided to get some hands-on data which I’d like to share with everyone. The good folks at IQAir allowed me to borrow one of their handheld particle scanners (see picture below); I then got a week of sample data from a variety of places, both indoors and outdoors, urban and rural. I must admit that many conclusions were surprising!

The non-smoking gun... (get it?)The Most Surprising Findings

OK, first some dull technical jargon: the particle machine uses a laser to measure fine dust particles in the air down to PM0.3 microns, which is much smaller than the measured PM10 or PM2.5 but a good reference point. (The conversion chart is at the bottom of this post). One basic to remember is that the machine’s safest ranges are under 150,000 (converts to <50ug/m3). Lower readings are even safer, since pollution’s dose-dependent damage starts above 20ug/m3. OK, back to the findings!

  • Mountain air is not necessarily cleaner than urban air. On October 31 we went to lovely Tanzhesi, the temple complex in the western hills only 1 hour west on route 108. Downtown 3rd ring wasn’t awful, at 160,000. You would think “clean mountain air”, right? But surprise surprise, at the base of the hill it was already 350,000, and 3 hours later, after leaving the temple, it was 520,000 in the hills! The main culprit today was definitely hazy skies from both burning autumn leaves as well as cheap coal in rural homes. Perhaps, in the summer, the mountain air may actually be safer, but all winter, of course, those sulfur-laden coal bricks are keeping rural residents warm. I bet their indoor air is even worse, due to the coal.
  • Ring road and canal-side pollution was the same. I was also disappointed that my canal-side roads had the exact same pollution levels as the ring roads. I had always assumed that there’d be some type of 50-meter protection, but alas this was not reality. But, on the reverse side, pollution levels directly on ring roads were not higher than nearby roads. But before you get too excited about that, don’t forget that there are other pollution indicators that I didn’t monitor, such as carbon monoxide and nitrogen oxides, which are probably much higher along ring roads, coming directly from car exhaust. Bottom line? I would still recommend your outdoor strolls along the tree-lined canals instead of ring roads, if only for aesthetics and sanity, but perhaps the pollution is the same. Sigh…
  • Upper floor pollution was the same as ground floor. Again, I had thought (hoped?) that one could live “above” the worst pollution. Alas, this also was disproved. My 22nd floor apartment had exactly the same PM readings as ground floor.
  • pollution2Indoor air is almost always better than outdoor air — but still unhealthy. I say “almost always better”; only inside Solana was the air worse. Otherwise, indoor air keeps the worst pollution at bay, and readings were usually 50% of outdoor air. I think indoor pollution is much worse in poorer, rural neighborhoods — anywhere with indoor coal/wood stoves as well as smokers. But, indoor air was still almost always in an unhealthy level. Why? Because Beijing’s air, usually around 140ug/m3, is about 7 times higher than the safety level of 20ug/m3; so, indoor air at half that is still 3-4 times higher than safe.
  • Morning air is not always the best time of day. I had previously mentioned that morning air may be the best time for that jog; but my data and other website data now leads me to believe that the cleanest times are early afternoon. But the overall effect is probably pretty small. However, it still remains true that most PM peaks over night with those diesel construction trucks running around after rush hour.
  • Not one day was technically healthy. Every day had outdoor ranges above 100,000, which converts to ~35ug/m3. As I hope is sinking in for everyone, PM readings over 20ug/m3 start to have health effects.
  • Some days were really bad. On October 29th the sky was milky-grey and smelled funny; I got readings over 1,100,000 all day. On November 5th I got 1,500,000. On the 29th, the official API was 139; Beijingair 415 “hazardous”.
  • Blue skies are still unhealthy. Even with this week’s crystal clear, blue sky post-snow days, I still had readings ~130,000. That converts to ~40ug/m3, which again is above the level of safety.

Um, Any Good News?

Well, I suppose there are some take-home messages. My personal feeling is that air pollution is a serious issue that anyone who lives here for more than 3 years should really assess — especially if you have young children. However, I do feel that we can control a great part of our exposure by controlling our indoor environments. After all, we probably spend 90% of our time indoors at work or home, right? So why not ensure that your indoor air is clean? Good air purifiers can get those PM levels to safe levels. Then, you can literally breathe easier and worry less about that 10% of the time outdoors. I have a previous post which discusses air purifiers.

Previous Posts…

Air Pollution: How Bad Is It, Really?
Air Pollution in China: New Slideshow
Air Pollution: What About Indoor Air?

The Fine Print

Here’s that conversion chart for my particle monitor:

Particles per liter of air Fine Dust (ug/m3) Health Effects Recommendations
0-30,000 0-9.9 Nothing Nothing
30-60,000 10-19.9 Nothing Nothing
60-105,000 20-34.9 Hardly any Nothing
105-150,000 35-49.9 Slight effects with asthmatics, cardiac & vascular disease High-risk reduce exposure
150-300,000 50-99.9 As above, + headaches, cough, lung irritation As above, more strict
300,000+ 100+ As above, more severe Reduce exposure to a minimum